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Cormophyton gen. nov., a cormose lycopod from the middle Pennsylvanian Mazon creek flora
Review o f Palaeobotany and Palynology , 44 (1985) : 165--181 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
165
CORMOPHYTON GEN. NOV., A CORMOSE LYCOPOD FROM THE MIDDLE P E N N S Y L V A N I A N M A Z O N CREEK F L O R A
KATHLEEN
B. PIGG and T H O M A S
N. T A Y L O R
Department of Botany, The Ohio State University, 1 735 Neil Avenue, Columbus, OH 43210 (U.S.A.) (Received May 5, 1984 ; revised and accepted November 14, 1984)
ABSTRACT Pigg, K.B. and Taylor, T.N., 1985. Cormophyton gen. nov., a cormose lycopod from the middle Pennsylvanian Mazon Creek flora. Rev. Palaeobot. Palynol., 44: 165--181.
Cormophyton mazonensis gen. et sp. nov. is proposed for an authigenically preserved cormose lycopod base in Mazon Creek nodules from the middle Pennsylvanian of Illinois. Based on size, shape, and morphological features, Cormophyton is assigned to the Chaloneriaceae and is thought to represent a plant similar to Chaloneria cormosa. The discovery of this form allows for the description of several external features of Chaloneria-like plant bases and further demonstrates the diversity of isoetalean lycophytes in Carboniferous sediments. INTRODUCTION
For many years paleobotanists have regarded the underground parts of most Paleozoic lycopods as consisting of dichotomously branched axial systems. This concept is based to a large extent on the knowledge of stigmarian systems (Fig.lA) associated with such taxa as Lepidodendron, Lepidophloios, and SigiUaria (e.g. Frankenberg and Eggert, 1969; Eggert, 1972). These ideas are in part responsible for the hypothesized phylogeny of the lycopods as a reduction series beginning with an arborescent m e m b e r such as Sigillaria, and culminating with the extant taxon Isoetes (e.g. Potoni~, 1894; M~igdefrau, 1968). However, despite this rather well-established series, a number of diverse Paleozoic lycopods are n o w known to possess underground parts that are morphologically distinct from the dichotomous systems. Among Devonian forms, Lepidosigillaria whitei was an arborescent lycopod with a swollen, rounded underground axial system bearing numerous rootlets (Fig.lE; White, 1907; Kr~iusel and Weyland, 1949). Nothing is k n o w n about the anatomy of this taxon, b u t the lack of a stigmarian system together with its Devonian age has for some time suggested that this plant might represent a predecessor to later isoetalean forms (Jennings et al., 1983). Specimens of Cyclostigma kiltorkense are also believed to have been arborescent and possess a conspicuous bilobed base with "stigrnarian" scars (Johnson, 1913; Schweitzer, 1969). As basal specimens are incomplete, it is difficult to deter0034-6667/85/$03.30
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Fig.1. Paleozoic lyeopod bases. Figures are redrawn from original sources and indicate the typical reconstructions of taxa. They do not, in all cases, accurately demonstrate all known features of genera, but serve to illustrate basic morphological diversity inherent in known forms. Not to scale. A. Stigmaria ficoides, z 1/30. B. Cormophyton mazonensis, x 1. C. Oxroadia gracilis (from Long, 1971). × 1. D. Paurodendron fraiponli (from Philips and Leisman, 1966). x 10. E. Lepidosigillaria whitei (from White, 1907). ~ 1/8. F. Protostigrnaria eggertiana (from Jennings, 1975). x 1/4. G. Chaloneria cormosa with broken lines representing cortex (from Pigg and Rothwell, 1979). x 1. H. Lycophyte base from the Carboniferous of Argentina (from Archangelsky et al., 1981). x 3/4.
167 mine whether plant bases were cormose, bilobed organs (e.g. Chaloner, 1984) or bore stigmarian axes (Johnson, 1913; Schweitzer, 1969). It is our opinion that an accurate reconstruction of Cyclostigma cannot be made with confidence from presently figured material. The Mississippian genus Protostigmaria consists of a variable n u m b e r (up to thirteen) of irregular lobes bearing numerous rootlets (Fig.lF; Jennings, 1975; J ennings et al., 1983). Like Lepidosigillaria, this plant was arborescent, with segments of the above-ground stem Lepidodendropsis, preserved up to 1.7 m in length. It has been suggested that this multilobed plant base presumably grew similarly to that of a multilobed lsoetes with contractile roots which provided support and anchorage for a fairly large tree (Jennings et al., 1983). Smaller Carboniferous lycophytes that are anatomically preserved include Paurodendron and Oxroadia. Paurodendron fraiponti exhibits a swollen base, termed a rhizomorph, that bears helically arranged roots (Fig.lD; Phillips and Leisman, 1966). Although Paurodendron was renamed Selaginella fraiponti by Schlanker and Leisman (1969), based on its association with a Selaginellites crassicinctus cone (Hoskins and Abbott, 1956), interpretations of Paurodendron have varied. F o r example, Karrfalt (1981) pointed out that the bipolar growth habit suggests a plant unlike Selaginella. Following the interpretation of Schlanker and Leisman, eaolillo (1982) relied on Paurodendron as a model for phylogeny among cormose-based lycophytes. He compared the known ontogenetic features of Selaginella selaginoides with the implied development of Paurodendron. At that time complete specimens of Paurodendron plant bases were unknown. Interestingly, more recent work suggests that Paurodendron is ontogenetically more similar to Stigmaria, than Selaginella (Rothwell and Erwin, 1985). Oxroadia gracilis (Alvin, 1965) is a slender plant that branches sparsely and produces new lateral roots from older roots (Fig.lC). The basal portion of the plant is interpreted as lacking a swollen cormlike base (Long, 1971). It has been suggested (Karrfalt, 1981) that Oxroadia may belong to a group of yet unrecognized, small upright lycopods that are unlike those of the typical, extant herbaceous lycopods with unidirectional growth (e.g., Selaginella
selaginoides ). Recent investigations of G o n d w a n a plants from Argentina have revealed several dwarf lycophytes with cormose plant bases that occur in situ in both Carboniferous (Archangelsky et al., 1981) and Permian sediments (Cuneo and Andreis, 1983). The Carboniferous specimen (Fig.lH) has been found in association with stems described as Bumbumdendron b u t complete details of the plant are n o t known. Numerous molds of plant bases lacking stigmarian axes have been described from the Chubut Province of Argentina (Cuneo and Andreis, 1983). The prevalance of lycophytes with this growth form has been taken by the authors as paleoecological evidence that plants grew in drier, rather than swamp-like, environments. Perhaps the most completely known Paleozoic lycopod that lacks the stigmarian subaerial system is Chaloneria cormosa (Pigg and Rothwell, 1983a;
168 Fig.lG). Chaloneria demonstrates a combination of morphological, anatomical and reproductive features that are more similar to those of Isoetes than to the Lepidodendrales (Pigg and Rothwell, 1983a, b). Vegetative similarities between Chaloneria and Isoetes include a cormose, bilaterally symmetrical plant base, small amounts of secondary tissues, sporangial trabeculae, parichnos, and non-abscising leaf bases (Pigg and Rothwell, 1979, 1983a). The reproductive structures of b o t h Isoetes and Chaloneria consist of simple, diffuse bisporangiate fertile regions as opposed to compact strobili. Morphologically, Chaloneria exhibits an unbranched stem several meters tall which differs markedly from both the stunted stem of Isoetes and the arborescent habit so c o m m o n in the lepidodendrids. Although the anatomy of the basal regions of Chaloneria has been documented (Pigg and Rothwell, 1979), extrastelar tissues are generally absent. Moreover, with the exception of vegetative stem axes attributed to Sporangiostrobus (e.g., Puertollania [ R e m y and Remy, 1 9 7 5 ] ; Bodeodendron [Wagner and Spinner, 1976]), compressions assigned to the Chaloneriaceae consist entirely of fertile parts [e.g., Polysporia (Chaloner, 1958; Drfibek, 1976); Sporangiostrobus (Chaloner, 1956; Remy and Remy, 1975)]. Since the external morphology of basal portions of these plants continues to remain poorly known, a comparison with the well-known Mesozoic lycophyte compressions (e.g., Pleuromeia) has not been possible. The present contribution describes a newly recognized, cormose lycopsid plant base from the middle Pennsylvanian Mazon Creek nodule flora. Although internal tissues are lacking, specimens of Cormophyton mazonensis gen. et sp. nov. exhibit a complement of morphological features suggesting its inclusion within the Chaloneriaceae. Cormophyton increases our understanding of the morphology of the underground parts of lycopods and provides a potential method of comparing the Pennsylvanian members of the Chaloneriaceae with Mesozoic lycopods such as Pleuromeia. The presence of lycopods possessing isoetalean features by the middle Pennsylvanian underscores the early radiation of the group. MATERIALS AND METHODS The following description is based on two specimens preserved in ironstone nodules collected from the famous Mazon Creek locality in northern Illinois (Nitecki, 1979). The specimens are authigenically preserved concretions associated with the Francis Creek Shale which is stratigraphically placed in the Desmoinesian Series (= upper Westphalian D) (Pfefferkorn, 1979). T h e y represent a portion of the Mazon Creek nodule collection of the Field Museum of Natural History (Chicago) and bear the acquisition numbers PP3055 and PP26291. Hot dilute (2.5%) hydrochloric acid was used to remove oxidized materials on the surfaces of specimens according to the procedures outlined by Schopf (1979). Specimens were also sectioned and fractured to reveal three-dimensional shape of some morphological features. Surface features were recorded
169
using low angle lighting to enhance delicate features. Specimen surfaces were also examined via scanning electron microscopy. For comparative purposes, the t y p e specimen of Stigmarioides truncatus was also examined. The specimen is housed at the Illinois State Museum, Springfield and bears the acquisition n u m b e r 8688. SYSTEMATIC DESCRIPTION
Cormophyton mazonensis gen. et sp. nov. Pigg et Taylor Type species: Cormophyton mazonensis Diagnosis: R o u n d e d and/or lobed lycopsid plant base, up to 5 cm long, 2.6 cm wide at broadest portion of base or approximately 17.3 mm in diameter prior to crushing; attached to upright stem 1.6 cm in diameter. Stele at the level of plant base 7.5 X 1.5 X 4 mm, or approximately 7.8 mm in diameter prior to crushing. Helically arranged leaf bases on stem; represented by rounded bulges 1 mm wide X 1.5 mm high at decortication level. R o o t traces arranged in pattern with orthosticies and parasticies equal in number. Roots approximately 1 mm in diameter, with inner single or double bulge and outer margin or broken to reveal prominent outer rim and central hollow region. Vertically elongate bulges associated with r o o t traces and lateral ridges present on plant base.
