Biogeography of late Silurian and devonian rugose corals

Palaeogeography, Palaeoclimatology, Palaeoecology, 22(197'7 ): 85--135 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

BIOGEOGRAPHY CORALS

OF LATE SILURIAN

AND DEVONIAN

RUGOSE

WILLIAM A. OLIVER Jr.

U.S. Geological Survey, Washington, D.C. (U.S.A.) (Received May 18, 1976; revised version accepted September 2, 1976)

ABSTRACT Oliver Jr., W. A., 1977. Biogeography of Late Silurian and Devonian rugose corals. Palaeogeogr., Palaeoclimatol., Palaeoecol., 22 : 85--135. Three marine benthic faunal realms can be recognized in the Early and Middle Devonian. The Eastern Americas Realm consisted of most of the eastern half of North America and South America north of the Amazon. This realm extended in a southwest direction from the Devonian equator to approximately 35°S and was an isolated epicontinental sea during much of its history. The Eastern Americas Realm was bounded on the west by the Transcontinental Arch, on the north by the Canadian Shield and on the east and southeast by a peninsular extension of the Old Red Continent. These barriers were emergent during much, but not all, of Devonian time. Seaways beyond these barriers belonged to the Old World Realm. The Malvinokaffric Realm that was farther south was apparently temperate to arctic in climate and latitudinal position and contained few corals. Rugose corals in the Eastern Americas Realm show increasing generic-level endemism from the Late Silurian through the Early Devonian; during the late Early Devonian, 92% of the rugosan genera are not known anywhere else in the world. Endemism decreased through the Middle Devonian to zero in the early Late Devonian. The Early Devonian increase in endemism paralleled, and was probably related to, the development of the Old Red Continent as a barrier between America and Africa--Europe. The waning of endemism in the Middle Devonian reflects the breaching of the land barriers. This permitted some migration in and out of the realm in early Middle Devonian time but greatest movements were in late Middle Devonian time. Principal migration directions were from western or Arctic North America into the Michigan--Hudson Bay area and from the southern Appalachian area into Africa.

INTRODUCTION Positions and movements of the major continents during Mesozoic and C e n o z o i c t i m e s s e e m t o b e r e a s o n a b l y w e l l k n o w n o n t h e basis o f g e o p h y s i c a l d a t a . T h i s is n o t so f o r E a r l y a n d M i d d l e P a l e o z o i c t i m e f o r w h i c h v a r i o u s histories and continental arrangements have been proposed by geophysicists depending on different data or differing interpretations of the same data. D i s t r i b u t i o n o f a n i m a l s a n d p l a n t s c a n n o t be u s e d t o p r o v e a p r o p o s e d g e o graphic a r r a n g e m e n t because t h e r e are t o o m a n y possible ways for organisms

85

86 to m o v e f r o m place to place. H o w e v e r , some p r o p o s e d geographies p r o d u c e a m o r e logical p a t t e r n o f a n i m a l - - p l a n t distribution t h a n o t h e r s and in this sense b i o g e o g r a p h y can be used t o t e s t p r o p o s e d c o n t i n e n t a l a r r a n g e m e n t s to d e t e r m i n e h o w p r o b a b l e t h e y are. This p a p e r r e p o r t s an analysis o f the world distribution o f rugose coral genera t h a t are k n o w n t o have o c c u r r e d in eastern N o r t h A m e r i c a in the latest Silurian (Pridolian Stage) and D e v o n i a n ( G e d i n n i a n t h r o u g h Frasnian stages). The s t u d y is qualitative e x c e p t in t h e calculation for each stage of the p e r c e n t a g e o f genera k n o w n f r o m eastern N o r t h America (and peripheral areas d e f i n e d b e l o w ) t h a t are e n d e m i c to t h a t area {Table I).

TABLE I Number of genera of Rugosa (N) and number and percent of endemic genera (according to present data), from each stage (latest Silurian through early Late Devonian) in the Eastern Americas Realm Endemic N

~

~

N

Percent

Frasnian

13

0

0

Givetian Eifelian

36 28

15 18

42 64

Emsian (late) Emsian (early) Siegenian Gedinnian

25 12 6 14

23 5 2 8

92 42 33 57

Pridolian

15

3

20

Ludlovian

25

9

36

e~ o

03

f~

_=

09

I define " e n d e m i c " as r e s t r i c t e d t o a given geographic area. Here, I list a genus as e n d e m i c if, in the r o c k s o f a given stage and any earlier stage, it is k n o w n o n l y f r o m the geographic area stated. A genus m a y be e n d e m i c t h r o u g h o n e or m o r e stages and t h e n b e c o m e m o r e widespread and even c o s m o p o l i t a n , b u t o n c e it is m o r e widespread it is n o t listed as e n d e m i c in a n y later stage, even if it was a p p a r e n t l y again r e s t r i c t e d to the same or a n o t h e r geographic area. The implication is t h a t m y " e n d e m i c s " originated in the region to which t h e y were e n d e m i c . If so t h e y have some o f t h e

87 attributes of both " a u t o c h t h o n o u s " and " e n d e m i c " taxa in the sense of Simpson {1965, pp.95, 98) and Darlington (1957, pp. 23--24). Eastern North America (ENA) is used to refer to the present geographic area of North America that is east of the Devonian Transcontinental Arch (Eardley, 1951) and south of the central part of Hudson Bay. Known coral assemblages extend from Alabama to the Hudson B a y Lowlands and from Quebec and the Canadian Maritime Provinces to Oklahoma. Other fossil groups indicate that central Texas and Chihuahua, Mexico, were part of ENA also, but rugose corals from both areas are too few for analysis. During Early and Middle Devonian time, three faunal realms are recognized (Fig.l): (1) the Eastern Americas Realm included ENA and northern South America (Venezuela, Colombia) and at one time apparently extended into Nevada {see following discussion); (2) the Old World Realm included western and Arctic North America, Eurasia, northern Africa, and Australia; {3)the Malvinokaffric Realm included central and southern South America, southern Africa, and Antarctica. Rugose corals were abundant in the shallow seas of the first two realms but were very rare in the Malvinokaffric Realm. ENA is used here as a term of convenience; it is an area that is today separated from other parts of the Eastern Americas Realm by physical barriers. At various times in the Devonian, the realm was divisible on the basis of benthic animal distributions into various smaller biogeographic units, here termed faunal provinces. The following are recognized (Fig.l): (1) The Appohimchi Province includes all of ENA during the Early and early Middle Devonian b u t excludes the area of the Michigan Basin and Hudson Bay Lowlands during the late Middle Devonian. (2) The Michigan Basin--Hudson Bay Province includes the most northerly two basins that lay west of the Appalachian Basin (Fig.lB). This area was biogeographically distinct during late Middle Devonian time. (3} The Great Basin Province includes Nevada and surrounding areas. This was apparently part of the Eastern Americas Realm during middle Early Devonian time b u t is not included in the term ENA. (4) The Amazon--Colombian Province (Boucot, 1975, pp. 316--319, as a subprovince) includes northern South America. This area was clearly a part of the Eastern Americas Realm during late Early and early Middle Devonian time, but its recognition as a province cannot be justified on the basis of the corals known from the area; the term is used here as a matter of convenience and because of brachiopod data presented by B o u c o t (1975). Oliver (1976c) was intended to be a summary of the present paper, b u t the world maps have since been modified to more accurately reflect the paleomagnetic data in McElhinny {1973), and the conclusions have been greatly expanded. The present study is based on an update and refinement of earlier data and discussions (Oliver, 1968, 1973, 1975) and all maps and tables have been completely revised to incorporate newer information, and to include the world distribution of rugose coral assemblages.

88

'

~'>-5;~:-

_./r.f)

-'°/

/~

(-9

~--

Z!;'

/

,

"

~

"~ ,,

'

~

~"~


o

i

?

zk

,

•

;

I

z

(D

.._',,'.v~.

~(,/")

".D,.~ -",

.............

-J

130;

~ '

,

-

'

o.

'~'/~,' ' . . . . . 0 0 ^~; " ,4

'

,

~t~.

-

"

"

: / ~

.~'~=

"

~

~

.

0

= =~ _ =#=~ o

~=

...-. "'. "

,

-

,,J

~y

-/ ,/ - " ~ .'

,"'

q)

~

~ o

-"."- " ' "."~

. m J/'" '''~'--~ " ......

~ = o .~ "a o =~:

.=~

~ . ~ .~. o o2~

•

~;.~

0

El

89 PREVIOUS WORK Earlier work on North American Devonian biogeography cal~ be divided into three more or less distinct phases: (1) initial recognition of distinct differences between eastern American Early and Middle Devonian faunas and those of the rest of the world (1897 or earlier to approximately 1910); (2) increasing information, resulting in overly complex explanations and interpretations (1910 to approximately 1960); and (3) the period of " m o d e r n " analyses. In this section, I have not attempted to trace the full history of thought on North American Devonian biogeography b u t rather to outline it and demonstrate that it does have a long and respectable past. Phase 1

Frech (1897, p. 238, map 3 with expl.) discussed and illustrated a North Helderberg Sea occupying eastern North America in the Early Devonian and containing an isolated, peculiarly developed fauna. His map showed land to the west of this sea and the Old Red Continent (North Atlantic Peninsula) to the east, and he noted some similarities to South American faunas (in his South Helderberg Sea). Kayser (1902, p. 154) noted a "Eurasian" province " p r o b a b l y " including western Canada, and an "American" province including South America. This is a clear perception of two of the realms recognized today. Weller (1902) noted that the Devonian was "pre-eminently a period of provincial development of marine faunas", and described an "Appalachian Province" between "Appalachia" and the "Wisconsin-Ozark land", while mentioning a more cosmopolitan Silurian fauna (p. 423). He further noted the Appalachian connections with South America (p. 423) and Hudson Bay (p. 428) and that the Late Devonian fauna was cosmopolitan (p. 424). Weller also referred to a "southern hemisphere province" and a "Eurasian province" but he was apparently n o t using these terms in the present meaning of Malvinokaffric and Old World. Ulrich and Schuchert (1902) dealt mainly with eastern North America b u t they noted Appalachian faunas of Helderberg (Gedinnian) age in what is now Oklahoma (p. 651), and also noted that the Hamilton (Givetian) faunas of Michigan, Wisconsin, and Iowa belonged to a distinct subprovince (p. 656), here the Michigan Basin--Hudson Bay Province. Schuchert (1903) used the work of Lebedev (1902) on the "Devonian coral provinces of Russia", as a basis for comparing North American Middle Devonian faunas with those of Eurasia. He noted "American" and "Eurasiatic" provinces within North America (p. 137). His "American" province of Onondaga (Eifelian) time was essentially the same as that recognized today; his Hamilton "Eurasiatic" province extended as far east as Iowa, northwest Illinois and Michigan (p. 144), reflecting the mixed faunas of this area. In addition he noted the "American" nature of Middle Devonian faunas from

90 South America, Hudson Bay, and southeastern Quebec. The two maps published with this paper, are the first of a long series of Schuchert's paleogeographical maps of North America. Most of his later maps have little interest in the present context, b u t three relatively u n k n o w n ones (Schuchert, in Eastman, 1908, pp. 348, 354, 3 6 0 ) are probably the closest to modern paleogeographic maps of all the Devonian maps that he produced. Schuchert (1910, pp. 541--542) further noted that Great Basin faunas beginning with the Helderbergian (Gedinnian) were of a different province from those of eastern America and that the seas joined late in the Middle Devonian. Phase 2

The next fifty years saw a steady increase in the a m o u n t of faunal data available to paleogeographers and a corresponding increase in the complexity of paleogeographical maps and interpretations of the data. There were many notable observations, but in general, the geography was forced to fit assumed migration patterns that were based on inadequate or even erroneous data. Grabau (1931) was refreshingly free of many of the prevailing biases. He mentioned the probable nonexistence of the Paleozoic Atlantic (pp. 227, 235), the endemic Helderbergian (Gedinnian) fauna of eastern North America (p. 234) and the "distinctively East American" Hamilton (Givetian) fauna, u n k n o w n elsewhere (p. 235). However, Grabau, like most of his contemporaries, was more concerned with world migration patterns than with distributions. Joleaud (1939) is interesting for his eariy plotting of Devonian biogeographical data on a Pangea base (pl. 94). His Eifelian map (pl. 6) is on a Mercator projection of the modern world b u t shows an eastern North American seaway completely isolated from the west, and suggests the isolation from the east by the distribution of the coral C a l c e o l a - c o m m o n in Europe and North Africa b u t completely absent from America. Joleaud (pl. 6, expl.) named two Middle Devonian marine provinces, "American" and " E u r o p e a n " , and noted the North African mixing of elements from both, b u t he attributed this to migration along a south Atlantic land bridge. Several papers during this period plotted coral and/or reef distributions, but few of these made significant biogeographical contributions. Ma (1936, 1937, 1943, and 1956) plotted a Devonian equator based on the distribution of coral growth line patterns (see Ma, 1956, for references). In the latest of these papers, Ma (1956, p. 103) plotted Devonian "reef" distribution on a "pre-drift" base. Termier and Termier (1952, maps 10--12) plotted "coral reefs" on maps representing Early, Middle, and Late Devonian paleogeography on Mercator projections of the modern world. The known occurrences of C a l c e o l a are shown o n the Middle Devonian map.

