Paleobiogeographic relationships of the paleogene flora from the southeastern U.S.A: Implications for West Gondwanaland affinities

Palaeogeography, Palaeoclimatology, Palaeoecology, 66 (1988): 265 275 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

265

PALEOBIOGEOGRAPHIC RELATIONSHIPS OF THE PALEOGENE FLORA FROM THE SOUTHEASTERN U.S.A: IMPLICATIONS FOR WEST GONDWANALAND AFFINITIES DAVID WINSHIP TAYLOR 1

Department of Ecology and Evolutionary Biology U-43, University of Connecticut, Storrs, CT 06268 (U.S.A.) (Revised and accepted January 7, 1988)

Abstract Taylor, D.W., 1988. Paleobiogeographic relationships of the Paleogene flora from the southeastern U.S.A.: implications for West Gondwanaland affinities. Palaeogeogr., Palaeoclimatol., Palaeoecol., 66:265 275. Recent biogeographic, paleontological and continental position studies suggest that limited interchange between North and South America probably occurred during the late Cretaceous and early Tertiary. Well preserved angiosperm fossils and published fossil reports from the early Tertiary of the southeastern United States were analyzed to see if the relationship~ of any of these fossils were with South American and/or African extant taxa. A group of these fossils do have these affinities. The phylogeny and biogeography of the extant taxa, and the distribution of fossil reports outside North America, are compatible with an early Tertiary to late Cretaceous interchange. Those extant taxa with disjunct South American and southeastern Asia-Australasian distribution have a fossil record which either shows a northern distribution pathway along the route of the Boreotropical flora, or a southern path through West Gondwanaland. This suggests that the high diversity of the Neotropical flora may be a result of the original West Gondwanaland flora with additional elements from the Boreotropical flora which migrated southwards.

Introduction The p a l e o b i o g e o g r a p h i c r e l a t i o n s h i p s of the N o r t h A m e r i c a n flora h a s been the subject of c o n s i d e r a b l e c o n j e c t u r e . The r e c e n t d i s c u s s i o n of the p a l e o b o t a n i c a l evidence (Wolfe, 1975, 1977; G r a h a m , 1985; Tiffney, 1985) h a s left little d o u b t t h a t d u r i n g the e a r l y T e r t i a r y p o r t i o n s of this flora possessed affinities with e x t a n t t a x a p r e s e n t l y f o u n d in the n o r t h e r n hemisphere. The fossils w h i c h h a v e affinities with t e m p e r a t e t a x a p r o b a b l y were d i s t r i b u t e d over the h i g h l a t i t u d e land bridges b e t w e e n N o r t h A m e r i c a and Asia, a n d N o r t h A m e r i c a and 1Present address: Department of Biology, Peabody Museum, Yale University, New Haven, CT 06511, U.S.A. 0031-0182/88/$03.50

Europe. O t h e r fossils, w h i c h h a v e affinities with Old W o r l d t r o p i c a l taxa, were p r o b a b l y m e m b e r s of a w i d e s p r e a d L a u r a s i a n (Boreotropical) flora. This flora r e a c h e d from N o r t h A m e r i c a to Europe, and p r e s u m a b l y a l o n g the T e t h y s s e a w a y to s o u t h e a s t Asia (Wolfe, 1975; V a n der H a m m e n and Cleef, 1983; Tiffney, 1985). Yet t h e r e also h a v e been s u g g e s t i o n s t h a t t h e r e are elements w h i c h h a v e affinities with e x t a n t S o u t h A m e r i c a n t a x a ( G r a h a m and J a r z e n , 1969; D i l c h e r and D a g h l i a n , 1977; R o t h a n d Dilcher, 1979; G r a h a m , 1985). B o t h Leopold a n d M a c G i n i t i e (1972) and H i c k e y (1977) h a v e s u g g e s t e d t h a t the P a l e o g e n e floras of the R o c k y M o u n t a i n s a n d s u r r o u n d i n g a r e a s had t a x a with S o u t h A m e r i c a n affinities, while B e r r y (1916, 1924) s u g g e s t e d the same for some

© 1988 Elsevier Science Publishers B.V.

266 of the elements from the Lower Tertiary Mississippi embayment. Berry (1916, 1924, 1930, 1941) was the first paleobotanist to extensively study the Paleogene flora of the southeastern U.S.A. His analysis suggested that this early Tertiary flora had affinities with extant floras both in the northern hemisphere and the Neotropics. Unfortunately, reexamination of these fossils by subsequent workers have shown that the relationships of a number of the fossils are misunderstood (Brown, 1944, 1946; Dilcher, 1973). It is possible that up to 60°//0 of the fossil taxa described by Berry are misidentified (Dilcher, 1973). This led Wolfe (1975) to conclude that the fossil species of Philodendron (described by Dilcher and Daghlian, 1977) from the Eocene of Tennessee was the only definite record of a South American taxon in North America. Older studies of the vertebrate record (Simpson, 1940) supported evidence of little interchange. The evidence seemed to suggest that South America was an isolated island during the Paleogene, and nearly all the interchange occurred over the continuous land bridge which appeared during the Pliocene. Thus, until recently paleobotanists have not been searching for North American-South American interchange. These views of limited interchange are currently being revised with recent biogeographic analyses of extant taxa, paleontological reports, and continental position studies. Raven and Axelrod (1974) in their classic paper on angiosperm biogeography concluded that interchange between the two continents occurred during the early Tertiary. They admitted that although the fossil evidence was equivocal at the time of their study, the current biogeography and relationships of a number of extant families suggest migration across the proto-Caribbean. Rosen (1976) initiated the use of vicariance biogeography in the Caribbean area, and his examination of several taxonomic groups indicated that early interchange between the two continents was probable. Other studies of extant organisms have continued to examine the paleobiogeog-