Holotype: PP26291 {Plate I, 1; Plate II, 1,2,4,5). Paratype: PP3055 {Plate I, 2--4; Plate II, 1, 6). Type localities: Will and Grundy Counties, Illinois. Horizon: Mazon Creek nodules associated with the Francis Creek Shale; Desmoinesian Series (= upper Westphalian D) (Pfefferkorn, 1979), middle Pennsylvanian. Etymology: The generic designation Cormophyton [kormion, Gr.: corm; phyton, Gr.: plant] refers to the cormlike plant base. The specific epithet, mazonensis is taken from Mazon Creek, Illinois, the site at which the specimens occur. DESCRIPTION
The t w o specimens o f Cormophyton mazonensis consist of cormose plant bases attached to short stem segments. One specimen is 4.5 cm long, 1.6 cm in diameter in the stem region, and 2.6 cm wide in the broadest region of the base {Plate I, 1). The specimen is asymmetrical perhaps due to incomplete preservation. Whether the base o f the living plant was radially symmetrical like Stigmaria (RothweU, 1984), Paurodendron (Rothwell and Erwin, 1985}, and young specimens of Nathorstiana (Karrfalt, 1984), or bilaterally symmetrical like that of Chaloneria (Pigg and Rothwell, 1979), Isoetes, and some older specimens of Nathorstiana (Karrfalt, 1984) cannot be determined.
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171 F r a g m e n t s o f c a r b o n a c e o u s material are p r e s e n t o n t h e stem surface; however, it was n o t possible t o d e t e r m i n e a n y i n f o r m a t i o n a b o u t t h e epidermis or cuticle. Helically arranged, oval, widely-spaced bulges a p p r o x i m a t e l y 1 m m wide X 1.5 m m high o r n a m e n t t h e stem. T h e i r c o n s i s t e n t shape and arrangem e n t suggests t h a t these s t r u c t u r e s r e p r e s e n t leaf traces at a subsurface level (Plate II, 5}. Similar appearing bulges have b e e n r e p o r t e d o n a n u m b e r o f partially d e c o r t i c a t e d l y c o p h y t e c o m p r e s s i o n s [e.g., Sigillaria reticulata (Weiss a n d Sterzel, 1 8 9 3 , T a f . V I I , f i g . 3 3 ) ] . T h e y are also o f a size and shape comparable t o p a r i c h n o s strands in t h e o u t e r c o r t e x o f p e r m i n e r a l i z e d Chaloneria stems (Pigg and R o t h w e l l , 1983a). O n the base o f Cormophyton are n u m e r o u s r o o t traces (Plate I, 1). Alt h o u g h a d e f i n i t e r h i z o t a x y c o u l d n o t be d e t e r m i n e d f r o m specimens, o r t h o sticies and parasticies are equal in n u m b e r . Such a p a t t e r n is similar t o t h a t o f a t y p i c a l stigmarian axis d e s c r i b e d f o r stigmarian m o l d casts (Karrfalt, p e r s o n a l c o m m u n i c a t i o n ; C h a r l t o n a n d Watson, 1982). S u b t e n d i n g t h e individual r o o t traces are vertically e l o n g a t e d bulges t h a t give t h e s p e c i m e n an overall irregular surface (Plate II, 2). Each is u p t o 1.5 m m high, 0.7 m m wide, and e x t e n d s u p t o 0.7 m m at its d e p a r t u r e f r o m t h e plane o f t h e axis. In t h e m o s t c o m p l e t e l y preserved areas o f t h e c o u n t e r p a r t s p e c i m e n (Plate I, 1; at right), several r o o t s are p r e s e n t (Plate II, 4). T h e s p e c i m e n is f r a c t u r e d near t h e p l a n t / s e d i m e n t i n t e r f a c e w h e r e r o o t s were p r e s u m a b l y growing o u t into t h e s u r r o u n d i n g matrix. R o o t s are a p p r o x i m a t e l y 1 m m in d i a m e t e r and some are c h a r a c t e r i z e d b y an o u t e r margin t h a t s u r r o u n d s a single or d o u b l e inner bulge t h a t represents t h e area o f vascular tissue (Plate II, 4). A d d i t i o n a l r o o t traces o n t h e c o u n t e r p a r t are p o o r l y preserved, b u t their positions are clearly i n d i c a t e d b y w h i t e kaolinitic material w h i c h fills the cavities (Plate I, 1; Plate II, 4). R o o t s o n t h e p a r t s p e c i m e n lack a well preserved central region. E a c h r o o t consists o f an o u t e r rim and a central d e p r e s s i o n (Plate II, 2) w h e r e it a p p a r e n t l y b r o k e o f f or abscised at t h e base. M o r p h o l o g i c a l l y these r o o t s are quite similar t o ones t h a t have b e e n d e s c r i b e d in Lepidosigillaria (White, 1 9 0 7 ) , Protostigmaria eggertiana (Jennings et al., 1 9 8 3 ) , and a n u m b e r o f Mesozoic l y c o p h y t e s (e.g., Pleuromeia longicaulis [Retallack, 1 9 7 5 ] ). T h e r o o t s o f C. mazonensis a p p e a r similar t o stigmarian
PLATE I
Corrnophyton mazonensis (A = axis;S = stele) 1. Counterpart specimen showing plant--sediment interface and stem axis attached to bulbous base. Arrow indicates well preserved roots at right (see also Plate II, 4). White kaolinite fillings represent positions of poorly preserved root traces. Specimen has been cleared with hot hydrochloric acid. PP26291. x 2.4. 2. Striate surface pattern of axis, believed to be preservational. PP3055. x 9. 3. Cross section of proximal stem axis (A) seen in Plate I, 4 (at arrows) and inner distorted area that may represent stelar tissues (S). PP3055. × 2.6. 4. Plant base sectioned and uncovered to reveal three dimensionality of axis. Infilling mineral material has been removed. Arrows indicate position of section in Fig. 3. PP3055. X 1.8.
173 appendages, with t h e o u t e r rim r e p r e s e n t i n g the o u t e r c o r t e x and t h e inner h o l l o w c o r r e s p o n d i n g t o a b r o k e n area o f i n n e r vascular tissue and a hollow, a e r e n c h y m a t o u s m i d d l e c o r t e x (Jennings et al., 1983). T h e s e c o n d specimen o f C. m a z o n e n s i s is slightly larger (5.4 cm long, 1.1 c m in d i a m e t e r at t h e s t e m level and 2.9 c m across t h e widest area o f the plant base) (Plate I, 4; Plate II, 1). It is also a s y m m e t r i c a l d u e t o a lateral bulge (Plate I, 4; at right), and is f l a t t e n e d p r o x i m a l l y . T h i s s p e c i m e n is preserved as a c o m b i n a t i o n mold-cast. T h e central p o r t i o n o f t h e stem axis is m i n e r a l i z e d with sphalerite a n d calcite (Plate I, 4; at t o p ) . Near t h e p r o x i m a l end, t h e axis is filled in with h o m o g e n o u s sediment. A transverse section at t h e level o f t h e p l a n t base shows t h e cast o f t h e axis (Plate I, 3, 4). A l t h o u g h t h e s y m m e t r y o f t h e living p l a n t base c a n n o t conclusively be d e t e r m i n e d , at this level t h e axis was clearly f l a t t e n e d laterally (Plate I, 3, 4). D i f f e r e n t i a l p r e s e r v a t i o n within t h e axis provides a line o f d e m a r c a t i o n b e t w e e n t h e central, d i s t o r t e d c y l i n d e r (Plate I, 3) and t h e r e m a i n d e r o f t h e axis. Prior to crushing t h e i n n e r c y l i n d e r c o m p r i s e d a p p r o x i m a t e l y o n e half t h e d i a m e t e r o f the entire axis {7.8--17.3 m m ) . Considering the ratio o f stele t o axis a m o n g l y c o p o d s such as Chaloneria with limited s e c o n d a r y tissue p r o d u c tion, it is reasonable t o assume this d e m a r c a t i o n r e p r e s e n t s the o u t e r bound a r y o f t h e stelar region (Eggert, 1 9 6 1 ; Jennings e t al., 1 9 8 3 ; R o t h w e l l , 1 9 8 4 ) . W h e t h e r it represents p r i m a r y b o d y or a c o m b i n a t i o n o f p r i m a r y and s e c o n d a r y tissues c a n n o t be d e t e r m i n e d . U n c o v e r i n g o f t h e u n e x p o s e d side o f t h e plant base shows 2--3 conspicu o u s lateral ridges (Plate II, 1 ; at arrows). T h e s e are similar t o cortical ridges seen o n t h e Mesozoic l y c o p o d Nathorstianella (Glaessner and Rao, 1 9 5 5 ) , and l y c o p h y t e bases f r o m A r g e n t i n a ( A r c h a n g e l s k y et al., 1 9 8 1 ; C u n e o and Andreis, 1983) and m a y r e p r e s e n t e i t h e r areas o f u n e v e n cortical proliferation [e.g., Chaloneria (Pigg a n d R o t h w e l l , 1 9 8 3 a ) ] o r t h e result o f vertical c o m p r e s s i o n o f t h e axis. N u m e r o u s small p u n c t a e 0.3 m m in d i a m e t e r o c c u r o n t h e base, b u t their lack o f m o r p h o l o g y and a p p a r e n t l y r a n d o m p o s i t i o n preclude further interpretation.