91 Schwarzbach {1958; map republished in 1963 and 1974 editions of book) published a map showing the distribution of "coral limestones" relative to paleomagnetic poles and equator. At one level, this represents the beginning of the modern phase, although it is not a significant contribution to Devonian biogeography.

Phase 3 Hill (1957) presented a very clear statement on the nature and distinctness of eastern North American coral provincialism (p. 47), and this, for present purposes, initiated the modern phase of study and analysis. She termed the Emsian to Givetian eastern fauna the Heliophyllum fauna (p. 49) and noted its extension into Africa during the Middle Devonian (p. 49). Hill termed the contemporary faunas of the rest of the world (including western North America) "Eurasaustralian" (p. 49; Old World of this paper), and she noted that regional differences within this Old World fauna during Emsian, Eifelian, and Givetian times were small in comparison with the differences between this fauna and the eastern North American fauna. Spassky (1967, 1968, 1972), Dubatolov and Spassky (1970, 1973), Dubatolov (1972a, b) and Spassky et al. (1973) tabulated the distribution of Devonian coral genera for the world and presented generalized maps of Early, Middle, and Late Devonian biogeography, on which they clearly distinguished the "Appalachian" province during the first two of the epochs. Spassky et al. (1968) noted that the " Appalachian" province was the most isolated of the recognizable Early Devonian provinces and on this basis recognized it as an "independent paleobiogeographical area" in contrast to the "Australoeurasiatic" (Old World) area which constituted the rest of the world. Oliver (1973, 1975) showed the distribution of Middle Devonian Eastern American and Old World coral assemblages on the Bullard et al. (1965) reconstruction of the pre-drift Transatlantic continents. In addition, Oliver (1975) showed eastern North American distributions for the Gedinnian and Emsian stages and North American distributions for the Middle Devonian. Other recent coral-based contributions are more limited in scope. Hamada (1971) published a map of the Calceola distribution, again showing the complete absence of this genus from North America. Mintz (1972, p. 312), Furon (1972, p. 97) and Seyfert and Sirkin (1973, p. 259) all published world maps showing the distribution of Devonian reefs and paleomagnetic poles or equators but only the Seyfert and Sirkin maps were on a Pangea (pre-drift) base. ENA PROVINCIALISM Boucot and Johnson, together and separately, and with other collaborators, have produced a series of papers (1967--1975, see bibliography for principal ones) on Late Silurian and Devonian brachiopod biogeography.

92 Together, these authors have presented paleogeographic maps (mostly on modern bases) of North America and the world for the Late Silurian and most of the Devonian stages and lists of key brachiopod genera by stage for various biogeographic areas. These works have provided an excellent framework in which to study the coral biogeography. The principal results of the brachiopod studies have been to confirm the existence of the three realms and to define their boundaries and their duration in time. In addition, Boucot and Johnson have provided or suggested many details of the history of the realms such as migration times and routes and the nature and history of barriers to migration that caused provincialism in the first place. Study of ENA trilobites (Ormiston, 1972, 1975; Burton and Eldredge, 1974), atrypoid brachiopods (Copper, 1973), and corals (Oliver, 1973, 1975) have shown that other benthic groups have much the same distribution pattern as the Boucot and Johnson brachiopods, whereas probable pelagic forms such as goniatites (House, 1968, 1973a, b) were less restricted. The Boucot and Johnson brachiopod biogeographical studies have been based on a comparison of brachiopod genera occurring in rocks of the same .age in different parts of the world and the recognition of key genera. My coral analyses have differed in taking advantage of the known situation which contrasts an Eastern Americas Realm with the rest of the world. I have studied the world distribution of every rugose coral genus known to occur in ENA and in other areas thought to have been a part of this realm during Late Silurian through Devonian time. Thus, I make no a t t e m p t to subdivide the Old World Realm, although the works of Dubatolov and Spassky, B o u c o t and Johnson, and others make it clear that the Old World is divisible into many subunits. My approach, and the apparent fact that corals were less mobile than brachiopods and other animals, makes this a history of eastern American Devonian biogeography rather than of the world. However, the work has wide-ranging implications for all continents, which, for the most part, have been insufficiently dealt with by other workers. DEVONIAN BASE MAP One purpose of this study was to determine whether the distribution of Devonian corals is compatible with Devonian continental arrangements suggested by paleomagnetic data. As two different basic arrangements of the continents have been used by other paleontologists, a secondary purpose was to determine which of these provided the better fit for the data. I conclude that the coral distribution is compatible with the Pangea-minus-Asia map that results from the data in McElhinny (1973) and that for several reasons the base map of Smith et ah (1973) and Briden et al. (1974) should be rejected (as was suggested by these authors while presenting the map). The base map for Middle Devonian time used in this study was constructed by tracing equal-area projections of the present shorelines and shelf edges of the continents. The four Atlantic-bordering continents were arranged accord-

93 ing to the best-fit map of Bullard et al. (1965); the Gondwanaland arrangement is adapted from McElhinny and Briden (1971). The a t t a c h m e n t of the eastern margin of North America and of southern Europe, Turkey, Arabia, Iran, and western Afghanistan to Gondwanaland is from various sources but is not important to any of m y conclusions. The a t t a c h m e n t of eastern Siberia to Alaska is important and is discussed more fully elsewhere. Geophysicists generally agree that the South Pole was in southern Africa during the Devonian. McElhinny and Briden (1971) and McElhinny (1973, pp. 220, 226) think that the pole position was more or less constant from the Middle Silurian into the Carboniferous, so I have used the same pole for my Late Silurian and Early Devonian maps. This pole (for South America and Africa) and other pole positions given by McElhinny (1973) for Euramerica (pp. 2 0 2 , 2 4 4 ) were used to construct the lines of latitude shown on Figs.l, 3, 4 and 13. The only problem in putting the map together was in Australia, where the equator resulting from the pole position of McElhinny (1973, p. 228) passes through central Australia rather than north of Australia as shown. McElhinny discussed possible resolution of this problem (pp. 227-230, 260--262), but because none of the apparent solutions affect m y conclusions, I have left Australia in its conventional Gondwanaland position and compromised the lines of latitude, using the equator of Smith et al. (1973). Asia is shown in a separate figure (Fig.13B). McElhinny's Devonian pole positions for the Siberian Platform and for the Kuznetsk--Minusinsk--Tuva area (McElhinny, 1973, p. 244) and his data on post-Devonian positions of the Kolyma Platform, the Sikhote Alin area, and China indicate that Asia is a complex of independent and quite separate Paleozoic continents. Possible boundaries of these are shown on Fig.13B, and possible Devonian positions of the units are discussed in the section on the Old World Realm. The Devonian map used here is in accord with the available paleomagnetic data for both latitudinal position and orientation of the continents, with the exceptions mentioned. The paleontologic data, discussed elsewhere in this paper, strongly suggests that the seaway between Euramerica and Gondwanaland had closed by the beginning of the Middle Devonian, and this determined the sequence of relationships shown in Figs.3, 4, and 13. Three different projections of a quite different Devonian map were published by Smith et al. (1973, figs.12, 20) and Briden et al. (1974, figs.15, 16). The map was presented with misgivings (see Oliver, 1976c, for full discussion and illustration) and they suggested an alternative arrangement of continents (Oliver, 1976c, text-fig.2) which is very similar to the map used here. In summary the Devonian base map of Smith et al. (1973) and Briden et al. (1974) was questioned or rejected by its authors who now seem to be in agreement with McElhinny upon whose data m y map is based. The paleontologic and geologic data discussed elsewhere in this paper fit very well the Late Silurian-Early Devonian closing of the early Atlantic and the achieving of Pangea (minus Asia) by the beginning of the Middle Devonian. It is much more

94 difficult to fit these data to the Smith et al. map, which thus seems unlikely on both geophysical and paleontological--sedimentological grounds. McKerrow and Ziegler (1972) and Cocks and McKerrow (1973) based their Silurian and Devonian reconstructions of the continents on a prepublication copy of the Smith et al. (1973) Early Devonian map and m a y n o t have been aware of the reservations about the map and alternative suggestions published in 1973 and 1974. McKerrow and Ziegier hypothesized a Late Silurian collision between North America and the part of Gondwanaland that is now Colombia. According to them, the continents then separated and collided again (with Africa against North America) in the Late Paleozoic to form Pangea. This now seems untenable on paleomagnetic grounds and unlikely on paleontologic grounds. Cocks and McKerrow (1973, pp. 298--302) plotted Late Silurian and Emsian (late Early Devonian) brachiopod distributions; they n o t e d some difficulties in explaining the apparent distributions and suggested that the continents may have been closer together than shown by the maps.

EA S T ER N AMERICAS REALM CORAL ASSEMBLAGES

The genera of rugose corals known from the Eastern Americas Realm in rocks of each stage from the Ludlovian and Pridolian through the Frasnian and listed in Tables II--XI, and the geographic distributions of assemblages including some or all of the genera are shown on Figs.3, 4, and 7--13. The lists are certainly subjective, fallible, and incomplete, but they are relatively consistent because I have reviewed all the identifications on which they are based except for those on the midwestern Ludlovian list, which is based on published work of others. Some of the genera listed as endemic to the Eastern Americas Realm have been reported or even "described" from areas within the Old World Realm. For these genera I have satisfied myself either t h a t the Old World occurrences are in a later stage or that the reports are erroneous. In all comparisons, I have tried to err on the conservative side; if I am n o t satisfied that the Old World form is significantly different, the genus is listed as "widespread" rather than endemic. Any Eastern Americas Realm genus that occurred outside of the realm, except for certain North African forms, are "widespread"; this term is used to avoid the possible implications of " c o s m o p o l i t a n " . Some widespread genera were certainly cosmopolitan, but many are n o t known to have been and may n o t have been. It is important to emphasize that although the Devonian Old World Realm is divisible into faunal provinces, as noted above, none of these Old World subdivisions are distinguished by nearly the percentage of endemic genera that serve to set off the Eastern Americas Realm from the rest of the world. Fig.2 shows the c o , e l a t i o n s used in assigning the ENA coral assemblages to the European stages.

95 ENA Stage

European Stage

Bradfordian Famennian Cassadagan ~2

Cohoetonian Frasnian

Fingerlakesian Taghanican Tioughniogan

o >

Givetian

Cazenovian

E

Southwoodian

Eifelian

Sawkillian

Emsian

Deerparkian

Siegenian

Helderbergian

Gedinnian

Cayugan

Pridolian

Niagaran

Ludlovian

Fig.2. Eastern North American stage nomenclature showing approximate correlation with European stages as used in text.

Ludlovian and Pridolian stages According to most analyses, the Silurian Period was characterized by relatively cosmopolitan marine faunas (Holland, 1971; Boucot and Johnson, 1973; Cocks and McKerrow, 1973; Boucot, 1975) although most of these authors recognized moderate degrees of provincialism in the Late Silurian. Kaljo and Klaamann (1973, p. 42) stated that "the Late Silurian as a whole is characterized by a presence of a rather considerable group of r u g o s a . . . that were nearly cosmopolitan." However, their distribution chart for the Ludlovian Stage (Kaljo and Klaamann, 1973, table 5) shows some 32% of their ENA genera to be endemic by my definition. According to their data, the highest level of endemism for any other area is 17%. My own list of ENA Ludlovian genera is on Table II. It differs somewhat from the list of Kaljo and Klaamann but shows approximately the same endemic level: 36%, if based on Oklahoma--Tennessee (midwestern) occurrences only, or 34%, if northern Appalachian coral assemblages of possible Ludlovian age are included. These figures indicate greater regional differentiation than is

96 TABLE II Ludlovian genera of rugose corals in eastern North America (Henryhouse and Brownsport Formations, see text discussion) (E = endemic; W = widespread). A llo trop iop hy llu rn ? Amsdenoides A n isop h y flu m Arachnophyllum Capnophyllum Craterophyllurn Cystiphyllum Ditoecholasma Duncanella Entelophyllum Enterolasma Lamprophyllum Micula?