raphy of the Caribbean (e.g. Gentry, 1982; Savage, 1982; Cadle, 1985; Rosen, 1985; White, 1986) and all concur that interchange occurred during the Late Cretaceous to Early Tertiary, though there is some disagreement on the specific timing and regional plate relationships. The reports of Eocene pollen from Panama also show evidence of interchange (Graham, 1985). Most recently, detailed analysis of paleontological records and some extant groups have shown that there were periods of interchange and periods of endemic evolution (Bussing, 1985; Webb, 1985; White, 1986) in North and South America. Apparently limited interchange occurred over island arcs during the Maestrichtian (late Cretaceous) to Paleocene, and from the late Oligocene until the continuous land bridge in the Pliocene (Bussing, 1985; Este and Baez, 1985; Gingerich, 1985). Reconstructions of continental positions in the proto-Caribbean have provided a framework for the interchange between the two continents, though the exact position of the blocks and their movement is still in dispute. Basically two general hypotheses have been proposed, and recently summarized by Rosen (1985). The first suggests longitudinal displacement was the major event in the history of the Caribbean, and the Greater Antilles formed much further west with subsequently movement through the gap between Mexico and Colombia to their present positions. Some researchers (e.g. Coney, 1982; Pindell and Dewey, 1982) suggest there were a number of smaller plates, while others (e.g. Sykes et al., 1982) suggest the entire Caribbean area is essentially one plate. The second hypothesis suggests that latitudinal movement was critical, and the Greater Antilles were formed in situ with little subsequent lateral movement (e.g. Salvador and Green, 1980; Anderson and Schmidt, 1983; Donnelly, 1985). From a biogeographer's view both models provide island pathways between North and South America over the Greater Antilles (Rosen, 1985) if they were not submerged. Unfortunately, the degree of emergence during various time periods is

267 still not well understood, though the eustatic sea level curves suggest lower world-wide sea levels after the late Oligocene (Savin and Douglas, 1985). Only recently has the fossil record become useful for examining the paleobiogeography of tropical taxa. Many of the recently described fossils have diagnostic characters to show their relationships to extant taxa. Using the well described fossils from the literature as well as fossils from a preliminary study from the Claiborne formation, I discuss the evidence that some of the members from the paleoflora of the southeastern U.S. have affinities with South American and/or African extant taxa. Careful comparison of the fossils with extant counterparts, usually at the supergeneric level, suggest t h a t portions of the paleoflora have affinities with the southern taxa. Materials and m e t h o d s The data for this study were obtained from two sources. The first source was an analysis of pollen and flowers from the Warman locality, Como, Tennessee, located in the University of Connecticut Paleobotanical Collection. The Warman locality is in the Claiborne formation and is Middle Eocene (Dilcher, 1971; Potter and Dilcher, 1980) to Upper Eocene age (M.S. Zavada, pers. comm., 1985; Crepet and Taylor, 1986). The pollen was examined and photographed with light microscopy, and then the same grains were removed for scanning electron microscopy (Taylor, 1987, 1988b). Once the characters of the fossil pollen were known, I compared the fossil pollen to pollen from extant genera and looked for shared diagnostic characters or character suites. If the pollen was not well known, pollen was obtained from herbarium specimens from GH and CONN and acetolyzed. Light reference slides and scanning electron microscope preparation were made with the acetolyzed pollen (the detailed comparisons are in Taylor, 1988b). The flowers also have been described elsewhere (Crepet and Taylor, 1985, 1986; Taylor and Crepet,

1987; Taylor, 1988a), and see therein for techniques. The second source of data included a literature search of recent well described Paleogene fossils from the southeastern U.S. published beginning in 1950. Those studies which described the fossil taxon in detail and discussed the diagnostic characters were included. Choice of valid pollen identifications were aided by Muller's (1981) review of pollen. The resulting list is conservative, as some of the equivocal fossil from the flora that were not used may have the affinities suggested by their respective authors. Once the list was formed, the biogeographic affinities of the fossil taxon were examined in detail. The distribution of the extant taxa to which the fossil had affinities was obtained. In addition, I also examined the biogeography of extant taxa which were also similar in pollen or floral characters to the fossil, or were sister groups to the extant taxa. This approach broadened the comparison and made it more likely that the fossil taxon did have affinities with the extant taxa and that the biogeographic pattern of the extant group was correct. Results Sixteen fossil taxa from thirteen families from the early Tertiary of the southeastern United States have affinities with tropical-subtropical extant taxa which are basically from South America or South America and Africa. The families are scattered through numerous angiosperm orders, and the fossils include flowers, fruits, leaves and pollen. Each of the fossils are described, their occurrence in the southeast reported, and their affinities discussed. Fossil pollen of Annonaceae has been reported from the Middle Eocene of' Tennessee (Elsik and Dilcher, 1974) and the Middle and Upper Eocene of Texas (Elsik, 1974). The pollen is approx. 50 ~m in diameter, zonisulcate, reticulate and tectate-columellate. The affinities of the pollen are with two genera

268 Annona and Cymbopetulum (Muller, 1981) which are from two closely related tribes in the Annona subfamily. The first genus is primarily South American in distribution, with a few species in Africa, and the latter is completely Neotropical. The subfamily is also mostly South American. A number of different types of fossils have been reported from Lauraceae. Dispersed leaf cuticles (Kovach and Dilcher, 1984) and leaves with cuticle (Dilcher, 1963) have been reported from the Middle Eocene; and flowers have been reported from the Middle to Upper Eocene (Taylor, 1988a). The leaves are pseudopalmate and the venation and cuticular features suggest affinities with Neotropical Ocotea. The flowers are small, pedicellate, glabrous, with six perianth parts connate into a hypanthium. The stamens have paired basal glands and the flowers have ethereal oil cells and paracytic stomates throughout. The flowers and leaves have similar cuticular features, and both taxa have affinities with the subtribe Cinnamomineae (sensu Kostermans), particularly the Neotropical Ocotea clade. Unfortunately, the closely related east Asian genus Cinnamomum is broadly circumscribed, and the one character which distinguishes the flowers from the Ocotea group is not preserved in the fossil. Yet the leaves have branching veinlets (Dilcher, 1974; D. L. Dilcher, pers. comm., 1987) which is found in Ocotea and not in Cinnamomum (Wolfe, 1977). If the leaves and fossils are conspecific, they have closer affinities to Ocotea; otherwise, the fossil flowers should be considered sister taxa to one of the taxa from the OcoteaCinnamomum complex (Fig.1 in Kostermans, 1957) or sister group to the entire complex. The biogeography of the subtribe is disjunct South America-Southeast Asia. Flowers from this complex have been reported from the Upper Eocene of Europe (Conwentz, 1886). Pollen of Nyctaginaceae has been reported from the Middle Eocene to the Lower Oligocene of Mississippi and Alabama (Frederiksen, 1980a) and the Middle Eocene of Tennessee (Elsik and Dilcher, 1974). Lymingtonia cf. L. rhetor is approx. 30 ~tm in diameter, polyru-