PLATE II Cormophyton mazonensis 1. Proximal end of specimen in Plate I, 4. Specimen has been uncovered from opposite side to reveal surface. Note horizontal--oblique bulges on specimen (arrow). PP3055. x2.1. 2. Root trace broken differentially to reveal inner hollow and outer rim (arrow at bottom). Root traces are subtended by cortical bulges (arrow at top). From part specimen. PP26291. x 9.7. 3. Stigmarioides surface pattern of axis. Ill. State Mus. 8688. x 7. 4. Roots of counterpart specimen (higher magnification of Plate I, 1 at right). PP26291. ×9.7. 5. Stem axis in counterpart specimen of Plate I, 1 showing helically arranged leaf traces at decortication level. PP26291. x 10. 6. Invertebrate structures in matrix of mold-cast specimen thought to represent spirorbid worm tubes. Lateral view at top, and cross section (arrow). PP3055. x 9.8.
174 A delicate striate pattern occurs both on the surface and several subsurfaces of the specimen (Plate I, 2). Since the pattern consistently occurs parallel to the plane of fracture, and across a variety of tissues, it probably represents a mineralization or fracture pattern, and as such is of preservational origin rather than of biological significance. Associated with the cast are a number of small invertebrates approximately 2.1 mm across and 0.7 mm in diameter (Plate II, 6). Based on their size and shape, and known occurrence in Mazon Creek nodules they appear similar to spirorbid worm tubes. DISCUSSION
Systematic relationships Size, shape and morphological features of Cormophyton suggest that among known cormose lycophytes of Carboniferous age, Cormophyton is most closely associated with the Chaloneriaceae. Plant bases are comparable in size to the base of Chaloneria if the cortical tissues are removed (Fig.lB, G). In contrast, they are both much larger than the diminutive Paurodendron (2.0 mm, Phillips and Leisman, 1966; Rothwell and Erwin, 1985), and morphologically unlike Oxroadia (Long, 1971) which apparently lacks a cormose base. In addition, decorticated leaf trace scars correspond in size and general shape to parichnos scars of Chaloneria (Pigg and Rothwell, 1983a). Roots and root traces are slightly smaller, but possess morphological features identical to those of both Paleozoic lycopods (e.g., Lepidosigillaria, Protostigmaria) and some Mesozoic forms. Based on the presence of the inner vascular tissue, a central hollow zone and an outer cortical rim, they can further be interpreted as analogous to stigmarian rootlets (Jennings et al., 1983). In Chaloneria, root traces with monarch, wedge-shaped vascular bundles have been f o u n d only within the outer cortical tissues. Each is surrounded by delicate, thin walled zone of inner cortical cells that accompany the trace into the outer cortex (Pigg and Rothwell, 1979). Including the accompanying inner cortex, each is approximately 0.5 mm in diameter. Although external features and rhizotaxy of Chaloneria are not known, it is reasonable to assume that the addition of an outer cortical region (making up the "rim") would result in roots of size comparable to Cormophyton. In contrast, roots of Oxroadia are known to be considerably larger (up to 6 mm) and helically arranged (Long, 1971), while those of Paurodendron are less than 0.5 mm in diameter and very numerous (Phillips and Leisman, 1966). The presence of spores diagnostic of the Chaloneriaceae in the Mazon Creek nodule flora provides some indirect evidence of a Chaloneria-like plant in these sediments. Numerous nodules contain isolated megasporangia assigned to Lepidocystis or Lepidostrobopsis Abbott (1963) which contain Triletes (Valvisisporites) megaspores (Lesquereux, 1880; Chaloner, 1958) and microsporangia containing Endosporites; spore types considered diagnostic of the Chaloneriaceae (Pigg and Rothwell, 1983b). Specimens of
175 both isolated mega- and microsporangia from Mazon Creek were included in the compression genus Polysporia b y Chaloner (1958). However, among compression and authigenetically preserved fossils, complete fructifications bearing these spore types are generally rare. Presumably, these fructifications disarticulated into individual sporangia, resulting in the more c o m m o n l y encountered isolated sporangia Lepidocystis and Lepidostrobopsis. The fructifications of Polysporia (Chaloner, 1958) and Chaloneria (Pigg and Rothwell, 1983a) are characterized by large, loosely aggregated sporangia that are n o t unlike those of Lycopodium obscurum. The Chaloneriaceae was established as a family within the Isoetales for vegetative and reproductive stems of the permineralized plant Chaloneria. Diagnostic features could not be adequately compared with members of the Pleuromeiales, which represent stratigraphic intermediates. The only compressions presently assigned to the Chaloneriaceae (e.g., Sporangiostrobus, Bodeodendron, and Puertollania) are stem segments and fertile regions which provide no information a b o u t the plant base. Cormophyton provides evidence of several morphological features of the external plant base characteristic of the Chaloneriaceae, and thus provides an initial comparison with late Paleozoic and Mesozoic forms. Species of Pleuromeia and related forms (i.e., Cylomeia, Nathorstiana, Nathorstianella) are a diverse assemblage of plants that vary in size, shape, and degree of lobing of the plant base, as well as in vegetative and fertile features (Fig.2). T h e y are widely distributed both geographically and stratigraphically throughout the late Paleozoic and Mesozoic. In general size Cormophyton is very similar to several species of Pleuromeia, as well as Cylomeia and Nathorstiana (compare Fig.lB with Fig.2A, D, C). Of features present that can be compared to the Mesozoic forms, differences exist in shape of the Cormophyton base, degree of lobing, and stem decortication pattern. Traces in Pleuromeia, even at decortication levels, tend to show a conspicuous transversely elongated, often double, vascular trace (e.g. M~igdefrau, 1932; Neuburg, 1961). At the present time perhaps the most significant aspect that emerges from this comparison is the degree of diversity present throughout the Paleozoic and Mesozoic. Whether similarity in size and growth habit of Paleozoic and Mesozoic cormose forms reflects a phylogenetic relationship or one or more adaptive convergences remains an open question. The discovery of additional forms, information a b o u t whole plant reconstructions, and a more complete understanding of pleuromeialean ontogeny (e.g. Karrfalt, 1984) will undoubtedly further refine ideas of phylogeny among the lycopods.
Relationship to Stigmarioides The Mazon Creek flora has been extensively collected and studied b y amateurs and paleobotanists for over a century (Nitecki, 1979). Among the earliest to investigate this flora was Lesquereux (1870, 1880). He described several specimens as rooting organs of uncertain affinities, some of which he
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Fig.2. Mesozoic lycopod plant bases. A. Pleuromeia longicaulis (from Retallack, 1975). × 1. B. Nathorstianella arborea (from M~igdefrau, 1932). x 1. C. Nathorstiana babbagensis (From Glassner and Rao, 1955). x 1. D. Cylomeia undulata (from White, 1981). x 1. E. Pleuromeia hattaii (from Kon'no, 1973). x 1. F. Pleuromeia sternbergii (from SolmsLaubach, 1899). × 1. G. Pleuromeia rossica (from Neuburg, 1961). x 1. H., J. Pleuromeia jiaochengensis (from Wang and Wang, 1982). x 1.
suspected were of l y c o p o d a c e o u s origin. T h e s e include Stigmarioides trun-
catus, S. villosus, S. tuberosus, S. lineralis, S. affinis, S. rugosus, Stigrnaria evenii, Sigillarioides radicans, and Rachiopteris (Stigmarioides) selago. O f these, S. truncatus is m o s t c o m p a r a b l e t o t h e p r e s e n t material. However, a reinvestigation o f the t y p e specimen o f Stigmarioides truncatus reveals t h a t its r o o t i n g n a t u r e is questionable.