E E W W E E W E E W W W W

0 ligophy llu m ? Oliveria Pe tra ia ? Phaulactis Pseudocryptophyllum? Ptychophyllum Rhizophyllum Sutherlandinia Spo ngo phy lloides Syringaxon Tryplasma (solitary) Zelophyllum?

E E W W E W W W W W

W W

suggested by the phrase "cosmopolitan marine faunas." The midwestern coral list (Table II) is based on the published work of Sutherland (1965; Oklahoma, Henryhouse Shale and Amsden (1949; Tennessee, Brownsport Formation) as modified by Sutherland (1965) and myself. The midwestern coral area was separated from the northern Appalachian area by an area in which dolomite and clastic rocks were pred o m i n a n t (Berry and Boucot, 1970, p. 57, figure 4) and rugose corals scarce or nonexistent (Fig.3). This and the Transcontinental Arch, discussed more fully below, may have provided the isolation in which many endemic genera were developed within the midwestern coral assemblage. ENA corals of Pridolian age are restricted to the central and northern Appalachians (Fig.3). Only three endemic genera are known (20%, Table I), the bulk of the corals belonging to well-known western European (mostly cosmopolitan) genera. In the central Appalachian area (New York to the Virginias) Pridolian coral-bearing units are the Cobleskill Limestone, the Glasco and Wilbur Members of the R o n d o u t Limestone, the Decker Limestone, and the lower Keyser Formation. These units are late Pridolian in age (Berry and Boucot, 1970). In all these units, the rugose corals are closely associated with stromatoporoids, but the basic descriptive and distributional data on the corals are unpublished. For the northern Appalachians (Maine and southeastern Quebec) the coral lists are based on assemblages from the Hardwood Mountain and Lobster Lake Formations and the Cranboume Limestone (Stumm, 1963), the Mont Wissick Formation (Oliver, 1963), and the Third Lake Formation (see Hall, 1970, pp. 32--33 and 52 for discussion and lists of corals identified by Oliver). These units are Ludlovian and/or Pridolian in age, according to Berry and Boucot (1970), except for the Lobster Lake Formation (Ludlovian). At this time, it is n o t practical to separate Ludlovian

97

e.

~

z

~.~ 0'~

~

c.~

~.

". ' ' ~~ d

-~a .~.~ ~ ~

0

0

Z

'~ o ...9.~ '~, z 7

>o w c3

.=~ ~ o

a2

C)

~-

L

i¸¸

t

!

, ÷

•

I

/

o

~

-~,, ~k

Z <~

w~ I--

._1 m c.c)

oo

3 ° , ' " ~~~ I'~

!i i

98 TABLE III Pridolian Genera of Rugose Corals in Eastern North America (E ~- endemic; C = common; R = rare; X = known to occur)

Acanthophyllum Acmophyllum? Cystiphyllum Entelophylloides (E) Entelophyllum Holmophyllu m "L yrielasma" (E) Microplasma Phaulactis Ptychophyllum? Pycnactis Rhizophyllum Spongophylloides Tryplasma (solitary) Zelophyllia? (E)

Pridolian

*Ludlovian-Pridolian

Pridolian

Newfoundland

Maine--Quebec

New York-Virginia

X X

X X

R

C

C

X X C

C X

C X X X X X

*Some of the corals from Maine and Quebec are probably Ludlovian in age. See text for discussion. and Pridolian assemblages in all o f these areas, and the d a t a are c o m b i n e d in Table III. The general d i s t r i b u t i o n p a t t e r n o f corals in Late Silurian t i m e (Fig.3), suggests partial isolation o f the m i d w e s t e r n area b y e n v i r o n m e n t s inimicable to coral g r o w t h , and easy access t o t h e Appalachian area b y Old World corals. T h e Pridolian coral assemblage in t h e central Appalachian area is o f low diversity (seven genera), b u t t h r e e o f these are e n d e m i c . T h e n o r t h e r n A p p a l a c h i a n P r i d o l i a n / L u d l o v i a n corals are m o r e diverse ( t h i r t e e n genera), b u t o n l y t w o genera are e n d e m i c , and o n e o f these is e x t r e m e l y rare ( b u t c o m m o n f a r t h e r s o u t h ) . This suggests t h a t the corals gained access to the area f r o m the n o r t h e a s t (Fig.3) f r o m an adjacent w e s t e r n E u r o p e , and t h a t the s o u t h w e s t e r l y decrease in diversity and increase in e n d e m i s m was p a r t l y a result o f distance f r o m the source. T h e Pridolian western margin o f the coral area was an area o f e v a p o r i t e d e p o s i t i o n (Fig.3; B e r r y and B o u c o t , 1 9 7 0 , p. 58, fig. 5). If salinity c o n d i t i o n s in the central Appalachians were slightly a b n o r m a l , this also c o u l d a c c o u n t f o r the low diversity. In western N e w f o u n d l a n d , the Clam Bank Series is o f Pridolian age (Berry and B o u c o t , 1 9 7 0 ) . O n l y o n e species o f rugose coral is p r e s e n t l y k n o w n f r o m

99

this unit, but it is abundant in unit 7 of Schuchert and Dunbar (1934, p. 105}. This appears to be a species of Acanthophyllum, and, if so, is one of the earliest ones known.

Gedinnian Stage The corals listed in Table IV as Gedinnian are from rocks of the lower and middle parts of the Helderbergian Stage (sub-Becraft on charts of Rickard, 1962, 1964, 1975; and equivalent units) in the central and northern Appalach. ians. These rocks are generally correlated with the Gedinnian Stage (see Rickard, 1964; Boucot and Johnson, 1968a; Oliver et al., 1968, 1969). The rugose corals occur in four different facies, each of which is rather widely distributed in the Appalachian Basin (Fig.5). The facies assemblages of corals are listed separately in Table IV. Most genera are limited to one assemblage, but a few are known from two or three. The physical relationship of the facies in New York was diagrammed and described by Rickard (1962, figs. 25 and 27 ) and is here simplified in Fig.6. The apparent situation in other parts of the basin is similar, although the details have not been worked out so thoroughly. West of the Appalachian belt, corals of this age are less c o m m o n but are known as far west as Oklahoma (Fig.7). Table IV is based on Appalachian occurrences, but no additional genera have been described from the midwest. T A B L E IV

Gedinnian (early and middle Helderbergian) genera of rugose corals in Eastern North America (C = c o m m o n ; R = rare)

Facies or assemblage

Endemic

Widespread

Bioherm (patch reef) assemblage

Briantelasma Pseudoblothrophyllum Breviphrentis

Tryplasma (colonial) (C)

"L y r i e l a s m a "

new genus A

"Nalivkinella" Fletcherina Spongophylloides

Stromatoporoid bed assemblage

"Lyrielasma"

Tryplasma (colonial) ( R ) Zelophyllia?

Argillaceous limestone assemblage

Heterophrentis Breviphrentis

Calcarenite assemblage

A k n i s o p h y llum

"L y r i e l a s m a "

new genus A

Tryplasma (colonial) ( R )

En terolasma Syringaxon

100 I

I

I

I

0

I00

200

/

',,

300 MILES

¢

\

N BRUNS

QUE.

\~- \.~

(~

'~_.. .J-'m ~

ONT.

CANADA

• f F s ~) - ,,, / ,x~(ST--At

MICH•

1

e

L

J

( v;

--

C

'

MASS

-.

IND/ -.:

].//

OHO I?t l"'r

., f

s/

(-~,--y

~R~F~/"

PA.

f / / ~'"-'4 ,; KY. / ~

/~

'~'k.

W.VA.

//

,-.//

f y

/ ")

MD. '

j .... '~'m,

vA.

"

L

Helder'berglan Coral AssemOlages: A Argillaceous Limestone C Calearenite R Patch Reef (B~oherm) S Stromatoporoid Biostrome

Fig.5. D i s t r i b u t i o n o f G e d i n n i a n (early a n d m i d d l e H e l d e r b e r g i a n ) coral a s s e m b l a g e s in t h e A p p a l a c h i a n area. Solid lines enclose areas u n d e r l a i n b y r o c k s o f this age.

Taken as a whole, the ENA Gedinnian genera are 57% endemic (Table I), suggesting that the corals were, or were becoming, well isolated. The four facies assemblages are quite different in their levels of endemism, ranging from 75% endemic to 100% widespread. The stromatoporoid bed assemblage of corals is probably derived from the Pridolian assemblage of the same area, as all the genera were present in the earlier stage. As already noted, the Pridolian corals of the New York-Virginia area are c o m m o n l y associated with stromatoporoids, so the environmental change from Pridolian to Gedinnian time may have been slight. Two of the Gedinnian genera (Spongophylloides and Tryplasma) were already widespread in Pridolian time; the other two ("Lyrielasma" and Zelophyllia?) are widespread in rocks of Gedinnian age, although they were apparently ENA endemics in the Pridolian Stage. The patch reef assemblage is the most diverse of the four facies

101

West

-Cast /

Patch Reef Facies Unconformity/ ~ / ~ ,

~

~

~

~

,

.

~

/'/ ! ~

/

/

-

_

Unconformity | Patch reef (bioherm) m. Stromatoporoid biostrome Fig.6. Late Silurian and Helderbergian facies in New York showing time relationship of four coral assemblages discussed in text. Horizontal lines are isochronous; diagonal and vertical lines mark lateral facies changes; heavy bounding lines are unconformities. Symbols for patch reefs and stromatoporoid biostromes show stratigraphic and geographic range of facies but not the actual dimensions of the individual units. The section is approximately 320 km long and 140 m thick. After Oliver (1968, fig.3); data from Rickard (1962, 1964, 1975). assemblages o f corals. New Y o r k corals o f this assemblage were d e s c r i b e d by Oliver ( 1 9 6 0 a ) . Since t h e n the assemblage has been r e c o g n i z e d in Maine (Oliver, 1 9 6 0 b ) , Pennsylvania, and New J e r s e y with essentially the same generic c o n s t i t u e n t s . T h e assemblage is 75% e n d e m i c . The calcarenite assemblage is small, and corals are n o w h e r e c o m m o n . Species o f t h r e e o f the genera were d e s c r i b e d b y Oliver ( 1 9 6 0 a , b). The argillaceous l i m e s t o n e assemblage is also small, b u t s o m e o f the species are locally very c o m m o n . T h e rugose corals described b y Hall and S i m p s o n ( 1 8 8 7 ) and G i r t y ( 1 8 9 5 ) b e l o n g t o this assemblage. G i r t y ( 1 8 9 9 ) described one coral f r o m O k l a h o m a . T h e O k l a h o m a corals are u n d e r s t u d y by P. K. S u t h e r l a n d (personal c o m m u n i c a t i o n , 1968). These include Enterolasma, Syringaxon, and a few o t h e r genera, s o m e o f which are n o t y e t k n o w n in the A p p a l a c h i a n Basin. T h e k n o w n taxa are m o s t similar t o those o f the argillaceous l i m e s t o n e assemblage o f the east. T h e calcarenite and argillaceous l i m e s t o n e assemblages each include t w o e n d e m i c and t w o widespread genera with n o n e in c o m m o n .