gulate, reticulate to perforate and tectatecolumellate. It is similar to the pollen found in tribe Nyctagineae, subtribe Phaeoptilieae (Muller, 1981), and a few genera from the tribe Pisnieae (Nowicke and Luikart, 1971). Phaeoptilieae is monogeneric and found in Africa. The fossil pollen species is also found from the Eocene of Europe and Oligocene of New Zealand (Muller, 1981). Fossil pollen, similar to that found in many Neotropical Bombacaceae genera, has been reported from throughout the northeast and southeast. The oldest is from the Maestrichtian of New Jersey (Wolfe, 1975, 1976) and is transitional to later forms (Muller, 1981). Other reports are from the Lower and Upper Paleocene of South Carolina (Frederiksen, 1980b) and Alabama (Srivastava, 1972), Upper Paleocene of Virginia, Paleocene of Texas and Tennessee (Elsik, 1968; Fairchild and Elsik, 1969), Eocene of Texas (Elsik, 1974), Middle Eocene to Lower Eocene of Mississippi and Alabama (Frederiksen, 1980a), and Mississippi (Tschudy and Van Loenen, 1970). Bombacacidites nacimientoensis is approx. 40 ~m in diameter, ovate with a triangular amb with straight sides and narrowly rounded corners, tricolporate with short colpi, and mediumcoarse reticulate sculpturing which is finer to the corners. The pollen is most similar to that found in the Bombax clade. This group is most diverse in South America, with closely related taxa in South America and Africa which extend into southeast Asia. Based on phylogeny and fossil records, Wolfe (1975) has suggested the family has a tropical Nearctic origin. He suggests that some taxa migrated into South America where they radiated and dispersed from there into the Old World Tropics. He believes that other groups in the family, migrated to southeast Asia via a Laurasian route. Other fossil reports include pollen from the Paleocene of South America, Paleocene-Eocene of Africa and Eocene of Australasia (Muller, 1981). Fossil legumes are extensively reported, and of particular importance are the reports of flowers with affinities to the Mimosoideae. The

269 fossil flower Eomimosoidea is reported from Middle Eocene of Tennessee and the Oligocene of Texas (Crepet and Dilcher, 1977; Daghlian et al., 1980). The flowers are sessile, hairy, with a four parted corolla, and eight to ten stamens with prolate, tricolporate, verrucate, perforate pollen in tetrads. The species has affinities with somewhat derived members of the tribe Mimoseae, which has a West Gondwanaland distribution. The fossil Protomimosoidea is from the Upper Paleocene to Upper Eocene of Tennessee (Crepet and Taylor, 1985, 1986). These flowers are pedicellate with a five parted corolla with valvate aestivation, and ten exserted stamens, with prolate, tricolporate, perforate pollen in monads. The stigma is tubular, the style filiform, and the carpel hairy. The morphology of the flowers is similar to the archetype for the Mimoseae which is the ancestral tribe for the subfamily (Elias, 1981). The distribution of the eight ancestral taxa (Lewis and Elias, 1981 in fig.2) is West Gondwanaland except for Prosopis which is also found in India. Twelve of the eighteen genera compared florally with the fossil also have a West Gondwanaland distribution, another three are mostly found in West Gondwanaland, and the remainder are widespread. Fossil pollen of the subfamily and tribe has been reported from west Africa (Muller, 1981; Crepet and Taylor, 1986). Pollen with affinities to Myrtaceae (Myrtaceidites parvus) has been reported from Middle Eocene of Tennessee (Elsik and Dilcher, 1974; Potter, 1976) and Mississippi (Engelhardt, 1964a); Eocene of Texas (Elsik, 1968); Upper Eocene of Mississippi (Tschudy and Van Loenen, 1970); and Middle Eocene to Lower Oligocene of Mississippi and Alabama (Frederiksen, 1980a). The species is approx. 15 pm in diameter, ovate with a triangular amb with rounded sides and rounded corners, syntricolporate and psilate to perforate sculpturing. The pollen is similar to Eugenia and Myrcia from the Myrtoideae (Muller, 1981), and pollen from the two genera are not easily distinguished (Graham, 1980). The subfamily is widespread but particularly diverse in the