177
Our investigation of the figured h o l o t y p e of Stigmarioides truncatus reveals a cylindrical lycopsid axis 5.7 cm long and 2.4 cm across, with helically arranged ellipsoid-rounded appendage scars 1.8 mm across and 1.2 mm high covering the surface (Plate II, 3; Plate III, 1, 3). Scars lack evidence of vascular traces or parichnos strands, b u t are similar in size and shape to scars of some species of Cyclostigma [e.g., C. minutum (Haughton, 1859); the late Devonian C. kiltorkense (Schweitzer, 1969)]. The branching of the axis at the distal end (Plate III, 1) also bears appendage scars and is apparently a continuation of the major axis. Eight appendages were f o u n d in attachment to the axis (Plate III, 2, 4). They are 1.2 mm wide and up to 10.4 mm long. Most are oriented at an oblique angle to the main axis (Plate III, 1, 4) while one is oriented at nearly a right angle (Plate III, 1, 2). Based on available evidence it is difficult to determine whether the appendages represent leaves or roots. Lesquereux (1880) illustrated the specimen in such a way as to suggest they represent downward-growing roots, b u t it is equally possible that the specimen is either inverted from its proper orientation, or, if the appendages represent leaves, they are bent downward. T w o features suggest the appendages m a y represent leaves. First, the appendages appear to be composed of cells whose long axes are parallel to that of the appendage, resembling the epidermis of lycophyte leaves (Plate III, 4). Second, appendage scars are similar to those of stem segments of Cyclostigma, which although confused in the past with Stigmaria, have been generally regarded as an above ground axis (Crookall, 1964). A vertically oriented striate pattern covers the surface of the axis and like that of Cormophyton, is probably due to mineralization patterns of the axis rather than to stem anatomy. Other species of Stigmarioides are equally problematical. In his investigation of Lesquereux's t y p e material, Janssen (1940) reinterpreted S. radicans as an inverted l y c o p o d stem segment, which he reassigned to Bothrodendron sp. Stigmarioides tu berosus was thought b y Janssen to be a poorly preserved seed coat and he reassigned it to Carpolithus sp., while Rachiopteris (Stigmaroides) selago of Lesquereux was placed in Incertae Sedis and interpreted as a composite of several plant parts (Janssen, 1940). Based on the available evidence, including Janssen's (1940) figures and photographs of types, we agree with Janssen's conclusions regarding these forms. O f the remaining species, S. lineralis and S. affinis represent elongate rootlike structures that m a y represent either poorly preserved stigmarian rootlets or roots of other plant types. From photographs, Stigmarioides viUosus is apparently quite similar to S. tuberosus, which Janssen renamed Carpolithus, and m a y also represent a poorly degraded seed. Stigmaria evenii, a taxon Lesquereux allied with Stigmarioides clearly represents a portion of lycopsid axis, b u t there is no reason to consider it a rooting structure. Material or figures of Stigmarioides rugosus was unavailable for study. The generic concept of Stigmarioides has been considered because it may encompass the present specimens. This assignment is rejected, however, because n o t only are specimens clearly different, b u t the h o l o t y p e of Stigma-
Qo
179
rioides cannot conclusively be identified with its original generic concept (i.e., rooting organs) and there is, basically, no well defined category that could be expanded to include new genera. Cursory examination of the seven species of Stigmarioides and t w o similar taxa (i.e., Stigmaria evenii and Sigillarioides radicans) indicates that only t w o (S. lineralis and S. affinis) m a y actually represent rooting organs assignable to Stigmarioides. These forms are markedly different in morphology, size and structure. Since the holotype, S. truncatus cannot be interpreted as representing a rooting organ, the genus Stigmarioides cannot be based on its original holotype and a new holot y p e should be designated and the name retained for Incertae Sedis rooting organs. The t a x o n o m y should be reorganized so as not to confuse it with true lycopsid plants with cormose bases (e.g. Cormophyton), true Stigmaria or true roots of other vascular plants. ACKNOWLEDGEMENTS
We thank Dr. Peter R. Crane, Department of Geology, Field Museum of Natural History, Chicago for loaning us the Mazon Creek nodules studied in the present contribution. Thanks are also due to Drs. Richard L. Leafy and James E. Mickle, Illinois State Museum, for allowing us to examine t y p e material of Stigmarioides truncatus illustrated by Lesquereux and photographs of other Illinois State Museum specimens, and Dr. Andrew H. Knoll, Harvard Biological Museum, for providing photographs of additional material of Stigmarioides species. We also thank Dr. Eric E. Karrfalt for his interpretation of the rhizotaxy of our material, and Mr. David Dennis, for illustrations. This study was supported in part b y Grant DEB-8001803 from the National Science Foundation. REFERENCES Abbott, M.L., 1963. Lycopod fructifications from the Upper Freeport (No.7) coal in southeastern Ohio. Palaeontographica, 112B: 93--118. Alvin, K.L., 1965. A new fertile lycopod from the Lower Carboniferous of Scotland. Palaeontology, 8 : 281--293. Archangelsky, S., Azcuy, C.L. and Wagner, R.H., 1981. Three dwarf lycophytes from the Carboniferous of Argentina. Scr. Geol., 64: 1--35. Chaloner, W.G., 1956. On Sporangiostrobus langfordi sp. nov., a new fossil lycopod c o n e from Illinois. Am. Midl. Nat., 55: 437--442. Chaloner, W.G., 1958. Polysporia mirabilis Newberry, a fossil lycopod cone. J. Paleontol., 32: 199--209.
PLATE III 1. Type species of Stigmarioides truncatus Lesquereux. Note attached appendages (at arrows). Ill.State Mus. 8688. × 1.6. 2. Appendage attached at right angles to axis. x 7. 3. Appendage scars on surface of specimen, x 7. 4. Appendage at acute, d o w n w a r d angle to axis. x 7.
180 Chaloner, W.G., 1984. Evidence of ontogeny of two late Devonian plants from Kiltorcan, Ireland. In: Abstr. Contrib. Pap. Poster Sess., 2nd Int. Organ. Paleobot. Conf., Edmonton, Alta. Charlton, W.A. and Watson, J., 1982. Patterns of arrangement of lateral appendages on axes of Stigmaria ficoides (Sternberg) Brongniart. Bot. J. Linn. Soc., 84: 209--221. Crookall, R., 1964. Fossil plants of the Carboniferous rocks of Great Britain, 2nd section. Palaeontology, 4: 217--354. Cuneo, R. and Andreis, R.R., 1983. Estudio de uno bosque de licofitas en la formacion Nueva Lubecka, Permico de Chubut, Argentina. Implicancias paleoclimaticas y paleogeograficas. Ameghiniana, 20: 132--140. Drfibek, K., 1976. Polysporia robusta sp. n. from the Carboniferous of Central Bohemia. Cas. Nar. Muz. Odill Prirodoved., 145: 204--208. Eggert, D.A., 1961. The ontogeny of the arborescent Carboniferous Lycopsida. Palaeontographica, 108B: 43--92. Eggert, D.A., 1972. Petrified Stigmaria of sigillarian origin from North America. Rev. Palaeobot. Palynol., 14: 85--99. Frankenberg, J.M. and Eggert, D.A., 1969. Petrified Stigmaria from North America: Part I. Stigmaria ficoides, the underground portions of Lepidodendraceae. Palaeontographica, 128B: 1--47. Glaessner, M.F. and Rao, V.R., 1955. Lower Cretaceous plant remains from the vicinity of Mount Babbage, South Australia. Trans. R. Soc. South Aust., 78: 134--140. Haughton, R., 1859. On Cyclostigma, a new genus of fossil plants from the Old Red Sandstone of Kiltorcan, Co. Kilkenny; and on the general law of phyllotaxis in the natural orders -- Lycopodiaceae, Equisetaceae, Filices, etc. R. Dublin Soc. J., 2 : 407--420. Hoskins, J.H. and Abbott, M.L., 1956. Selaginellites crassicinctus, a new species from the Desmoinesian series of Kansas. Am. J. Bot., 43: 36--46. Janssen, R.E., 1940. Some fossil plant types of Illinois. In: Sci. Pap., Vol. I, Illinois State Museum. Jennings, J.R., 1975. Protostigmaria, a new plant organ from the Lower Mississippian of Virginia. Palaeontology, 18: 19--24. Jennings, J.R., Karrfalt, E.E. and Rothwell, G.W., 1983. Structure and affinities of Protostigmaria eggertiana. Am. J. Bot., 70: 963--974. Johnson, T., 1913. On Bothrodendron (Cyclostigma) kiltorkense sp. Haughton. In: Proc. R. Dublin Soc., 18: 500--528. Karrfalt, E.E., 1981. The comparative and developmental morphology of the root system of SelagineUa selaginoides (L.) Link. Am. J. Bot., 68: 244--253. Karrfalt, E.E., 1984. Further observations on Nathorstiana (Isoetaceae). Am. J. Bot., 71: 1023--1030. Kon'no, E., 1973. New species of Pleuromeia and Neocalamites from the Upper Scythian Bed in Kitakiani Massif, Japan. In: Sci. Rep. 2nd ser. (Geol.), Tohoku Univ., 43: 99-115. Kr~iusel, R. and Weyland, H., 1949. Gilboaphyton and the Protolepidophytales: Plant remains of the Devonian. XIV. Senckenbergiana, 30: 129--152. Lesquereux, L., 1870. Report of the fossil plants of Illinois. Part lI. Sect. II. Ill. State Geol. Surv., 4: 375--508. Lesquereux, L., 1879--1884. Description of the coal flora of the Carboniferous formation in Pennsylvania and throughout the United States. In: 2nd Penna. Geol. Surv. P., 3 vols. (Atlas plate 1--85, 1879; Part I: 1--354; Part II: 355--694, 1880; Part III: 695--977, 1884). Long, A.G., 1971. A new interpretation of Lepidodendron calamopsoides Long and Oxroadia gracilis Alvin. Trans. R. Soc. Edinburgh, 68: 491--506. Miigdefrau, K., 1932. Ober Nathorstiana, eine Isoi~tacee aus dem Neokom yon Quedlinburg a. Harz. Beih. Bot. Centralbl., 49: 706--718. M~igdefrau, K., 1968. Pal~iobiologie der Pflanzen. Fischer, Jena, p.549.