102

Note On the succeeding maps (Figs.7--12) the distribution of land (shaded) and sea is generalized ; see text discussion. Symbols mark location of areas from which rugose corals have been studied: circles, EAR corals; squares, Old World corals; sblid circles and squares indicate major data points; open circles and squares represent one or few genera. The heavy line from Newfoundland to Mexico is the lithospherie plate boundary used in Figs.3, 4 and 13A. Numbers mark sites of non-coral paleontologic data used in constructing maps: 1 = marine, Old World fossils in Nova Scotia; 2 = Turkey Creek, marine, Old World assemblage in southern Oklahoma; 3 = Chihuahua, Mexico, ENA brachiopods; 4 = Florida subsurface near shore marine pelecypods; 5 = non-marine. Major sources of data in Figs.7--12: Shoreline positions (generalized) from Boucot (1968), fig.7 (1975), figs.7, 9, 10, 11; Boucot and Johnson (1967), figs.7, 8, 9; (1968a), fig.7, 9; Boucot: et al. (1969), fig.8; Johnson (1970), fig.ll; (1971b), figs.8, 9, 11, 12; (1974), fig.10; and Johnson and Dasch (1972), fig.7. Chihuahua, Mexico, Early Devonian data from Sheehan (1975); subsurface Florida data from Pojeta et al. (1976). Nova Scotia faunal data from Boucot (various publications). T h e f o u r H e l d e r b e r g i a n or G e d i n n i a n facies are n o t o f e x a c t l y t h e s a m e age (Fig.6), b u t t h e y all o v e r l a p to s o m e e x t e n t , a n d t h e generic d i f f e r e n c e s are p r i m a r i l y e n v i r o n m e n t a l l y r a t h e r t h a n t i m e c o n t r o l l e d . All E N A Gedinnian (Helderbergian) genera that were not endemic were already p r e s e n t in E N A d u r i n g Pridolian t i m e , so t h e r e is n o e v i d e n c e o f the introd u c t i o n o f corals i n t o the a r e a d u r i n g G e d i n n i a n t i m e . If Lyrielasma did o r i g i n a t e w i t h i n E N A d u r i n g Pridolian t i m e , as t h e r e c o r d suggests, t h e n it was able to s p r e a d i n t o o t h e r areas d u r i n g the G e d i n n i a n b e c a u s e it was w i d e s p r e a d b y the late G e d i n n i a n o r early Siegenian (Pedder, 1 9 6 7 , p p . 5,

lO). Siegenian and Early Emsian stages E N A corals o f t h e s e ages are b o t h u n c o m m o n a n d u n s t u d i e d . T h e Siegenian includes r o c k s o f the late H e l d e r b e r g i a n (?), a n d D e e r p a r k i a n p r o v i n c i a l stages (Fig.2). T h e Sawkillian Stage is c o n s i d e r e d to be E m s i a n , a n d early Sawkillian r o c k s ( E s o p u s e q u i v a l e n t s ) are t r e a t e d h e r e as early E m s i a n , a l t h o u g h t h e y m a y be Siegenian o r p a r t l y so. T h e u n i t s are g r o u p e d f o r t h e p u r p o s e s o f this discussion b e c a u s e o f t h e i r c o m m o n p a u c i t y o f corals a n d b e c a u s e t h e y collectively r e p r e s e n t t h e interval o f t i m e d u r i n g w h i c h E a s t e r n A m e r i c a s f a u n a s i n v a d e d t h e G r e a t Basin ( B o u c o t , 1 9 7 5 , p. 319). L a t e H e l d e r b e r g i a n (early Siegenian) corals are rare in the E a s t e r n R e a l m , a n d n o n e h a v e b e e n d e s c r i b e d or identified. Small Siegenian ( D e e r p a r k i a n ) a s s e m b l a g e s are k n o w n f r o m t h e Glenerie L i m e s t o n e ( N e w Y o r k ) a n d t h e Frisco L i m e s t o n e ( O k l a h o m a ; P. K. S u t h e r l a n d , p e r s o n a l c o m m u n i c a t i o n , 1 9 6 8 ) (Fig.8}. T h e s e include Duncanella?, Enterolasma?, Syringaxon, and a f e w o t h e r u n i d e n t i f i e d g e n e r a ( T a b l e V). Early E m s i a n (early Sawkillian) corals are k n o w n f r o m t h e I n d i a n Cove

103 Q Z

Z 0') W

r

0

8~

m~ ~

/'-.i¸ ~

]'<.-,'! , i~

o~

~o ~Z

g Z 0

r,

.£

"U

0 "U r~

0 0 e~

"U

104 TABLE V Siegenian (late Helderbergian(?) and Deerparkian! genera of rugose corals in the Eastern Americas Realm (E = endemic)

AppohimchiProvince New York

Breviphrentis Duncanelta? Enterolasma? Ko beha Kozlo wiaphyllum Syringaxon

*Great Basin Province

Oklahoma E

X X E X X

?

*Merriam's (1973) "Billingsastraea" is a Radiastraea and probably of late Emsian age; hence it is not listed here. His "Siphonophrentis', is listed here as Breviphrentis.

TABLE VI Early Emsian (early Sawkillian) genera of rugose corals in Eastern Americas Realm (E = endemic) Appohimchi Province

Gaspe

Astero billingsa Aulacophyllum? Breviphrentis Cystiphylloides Enterolasma OdontophyUum? Papiliophyllum cf. Petraia Siphonophrentis Syringaxo n Undetermined genus 1 Undetermined genus 2

*Great Basin Province

**Turkey Creek Nevada

E E X

X

E X X X

*"Eurekaphyllum", reported by Merriam (1974c), is known from a single specimen; I agree with Hill (1957}, Birenheide (1974), and Merriam (1974c, p. 53) that it is probably an aberrant Papiliophyllum. **Old World assemblage within Appohimchi Province; see text discussion.

105 Member of the Grand Gr~ve Formation, Gasp~ Peninsula, Quebec (Billings, 1874; Clarke, 1908, pp. 215--218; Oliver, 1964; and herein (Fig.8). This includes the earliest known cylindrophyllinid (Oliver, 1974, p. 167), and a few solitary corals (Table VI). The Frisco and Glenerie assemblages are more similar to older generic assemblages than they are to younger ones. In contrast, the somewhat younger Indian Cove corals are allied with the succeeding late Emsian assemblage. These assemblages are too small to draw valid conclusions but indicate either (1) that a "coral b o u n d a r y " falls between the Deerparkian and Sawkillian stages in ENA, or (2) that new elements were evolving or being introduced in the northeast while remnants of the Gedinnian assemblage persisted in the central Appalachians and midwest. In spite of their small size, the assemblages are distinctly Eastern Americas in their affinities. Boucot et al. (1968, p. 1248; 1969, pp. 22--24, 40), and Boucot (1975, p. 319) have convincingly shown that during Siegenian and early Emsian time, Great Basin (Nevada) brachiopods were dominantly ENA ("Appalachian") types. Merriam (1973) described the Great Basin rugose corals of this age, but this included only four Siegenian and five early Emsian genera. These are listed on Tables V and VI, with an indication of their distribution status. Of the Great Basin Siegenian corals, only Breviphrentis and the cosmopolitan Syriugaxon, are certainly known in Lower Devonian rocks of ENA. Of the other genera, Kozlowiaphyllum is distinctly Old World and is u n k n o w n in ENA until the Givetian Stage, and Kobeha is known only from the Great Basin. The early Emsian corals are similarly diverse in their relationships. Breviphrentis is an Eastern Americas Realm endemic; Cystiphylloides is widespread or cosmopolitan; Papiliophyllum is a Great Basin endemic in the early Emsian but a possibly congeneric species has been described from late Emsian strata in Germany (Birenheide, 1974); Aulaeophyllum and Odontophyllum, if correctly identified, are Great Basin (therefore Eastern Americas) endemics during the Emsian, but Aulacophyllum was widespread in later stages. Following Boucot and others (as cited above), I treat the Great Basin as having been an extension (Great Basin Province) of the Eastern Americas Realm during 8iegenian and early Emsian times. The coral data are sparse but do support this in a limited way. The occurrence of Breviphrentis is of greatest interest. This genus ranges from Gedinnian to Eifelian in ENA. It apparently moved into the Great Basin area during the Siegenian, where it persisted to the late Emsian. It apparently gave rise to Siphonophrentis in one or both areas; this genus (or subgenus) is first known from the early Emsian of ENA and is c o m m o n t h r o u g h o u t the Middle Devonian in t h e Appohimchi Province and is known from the early Eifelian in the Great Basin.

106 Another small assemblage of rugose corals of early Emsian age is anomalous in that it apparently has Old World affinities b u t geographically is well within the Appohimchi Province. This is the fauna of the Turkey Creek inlier in south-central Oklahoma (loc. 2 on Fig.8). The brachiopods, conodonts, and trilobites from the Turkey Creek fauna have been discussed by Amsden et al. (1968) and Ormiston {1968). These workers agree that the fauna is of early Emsian age and that it is an Old World fauna. Only eight reasonably complete rugose corals are known from the unit (Table VI). These include Syringaxon (4 specimens), cf. Petraia (1), and two unidentified genera represented by one and two specimens. Syringaxon is widespread; the other three genera are otherwise u n k n o w n in the Eastern Realm, b u t corals of this age are so rare that this may n o t be significant. Petraia, however, is an Old World genus and this suggests that the corals as well as the brachiopods and trilobites are exotic, representing a brief incursion of Old World elements into the area of the Eastern Americas Realm.

Late Emsian Stage The late Emsian assemblage of rugose corals in ENA is both diverse {Table VII) and widespread (Fig.9). It contains the highest percentage of endemic genera of any of the ENA stages (92%; Table I). The Emsian is represented by rocks of the Sawkillian (early and middle Onesquethawan) Stage. Principal units from which the corals are known are the Schoharie Grit (eastern New York), Bois Blanc Formation (western New York, southwestern Ontario, northeastern Ohio subsurface, northern Michigan}, and the lower four feet of the "coral zone", Jeffersonville Limestone at the Falls of the Ohio (Kentucky--Indiana). The Aemulophyllum Zone of Oliver (1976a) is essentially equivalent to the upper Emsian as represented in ENA. Aemulophyllum is'easily recognized, almost as widespread as the assemblage, and limited to it. During this stage, Appohimchi corals may have spread to northern South America and northwest Africa, although k n o w n Appohimchi corals from these areas are more likely Eifelian and/or Givetian in age. These dispersals are discussed in a following section. Most of the Emsian rugose corals were named and described during the nineteenth century, and many were recently redescribed (Stumm, 1965) but in these works t h e y were said to come from the " O n o n d a g a " (New York and Ontario) or Jeffersonville limestones and were not separated from corals of Eifelian age. Significant age differences within these formations were recognized on the basis of the succession of distinct coral assemblages by Oliver (1960c, 1966, 1968, and 1976a), b u t the correct assignment of all species and genera is not y e t known, and Table VII includes only those genera now known to occur in rocks of this age. The Emsian assemblage is notable for its homogeneity. Many of the genera and species are k n o w n from rocks as varied as silt- and fine sandstones

107 TABLE VII Late Emsian (late Sawkillian) genera of rugose corals in eastern North America ENDEMIC Metriophyllidae? Aemulophyllum Bo wenelasma *Briantelasma *New genus cf. Enterolasma Ho malophyllu m Kionelasma Stereolasma Acrophyllidae Acrophyllum Scenophyllum "Zaphrentidae" Compressiphyllum Heterophrentis Halliidae Aulacophyllum

Zaphrentidae Heliophy llu m Crepidophyllinae Grewgiphyllum Cylindrophyllinae Acinophyllum Cylindrophyllum Prismatophyllum Astero billingsa Family? "Disphyllum" of Stumm (1965) Chonophyllidae ? Blothrophyllu m Cystimorphs Cladionophyllum Edaphophyllu m Skoliophyllum

WIDESPREAD Laccophyllidae Syringaxo n

Cystimorph Cystiph y llo ides

*Known f r o m t h e Needmore Shale in Pennsylvania and Virginia, Emsian or Eifelian age (see text discussion).

(Schoharie) and limestones (Bois Blanc, Jeffersonville), over large parts of the area shown on Fig.9. The correlations within ENA used here are based principally on the corals. Dating of the assemblage as Emsian is based on brachiopods (Boucot and Johnson, 1968b) and conodonts (Klapper et al., 1971, p. 292). Middle Devonian T h e Middle D e v o n i a n r o c k s o f E N A c o n t a i n m a n y m o r e corals a n d m a n y m o r e a s s e m b l a g e s o f corals in m o r e diverse facies t h a n d o the L o w e r D e v o n i a n r o c k s . A l t h o u g h s o m e coral a s s e m b l a g e s w e r e d e s c r i b e d m o r e t h a n 1 0 0 y e a r s ago, m a n y are still u n k n o w n or p o o r l y k n o w n . T h e O n o n d a g a a n d

108

0

z

0

"00

~.~

°~

~

0",'.