Neotropics. The genus is reported from the Santonian of Gabon, Semonian of Borneo, Maestrichtian of Colombia and Paleocene of the Ninetyeast Ridge (Indian Ocean south of India) and Australasia (Muller, 1981). The fossil pollen genus Gothanipollis has been reported with affinities with the Loranthaceae. The reports are from the Lower Paleocene of Alabama (Jarzen, 1978); Middle Eocene of Mississippi (Engelhardt, 1964a, b; Tschudy, 1973), Tennessee (Elsik and Dilcher, 1974), Texas (Elsik, 1968), Virginia (Frederiksen, 1984), and Mississippi-Alabama (Frederiksen, 1980a; and Upper Eocene of Arkansas (Tschudy, 1973) and Mississippi-Alabama (Frederiksen, 1980a). G. cockfieldensis is approx. 20 ~m in diameter, syncolpate, ovate with a triangular arab, concave sides and flared corners (Engelhardt, 1964b, modified by Elsik and Dilcher, 1974), and has sculpturing made up of rodlets (Taylor, 1987, 1988b). Until recently the pollen of the family was poorly studied. Recent studies (Freuer and Kuijt, 1979, 1980, 1985; Taylor, 1987, in press b) permit comparison of the fossils with extant taxa, and show that some of the species from the Tennessee have affinities with somewhat derived members of the Neotropical large flowered taxa. This is a monophyletic group with sister taxa in Australasia (Freuer and Kuijt, 1980). The large flowered taxa are mostly South American with some taxa in the rest of the Neotropics. Gothanipollis is also found from the Eocene of Europe, and Oligocene of the Ninetyeast Ridge (Indian Ocean; Muller, 1981). Several different types of fossils have been reported from Euphorbiaceae. Fossil fruits are reported from the Eocene of Virgina and Maryland (Mazer and Tiffney, 1982), flowers with pollen from the Middle Eocene of Tennessee (Crepet and Daghlian, 1982) and Amanoa type fossil pollen (Retitricolporites) from the Eocene of Texas (Elsik, 1974) and the Middle Eocene of Tennessee (Elsik and Dilcher, 1974). The fruits are syncarpous, three layered, six carpellate with axil/apical placentation and loculicidal dehiscence. The flowers are arranged on branched spikes with bracteate

270 cymules with staminate florets each with three stamens. The pollen is prolate, tricolporate, perforate and has a sculpturing of convoluted reticulum with striate muri. Both fossils have affinities with the genera in Hippomaneae. Hippomaneae sensu Webster (1975) is based in South America with thirteen of the nineteen genera Neotropical of which five reach North America; of the remaining, two are African and four widespread. Similar Hippomaneae fruits are found in Europe and Egypt (Mazer and Tiffney, 1982). The Amanoa type fossil pollen is approx. 30 ~m in diameter, subprolate, tricolporate, reticulate with some muri free standing and not completely enclosing lumina, and an ektexine much thicker than the endexine (Germeraad et al., 1968; Taylor, 1987, 1988b). The affinities of the fossil are with the Amanoa group (Germeraad et al., 1968; Elsik and Dilcher, 1974; Taylor, 1987, 1988b) of Punt (1962), from Amaneae. This group is monophyletic and mostly found in South America, with the remaining taxa Neotropical. The sister group (Savia group) is mostly West Gondwanaland in distribution with a few species extending northwards. This fossil pollen is also reported from the Eocene of South America (Muller, 1981). Malpighiaceae flowers with pollen have been reported from Middle Eocene (Taylor and Crepet, 1987). The flowers have paired glands on each sepal, clawed petals, and tricolporate reticulate pollen with an exine composed of a tectum and anastomosing tectal elements. The affinities of the fossil are either with the Byrsominoideae or the fossil is a sister taxon to derived Neotropical genera. The genera in the subfamily are mostly from South America, with a few taxa scattered throughout the Neotropics. The family is also mostly Neotropical, and the derived Older World members are missing or have reduced sepal glands. Pollen with affinities with Neotropical taxa has been reported from the Upper Eocene of Panama (Graham, 1985). Other pollen is reported from the Middle Eocene of South America and Upper Eocene of west Africa (Muller, 1981).

There are numerous reports of pollen with affinities to Sapindaceae. Cupanieidites (sensu Chmura, 1973; Duplopollis a junior synonym) is from the Upper Paleocene and Lower Eocene of Virgina (Frederiksen, 1979); Middle Eocene of Mississippi (Engelhardt, 1964a; Frederiksen, 1980a, 1981) and Tennessee (Elsik and Dilcher, 1974) and Alabama (Frederiksen, 1980a); Upper Eocene of Alabama (Frederiksen, 1980a) and Mississippi (Tschudy and Van Loenen, 1970); and Eocene of Tennessee (Fairchild and Elsik, 1969) and Texas (Fairchild and Elsik, 1969; Elsik, 1974). C. orthoteichus is approx. 25 ~m in diameter, ovate with a triangular amb, syntricolporate, with the colpi forming a polar island and reticulate (Cookson and Pike, 1954), with the sculpturing formed from anastomosing tectal elements (Taylor, 1987, 1988b). The pollen is similar to that found in taxa from the Cupaneae (Muller and Leenhouts, 1976; Muller, 1981). Comparisons with extant taxa show that it is most similar to pollen found in taxa from the Cupania group and the Cupaniposis group, though large polar islands are rare in the latter group (Taylor, 1987, in press b). The former group is from the Neotropics while the latter is from southeast Asia. The two groups are thought to be sister groups with the southeast Asian genera derived from the Neotropical taxa. The ancestor of both groups is South American. Cupanieidites has also been reported from Coniacian and Santonian of Gabon; Senonian of India; Senonian to Maestrichtian of South America and Paleocene of Australia (Muller, 1981). Gentianaceae is probably represented in the record by dispersed pollen Pistillipollenites macgregorii and a flower with the same pollen. The dispersed pollen is from the Upper Paleocene of South Carolina and Virginia (Frederiksen, 1980b); the Paleocene of Texas (Fairchild and Elsik, 1969; Elsik, 1974) and Tennessee (Fairchild and Elsik, 1969); the Lower Eocene of Mississippi (Tschudy, 1973). The grains are approx. 22 ~m in diameter, triporate and have distinctive gemmate sculpturing. The flower is from the Lower Eocene of Texas (Crepet and Daghlian, 1981) and has a sympetalous, funnel-

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form-salverform seven-lobed corolla, and the anthers with P. macgregorii pollen. The affinities of the flower and pollen are apparently with the Gentianeae specifically the Neotropical genus Macrocarpaea, but the fossil characters are not identical to those found in the genus and the affinities are currently being reexamined in light of new fossils (W. L. Crepet and C.P. Daghlian, pers. comm., 1986). The pollen is also found throughout the Northern Hemisphere (Crepet and Daghlian, 1981; Daghlian and Crepet, 1986). A fossil leaf with affinities to the Araceae has been reported from the Eocene of Tennessee (Dilcher and Daghlian, 1977). The leaf is large, ovate with a sagittate base, and the cuticle has brachyparacytic stomates. The affinities of the leaf are with the genus Philodendron. The genus is Neotropical, mostly South American, in distribution, and Philodendreae is restricted to West Gondwanaland. A fossil Zingiberaceae flower, probably from Heliconioideae, has been preliminarily reported from the Middle Eocene of Tennessee (Crepet, 1984). The flower is zygomorphic with exserted stamens and a connate corolla. The subfamily is mostly South American into the Neotropics with a few species found in the Oriental, Australasian and Oceanic regions. The entire family is widespread. Conclusions