181 Neuburg, M.F., 1961. New data o n the morphology of Pleuromeia Corda from the Lower Triassic of the Russian Platform. Dokl. Akad. Nauk SSSR, 1 3 6 : 4 4 5 - - 4 4 8 (in Russian); 1 3 6 : 2 0 0 - - 2 0 3 (English translation). Nitecki, M.H., 1979. Mazon Creek fauna and flora: a hundred years of investigation. In: M.H. Nitecki (Editor), Mazon Creek Fossils. Academic Press, New York, N.Y., 581 pp. Paolillo, D., 1982. Meristems and evolution: developmental correspondence among rhizomorphs of the lycopsids. Am. J. Bot., 69: 1032--1042. Pfefferkorn, H.W., 1979. High diversity and stratigraphic age of the Mazon Creek flora. In: M.H. Nitecki (Editor), Mazon Creek Fossils. Academic Press, New York, N.Y., 581 pp. Phillips, T.L. and Leisman, G.A., 1966. Paurodendron, a rhizomorphic lycopod. Am. J. Bot., 53: 1086--1100. Pigg, K.B. and Rothwell, G.W., 1979. Stem-root transition of an Upper Pennsylvanian woody lycopsid. Am. J. Bot., 66: 914--924. Pigg, K.B. and Rothwell, G.W., 1983a. Chaloneria gen. nov., heterosporous lycophytes from the Pennsylvanian of North America. Bot. Gaz., 144: 132--147. Pigg, K.B. and Rothwell, G.W., 1983b. Megagametophyte development in the Chaloneriaceae faro. nov., permineralized Paleozoic Isoetales (Lycopsida). Bot. Gaz., 144: 295-302. Potoni6, H., 1894. Die Wechselzonenbildung der Sigillariaceen. In: Jahrb. Preuss. Geol. Landesanst., pp.24--67. Remy, W. and Remy, R., 1975. Sporangiostrobus puertollanensis n. sp. und PuertoUania sporangiostrobifera n. gen., n. sp., aus dem Stefan yon Puertollano, Spanien. Argumenta Palaeobot., 4 : 13--29. Retallack, G., 1975. The life and times of a Triassic lycopod. Alcheringa, 1 : 3--29. Rothwell, G.W., 1984. The apex of Stigmaria (Lycopsida), rooting organ of Lepidodendrales. Am. J. Bot., 71: 1031--1034. Rothwell, G.W. and Erwin, D.M., 1985. The rhizomorph apex of Paurodendron and homologies among the rooting organs of Lycopsida. Am. J. Bot. (in press). Schopf, J.M., 1979. Evidence of soft-sediment cementation enclosing Mazon plant fossils. In: M.H. Nitecki (Editor), Mazon Creek Fossils. Academic Press, New York, N.Y., 581 pp. Schlanker, C.M. and Leisman, G.A., 1969. The herbaceous Carboniferous lycopod Selaginella fraiponti comb. nov. Bot. Gaz., 130: 35--41. Schweitzer, H.-J., 1969. Die Oberdevon-Flora der B~eninsel, 2. Lycopodiinae. Palaeontographica, 126B: 101--153. Solms-Laubach, H., 1899. Ueber das GenusPleuromeia. Bot. Z., 12: 230--243. Wagner, R.H. and Spinner, E., 1976. Bodeodendron, tronc associ6 ~t Sporangiostrobus. C.R. Acad. Sci. (Paris), S4r.D., 282: 353--356. Wang, Z. and Wang, L., 1982. A new species of the lycopsid Pleuromia from the early Triassic of Shanxi, China, and its ecology. Palaeontology, 25: 215--225. Weiss, E. and Sterzel, T., 1893. Die Sigillarien der preussischen Steinkohlen- und Rothliegenden-Gebiete. II. Die Gruppe der Subsigillarien. Abh. KSnig. Preuss. Geol. Landesanst. N. F., 2: 1--255; Atlas Tafel 1--128. White, D., 1907. A remarkable fossil tree trunk from the Middle Devonic of New York. N.Y. State Mus. Bull., Geol. Pap., 107. White, M.E., 1981. Cylomeia undulata (Burges) gen. et comb. nov., a lycopod of the early Triassic strata of New South Wales. Rec. Aust. Mus., 33: 723--734.
165
CORMOPHYTON GEN. NOV., A CORMOSE LYCOPOD FROM THE MIDDLE P E N N S Y L V A N I A N M A Z O N CREEK F L O R A
KATHLEEN
B. PIGG and T H O M A S
N. T A Y L O R
Department of Botany, The Ohio State University, 1 735 Neil Avenue, Columbus, OH 43210 (U.S.A.) (Received May 5, 1984 ; revised and accepted November 14, 1984)
ABSTRACT Pigg, K.B. and Taylor, T.N., 1985. Cormophyton gen. nov., a cormose lycopod from the middle Pennsylvanian Mazon Creek flora. Rev. Palaeobot. Palynol., 44: 165--181.
Cormophyton mazonensis gen. et sp. nov. is proposed for an authigenically preserved cormose lycopod base in Mazon Creek nodules from the middle Pennsylvanian of Illinois. Based on size, shape, and morphological features, Cormophyton is assigned to the Chaloneriaceae and is thought to represent a plant similar to Chaloneria cormosa. The discovery of this form allows for the description of several external features of Chaloneria-like plant bases and further demonstrates the diversity of isoetalean lycophytes in Carboniferous sediments. INTRODUCTION
For many years paleobotanists have regarded the underground parts of most Paleozoic lycopods as consisting of dichotomously branched axial systems. This concept is based to a large extent on the knowledge of stigmarian systems (Fig.lA) associated with such taxa as Lepidodendron, Lepidophloios, and SigiUaria (e.g. Frankenberg and Eggert, 1969; Eggert, 1972). These ideas are in part responsible for the hypothesized phylogeny of the lycopods as a reduction series beginning with an arborescent m e m b e r such as Sigillaria, and culminating with the extant taxon Isoetes (e.g. Potoni~, 1894; M~igdefrau, 1968). However, despite this rather well-established series, a number of diverse Paleozoic lycopods are n o w known to possess underground parts that are morphologically distinct from the dichotomous systems. Among Devonian forms, Lepidosigillaria whitei was an arborescent lycopod with a swollen, rounded underground axial system bearing numerous rootlets (Fig.lE; White, 1907; Kr~iusel and Weyland, 1949). Nothing is k n o w n about the anatomy of this taxon, b u t the lack of a stigmarian system together with its Devonian age has for some time suggested that this plant might represent a predecessor to later isoetalean forms (Jennings et al., 1983). Specimens of Cyclostigma kiltorkense are also believed to have been arborescent and possess a conspicuous bilobed base with "stigrnarian" scars (Johnson, 1913; Schweitzer, 1969). As basal specimens are incomplete, it is difficult to deter0034-6667/85/$03.30
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Fig.1. Paleozoic lyeopod bases. Figures are redrawn from original sources and indicate the typical reconstructions of taxa. They do not, in all cases, accurately demonstrate all known features of genera, but serve to illustrate basic morphological diversity inherent in known forms. Not to scale. A. Stigmaria ficoides, z 1/30. B. Cormophyton mazonensis, x 1. C. Oxroadia gracilis (from Long, 1971). × 1. D. Paurodendron fraiponli (from Philips and Leisman, 1966). x 10. E. Lepidosigillaria whitei (from White, 1907). ~ 1/8. F. Protostigrnaria eggertiana (from Jennings, 1975). x 1/4. G. Chaloneria cormosa with broken lines representing cortex (from Pigg and Rothwell, 1979). x 1. H. Lycophyte base from the Carboniferous of Argentina (from Archangelsky et al., 1981). x 3/4.