0

z

.o

"0

~0 0

•

109

Tully limestones and the Hamilton Group of New York are richly coralliferous in many areas, as are correlative units over large parts of ENA (Figs.10, 11). The Emsian--Eifelian boundary as presently recognized (Fig.2), represents a marked break in the sequence of coral assemblages and a change in their nature. The Emsian assemblage has relatively few genera in c o m m o n with preceding or succeeding assemblages and is notably homogeneous. In contrast, the Middle Devonian assemblage(s) persist through great thicknesses of rock with gradual changes that permit the recognition of many "zones". However, the overall similarity between the corals of the earliest (Edgecliff) and latest (Tully) of the Middle Devonian units is much greater than that of the lowest (Edgecliff) unit and the underlying Emsian assemblage. The Middle Devonian corals are still too poorly known for detailed zonal or distributional analysis within ENA (see 1967 discussion in Oliver, 1968). Here, the coral assemblages are analyzed by stage only, following the general correlations of Oliver et al. (1968, 1969). Disagreements over the position of the Eifelian--Givetian boundary in ENA (see discussion in Oliver et al., 1968, p. 1034, and Rickard, 1975, p. 8) have some bearing on generic level distribution in the two stages (Table VIII), as the disputed interval includes some corals. However, most of these occur in both stages no matter which boundary is used. The important Miami Bend--Rogers City coral assemblages (see next section) are included on the Givetian list; the Seneca--Delaware-Dundee assemblages are listed as Eifelian. This follows the boundary and correlations of Cooper and Phelan (1966, p. 8) and is convenient, as it places the stage boundary at formational boundaries in all coral-bearing sequences. The late Givetian Taghanican Stage (Fig.2) is n o t separated o u t in Table VIII, b u t all Taghanican genera except Metriophyllum are known also from the pre-Taghanican part of the Givetian. Eifelian and Givetian times were marked by a decrease in the level of rugose coral endemism. From a high of 92% in the Emsian (late Early Devonian), endemism decreased to 64% and 42% in the Eifelian and Givetian respectively, and ultimately to zero in the Late Devonian (Frasnian) (Table I). The Middle Devonian decrease in endemicity can be related to the outward movement, apparently through North Africa to Europe and Asia, of some of the ENA endemic genera, b u t even more to a Givetian influx of Old World genera into the Michigan Basin and Hudson Bay Lowland areas (Table IX). These Old World genera, identified on Table VIII, are numerous enough for the recognition of a Michigan Basin--Hudson Bay Lowland Province as a distinct subdivision of the Eastern Americas Realm during the Givetian Stage (Fig.11). The Middle Devonian faunal exchanges between ENA and South America and Africa are discussed in separate sections of this paper, as are special aspects of Michigan Basin--Hudson Bay Province history.

110 TABLE VIII Middle Devonian genera in eastern North America [E = endemic to realm; W = widespread; (M) = Miami Bend Formation; (M, T) = Miami Bend and Traverse Group (other genera listed from Michigan Basin--Hudson Bay Lowland Province are known from Traverse Group only) ]

Stage: Province: Metriophyllidae Metriophyllum "Nalivkinella " Ste wartophyllu m Stereolasma Laccophyllidae Syringaxon

Eifelian

Givetian

Appohimchi

Appohimchi

Michigan

E

W W E E

E

W

W

W

Hadrophyllidae Hadrophyllum Microcyclus Xenocyathellus "Zaphrentidae" Breviphrentis Heterophrentis Sipho nophren tis Halliidae A ulacophyllum Hallia Odontophyllum Zaphrentidae Cyathocylindrium Heliophyllum Zaphrentis

E W

E

E E W W E

E E E

"Cyathophyllidae" Alaiophyllu m Tortophyllum

W W

W

W W E

W W

W

W(M, T)

W(M) E

Bethanyphyllidae Bethanyphyllum Disphyllidae Disphyllum Hexagonaria

W

E(M, T)

W

W W(M,T)

111 TABLE VIII (continued)

Stage: Province:

Eifelian

Givetian

Appohimchi

Appohimchi

Michigan

E

E

E E E

E E E

E

E

Crepidophyllidae (Crepidophyllinae) Eridophyllu m Grewgiphyllu m

E E

Crepidophyllidae (Cylindrophyllinae) Acinophyllum Asterobillingsa Cylindrophyllu m Prisma tophyllu m

E E E E

"Stauriidae" Dendrostella Depasophyllum Synaptophyllum Chonophyllidae Blothrophyllum cf. Chlamydophyllum Diversophyllum Iowaphyllum Phymatophyllum Tabulophyllum

W E

E

E W(M)

E W E

E W

W

Spongophyllidae "Spongophyllu m "

W

Ptenophyllidae Kozlowiaphyllum

W(M)

Stringophyllidae Stringophyllu m ? New genus Cystimorphs Bucanophyllum Cystiphylloides Diplochone Lekanophyllum Mieroplasma Sk o liophy llu m

W(M)

E W W W W

W

W W(MT) W

112 TABLE IX Analysis of origin of Middle Devonian Eastern Americas Realm genera listed in Table VIII Stage :

Eifelian

Givetian

Province:

Appohimchi

Appohimchi

Michigan

Total ENA

28 18 -10

23 12 5 11

27 10 3 17

36 15 8 21

--

4

10

14

1 3 4 2

2 3 6 0

9 3 4 1

9 3 8 1

Number of genera Total Endemic to realm Endemic to one province Widespread Widespread but known from only one province

Status of widespread genera in previous stage Old World endemic EAR endemic Widespread No occurrence known

Michigan Basin--Hudson Bay Lowland Province T h e M i a m i Bend F o r m a t i o n in n o r t h e r n I n d i a n a ( C o o p e r a n d Phelan, 1 9 6 6 ) a n d t h e R o g e r s City F o r m a t i o n in Michigan c o n t a i n several g e n e r a o f Old World corals a n d o t h e r b e n t h i c i n v e r t e b r a t e s t h a t are n o t e l s e w h e r e k n o w n in t h e E a s t e r n A m e r i c a s R e a l m . T h e e x o t i c n a t u r e o f t h e R o g e r s City f a u n a was r e c o g n i z e d b y Ehlers a n d R a d a b a u g h (1938), w h o first n a m e d t h e f o r m a t i o n : This a n d s u b s e q u e n t w o r k was r e v i e w e d b y Linsley (1973). T h e o n l y rugose coral t h a t has b e e n d e s c r i b e d f r o m t h e R o g e r s C i t y is Hexagonaria borealis S t u m m (1948). This is a Hexagonaria s.s., a n d t h e s a m e species o c c u r s in t h e M i a m i B e n d F o r m a t i o n . T h e M i a m i B e n d F o r m a t i o n in n o r t h e r n I n d i a n a was n a m e d a n d c h a r a c t e r i z e d b y C o o p e r a n d Phelan (1966), w h o r e c o r d e d t h e r e i n t h e first and still o n l y k n o w n o c c u r r e n c e o f Stringocephalus in E N A . A l t h o u g h Stringocephalus is n o t k n o w n f r o m t h e R o g e r s City, t h e f a u n a s are o t h e r w i s e v e r y similar, b o t h c o n t a i n i n g o t h e r b r a c h i o p o d s a n d m o l l u s c s t h a t are closest t o g e n e r a a n d species d e s c r i b e d f r o m t h e Winnipegosis F o r m a t i o n in M a n i t o b a . T h u s , t h e k n o w n fossils are Old World in affinities. G e n e r a o f corals f r o m t h e Miami B e n d are listed in T a b l e V I I I . M o s t are n o t o t h e r w i s e k n o w n f r o m E N A , a l t h o u g h s o m e are k n o w n t o o c c u r elsew h e r e in t h e Michigan Basin. The Miami Bend F o r m a t i o n crops out on the south margin of the Michigan Basin. It overlies Silurian r o c k s a n d is u n c o n f o r m a b l y overlain b y

113

/£o

0

z

.o

Z

z •

¢;

qi31111ii !!il]il ~:! !!:! ~iiiiiiii!~i!!]ill b ~ !!ii~i!i

!

P'-, 0 .,c= r ~ c~

!iiiiiilJi~iil '~' c~ 0

~d •

¢J

C'q . ~

~.~

o~ ..~

~ 0

0

~o~ c~ 0 ~'~

Zo~

~.~ •

r.,;

c~

114

the Logansport Limestone (Givetian) which contains a typical ENA coral assemblage. The Rogers City Formation is more centrally located in the basin. It overlies rocks of Cazenovian age (here considered late Eifelian) and is overlain by a thick sequence of Givetian rocks (Traverse Group). Many of the rugose corals of the Traverse Group have been described (Stumm, 1949-1970) (herein Table VIII); they are a mixture of ENA endemics and Old World genera that are not otherwise k n o w n in ENA. However, it is n o t clear whether the Old World corals tend to be stratigraphically isolated in Michigan (as in the Miami Bend and Rogers City Formations) or whether they were living in association with ENA endemic corals in this area. Perhaps Disphyllum and Hexagonaria and at least some other genera were actually associated with ENA analogies such as Cylindrophyllum and Prismatophyllum, but much work remains to be done, and a number of Traverse corals that are clearly exotic (such as several chonophyllids) are at present undescribed. The Hudson Bay Lowland corals are mostly undescribed, b u t Geological Survey of Canada collections n o w being studied show that the Givetian assemblage (Williams Island Formation; see Fritz et al., 1957) is more closely allied with the Michigan Basin assemblage than it is with that of New York and the Appalachian Basin. The basis for recognizing separate ENA provinces in the Givetian is the presence in the Michigan Basin--Hudson Bay Lowland areas of the exotic (Old World) genera that are not known farther east or south in the Appohimchi Province (Tables VIII, IX). The relative positions of these areas indicate that the exotic genera must have come from the west or north and perhaps most likely from the Williston Basin (Figs.lB, 11). Intermittent links between the Michigan Basin and western North America may have existed off and on through the Devonian, b u t there is little evidence for this at present. Old World Dendrostella is locally c o m m o n in middle or upper Eifelian (Southwoodian) rocks of the area, and Disphyllum s.s. is known from lower Cazenovian rocks. The latter also occurs in rocks of the same age in the northern Appalachians (Famine Limestone; Quebec) where it is the only Old World genus thought to have penetrated this far b y way of the Michigan Basin.

Late Devonian Corals of Frasnian age (Table X; Fig.12) are mostly limited to the Mississippi Valley area (Iowa, Illinois, Missouri) although a few are known from the central Appalachians as well. The best known faunules are from Iowa (Fenton and Fenton, 1924; Belanski, 1928; Stainbrook, 1946}. Appalachian corals have been described from Maryland (Clarke and Swartz, 1913) and New York (Ehlers, 1949; Stumm, 1960), b u t the Upper Devonian in large parts of ENA consists of black shales and other clastic rocks containing few corals.

115 TABLE X F r a s n i a n g e n e r a in e a s t e r n N o r t h A m e r i c a "A mplexus" Charactophyllum "Cho nophy llu m " Disphyllum Hexagonaria ?

Iowaphyllum Macgeea Me triophy llu m "Mictophyllum "

Pachyphyllu m Smithiphyllum Sy ringax o n Tabulophyllu m

To date, thirteen genera of rugose corals are known from ENA Frasnian rocks (Table X), all of which are widespread or cosmopolitan in their distribution. Faunas of this age were no longer provincial, and, for the corals at least, ENA endemism ended approximately with the Middle Devonian. E N A Versus Western and Arctic N or t h America

It is important to emphasize h o w different the Eastern Americas corals are from those that are becoming well known from the Great Basin (Merriam, 1973, 1974a, b, c; summarized by Oliver, 1976b), Western Canada (A. E. H. Pedder, various publications; McLaren in McLaren ar/d Norris, 1964), Alaska (Oliver et al., 1975; C. M. Merriam, written communication), and Arctic Canada (listed by Pedder and McLaren in areal geological publications of the Geological Survey of Canada). Oliver (1968, p.733) noted that the ENA corals as a whole were more similar to those of western Europe than to those of western North America. I n o w think that this statement was incorrect, being unduly influenced by knowledge of the northern Appalachian Pridolian assemblage which is European and of the ENA corals in Africa. As North American corals have become better known, the differences between the ENA corals and those from both western North America and Europe have become much clearer. Difficulties of biostratigraphic correlation between eastern and western North America were ascribed to inadequate knowledge of western faunas by Cooper et al. (1942). At the same time, difficulties in correlating with the European stages resulted in the establishment of provincial stages based on the New York section (Cooper et al., 1942, p. 1733--1734). These stages have proven value within ENA (Oliver et al., 1968, 1969) b u t have not been generally adopted for work in western states and provinces because in these areas it is easier to correlate with Europe than with New York. This is demonstrated by the fact that in the regional section of the 1967 Calgary International Symposium on the Devonian System (Oswald, 1968, Vol. 1), every author dealing with an area of western or arctic North America used the European stages as his reference base, whereas, with only one exception, authors dealing with ENA areas used either the New York stages or both reference sequences. This schism is a clear b u t generally unstated result of the division of North America between the two realms, as discussed in this paper.