The affinities of the fossils are indicated by the diagnostic characters they share with select extant taxa. These comparisons show that the fossils have closest affinities with extant taxa from South America and/or Africa, and the existence of these taxa in the early Tertiary of the southeastern U.S. would indicate interchange over the proto-Caribbean. The extant taxa show two biogeographic patterns: mostly South American and/or Africa (Table I), or South American with a disjunct sister group in southeast Asia (Table II). These patterns have ramifications for the direction of interchange, and for understanding wider biogeographic patterns.

TABLE I The relationships of fossils reported with affinities to extant taxa found mostly in South America or West Gondwanaland Family

E x t a n t group fossil has affinities with

Annonaceae

Annona and Cymbopetulum in Annona subfamily Phaeoptiliaea Bombax complex Mimoseae Amanoeae, Hippomaneae Byrsonimoideae or sister taxon Gentianeae Philodendron Heliconioideae

Nyctaginaceae Bombacaceae Leguminosae Euphorbiaceae Malpighiaceae Gentianaceae Araceae Zingiberaceae

A number of authors have discussed the paleohistory of angiosperm families based on extant phylogeny and biogeography. Of the families described here as fossils, Raven and Axelrod's (1974) analysis suggests that Mimosoideae (Leguminosae), Malpighiaceae and Zingiberaceae interchanged northward during the Eocene period or later. The fossils examined here suggest that the Eocene was the minimum time and interchange probably occurred earlier. Their data also suggest that certain clades of other families interchanged northwards. The families which are described here included Annonaceae, Araceae, Bombacaceae, Euphorbiaceae, Lauraceae, Myrtaceae and Sapindaceae, and the subfamilial affinities

TABLE II The relationships of fossils reported with affinities to extant taxa found mostly in South America or West Gondwanaland with a major sister group found in Southeast A s i a - A u s t r a l a s i a Family

E x t a n t group fossil has affinities with

Lauraceae Myrtaceae Loranthaceae Sapindaceae

Ocotea-Cinnamomum complex Myrtoideae Large flower Neotropical group Cupanieae

272 of the fossils indicate they have affinities with southern clades of these families. Gentry (1982) also has discussed the flora of South America and its biogeographic histories. His analysis suggests that all the families represented by the fossils (except Gentianaceae, though tropical Tachiinae from Gentianeae is clearly South American to Neotropical) have West Gondwanaland histories. The existence of the fossils with affinities to these families also implies northward interchange. Van der Hammen and Cleef (1983) have discussed the extant taxa which have disjunct South American-Southeast Asian distribution. They suggest (as others have, e.g. Raven and Axelrod, 1974) that the temperate Laurasian elements in South America interchanged southward during the Neogene. The evidence that they are Laurasian is based on their affinities to ancestral taxa in the Northern Hemisphere, and timing based on minimal dates of occurrence from the pollen record (Van der Hammen, 1974; Van der Hammen and Cleef, 1983; Van der Hammen et al., 1973; Van der Hammen et al., 1971). On the other hand, they suggest that the tropical elements interchanged earlier (Van der Hammen and Cleef, 1983) and may have been distributed from South America to southeast Asia via North America, Europe, and the coast of the Tethys seaway (the distribution of the Boreotropical flora), with later extinction in these intervening areas (Van der Hammen and Cleef, 1983; Van der Hammen et al., 1971). Unfortunately, this disjunct pattern could also be due to extinction in Africa, or Antarctica and Australia. The four fossil taxa which have this disjunct pattern are reported elsewhere in other paleobiogeographic areas. The fossils with affinities with Cupineae (Sapindaceae) and Myrtoideae (Myrtaceae) are also reported from South America, Africa and Asia-Australasia. This suggests that these fossil taxa had a southern hemisphere distribution from South America and Africa to southeast Asia, and had the typical northward interchange to North America. Yet the fossils with affinities to the Ocotea-Cinnamomum complex (Lauraceae)

and the large flowered Neotropical Loranthaceae are also reported from Europe suggesting a northern hemisphere path. These fossils would corroborate the ideas of Van der Hammen and Cleef (1983). Distributions in Antarctica and Australia are difficult to assess since the record is poor. The existence of the fossils in the southeastern U.S. during the early Tertiary with affinities with extant taxa having West Gondwanaland histories suggests that northward interchange had occurred by this time. The timing of southward interchange of Boreotropical families such as Lauraceae and Loranthaceae is also suggested to be early, as the phylogeny and diversity of these families is different than the Laurasian families which are thought to have interchange more recently (Raven and Axelrod, 1974; Van der Hammen et al., 1971, 1973; Gentry, 1982; Van der Hammen and Cleef, 1983). Yet the fossil record can only provide minimum times for the interchange. Recent geological evidence now suggests that interchange over island arcs or land connection would have been possible during the late Cretaceous to early Tertiary. Biogeographic studies of extant organisms also suggest similar timing. The fossils from the southeast are compatible with a Maestrichtian-Paleocene time. These fossil occurrences have a number of implications. Their existence in the southeast imply that the tropical flora of North America had both Boreotropical elements, as others have suggested (Wolfe, 1977; Tiffney, 1985) and West Gondwanaland elements. Analysis of the biogeographic distributions of the extant taxa (to which the fossils have affinities) indicate that the interchange between North and South America was bidirectional (though apparently greater to the north), and the age of the fossils is compatible with a late Cretaceous-early Tertiary time. The global record of the fossils with affinities to extant taxa with disjunct South America-Southeast Asian distributions suggests that the paleodistributions of these particular fossils were via North America, Europe and Tethys seaway, or via Africa.