167 mine whether plant bases were cormose, bilobed organs (e.g. Chaloner, 1984) or bore stigmarian axes (Johnson, 1913; Schweitzer, 1969). It is our opinion that an accurate reconstruction of Cyclostigma cannot be made with confidence from presently figured material. The Mississippian genus Protostigmaria consists of a variable n u m b e r (up to thirteen) of irregular lobes bearing numerous rootlets (Fig.lF; Jennings, 1975; J ennings et al., 1983). Like Lepidosigillaria, this plant was arborescent, with segments of the above-ground stem Lepidodendropsis, preserved up to 1.7 m in length. It has been suggested that this multilobed plant base presumably grew similarly to that of a multilobed lsoetes with contractile roots which provided support and anchorage for a fairly large tree (Jennings et al., 1983). Smaller Carboniferous lycophytes that are anatomically preserved include Paurodendron and Oxroadia. Paurodendron fraiponti exhibits a swollen base, termed a rhizomorph, that bears helically arranged roots (Fig.lD; Phillips and Leisman, 1966). Although Paurodendron was renamed Selaginella fraiponti by Schlanker and Leisman (1969), based on its association with a Selaginellites crassicinctus cone (Hoskins and Abbott, 1956), interpretations of Paurodendron have varied. F o r example, Karrfalt (1981) pointed out that the bipolar growth habit suggests a plant unlike Selaginella. Following the interpretation of Schlanker and Leisman, eaolillo (1982) relied on Paurodendron as a model for phylogeny among cormose-based lycophytes. He compared the known ontogenetic features of Selaginella selaginoides with the implied development of Paurodendron. At that time complete specimens of Paurodendron plant bases were unknown. Interestingly, more recent work suggests that Paurodendron is ontogenetically more similar to Stigmaria, than Selaginella (Rothwell and Erwin, 1985). Oxroadia gracilis (Alvin, 1965) is a slender plant that branches sparsely and produces new lateral roots from older roots (Fig.lC). The basal portion of the plant is interpreted as lacking a swollen cormlike base (Long, 1971). It has been suggested (Karrfalt, 1981) that Oxroadia may belong to a group of yet unrecognized, small upright lycopods that are unlike those of the typical, extant herbaceous lycopods with unidirectional growth (e.g., Selaginella
selaginoides ). Recent investigations of G o n d w a n a plants from Argentina have revealed several dwarf lycophytes with cormose plant bases that occur in situ in both Carboniferous (Archangelsky et al., 1981) and Permian sediments (Cuneo and Andreis, 1983). The Carboniferous specimen (Fig.lH) has been found in association with stems described as Bumbumdendron b u t complete details of the plant are n o t known. Numerous molds of plant bases lacking stigmarian axes have been described from the Chubut Province of Argentina (Cuneo and Andreis, 1983). The prevalance of lycophytes with this growth form has been taken by the authors as paleoecological evidence that plants grew in drier, rather than swamp-like, environments. Perhaps the most completely known Paleozoic lycopod that lacks the stigmarian subaerial system is Chaloneria cormosa (Pigg and Rothwell, 1983a;
168 Fig.lG). Chaloneria demonstrates a combination of morphological, anatomical and reproductive features that are more similar to those of Isoetes than to the Lepidodendrales (Pigg and Rothwell, 1983a, b). Vegetative similarities between Chaloneria and Isoetes include a cormose, bilaterally symmetrical plant base, small amounts of secondary tissues, sporangial trabeculae, parichnos, and non-abscising leaf bases (Pigg and Rothwell, 1979, 1983a). The reproductive structures of b o t h Isoetes and Chaloneria consist of simple, diffuse bisporangiate fertile regions as opposed to compact strobili. Morphologically, Chaloneria exhibits an unbranched stem several meters tall which differs markedly from both the stunted stem of Isoetes and the arborescent habit so c o m m o n in the lepidodendrids. Although the anatomy of the basal regions of Chaloneria has been documented (Pigg and Rothwell, 1979), extrastelar tissues are generally absent. Moreover, with the exception of vegetative stem axes attributed to Sporangiostrobus (e.g., Puertollania [ R e m y and Remy, 1 9 7 5 ] ; Bodeodendron [Wagner and Spinner, 1976]), compressions assigned to the Chaloneriaceae consist entirely of fertile parts [e.g., Polysporia (Chaloner, 1958; Drfibek, 1976); Sporangiostrobus (Chaloner, 1956; Remy and Remy, 1975)]. Since the external morphology of basal portions of these plants continues to remain poorly known, a comparison with the well-known Mesozoic lycophyte compressions (e.g., Pleuromeia) has not been possible. The present contribution describes a newly recognized, cormose lycopsid plant base from the middle Pennsylvanian Mazon Creek nodule flora. Although internal tissues are lacking, specimens of Cormophyton mazonensis gen. et sp. nov. exhibit a complement of morphological features suggesting its inclusion within the Chaloneriaceae. Cormophyton increases our understanding of the morphology of the underground parts of lycopods and provides a potential method of comparing the Pennsylvanian members of the Chaloneriaceae with Mesozoic lycopods such as Pleuromeia. The presence of lycopods possessing isoetalean features by the middle Pennsylvanian underscores the early radiation of the group. MATERIALS AND METHODS The following description is based on two specimens preserved in ironstone nodules collected from the famous Mazon Creek locality in northern Illinois (Nitecki, 1979). The specimens are authigenically preserved concretions associated with the Francis Creek Shale which is stratigraphically placed in the Desmoinesian Series (= upper Westphalian D) (Pfefferkorn, 1979). T h e y represent a portion of the Mazon Creek nodule collection of the Field Museum of Natural History (Chicago) and bear the acquisition numbers PP3055 and PP26291. Hot dilute (2.5%) hydrochloric acid was used to remove oxidized materials on the surfaces of specimens according to the procedures outlined by Schopf (1979). Specimens were also sectioned and fractured to reveal three-dimensional shape of some morphological features. Surface features were recorded
169
using low angle lighting to enhance delicate features. Specimen surfaces were also examined via scanning electron microscopy. For comparative purposes, the t y p e specimen of Stigmarioides truncatus was also examined. The specimen is housed at the Illinois State Museum, Springfield and bears the acquisition n u m b e r 8688. SYSTEMATIC DESCRIPTION
Cormophyton mazonensis gen. et sp. nov. Pigg et Taylor Type species: Cormophyton mazonensis Diagnosis: R o u n d e d and/or lobed lycopsid plant base, up to 5 cm long, 2.6 cm wide at broadest portion of base or approximately 17.3 mm in diameter prior to crushing; attached to upright stem 1.6 cm in diameter. Stele at the level of plant base 7.5 X 1.5 X 4 mm, or approximately 7.8 mm in diameter prior to crushing. Helically arranged leaf bases on stem; represented by rounded bulges 1 mm wide X 1.5 mm high at decortication level. R o o t traces arranged in pattern with orthosticies and parasticies equal in number. Roots approximately 1 mm in diameter, with inner single or double bulge and outer margin or broken to reveal prominent outer rim and central hollow region. Vertically elongate bulges associated with r o o t traces and lateral ridges present on plant base.
Holotype: PP26291 {Plate I, 1; Plate II, 1,2,4,5). Paratype: PP3055 {Plate I, 2--4; Plate II, 1, 6). Type localities: Will and Grundy Counties, Illinois. Horizon: Mazon Creek nodules associated with the Francis Creek Shale; Desmoinesian Series (= upper Westphalian D) (Pfefferkorn, 1979), middle Pennsylvanian. Etymology: The generic designation Cormophyton [kormion, Gr.: corm; phyton, Gr.: plant] refers to the cormlike plant base. The specific epithet, mazonensis is taken from Mazon Creek, Illinois, the site at which the specimens occur. DESCRIPTION
The t w o specimens o f Cormophyton mazonensis consist of cormose plant bases attached to short stem segments. One specimen is 4.5 cm long, 1.6 cm in diameter in the stem region, and 2.6 cm wide in the broadest region of the base {Plate I, 1). The specimen is asymmetrical perhaps due to incomplete preservation. Whether the base o f the living plant was radially symmetrical like Stigmaria (RothweU, 1984), Paurodendron (Rothwell and Erwin, 1985}, and young specimens of Nathorstiana (Karrfalt, 1984), or bilaterally symmetrical like that of Chaloneria (Pigg and Rothwell, 1979), Isoetes, and some older specimens of Nathorstiana (Karrfalt, 1984) cannot be determined.
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171 F r a g m e n t s o f c a r b o n a c e o u s material are p r e s e n t o n t h e stem surface; however, it was n o t possible t o d e t e r m i n e a n y i n f o r m a t i o n a b o u t t h e epidermis or cuticle. Helically arranged, oval, widely-spaced bulges a p p r o x i m a t e l y 1 m m wide X 1.5 m m high o r n a m e n t t h e stem. T h e i r c o n s i s t e n t shape and arrangem e n t suggests t h a t these s t r u c t u r e s r e p r e s e n t leaf traces at a subsurface level (Plate II, 5}. Similar appearing bulges have b e e n r e p o r t e d o n a n u m b e r o f partially d e c o r t i c a t e d l y c o p h y t e c o m p r e s s i o n s [e.g., Sigillaria reticulata (Weiss a n d Sterzel, 1 8 9 3 , T a f . V I I , f i g . 3 3 ) ] . T h e y are also o f a size and shape comparable t o p a r i c h n o s strands in t h e o u t e r c o r t e x o f p e r m i n e r a l i z e d Chaloneria stems (Pigg and R o t h w e l l , 1983a). O n the base o f Cormophyton are n u m e r o u s r o o t traces (Plate I, 1). Alt h o u g h a d e f i n i t e r h i z o t a x y c o u l d n o t be d e t e r m i n e d f r o m specimens, o r t h o sticies and parasticies are equal in n u m b e r . Such a p a t t e r n is similar t o t h a t o f a t y p i c a l stigmarian axis d e s c r i b e d f o r stigmarian m o l d casts (Karrfalt, p e r s o n a l c o m m u n i c a t i o n ; C h a r l t o n a n d Watson, 1982). S u b t e n d i n g t h e individual r o o t traces are vertically e l o n g a t e d bulges t h a t give t h e s p e c i m e n an overall irregular surface (Plate II, 2). Each is u p t o 1.5 m m high, 0.7 m m wide, and e x t e n d s u p t o 0.7 m m at its d e p a r t u r e f r o m t h e plane o f t h e axis. In t h e m o s t c o m p l e t e l y preserved areas o f t h e c o u n t e r p a r t s p e c i m e n (Plate I, 1; at right), several r o o t s are p r e s e n t (Plate II, 4). T h e s p e c i m e n is f r a c t u r e d near t h e p l a n t / s e d i m e n t i n t e r f a c e w h e r e r o o t s were p r e s u m a b l y growing o u t into t h e s u r r o u n d i n g matrix. R o o t s are a p p r o x i m a t e l y 1 m m in d i a m e t e r and some are c h a r a c t e r i z e d b y an o u t e r margin t h a t s u r r o u n d s a single or d o u b l e inner bulge t h a t represents t h e area o f vascular tissue (Plate II, 4). A d d i t i o n a l r o o t traces o n t h e c o u n t e r p a r t are p o o r l y preserved, b u t their positions are clearly i n d i c a t e d b y w h i t e kaolinitic material w h i c h fills the cavities (Plate I, 1; Plate II, 4). R o o t s o n t h e p a r t s p e c i m e n lack a well preserved central region. E a c h r o o t consists o f an o u t e r rim and a central d e p r e s s i o n (Plate II, 2) w h e r e it a p p a r e n t l y b r o k e o f f or abscised at t h e base. M o r p h o l o g i c a l l y these r o o t s are quite similar t o ones t h a t have b e e n d e s c r i b e d in Lepidosigillaria (White, 1 9 0 7 ) , Protostigmaria eggertiana (Jennings et al., 1 9 8 3 ) , and a n u m b e r o f Mesozoic l y c o p h y t e s (e.g., Pleuromeia longicaulis [Retallack, 1 9 7 5 ] ). T h e r o o t s o f C. mazonensis a p p e a r similar t o stigmarian
PLATE I
Corrnophyton mazonensis (A = axis;S = stele) 1. Counterpart specimen showing plant--sediment interface and stem axis attached to bulbous base. Arrow indicates well preserved roots at right (see also Plate II, 4). White kaolinite fillings represent positions of poorly preserved root traces. Specimen has been cleared with hot hydrochloric acid. PP26291. x 2.4. 2. Striate surface pattern of axis, believed to be preservational. PP3055. x 9. 3. Cross section of proximal stem axis (A) seen in Plate I, 4 (at arrows) and inner distorted area that may represent stelar tissues (S). PP3055. × 2.6. 4. Plant base sectioned and uncovered to reveal three dimensionality of axis. Infilling mineral material has been removed. Arrows indicate position of section in Fig. 3. PP3055. X 1.8.