116

-30

°

~0°~

~0o

J

// - /

I I I

/° 0

/

\

/

Coral assemblages o•

Eastern

[]•

Old World Land

A

Americas /

118

Northern Sou th America (Amazon--Colom bian Province) Weisbord (1926) first described Devonian rugose corals from the Rfo Cachiri Groul~ in Venezuela (location shown on Fig.13) and recognized them as showing "closest relationships to upper Lower and lower Middle Devonian species from the eastern United States". These descriptions were revised and added to by Wells (1943) and by Scrutton (1973), each on the basis of the earlier and new collections. These works and m y own analysis leave no question of the ENA affinities of these corals. Every genus known from this assemblage is also known from ENA, and species-level similarities are impressive. The previous coral studies as well as studies of associated brachiopods, have related these assemblages to Schoharie--Onondaga (late Emsian-Eifelian) faunas in New York where they are best known. Scrutton (1973) concluded that the closest relationship of the corals was to the Onondaga (Eifelian), and with this I fully agree. Several authors have noted that the assemblage may represent both faunas and that more detailed work may separate these out. Some of the anomalies noted by Scrutton (1973, pp. 229--232) have disappeared with the discovery of Briantelasma and Stereolasma in the Needmore Shale in Virginia and south-central Pennsylvania and with the recognition of Bowenelasma in the Bois Blanc Formation (Emsian) of western New York. The age of the Needmore is either Schoharie or Onondaga or both (Emsian and/or Eifelian), so this does n o t help settle the question of age. However, Briantelasma in ENA was not previously known above the Helderbergian (Gedinnian), and Stereolasma was not known below the Hamilton Group (Givetian). Recognition of Bowenelasma in New York significantly extends its geographic range (from Venezuela) b u t also does n o t clarify the age problem. Table X! lists the known Venezuelan rugose coral genera and shows their stratigraphic ranges in ENA. The generic ranges taken alone show a fairly even balance between the Early and Middle Devonian, b u t species affinities (Table XI, right-hand column) clearly favor an Eifelian age. I have just completed a monographic study of the colonial genera in ENA (Oliver, 1974 and 1976a), and find the Venezuelan species of Acinophyllum and Cylindrophyllum to be morphologically close to and possibly conspecific with the early Eifelian (Edgecliff) species noted (Table XI), and distinctly separable from Emsian ones. The principal anomaly is Bowenelasma which is c o m m o n in the Schoharie (Emsian) and u n k n o w n in the Eifelian, although a single fragment from the Needmore Shale may belong to this genus. If the Venezuelan corals are treated as a single assemblage, their closest affinities are with ENA corals of early Eifelian (Edgecliff) age. It remains very possible that we are dealing with a mixed assemblage that represents Emsian (and even Givetian) age as well. Assuming that the Venezuelan assemblage is no younger than early Eifelian, ten of the twelve genera are Eastern Americas Realm endemics (82%).

119 TABLE XI Eifelian genera of Rugosa from northern South America (Venezuela) (E = endemic to Eastern Americas Realm; (~), age of species listed in right-hand column) ENA Species-level analog analog

Occurrence in ENA: ~

~

Acinophyllum Bo wenelasma Breviphrentis Briantelasma Cylindrophyllum

E E E E E

Cystiphylloides Hadrophyllum Heliophyllum Heterophrentis Stereolasma Stewartophyllum? Syringaxon

E E E E E

X

X X

X

X

X X X

.~

A. straminium

@ X X

X

®

X

×

®

X X X

® X X

X

X

® X ® ® X X X

X

C. elongatum or C. propinguum C. americanuum H. halli

H. simplex

*Needmore Shale, Pennsylvania--Virginia, Emsian or Eifelian (see text discussion).

The ENA affinities of northern South American Devonian faunal assemblages were discussed by Harrington (1968), Kr5mmelbein (1968), Weisbord (1968), and Boucot et al. (1968, 1969). These authors indicate that Appalachian (ENA) elements extend as far south as central-western Bolivia but that the fauna was (pure) Appalachian only at the northern end of its distribution area and became progressively diluted to the south (Harrington, 1968, p. 664; Boucot et al., 1968, p. 1251; 1969, pp. 27--28). Boucot (1975, p. 316) described an Amazon--Colombian "Subprovince" of the Eastern Americas Realm (Fig.lA) extending as far south as the Amazon area before Malvinokaffric faunal elements became predominant. Very few corals are known from the area, except for the Venezuelan assemblage. From Colombia, Caster (1939, p. 180) noted only a single small rugose coral preserved as a calice mold in his extensive collections. MALVINOKAFFRIC REALM

Rugose corals are extremely rare in central and southern South America and in sub-Saharan Africa and are unreported in Antarctica, the areas that make up the Late Silurian to Eifelian Malvinokaffric Realm. Boucot, Johnson, and other workers (see following references for discussions) have interpreted this realm as one characterized by cold water and this is in

122

firm the similarity of some of the Spanish forms to ENA species (Table XII). However, my examination of Altevogt's (1968) material shows t h a t Scenophyllum, Kionelasma, Bethanyphyllum, and "Heliophylloides", all typical ENA genera, were misidentified. The fauna is dominated by Acanthophyllum, Disphyllum, and other Old World genera. Joseph and Tsien (1975a, b) noted and illustrated specimens of Heliophyllum, Siphonophrentis, and Heterophrentis from the western Pyrenees, France, as part of a dominantly Old World coral assemblage. Only Heliophyllum can be confirmed from their illustrations, but as these genera were confirmed from northern Spain, there is no reason to question their occurrence only a relatively short distance farther east. Joseph and Tsien (1975b) estimated t h a t 12% of the Pyrenees corals show ENA affinities. This is essentially the same as the 10% that I have estimated for northern Spain on the basis of the Asturian occurrences. OLD WORLD REALM

A very generalized distribution of Old World Middle Devonian rugose coral assemblages is shown on Fig.13A and B. I have n o t attempted to show any of the subdivisions (provinces) proposed by Boucot et al. (1968, 1969) or by Spassky (1967) and Dubatolov and Spassky (1970). I think it significant that the southern limit of coral assemblages shown on Fig.13A is approximately 30°S. Farther south is the Malvinokaffric Realm t h a t has already been discussed and interpreted as a cold-water area. An interesting but unanswered question is whether a comparable northern limit of prolific coral growth may also have existed. If m y map (Fig.13A) is approximately correct, western Alaska and the northern Urals were approximately 30°N during the Middle Devonian. If Asia had been in its present relative position at this time, it would have extended to approximately 60--70°N latitude (Fig.13B), and well-developed coral assemblages would have existed as far north as 60 ° . However, it is probable t h a t Asia is made up of several Paleozoic continental units (or plates) and that they were n o t in their present relative positions during the Devonian. Those units from which Middle Devonian coral assemblages have been described are indicated on Fig.13B. Hamilton (1970) proposed a plate-tectonics model for the Uralides, in which subduction proceeded through much of the Paleozoic with final collision of Europe and Siberia in the Permian. However, "The two subcontinents need not have approached one another during the early part of the long period recorded by their subduction-zone geology. They might have fronted on quite different oceans than the one across which they finally converged". (Hamilton, 1970, p. 2568.) McElhinny (1973) indicated the complexity of the Paleozoic history of Asia. His data include a Devonian pole for Siberia, but this may not apply to any of the known coral assemblages because of the number of units composing what is now Asia. His pole for the Kuznets--Tuva--Minusinsk area

123 would place these corals between approximately 20 ° and 28°N. Data for later periods indicate that the Kolyma, Sikhote Alin, and China areas have polar-wandering paths that were widely divergent in the Paleozoic and that joined only in the Late Mesozoic (McElhinny, 1973, p. 218), but Devonian pole positions are not known. There seems to be general agreement t h a t a major plate boundary separated the Siberian Shield from the Kolyma area during most of the Paleozoic (see Churkin, 1972 for discussion and references). For m y purpose, it does not matter whether the Verkhoyansk or Cherskiy fold belt marks the boundary, because the coral assemblages are east of either line. Herron et al. (1974) suggested that the K o l y m a block (separated from the Chukotsky Peninsula) was on the American side of the Arctic Ocean against the Canadian Arctic Islands and northern Alaska during the mid-Paleozoic. This would have placed t h e K o l y m a group of coral assemblages (Fig.13B) between approximately 25 ° and 35°N. If the Chukotsky Peninsula (easternmost Siberia) has been continuous with the Alaska Brooks Range since Paleozoic or earlier time, as argued by Churkin (1972); then the few corals from this area would have been about 35°N in the Devonian. Tailleur (1973) suggested the rotation of northern Alaska--Chukotsky-Kolyma into the Arctic Basin and against the Canadian Arctic Islands. This also would have the effect of placing the Kolyma--Chukotsky Devonian corals at and south of approximately 35°N during Devonian time. M. J. Terman (oral communication, 1976) considers the Kazakh area to have been another separate plate. Hamilton (1970, p. 2567) suggested that this area may have come from south of either the Ural belt or the Altay belt. In either case, the coral assemblages on this block would have been well south of 30°N during the Devonian. The Devonian positions of Kazakh, if determined by the Siberian pole or the northern European pole are shown on Fig.13B, again south of 30 ~N. The Devonian position of south China--Viet Nam is not known, although this area apparently was quite separate from the other areas discussed (McElhinney, 1973, p. 218). Colbert (1973, p. 65, 85) has suggested that it was part of Gondwanaland. All these data and interpretations indicate that the various parts of Asia were not in their present positions relative to each other or to Europe during the Middle Paleozoic, but individual positions are still uncertain. The various areas delineated on Fig.13B have been suggested to have been separate plates during the Paleozoic by one or more students of Asian tectonics. Additional plates have been recognized or suggested, but those shown are the ones that include k n o w n Middle Devonian coral assemblages within their boundaries. The above discussion is not a review of proposed Asian plate histories but is designed to indicate that all the principal assemblages of Middle Devonian rugose corals m a y have been south of 30--35°N during the Devonian and that there is paleomagnetic evidence that some w e r e south of this latitude.

126 brachiopods moved at least as far east as Chihuahua, Mexico (no. 3 on Fig.8). The rugosan genus Breviphrentis seems to have moved from ENA into the Great Basin at this time, and one possible Great Basin endemic genus, Aulacophyllum, may have moved into ENA. The Great Basin continued to be a province of the Eastern Americas Realm in early Emsian time. The Turkey Creek fauna in southern Oklahoma (Fig.8, no. 2) is distinctly Old World in its affinities. This fauna probably came from the west, presumably the Great Basin. By late Emsian time (Fig.9) the Eastern Americas corals must have been completely isolated. This is the high point of endemism, with 23, o u t of 25 known genera, or 92%, not k n o w n from any other part of the world during this or any earlier stage. The Canadian Shield and much of interior North America were probably emergent. There is direct evidence for part of this but partly this is deduced from the isolation indicated by the corals and other benthic invertebrates. The Eifelian map (Fig.10) is very similar to that of the late Emsian, although it shows t h a t more is known about western and arctic coral faunas for this than for earlier stages. This was the time, however, of the best South American record. At present, twelve genera are known from Venezuela (area shown on Fig.13A). Every Venezuelan genus is also known from Eastern North America and ten of the twelve are endemic to the Eastern Americas Realm. During this time (or possibly as early as the Emsian) Eastern genera began appearing in Africa (Table XII), probably migrating either around or through breaks in the barrier shown. Also, it is in rocks of latest Eifelian age that the first known disphyllid is f o u n d in the Eastern Realm. This is a characteristic Old World family. The apparent increased movement of genera between the Eastern Americas Realm and the Old World is reflected in the decrease in endemism from the Emsian high of 92% to 64% in the Eifelian. The decrease continued in the Givetian (down to 42%) primarily because of movements of Old World genera into western ENA from the west. Nine distinct Old World genera, including other disphyllids, are f o u n d in the Michigan Basin and Hudson Bay Lowlands but only two of these are known from any part of the Appalachian belt. They strongly suggest a seaway connection to the Old World either to the west or northwest, as shown by the arrows on F i g . l l . It is probably significant that the exchange was dominantly one way. Nine or more Old World genera moved east and are rather c o m m o n there, whereas apparently only two eastern genera moved west during the same time and neither is c o m m o n in the west. Early Late Devonian corals of the world are notably cosmopolitan. Fairly large faunas are known from Iowa in what had been the Eastern Realm, and smaller faunas are known as far east as New York. None of the genera are endemics or former endemics, and none are even t h o u g h t to have evolved