273

The current disjunction is due to extinction in the intervening areas. Lastly, the distribution patterns suggest that the flora of the Neotropics is composed of West Gondwanaland groups as well as southeastern Asian or Boreotropical groups from the north. The high diversity of the Neotropics (e.g. Gentry, 1982) may be explained by mixing of the West Gondwanaland flora and the Boreotropical flora in South America. Further studies of fossils from North and South America will increase our understanding of the minimum time, extent and direction of the interchange. References Anderson, T. H. and Schmidt, V. A., 1983. The evolution of Middle America and the Gulf of Mexico Caribbean Sea region during the Mesozoic time. Bull. Geol. Soc. Am., 94:941 966. Berry, E.W., 1916. The Lower Eocene floras of southeastern North America. U.S. Geol. Surv. Prof. Pap., 91: L 481. Berry, E. W., 1924. The Middle and Upper Eocene floras of southeastern North America. U.S. Geol. Surv. Prof. Pap., 92:1 206. Berry, E. W., 1930. Revision of the Lower Eocene Wilcox flora of the southeastern States. U.S. Geol. Surv. Prof. Pap., 156:1 196. Berry, E.W., 1941. Additions to the Wilcox flora from Kentucky and Texas. U.S. Geol. Surv. Prof. Pap., 193E: 83 99. Brown, R. W., 1944. Temperate species in the Eocene flora of the southeastern United States. Wash. Acad. Sci. J., 34:349 351. Brown, R. W., 1946. Alterations in some fossils and living floras. Wash. Acad. Sci. J., 36: 344-355. Bussing, W.A., 1985. Patterns of distribution of the Central American Ichthyofauna. In: F.G. Stehli and S. D. Webb (Editors), The Great American Interchange. Plenum Press, New York, N.Y., pp. 453-473. Cadle, J. E., 1985. The Neotropical colubrid snake fauna (Serpentes: Colubridae): lineage components and biogeography. Syst. Zool., 34: 1-20. Chmura, C.A., 1973. Upper Cretaceous (CampanianMaastrichtian) angiosperm pollen from the western San Joaquin Valley, California, U.S.A. Palaeontographica Abt. B, 141: 89-171. Coney, P.J., 1982. Plate tectonic constraints on the biogeography of Middle America and the Caribbean region. Ann. Mo. Bot. Gard., 69: 432-443. Conwentz, H., 1886. Die Angiospermen des Bernsteins. In: H.R. Goeppert and A. Menge (Editors), Die Flora des Bernsteins. Engelmann, Danzig. Cookson, I. C. and Pike, K. M., 1954. Some dicotyledonous

pollen types from Cainozoic deposits in the Australian region. Aust. J, Bot., 2: 197-219. Crepet, W.L., 1984. Advanced (constant) insect pollination mechanisms: pattern of evolution and implications vis-a-vis angiosperm diversity. Ann. Mo. Bot. Gard., 71: 607-630. Crepet, W. L., and Daghlian, C. P., 1977. Investigations of angiosperms from the Eocene of North America: a mimosoid inflorescence. Am. J. Bot., 64: 714-725. Crepet, W. L. and Daghlian, C. P., 1981. Lower Eocene and Paleocene Gentianaceae: floral and palynological evidence. Science, 214:75 77. Crepet, W.L. and Dilcher, D. L., 1982. Euphorbioid inflorescence from the Middle Eocene Claiborne Formation. Am. J. Bot., 69:258 266. Crepet, W.L. and Taylor, D.W., 1985. The diversification of the Leguminosae: first fossil evidence of the Mimosoideae and Papilionoideae. Science, 228: 10871089. Crepet, W.L. and Taylor, D.W., 1986. Primitive mimosoid flowers from the Paleocene-Eocene and their systematic and evolutionary implications. Am. J. Bot., 73: 548-563. Daghlian, C. P. and Crepet, W.L., 1986. Pollen structure and variability in Pistillipollenites macgregorii, a Paleogene gentian. Am. J. Bot., 73: 698. Daghlian, C.P., Crepet, W.L. and Delevoryas, T., 1980. Investigations of Tertiary angiosperms: a new flora including Eominosoidea plumosa from the Oligocene of Eastern Texas. Am. J. Bot., 67:309 320. Dilcher, D. L., 1963. Cuticular analysis of Eocene leaves of Ocotea obtusifolia. Am. J. Bot., 50: 1-8. Dilcher, D.L., 1971. A revision of the Eocene flora of southeastern North America. Palaeobotanist, 20: 7-18. Dilcher, D. L., 1973. A paleoclimatic interpretation of the Eocene floras of southeastern North America. In: A. Graham (Editor), Vegetation and Vegetational History of Northern Latin America. Elsevier, Amsterdam, pp. 39-59. Dilcher, D.L., 1974. Approaches to the identification of angiosperm leaf remains. Bot. Rev., 40:1 157. Dilcher, D. L. and Daghlian, C. P., 1977. Investigations of angiosperms from the Eocene of southeastern North America: Philodendron leaf remains. Am. J. Bot., 64: 526-534. Donnelly, T.W., 1985. Mesozoic and Cenozoic plate evolution of the Caribbean region. In: F. G. Stehli and S. D. Webb (Editors), The Great American Interchange. Plenum Press, New York, N.Y., pp.89-121. Elias, T. S., 1981. Mimosoideae. In: R. M. Polhill and P. H. Raven (Editors), Advances in Legume Systematics. Proc. Int. Legume Conf., Royal Botanic Gardens, Kew, 1: 143 152. Elsik, W.C., 1968. Palynology of a Paleocene Rockdale lignite, Milam County, Texas. II. Morphology and taxonomy (end). Pollen Spores, 10: 599-664. Elsik, W. C., 1974. Characteristic Eocene palynomorphs in the Gulf Coast, U.S.A. Palaeontographica Abt. B, 149: 90-111. Elsik, W. C. and Dilcher, D. L., 1974. Palynology and age of