173 appendages, with t h e o u t e r rim r e p r e s e n t i n g the o u t e r c o r t e x and t h e inner h o l l o w c o r r e s p o n d i n g t o a b r o k e n area o f i n n e r vascular tissue and a hollow, a e r e n c h y m a t o u s m i d d l e c o r t e x (Jennings et al., 1983). T h e s e c o n d specimen o f C. m a z o n e n s i s is slightly larger (5.4 cm long, 1.1 c m in d i a m e t e r at t h e s t e m level and 2.9 c m across t h e widest area o f the plant base) (Plate I, 4; Plate II, 1). It is also a s y m m e t r i c a l d u e t o a lateral bulge (Plate I, 4; at right), and is f l a t t e n e d p r o x i m a l l y . T h i s s p e c i m e n is preserved as a c o m b i n a t i o n mold-cast. T h e central p o r t i o n o f t h e stem axis is m i n e r a l i z e d with sphalerite a n d calcite (Plate I, 4; at t o p ) . Near t h e p r o x i m a l end, t h e axis is filled in with h o m o g e n o u s sediment. A transverse section at t h e level o f t h e p l a n t base shows t h e cast o f t h e axis (Plate I, 3, 4). A l t h o u g h t h e s y m m e t r y o f t h e living p l a n t base c a n n o t conclusively be d e t e r m i n e d , at this level t h e axis was clearly f l a t t e n e d laterally (Plate I, 3, 4). D i f f e r e n t i a l p r e s e r v a t i o n within t h e axis provides a line o f d e m a r c a t i o n b e t w e e n t h e central, d i s t o r t e d c y l i n d e r (Plate I, 3) and t h e r e m a i n d e r o f t h e axis. Prior to crushing t h e i n n e r c y l i n d e r c o m p r i s e d a p p r o x i m a t e l y o n e half t h e d i a m e t e r o f the entire axis {7.8--17.3 m m ) . Considering the ratio o f stele t o axis a m o n g l y c o p o d s such as Chaloneria with limited s e c o n d a r y tissue p r o d u c tion, it is reasonable t o assume this d e m a r c a t i o n r e p r e s e n t s the o u t e r bound a r y o f t h e stelar region (Eggert, 1 9 6 1 ; Jennings e t al., 1 9 8 3 ; R o t h w e l l , 1 9 8 4 ) . W h e t h e r it represents p r i m a r y b o d y or a c o m b i n a t i o n o f p r i m a r y and s e c o n d a r y tissues c a n n o t be d e t e r m i n e d . U n c o v e r i n g o f t h e u n e x p o s e d side o f t h e plant base shows 2--3 conspicu o u s lateral ridges (Plate II, 1 ; at arrows). T h e s e are similar t o cortical ridges seen o n t h e Mesozoic l y c o p o d Nathorstianella (Glaessner and Rao, 1 9 5 5 ) , and l y c o p h y t e bases f r o m A r g e n t i n a ( A r c h a n g e l s k y et al., 1 9 8 1 ; C u n e o and Andreis, 1983) and m a y r e p r e s e n t e i t h e r areas o f u n e v e n cortical proliferation [e.g., Chaloneria (Pigg a n d R o t h w e l l , 1 9 8 3 a ) ] o r t h e result o f vertical c o m p r e s s i o n o f t h e axis. N u m e r o u s small p u n c t a e 0.3 m m in d i a m e t e r o c c u r o n t h e base, b u t their lack o f m o r p h o l o g y and a p p a r e n t l y r a n d o m p o s i t i o n preclude further interpretation.
PLATE II Cormophyton mazonensis 1. Proximal end of specimen in Plate I, 4. Specimen has been uncovered from opposite side to reveal surface. Note horizontal--oblique bulges on specimen (arrow). PP3055. x2.1. 2. Root trace broken differentially to reveal inner hollow and outer rim (arrow at bottom). Root traces are subtended by cortical bulges (arrow at top). From part specimen. PP26291. x 9.7. 3. Stigmarioides surface pattern of axis. Ill. State Mus. 8688. x 7. 4. Roots of counterpart specimen (higher magnification of Plate I, 1 at right). PP26291. ×9.7. 5. Stem axis in counterpart specimen of Plate I, 1 showing helically arranged leaf traces at decortication level. PP26291. x 10. 6. Invertebrate structures in matrix of mold-cast specimen thought to represent spirorbid worm tubes. Lateral view at top, and cross section (arrow). PP3055. x 9.8.
174 A delicate striate pattern occurs both on the surface and several subsurfaces of the specimen (Plate I, 2). Since the pattern consistently occurs parallel to the plane of fracture, and across a variety of tissues, it probably represents a mineralization or fracture pattern, and as such is of preservational origin rather than of biological significance. Associated with the cast are a number of small invertebrates approximately 2.1 mm across and 0.7 mm in diameter (Plate II, 6). Based on their size and shape, and known occurrence in Mazon Creek nodules they appear similar to spirorbid worm tubes. DISCUSSION
Systematic relationships Size, shape and morphological features of Cormophyton suggest that among known cormose lycophytes of Carboniferous age, Cormophyton is most closely associated with the Chaloneriaceae. Plant bases are comparable in size to the base of Chaloneria if the cortical tissues are removed (Fig.lB, G). In contrast, they are both much larger than the diminutive Paurodendron (2.0 mm, Phillips and Leisman, 1966; Rothwell and Erwin, 1985), and morphologically unlike Oxroadia (Long, 1971) which apparently lacks a cormose base. In addition, decorticated leaf trace scars correspond in size and general shape to parichnos scars of Chaloneria (Pigg and Rothwell, 1983a). Roots and root traces are slightly smaller, but possess morphological features identical to those of both Paleozoic lycopods (e.g., Lepidosigillaria, Protostigmaria) and some Mesozoic forms. Based on the presence of the inner vascular tissue, a central hollow zone and an outer cortical rim, they can further be interpreted as analogous to stigmarian rootlets (Jennings et al., 1983). In Chaloneria, root traces with monarch, wedge-shaped vascular bundles have been f o u n d only within the outer cortical tissues. Each is surrounded by delicate, thin walled zone of inner cortical cells that accompany the trace into the outer cortex (Pigg and Rothwell, 1979). Including the accompanying inner cortex, each is approximately 0.5 mm in diameter. Although external features and rhizotaxy of Chaloneria are not known, it is reasonable to assume that the addition of an outer cortical region (making up the "rim") would result in roots of size comparable to Cormophyton. In contrast, roots of Oxroadia are known to be considerably larger (up to 6 mm) and helically arranged (Long, 1971), while those of Paurodendron are less than 0.5 mm in diameter and very numerous (Phillips and Leisman, 1966). The presence of spores diagnostic of the Chaloneriaceae in the Mazon Creek nodule flora provides some indirect evidence of a Chaloneria-like plant in these sediments. Numerous nodules contain isolated megasporangia assigned to Lepidocystis or Lepidostrobopsis Abbott (1963) which contain Triletes (Valvisisporites) megaspores (Lesquereux, 1880; Chaloner, 1958) and microsporangia containing Endosporites; spore types considered diagnostic of the Chaloneriaceae (Pigg and Rothwell, 1983b). Specimens of
175 both isolated mega- and microsporangia from Mazon Creek were included in the compression genus Polysporia b y Chaloner (1958). However, among compression and authigenetically preserved fossils, complete fructifications bearing these spore types are generally rare. Presumably, these fructifications disarticulated into individual sporangia, resulting in the more c o m m o n l y encountered isolated sporangia Lepidocystis and Lepidostrobopsis. The fructifications of Polysporia (Chaloner, 1958) and Chaloneria (Pigg and Rothwell, 1983a) are characterized by large, loosely aggregated sporangia that are n o t unlike those of Lycopodium obscurum. The Chaloneriaceae was established as a family within the Isoetales for vegetative and reproductive stems of the permineralized plant Chaloneria. Diagnostic features could not be adequately compared with members of the Pleuromeiales, which represent stratigraphic intermediates. The only compressions presently assigned to the Chaloneriaceae (e.g., Sporangiostrobus, Bodeodendron, and Puertollania) are stem segments and fertile regions which provide no information a b o u t the plant base. Cormophyton provides evidence of several morphological features of the external plant base characteristic of the Chaloneriaceae, and thus provides an initial comparison with late Paleozoic and Mesozoic forms. Species of Pleuromeia and related forms (i.e., Cylomeia, Nathorstiana, Nathorstianella) are a diverse assemblage of plants that vary in size, shape, and degree of lobing of the plant base, as well as in vegetative and fertile features (Fig.2). T h e y are widely distributed both geographically and stratigraphically throughout the late Paleozoic and Mesozoic. In general size Cormophyton is very similar to several species of Pleuromeia, as well as Cylomeia and Nathorstiana (compare Fig.lB with Fig.2A, D, C). Of features present that can be compared to the Mesozoic forms, differences exist in shape of the Cormophyton base, degree of lobing, and stem decortication pattern. Traces in Pleuromeia, even at decortication levels, tend to show a conspicuous transversely elongated, often double, vascular trace (e.g. M~igdefrau, 1932; Neuburg, 1961). At the present time perhaps the most significant aspect that emerges from this comparison is the degree of diversity present throughout the Paleozoic and Mesozoic. Whether similarity in size and growth habit of Paleozoic and Mesozoic cormose forms reflects a phylogenetic relationship or one or more adaptive convergences remains an open question. The discovery of additional forms, information a b o u t whole plant reconstructions, and a more complete understanding of pleuromeialean ontogeny (e.g. Karrfalt, 1984) will undoubtedly further refine ideas of phylogeny among the lycopods.