127 fr o m f o r m e r endemic genera. The whole endemic coral fauna seems to have disappeared. Instead, the Late Devonian corals in the Eastern area are cosmopolitan genera, known f r o m all c ont i ne nt s where marine Upper Devonian rocks have been studied. They, or their ancestors are generally well k n o w n in Middle Devonian rocks of the Old World Realm. The Early and Middle Devonian ENA corals provide an excellent example of a fauna developing in isolation through a long period of time and t hen being unable to c o m p e t e when its isolation was ended. There are several possible reasons for this inability to com pet e. The Eastern Americas corals thrived in the Eastern Realm, but the e n v i r o n m e n t was probably n o t quite normal open marine. The epicontinental sea, bordered on three sides by land, and having only limited access to the open ocean (Fig.13A), p r o b ab l y was warmer and its salinity slightly higher than in comparable Old World areas. In addition, the Old World Realm was m uc h larger, by a factor of 10 or more. Most parts of the Realm b o r d e r e d the ocean (Fig.13), and water circulation must have been be t t e r than in the Eastern Realm. The area was ecologically mo r e diverse, as is indicated by its size, latitudinal e x t e n t , and the presence o f a continental slope (indicated by the presence of a surrounding ocean). Numbers of genera were n o t in p r o p o r t i o n to area, but at least two to three times as m a ny genera occurred in the Old World Realm as in the Eastern Americas Realm. The Old World corals were more diverse and inhabited a realm of m ore varied and mo r e " n o r m a l " environments. The Eastern Americas corals were less diverse and were living in m or e limited, probably somewhat specialized environments. When the Transcontinental Arch ceased to separate the realms in North America, the less adaptable Eastern corals were less able to cope with the changes t ha t resulted, and the Old World corals dominated. The increase in levels of endemism t hr ough the Early Devonian is a clear reflection o f the de ve l opm ent o f the Old Red Cont i nent as a barrier between ENA and Europe--Africa. Friend (1969) discussed the growth of the Old Red Continent and Halstead and T ur ne r (1973) and Edwards (1973) discussed the distribution of non-marine fish and land plants on the cont i nent . All available data suggest t ha t the Old Red area e x p a n d e d southward with time. Given the a p p r o x i m a t e geographic situation shown on Figs.7--12, the interchange o f corals between ENA and areas east (or southeast) of the Old Red C o n tin en t would have b e c o m e increasingly difficult. Later, some characteristic ENA genera did penetrate this barrier, either by migrating around the southern end or through breaks in the peninsula. A few of these migrants moved farther than others and became widespread: Heliophyllum may have emigrated this way in late Eifelian or early Givetian time and it was widespread by the late Givetian; Siphonophrentis and Heterophrentis may have mo v ed out at a b o u t the same time, but dispersal was slower for these genera, and t h e y may not have gone farther than southern and western

130 Belanski, C. H., 1928. Description of some typical fossils of the Shellrock Stage. Am. Midl. Nat., 11(5): 171--212. Berry, W. B. N. and Boucot, A. J., 1970. Correlation of the North American Silurian rocks. Geol. Soc. Am., Spec. Pap., 102: 1--289. Billings, E., 1874. On some of the fossils of the Gospe series of rocks. Geol. Surv. Can., Paleozoic. Fossils, 2 (pt. 1): 1--64. Birenheide, R., 1974. Papiliophyllum lissingenense n. sp. (Rugosa) aus dem Lissinger Schurfgraben (Emsium; Eifel). Senckenb. Lethaea, 55(1/5): 251--257. Boucot, A. J., 1968. Silurian and Devonian of the northern Appalachians. In: E-an Zen et al. (Editors), Studies of Appalachian Geology: Northern and Maritime. Interscience, New York, N.Y., pp. 83--94. Boucot, A. J., 1971. Malvinokaffric Devonian marine community distribution and implications for Gondwana. An. Acad. Brasil Ci~nc., 43 (suppl.): 23--49. Boucot, A. J., 1975. Evolution and Extinction Rate Controls. Elsevier, Amsterdam, 427 pp. Boucot, A. J. and Johnson, J. G., 1967. Paleogeography and correlation of Appalachian Province Lower Devonian sedimentary rocks. Tulsa Geol. Soc. Digest, 35: 35--87. Boucot, A. J. and Johnson, J. G., 1968a. Appalachian Province Early Devonian palaeogeography and brachiopod zonation. In: D. H. Oswald (Editor), International Symposium on the Devonian System, Calgary, Alta., 1967, 2: 1255--1267. Boucot, A. J. and Johnson, J. G., 1968b. Brachiopods of the Bois Blanc Formation in New York. U.S. Geol. Surv., Prof. Pap., 584-B: 27 pp. Boucot, A. J. and Johnson, J. G., 1973. Silurian brachiopods. In: A. Hallam (Editor), Atlas of Palaeobiogeography. Elsevier, Amsterdam, pp. 59--65. Boucot, A. J., Johnson, J. G. and Talent, J. A., 1968. Lower and Middle Devonian faunal provinces based on Brachiopoda. In: D. H. Oswald (Editor), International Symposium on the Devonian System, Calgary, Alta., 1967, 2: 1239--1254. Boucot, A. J., Johnson, J. G. and Talent, J. A., 1969. Early Devonian brachiopod zoogeography. Geol. Soc. Am., Spec. Pap., 1 1 9 : 1 1 3 pp. Branisa, L.,1965. Index fossils of Bolivia, Paleozoic. Serv. Geol. Bolivia, Bol., 6 : 2 8 2 pp. Briden, J. C., Drewry, G. E. and Smith, A. G., 1974. Phanerozoic equal-area world maps. J. Geol., 82(5): 555--574. Bullard, E. C., Everett, J. E. and Smith, A. G., 1965. The fit of the continents around the Atlantic. In: A Symposium on Continental Drift. R. Soc. Lond., Philos. Trans., Set. A, 258 (1088): 41--55. Burton, C. J. and Eldredge, N., 1974. Two new subspecies of Phacops rana (Trilobita) from the Middle Devonian of North-west Africa. Palaeontology, 17(2): 349--363. Camacho, H. H., 1966. Invertebrados fosiles. Editorial Univ. de Buenos Aires, 707 pp. Caster, K. E., 1939. A Devonian fauna from Colombia. Bull. Am. Paleontol., 24(83): 218 pp. Churkin Jr., M., 1972. Western boundary of the North American continental plate in Asia. Geol. Soc. Am., Bull., 83(4): 1027--1036. Clarke, J. M., 1908. Early Devonic history of New York and Eastern North America. N.Y. State Mus., Mem., 9(1): 366 pp. Clarke, J. M. and Swartz, C. K., 1913. Systematic paleontology of the Upper Devonian deposits of Maryland. Md. Geol. Surv., Middle and Upper Devonian, pp. 539--699. Cocks, L. R. M. and McKerrow, W. S., 1973. Brachiopod distributions and faunal provinces in the Silurian and Lower Devonian. Palaeontol. Assoc. Spec. Pap., 12: 291--304. Colbert, E. H., 1973. Wandering Lands and Animals. Dutton, New York, N.Y., 323 pp. Cooper, G. A. and Phelan, T., 1966. Stringocephalus in the Devonian of Indiana. Smithson. Misc. Coll., 151(1): 1--20. Cooper, G. A., et al. 1942. Correlations of the Devonian Sedimentary Formations of North America. Geol. Soc. Am. Bull., 53: 1729--1794.

131 Copper, P., 1973. New Siluro-Devonian atrypoid brachiopods. J. Paleontol., 47(3): 484--500. Cottreau, J., 1941. Coralliaires, Brachiopodes et Ccino'ides m~sodgvoniens du Sahara mauritanien et occidental. Soc. G~ol. Fr., Bull., S~r. 5, 10(7--9): 187--200. Darlington, P. J., 1957. Zoogeography; the Geographical Distribution of Animals. Wiley, New York, N.Y., 675 pp. Dubatolov, V. N., 1972a. Tabulates and biostratigraphy of the Middle and Upper Devonian of Siberia. Akad. Nauk S.S.S.R., Sib. Otd., Tr. Inst. Geol. Geofiz., 134: 184 pp. (in Russian). Dubatolov, V. N., 1972b. Zoogeography of Devonian seas of Eurasia (materials covering investigation of Tabulata). Akad. Nauk S.S.S.R., Sib. Otd., Tr. Inst. Geol. Geofiz., 1 5 7 : 1 2 8 pp. (in Russian). Dubatolov, V. N. and Spassky, N. Ya., 1970. Corals of the main Devonian paleobiogeographical provinces. All Union Symp. on Fossil Corals, 2nd, 3 : 1 5 - - 3 0 (in Russian). Dubatolov, V. N. and Spassky, N. Ya., 1973. On the principles of paleobiogeographic searegioning. Akad. Nauk S.S.S.R., Sib. Otd., Tr. Inst. Geol. Geofiz., 1 6 9 : 1 1 - - 1 8 (in Russian). Eardley, A. J., 1951. Structural Geology of North America. Harper and Brothers, New York, N.Y., 624 pp. Eastman, C. R., 1908. Devonian fishes of Iowa. Iowa Geol. Surv., 18: 29--386. Edwards, D., 1973. Devonian floras. In: A. Hallam (Editor), Atlas of Palaeobiogeography. Elsevier, Amsterdam, pp. 105--115. Ehlers, G. M., 1949. Pachyphyllum vagabundum, a new coral from the Upper Devonian strata of New York. Mich. Univ. Mus. Paleontol., Contrib., 8(1): 1--6. Ehlers, G. M. and Radabaugh, R. E., 1938. The Rogers City Limestone, a new Middle Devonian formation in Michigan. Mich. Acad. Sci., Arts Lett., 23: 441--446. Fenton, C. L. and Fenton, M. A., 1924. The stratigraphy and fauna of the Hackberry stage of the Upper Devonian. Contrib. Mus. Geol., Univ. Mich., 1 : 2 6 0 pp. Frech, F., 1897. Lethaea Geognostica, 1 Theil; Lethaea Paleozoica, 2 Bd., pt. 1, Stuttgart, 256 pp. Friend, P. F., 1969. Tectonic features of Old Red sedimentation in North Atlantic borders. In: North Atlantic Geology and Continental Drift, a Symposium. Am. Assoc. Pet. Geol. Mem., 12: 703--710. Fritz, M. A., Lemon, R. R. H. and Norris, A. W., 1957. Stratigraphy and paleontology of the Williams Island Formation. Geol. Assoc. Can., 9: 21--48. Furon, R., 1972. l~l~ments de paleoclimatologie. Paris, 217 pp. Girty, G. H., 1895. A revision of the sponges and coelenterates of the Lower Helderberg group of New York. New York State Mus., Annu. Rep., 48(2): 259--322. Girty, G. H., 1899. Preliminary report on Paleozoic invertebrate fossils from the region of the M'alester Coal Field, Indian Territory. U.S. Geol. Surv., Annu. Rep., 19(3): 539--602. Grabau, A. W., 1931. Palaeozoic centers of faunal evolution and dispersal. Geol. Soc. China, Bull., 11(3): 227--239. Hall, B. A., 1970. Stratigraphy of the southern end of the Munsungun Anticlinorium, Maine. Maine Geol. Surv. Bull., 2 2 : 6 3 pp. Hall, J. and Simpson, G. B., 1887. Descriptions and figures of corals and bryozoa from the Lower Helderberg, Upper Helderberg and Hamilton groups. New York Geol. Surv., Paleontol., 6 : 2 9 8 pp. Hallam, A., 1973. Atlas of Palaeobiogeography. Elsevier, Amsterdam, 531 pp. Halstead, L. B. and Turner, S., 1973. Silurian and Devonian ostracoderms. In: A. Hallam (Editor), Atlas of Palaeobiogeography. Elsevier, Amsterdam, pp. 67--80. Hamada, T., 1971. Early Devonian brachiopods from the Lesser Khingan District of northeast China. Paleontol. Soc. Jap., Spec. Pap., 1 5 : 9 8 pp. Hamilton, W., 1970. The Uralides and the motion of the Russian and Siberian Platforms.