274 clays exposed in Lawrence clay pit, Henry County, Tennessee. Palaeontographica Abt. B, 146: 65-87. Engelhardt, D.W., 1964a. Plant microfossils from the Eocene Cockfield Formation, Hinds County, Mississippi. Miss. Geol. Topogr. Surv. Bull., 104: 65-95. Engelhardt, D. W., 1964b. A new species of Gothanipollis Krutzsch from the Cockfield Formation (Middle Eocene) of Mississippi. Pollen Spores, 6: 597-600. Este, R. and Baez, A., 1985. Herpetofaunas of North and South America during the Late Cretaceous and Cenozoic: Evidence for Interchange? In: F. G. Stehli and S. D. Webb (Editors), The Great American Interchange. Plenum Press, New York, N.Y., pp.139-197. Fairchild, W.W. and Elsik, W.C., 1969. Characteristic palynomorphs of the Lower Tertiary of the Gulf Coast. Palaeontographica Abt. B, 128: 81-89. Frederiksen, N. O., 1979. Paleogene sporomorph biostratigraphy, northeastern Virginia. Palynology, 3: 129-167. Frederiksen, N. O., 1980a. Sporomorphs from the Jackson Group (Upper Eocene) and adjacent strata of Mississippi and western Alabama. U.S. Geol. Surv. Prof. Pap., 1084: 1-75. Frederiksen, N.O., 1980b. Paleogene sporomorphs from South Carolina and qualitative correlations with the Gulf Coast. Palynology, 4: 125-179. Frederiksen, N.O., 1981. Middle Eocene to early Oligocene plant communities of the Gulf Coast. In: J. Gray et al. (Editors), Communities of the Past. Hutchinson and Ross, Stroudsburg, Pa., pp.493-549. Frederiksen, N.O., 1984. Sporomorph correlation and paleoecology, Piney Point and Old Church Formations, Pamunkey River, Virginia. In: L.W. Ward and K. Krafft (Editors), Stratigraphy and Paleontology of the Outcropping Tertiary Beds in the Pamunkey River Region, Central Virginia Coastal Plain, Atlantic Coastal Plain. Geol. Soc. Guidebook 1984 Field Trip, pp.135-151. Freuer, S. and Kuijt, J., 1979. Pollen morphology and evolution in Psittacanthus (Loranthaceae). Bot. Not., 132: 295-309. Freuer, S. and Kuijt, J., 1980. Fine structure of mistletoe pollen. III. Large flowered Neotropical Loranthaceae and their Australian relatives. Am. J. Bot., 67: 34-50. Freuer, S. and Kuijt, J., 1985. Fine structure of mistletoe pollen. VI. Small flowered Neotropical Loranthaceae. Ann. Mo. Bot. Gard., 72: 187-212. Gentry, A. H., 1982. Neotropical floristic diversity: phytogeographical connections between Central and South America, Pleistocene climatic fluctuations or an accident of the Andean orogeny. Ann. Mo. Bot. Gard., 69: 557-593. Germeraad, J.H., Hopping, C.A. and Muller, J., 1968. Palynology of Tertiary sediments of tropical areas. Rev. Palaeobot. Palynol., 6: 189-348. Gingerich, P.D., 1985. South American mammals in the Paleocene of North America. In: F. G. Stehli and S. D. Webb (Editors), The Great American Interchange. Plenum Press, New York, N.Y., pp.123-137. Graham, A., 1980. Morfologia del polen de Eugenia/Myrica (Myrtaceae) y Combretum/Terminalia (Combretaceae)

en relacidn a su alcance estrgLtigrafico en el Tercieario del Caribe. Biotica, 5: 5-14. Graham, A., 1985. Studies of Neotropical paleobotany. IV. The Eocene communities of Panama. Ann. Mo. Bot. Gard., 72: 504-534. Graham, A. and Jarzen, D. M., 1969. Studies in Neotropical paleobotany: I. The Oligocene communities of Puerto Rico. Ann. Mo. Bot. Gard., 56: 308-357. Hickey, L.J., 1977. Stratigraphy and paleobotany of the Golden Valley Formation (early Tertiary) of western North Dakota. Geol. Soc. Am. Mem., 150: 1-181. Jarzen, D.M., 1978. The terrestrial palynoflora from the Cretaceous-Tertiary transition, Alabama, U.S.A. Pollen Spores, 20: 535-553. Kostermans, A.J.G.H., 1957. Lauraceae. Reinwardtia, 4: 193-256. Kovach, W. L. and Dilcher, D. L., 1984. Dispersed cuticles from the Eocene of North America. Linn. Soc. Bot. J., 88: 63-104. Leopold, E.B. and MacGinitie, H.D., 1972. Development and affinities of Tertiary floras in the Rocky Mountains. In: A. Graham (Editor), Floristics and Paleofloristics of Asia and Eastern North America. Elsevier, Amsterdam, pp. 147-200. Lewis, G.P. and Elias, T.S., 1981. Mimoseae. In: R.M. Polhill and P. H. Raven (Editors), Advances in Legume Systematics. Proc. Int. Legume Conf., Royal Botanic Gardens, Kew, 1: 155-168. Mazer, S. J. and Tiffney, B. H., 1982. Fruits of Wetherellia and Palaeowetherellia (?Euphorbiaceae) from Eocene sediments in Virginia and Maryland. Brittonia, 34: 300-333. Muller, J., 1981. Fossil pollen records of extant angiosperms. Bot. Rev., 47: 1-142. Muller, J. and Leenhouts, R. W., 1976. A general survey of pollen types in Sapindaceae in relation to taxonomy. In: I. K. Ferguson and J. Muller (Editors), The Evolutionary Significance of the Exine. Linn. Soc. Symp. Ser., 1: 407-445. Nowicke, J. W. and Luikart, T. J., 1971. Pollen morphology of the Nyctaginaceae. II. Colignonieae, Boldoeae, and Leucastereae. Grana, 11: 145-150. Pindell, J. and Dewey, J.R., 1982. Permo-Triassic reconstruction of western Pangea and the evolution of the Gulf of Mexico/Caribbean region. Tectonics, 1: 179211. Potter, F. W., Jr. 1976. Investigations of angiosperms from the Eocene of southeastern North America: pollen assemblages from Miller pit, Henry County, Tennessee. Palaeontographica Abt. B, 157: 44-96. Potter, F. W., Jr. and Dilcher, D. L., 1980. Biostratigraphic analysis of Eocene clay deposits in Henry County, Tennessee. In: D. L. Dilcher and T. N. Taylor (Editors), Biostratigraphy of Fossil Plants. Dowden, Hutchinson and Ross, Stroudsburg, Pa., pp.211-225. Punt, W., 1962. Pollen morphology of the Euphorbiaceae with special reference to taxonomy. Wentia, 7: 1-116. Raven, P.H. and Axelrod, D.I., 1974. Angiosperm biogeography and past continental movements. Ann. Mo. Bot. Gard., 61: 539-673.