Relationship to Stigmarioides The Mazon Creek flora has been extensively collected and studied b y amateurs and paleobotanists for over a century (Nitecki, 1979). Among the earliest to investigate this flora was Lesquereux (1870, 1880). He described several specimens as rooting organs of uncertain affinities, some of which he
176
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Fig.2. Mesozoic lycopod plant bases. A. Pleuromeia longicaulis (from Retallack, 1975). × 1. B. Nathorstianella arborea (from M~igdefrau, 1932). x 1. C. Nathorstiana babbagensis (From Glassner and Rao, 1955). x 1. D. Cylomeia undulata (from White, 1981). x 1. E. Pleuromeia hattaii (from Kon'no, 1973). x 1. F. Pleuromeia sternbergii (from SolmsLaubach, 1899). × 1. G. Pleuromeia rossica (from Neuburg, 1961). x 1. H., J. Pleuromeia jiaochengensis (from Wang and Wang, 1982). x 1.
suspected were of l y c o p o d a c e o u s origin. T h e s e include Stigmarioides trun-
catus, S. villosus, S. tuberosus, S. lineralis, S. affinis, S. rugosus, Stigrnaria evenii, Sigillarioides radicans, and Rachiopteris (Stigmarioides) selago. O f these, S. truncatus is m o s t c o m p a r a b l e t o t h e p r e s e n t material. However, a reinvestigation o f the t y p e specimen o f Stigmarioides truncatus reveals t h a t its r o o t i n g n a t u r e is questionable.
177
Our investigation of the figured h o l o t y p e of Stigmarioides truncatus reveals a cylindrical lycopsid axis 5.7 cm long and 2.4 cm across, with helically arranged ellipsoid-rounded appendage scars 1.8 mm across and 1.2 mm high covering the surface (Plate II, 3; Plate III, 1, 3). Scars lack evidence of vascular traces or parichnos strands, b u t are similar in size and shape to scars of some species of Cyclostigma [e.g., C. minutum (Haughton, 1859); the late Devonian C. kiltorkense (Schweitzer, 1969)]. The branching of the axis at the distal end (Plate III, 1) also bears appendage scars and is apparently a continuation of the major axis. Eight appendages were f o u n d in attachment to the axis (Plate III, 2, 4). They are 1.2 mm wide and up to 10.4 mm long. Most are oriented at an oblique angle to the main axis (Plate III, 1, 4) while one is oriented at nearly a right angle (Plate III, 1, 2). Based on available evidence it is difficult to determine whether the appendages represent leaves or roots. Lesquereux (1880) illustrated the specimen in such a way as to suggest they represent downward-growing roots, b u t it is equally possible that the specimen is either inverted from its proper orientation, or, if the appendages represent leaves, they are bent downward. T w o features suggest the appendages m a y represent leaves. First, the appendages appear to be composed of cells whose long axes are parallel to that of the appendage, resembling the epidermis of lycophyte leaves (Plate III, 4). Second, appendage scars are similar to those of stem segments of Cyclostigma, which although confused in the past with Stigmaria, have been generally regarded as an above ground axis (Crookall, 1964). A vertically oriented striate pattern covers the surface of the axis and like that of Cormophyton, is probably due to mineralization patterns of the axis rather than to stem anatomy. Other species of Stigmarioides are equally problematical. In his investigation of Lesquereux's t y p e material, Janssen (1940) reinterpreted S. radicans as an inverted l y c o p o d stem segment, which he reassigned to Bothrodendron sp. Stigmarioides tu berosus was thought b y Janssen to be a poorly preserved seed coat and he reassigned it to Carpolithus sp., while Rachiopteris (Stigmaroides) selago of Lesquereux was placed in Incertae Sedis and interpreted as a composite of several plant parts (Janssen, 1940). Based on the available evidence, including Janssen's (1940) figures and photographs of types, we agree with Janssen's conclusions regarding these forms. O f the remaining species, S. lineralis and S. affinis represent elongate rootlike structures that m a y represent either poorly preserved stigmarian rootlets or roots of other plant types. From photographs, Stigmarioides viUosus is apparently quite similar to S. tuberosus, which Janssen renamed Carpolithus, and m a y also represent a poorly degraded seed. Stigmaria evenii, a taxon Lesquereux allied with Stigmarioides clearly represents a portion of lycopsid axis, b u t there is no reason to consider it a rooting structure. Material or figures of Stigmarioides rugosus was unavailable for study. The generic concept of Stigmarioides has been considered because it may encompass the present specimens. This assignment is rejected, however, because n o t only are specimens clearly different, b u t the h o l o t y p e of Stigma-
Qo
179
rioides cannot conclusively be identified with its original generic concept (i.e., rooting organs) and there is, basically, no well defined category that could be expanded to include new genera. Cursory examination of the seven species of Stigmarioides and t w o similar taxa (i.e., Stigmaria evenii and Sigillarioides radicans) indicates that only t w o (S. lineralis and S. affinis) m a y actually represent rooting organs assignable to Stigmarioides. These forms are markedly different in morphology, size and structure. Since the holotype, S. truncatus cannot be interpreted as representing a rooting organ, the genus Stigmarioides cannot be based on its original holotype and a new holot y p e should be designated and the name retained for Incertae Sedis rooting organs. The t a x o n o m y should be reorganized so as not to confuse it with true lycopsid plants with cormose bases (e.g. Cormophyton), true Stigmaria or true roots of other vascular plants. ACKNOWLEDGEMENTS
We thank Dr. Peter R. Crane, Department of Geology, Field Museum of Natural History, Chicago for loaning us the Mazon Creek nodules studied in the present contribution. Thanks are also due to Drs. Richard L. Leafy and James E. Mickle, Illinois State Museum, for allowing us to examine t y p e material of Stigmarioides truncatus illustrated by Lesquereux and photographs of other Illinois State Museum specimens, and Dr. Andrew H. Knoll, Harvard Biological Museum, for providing photographs of additional material of Stigmarioides species. We also thank Dr. Eric E. Karrfalt for his interpretation of the rhizotaxy of our material, and Mr. David Dennis, for illustrations. This study was supported in part b y Grant DEB-8001803 from the National Science Foundation. REFERENCES Abbott, M.L., 1963. Lycopod fructifications from the Upper Freeport (No.7) coal in southeastern Ohio. Palaeontographica, 112B: 93--118. Alvin, K.L., 1965. A new fertile lycopod from the Lower Carboniferous of Scotland. Palaeontology, 8 : 281--293. Archangelsky, S., Azcuy, C.L. and Wagner, R.H., 1981. Three dwarf lycophytes from the Carboniferous of Argentina. Scr. Geol., 64: 1--35. Chaloner, W.G., 1956. On Sporangiostrobus langfordi sp. nov., a new fossil lycopod c o n e from Illinois. Am. Midl. Nat., 55: 437--442. Chaloner, W.G., 1958. Polysporia mirabilis Newberry, a fossil lycopod cone. J. Paleontol., 32: 199--209.
PLATE III 1. Type species of Stigmarioides truncatus Lesquereux. Note attached appendages (at arrows). Ill.State Mus. 8688. × 1.6. 2. Appendage attached at right angles to axis. x 7. 3. Appendage scars on surface of specimen, x 7. 4. Appendage at acute, d o w n w a r d angle to axis. x 7.
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