133 mauritanien (Sahara occidental). Gouv. G~n. Afr. Occident. Fr., Bull. Dir. Mines, 15: 299--382. Levi, B., et al., 1966. Reconocimiento geologico en las provincias de Llanguihue y Chilo~. Chile, Inst. Invest. Geol., Bull., 1 9 : 4 5 pp. Linsley, R. M., 1973. Paleoecological interpretation of the Rogers City Limestone (Middle Devonian, northeastern Michigan). Univ. Mich., Mus. Paleontol., Contrib., 24(11): 119--123. Ma, T. Y. H., 1956. A reinvestigation of climate and the relative position of continents during the Devonian. Res. Climate Cont. Drift, 9 : 1 1 6 pp. McElhinny, M. W., 1973. Paleomagnetism and Plate Tectonics. Cambridge University Press, London, 358 pp. McElhinny, M. W. and Briden, J. C., 1971. Continental drift during the Paleozoic. Earth Planet. Sci. Lett., 10: 407--416. McKerrow, W. S. and Ziegler, A. M., 1972. Palaeozoic Oceans. Nature, Phys. Sci., 240: 92--94. McLaren, D. J. and Norris, A. W., 1964. Fauna of the Devonian Horn Plateau Formation, District of Mackenzie. Geol. Surv. Can., Bull., 1 1 4 : 7 4 pp. Merriam, C. M., 1973. Paleontology and Stratigraphy of the Rabbit Hill Limestone and Lone Mountain Dolomite of central Nevada. U.S. Geol. Surv., Prof. Pap., 8 0 8 : 5 0 pp. Merriam, C. M., 1974a. Middle Devonian rugose corals of the central Great Basin. U.S. Geol. Surv., Prof. Pap., 7 9 9 : 5 3 pp. Merriam, C. M., 1974b. Silurian rugose corals of the central and southwest Great Basin. U.S. Geol. Surv., Prof. Pap., 7 7 7 : 6 6 pp. Merriam, C. M., 1974c. Lower and lower Middle Devonian rugose corals of the central Great Basin. U.S. Geol. Surv., Prof. Pap., 8 0 5 : 8 3 pp. Mintz, L. W., 1972. Historical geology; the science of a dynamic earth. Merrill Publ., Columbus, Ohio, 785 pp. Oliver Jr., W. A., 1960a. Rugose corals from reef limestones in the Lower Devonian of New York. J. Paleontol., 34: 59--100. Oliver Jr. W. A., 1960b. Devonian rugose corals from northern Maine. U.S. Geol. Surv., Bull., l l l l - A : 1--23. Oliver Jr., W. A., 1960c. Coral faunas in the Onondaga Limestone of New York. U.S. Geol. Surv., Prof. Pap., 400-B: 172--174. Oliver Jr., W. A., 1963. Silurian rugose corals from the Lake T~miscouata area, Quebec. U.S. Geol. Surv., Prof. Pap., 430-B: 11--20. Oliver Jr., W. A., 1964. The Devonian colonial coral genus Billingsastraea and its earliest known species. U.S. Geol. Surv., Prof. Pap., 483-B: 1--5. Oliver Jr., W. A., 1966. Bois Blanc and Onondaga formations in western New York and adjacent Ontario. N.Y. State Geol. Assoc. Gd. Bk., 38: 32--43. Oliver Jr., W. A., 1968. Succession of rugose coral faunas in the Lower and Middle Devonian of eastern North America. In: D. H. Oswald (Editor), International Symposium on the Devonian System, Calgary, Alta., 1967, 2: 733--744. Oliver Jr., W. A., 1971. Endemism and evolution of Late Silurian to Middle Devonian rugose corals in Eastern North America. Int. Paleontol. Symp. Corals, Novosibirsk, 1971, Abstr. Akad. Nauk S.S.S.R., Sib. Otd., Inst. Geol. Geofiz., pp. 142--143. Oliver Jr., W. A., 1973. Devonian coral endemism in eastern North America and its bearing on palaeogeography. Palaeontol. Assoc., Spec. Pap., 12: 318--319. Oliver Jr., W. A., 1974. Classification and new genera of noncystimorph colonial rugose corals from the Onesquethaw Stage in New York and adjacent areas. U.S. Geol. Surv., J. Res., 2(2): 165--174. Oliver Jr., W. A., 1975. Endemism and evolution of Late Silurian to Middle Devonian rugose corals in eastern North America. Akad. Nauk S.S.S.R., Sib. Otd., Tr. Inst. Geol. Geofiz., 202: 148--160. (Ancient Cnidaria, Proc. 1st Int. Symp. Fossil Corals, Novosibirsk, 2)

134 Oliver Jr., W. A., 1976a. Noncystimorph colonial rugose corals from the Onesquethaw and lower Cazenovia stages (Early and Middle Devonian) in New York and adjacent areas. U.S. Geol. Surv., Prof. Pap., 8 6 9 : 1 - - 1 5 6 (108 pls.) Oliver Jr., W. A., 1976b. Devonian rugose coral assemblages in the United States. Second Int. Symp. Fossil Corals, Paris. Mgm. B.R.G.M. Oliver Jr., W. A., 1976c. Biogeography of Devonian rugose corals. J. Paleontol., 50(3): 365--373. Oliver Jr., W. A., DeWitt Jr., W., Dennison, J. M., Hoskins, D. M. and Huddle, J. W., 1968. The Appalachian Basin, United States. In: D. H. Oswald (Editor), International Symposium on the Devonian System, Calgary, Alta., 1967, pp. 1001--1040. Oliver Jr., W. A., DeWitt Jr., W., Dennison, J. M., Hoskins, D. M. and Huddle, J. W., 1969. Correlation of Devonian rock units in the Appalachian Basin. U.S. Geol. Surv., Chart OC-64. Oliver Jr., W. A., Merriam, C. M. and Churkin, M., 1975. Ordovician, Silurian, and Devonian corals of Alaska. U.S. Geol. Surv., Prof. Pap., 823-B: 13--44. Ormiston, A. R., 1968. Lower Devonian trilobites of Hercynian type from the Turkey Creek inlier, Marshall County, south-central Oklahoma. J. Paleontol., 4 2 : 1 1 8 6 - - 1 1 9 9 . Ormiston, A. R., 1972. Lower and Middle Devonian trilobite zoogeography in northern North America. Int. Geol. Congr., 24th, Montreal, 1972, Sect. 7: 594--604. Ormiston, A. R., 1975. Siegenian trilobite zoogeography in Arctic North America. Fossils Strata, 4: 391--398. Oswald, D. H. (Editor), 1968. International symposium on the Devonian System, Calgary, 1967. Alta. Soc. Pet. Geol., Galgary, Alta., 1055 pp. (Vol.1); 1377 pp. (Vol.2). Pedder, A. E. H., 1967. Lyrielasma, and a newly related genus of Devonian tetracorals. Proc. R. Soc. Vic., N. S., 80(1): 1--29. Pojeta Jr., J., K ~ i , J. and Berdan, J. M., 1976. Silurian--Devonian pelecypods from deep wells in Florida and Georgia and related Silurian species from Bolivia and Turkey. U.S. Geol. Surv., Prof. Pap., 8 7 9 : 3 2 pp. Rickard, L. V., 1962. Late Cayugan (Upper Silurian) and Helderbergian (Lower Devonian) stratigraphy in New York. N.Y. State Mus. Bull., 3 8 6 : 1 5 7 pp. Rickard, L. V., 1964. Correlation of the Devonian rocks in New York State. N.Y. State Mus., Map and Chart 4. Rickard, L. V., 1975. Correlation of Silurian and Devonian rocks in New York State. N.Y. State Mus., Map Chart 2 4 : 1 6 pp. + 4 charts. Schuchert, C., 1903. On the faunal provinces of the middle Devonic of America and the Devonic coral subprovinces of Russia, with two Paleogeographic maps. Am. Geol., 32: 137--162. Schuchert, C., 1910. Paleogeography of North America. Geol. Soc. Am. Bull., 20: 427-606. Schuchert, C. and Dunbar, C. O., 1934. Stratigraphy of western Newfoundland. Geol. Soc. Am., Mere., 1 : 1 2 3 pp. Schwartz, E. H. L., 1906. South African Paleozoic fossils. Albany Mus. Rec., 1: 347--404. Schwarzbach, M., 1958. Das Klima der Vorzeit, eine Einf~ihrung in die Pal~oklimatologie. Stuttgart, 275 pp. Scrutton, C. T., 1973. Palaeozoic coral faunas from Venezuela, II, Devonian and Carboniferous corals from the Sierra de Perija. Br. Mus. (Nat. Hist.), Bull. Geol., 23(4): 223--281. Seyfert, C. K. and Sirkin, L. A., 1973. Earth History and Plate Tectonics, an Introduction to Historical Geology. Harper and Row, New York, N.Y., 504 pp. Sheehan, P. M., 1975. Lower Devonian brachiopods from the Solis Limestone, Chihuahua, Mexico. J. Paleontol., 49(3): 445--471. Simpson, G. G., 1965. The Geography of Evolution. Collected Essays. Chilton Books, Philadelphia, Pa., 249 pp.

135 Smith, A. G., Briden, J. C. and Drewry, G. E., 1973. Phanerozoic world maps. Palaeontol. Assoc., Spec. Pap., 12: 1--42. Sougy, J., 1964. Les formations palgozoiques du Zemmour noir (Mauritanie Septentrionale). Etude stratigraphique, pdtrologique, et palgontologique. 2h~se, Facult~ des Sciences de l'Universit~ de Nancy, 695 pp. Spassky, N. Ya., 1967. Guide to the extent of distribution of Devonian tetracorals. Leningrad Gornyi Inst., Zap., 53(2): 51--68 (in Russian). Spassky, N. Ya., 1968. Regularity of temporary spatial distribution of genera and species (primarily on Devonian tetracorals). Ezhegod. Vses. Paleontol. O.-Va., 1 8 : 3 - - 1 4 (in Russian). Spassky, N. Ya., 1972. Paleobiogeographic relations of Devonian provinces of the lands framing the Pacific (exemplified by tetracorals). Leningrad Gornyi Inst., Zap., 63(2): 144--153 (in Russian). Spassky, N. Ya., Dubatolov, V. N. and Kravtsov, A. G., 1968. Paleobiological zonation of the Early and Middle Devonian seas of the globe (exemplified by the Devonian corals). In: Abstr. Proc. 3rd Int. Symp. on the Silurian--Devonian Boundary. VSEGEI, Leningrad, pp. 214--218 (in Russian). Spassky, N. Ya., Dubatolov, V. N. and Kravtsov, A. C., 1973. Paleobiogeographic zonation of Early and Middle Devonian seas of the globe (exemplified by Devonian corals). In: Stratigr. of the Lower and Middle Devonian, Leningrad, 2 : 2 2 9 - - 2 3 6 (in Russian). Stainbrook, M. A., 1946. Corals of the Independence shale of Iowa. J. Paleontol., 20: 401--427. Stumm, E. C., 1948. Lower Middle Devonian species of the tetracoral ge/ms Hexagonaria of east-central North America. Contrib. Mus. Paleontol., Univ. Mich., 7(2): 7--49. Stumm, E. C., 1949--1970. Corals of the Devonian Traverse Group of Michigan. Contrib. Mus. Paleontol., Univ. Mich., 7(8), 8(3), 9(3), 17(9), 17(10), 17(12), 17(14), 18(8), and 23(5). Stumm, E. C., 1960. New rugose corals from the Middle and Upper Devonian of New York. J. Paleontol., 31(1): 161--163. Stumm, E. C., 1963. Silurian corals from the Moose River Synclinorium, Maine. U.S. Geol. Surv., Prof. Pap., 430-A: 1--10. Stumm, E. C., 1965. Silurian and Devonian corals of the Falls of the Ohio. Geol. Soc. Am., Mem. 9 3 : 1 8 4 pp. Sutherland, P. K., 1965. Rugose corals of the Henryhouse formation (Silurian) in Oklahoma. Okla. Geol. Surv., Bull., 1 0 9 : 9 2 pp. Tailleur, I. L., 1973. Probable rift origin of Canada Basin, Arctic Ocean. Am. Assoc. Pet. Geol., Mem., 19: 526--535. Termier, H. and Termier, G., 1952. Histoire G~ologique de la BiosphSre. Masson, Paris, 721 pp. Ulrich, E. O. and Schuchert, C., 1902. Paleozoic seas and barriers in eastern North America. N.Y. State Mus. Bull., 52: 633--663. Weisbord, N. E., 1926. Venezuelan Devonian fossils. Bull. Am. Paleontol., 11(46); 223--268. Weisbord, N. E., 1968. Th'e Devonian System in western Venezuela. In: D. H. Oswald (Editor), International Symposium on the Devonian System, Calgary, Alta., 1967, pp. 215--226. Weller, S., 1902. The composition, origin, and relationships of the Corniferous fauna in the Appalachian province of North America. J. Geol., 10: 423--432. Wells, J. W., 1943. Anthozoa. In: R. A. Liddle et al., The Rio Cachiri Section in the Sierra de Perija, Venezuela. Bull. Am. Paleontol., 27(108): 95--100.