275 Rosen, D.E., 1976. A vicariance model of Caribbean biogeography. Syst. Zool., 24: 431-464. Rosen, D.E., 1985. Geological hierarchies and biogeographic congruence in the Caribbean. Ann. Mo. Bot. Gard., 72: 636-659. Roth, J. L., Jr. and Dilcher, D. L., 1979. Investigations of angiosperms from the Eocene of North America: stipulate leaves of the Rubiaceae including a probable polyploid population. Am. J. Bot., 66: 1194-1207. Salvador, A. and Green, A.R., 1980. Opening of the Caribbean Tethys (origin and development of the Caribbean and Gulf of Mexico). In: J. Aubouin, J. Debelmas and M. Latreille (Editors), G~ologie de chaines Alpines Issues de la T~thys. M~m. Bur. Rech. Geol. Mini~res, 115: 224-229. Savage, J. M., 1982. The enigma of the Central American herpetofauna: dispersals or vicariance? Ann. Mo. Bot. Gard., 69: 464-547. Savin, S. M. and Douglas, R.G., 1985. Sea level, climate, and the Central American land bridge. In: F. G. Stehli and S.D. Webb (Editors), The Great American Interchange. Plenum Press, New York, N.Y., pp.303-324. Simpson, G. G., 1940. Mammals and land bridges. J. Wash. Acad. Sci., 30: 137-163. Srivastava, S. K., 1972. Some spores and pollen from the Paleocene Oak Hill Member of the Naheol Formation, Alabama (U.S.A.). Rev. Palaeobot. Palynol., 14:217 285. Sykes, L. R., McCann, W. R. and Kafka, A. L., 1982. Motion of Caribbean plate during the last 7 million years and implications of early Cenozoic movements. J. Geophys. Res., 87:10656 10676. Taylor, D.W., 1987. Survey of the Paleobiogeographic Relationships of North American Angiosperms from the Upper Cretaceous and Paleogene. Thesis. Univ. Connecticut, Storrs. Taylor, D. W., 1988a. Eocene floral evidence of Lauraceae: corroboration of the North American megafossil record. Am. J. Bot., in press. Taylor, D. W., 1988b. Select palynomorphs from the Middle Eocene Claiborne Formation, TN, U.S.A. Rev. Palaeobot. Palynol., in press. Taylor, D.W. and Crepet, W.L., 1987. Fossil floral evidence of Malpighiaceae and an early plant pollinator relationship. Am. J. Bot., 74: 274-286. Tiffney, B.H., 1985. The Eocene North Atlantic land

bridge: its importance in Tertiary and modern phytogeography of the Northern Hemisphere. J. Arnold Arbor., 66: 243-273. Tschudy, R. H., 1973. Stratigraphic distribution of significant Eocene palynomorphs of the Mississippi embayment. U.S. Geol. Surv. Prof. Pap., 743-B: 1-24. Tschudy, R. H. and Van Loenen, S.D., 1970. Illustration of plant microfossils from the Yazoo Clay (Jackson Group, Upper Eocene) Mississippi. U.S. Geol. Surv. Prof. Pap., 643-E: 1 5. Van der Hammen, T., 1974. The Pleistocene changes of vegetation and climate in tropical South America. J. Biogeogr., 1: 3-26. Van der Hammen, T. and Cleef, A. M., 1983. Trigonobalnus and the tropical amphi-pacific element in the North Andean forest. J. Biogeogr., 10:437 440. Van der Hammen, T., Wijmstra, T. A. and Zagwijn, W. H., 1971. The floral record of the late Cenozoic of Europe. In: K.K. Turekian (Editor), The Late Cenozoic Glacial Ages. Yale Univ. Press, New Haven, Conn. pp.391 424. Van der Hammen, T., Werner, J. H. and Van Dommelen, H., 1973. Palynological record of the upheaval of the northern Andes: a study of the Pliocene and Lower Quaternary of the Colombian eastern cordillera and the early evolution of its high-andean biota. Rev. Palaeobot. Palynol., 16: 1-172. Webb, S.D., 1985. Main pathways of mammalian diversification in North America. In: F.G. Stehli and S. D. Webb (Editors), The Great American Biotic Interchange. Plenum Press, New York, N.Y., pp.201~-217. Webster, G. L., 1975. Conspectus of a new classification of the Euphorbiaceae. Taxon, 24:593 601. White, B. N., 1986. The isthmian link, antitropicality and American biogeography: distributional history of the Atherimopsinac (Pisces: Atherimidae). Syst. Zool., 35: 176 194. Wolfe, J. A., 1975. Some aspects of plant geography of the northern hemisphere during the late Cretaceous and Tertiary. Ann. Mo. Bot. Gard., 62:264 279 Wolfe, J.A., 1976. Stratigraphic distribution of some pollen types from the Campanian and Lower Maestrichtian rocks (Upper Cretaceous) of the Middle Atlantic States. U.S. Geol. Surv. Prof. Pap., 977:1 18. Wolfe, J. A., 1977. Paleogene floras from the Gulf of Alaska region. U.S. Geol. Surv. Prof. Pap., 997:1 108.