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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions Vol. 58 (2008), Pages 853-855

EXTENDED ABSTRACT: New Vertebrates from the Paleogene of Eastern Texas

Thomas A. Stidham and Tracey A. Janus

Department of Biology, Texas A&M University, 3258 TAMU, College Station, Texas 77843-3258


Although early Paleogene vertebrates have been known since the 19th century in eastern Texas (Koken, 1888), major questions about the biota, biotic change, and the age and correlation of exposed formations have yet to be addressed. A combination of published data with new field, lab, and museum work has expanded the known vertebrate fossil record of the Paleogene of eastern Texas, and has begun to place the Texas stratigraphic column into a regional and global context. Recent work has uncovered the first fossil vertebrates from several Paleocene and Eocene formations, including the Calvert Bluff Formation, Reklaw Formation, and Queen City Formation. Additional new vertebrate records also have been located in the Weches and Crockett formations.

An outcrop in the upper part of the Paleocene-Eocene Calvert Bluff Formation (Wilcox Group) in Bastrop County, Texas, exposes what appears to be a near-shore marine storm bed deposit that contains invertebrate and vertebrate fossils. Lithologically, the outcrop is consistent with typical Calvert Bluff outcrops except for its distinctly marine nature. Some workers might consider the outcrop to be “Sabinetown,” but the glauconite typical of the Sabinetown/Pendleton Formation is absent from the outcrop and storm bed horizon. The storm bed overlies sandstones that contain networks of crustacean burrows, and the bed contains impressions of a variety of mollusc taxa. Surface collecting and screen-washing have produced over 1000 specimens representing a diverse vertebrate fauna from the bed. The assemblage includes fish, sharks, rays, crocodilians, and turtles. The fish fauna includes teeth, bone fragments, and scales of catfish (Siluriformes), drum (Sciaenidae), and gar (Lepisosteus) . The shark fauna is particularly diverse and includes species of Odontaspis, Carcharias, Striatolamia, Alopias, Serratolamna, Scyliorhinus, Galeorhinus, Abdounia, Physogaleus, Rhizoprionodon, and Ginglymostoma. The batoid fauna includes specimens of Myliobatis and Rhinoptera. The turtle specimens are all carapace and plastron fragments representing at least two taxa, including a trionychoid. The crocodilian remains are represented mostly by teeth, although some osteoderm fragments have been found. The osteoderm material indicates that the taxon may be an alligatorid. The mixture of freshwater taxa (gar, trionychoid), near-shore marine taxa (crocodilians, Rhizoprionodon), and marine taxa (sharks and batoids) in the bed indicates deposition of this vertebrate-bearing unit close to shore. With a stratigraphic position relatively high in the Calvert Bluff Formation, it is likely that this outcrop is latest Paleocene in age. If that age assessment were correct, then this fossil locality would contain the oldest specimens of thresher shark (Alopias) and sharpnose shark (Rhizoprionodon). Overall, this Calvert Bluff chondrichthyan fauna most closely resembles the shark faunas from near the Paleocene-Eocene Boundary in the Tuscahoma and Bashi formations in Mississippi. The major difference between these eastern and western faunas is the absence of sharpnose and thresher shark from the much larger Mississippi sample.

At present, the lower Eocene Carrizo Sandstone has no known vertebrate fauna. However, a locality in the Newby Member of the overlying Reklaw Formation in Rusk County has produced the first known fossil vertebrates from that formation. The fauna includes teeth of the batoids Myliobatis and Rhinoptera. The shark fauna includes speci mens of Striatolamia, Serratolamna, and Hypotodus. An otolith appears to be a specimen of a species of Bauzaia (cusk-eel), a genus common in the Eocene of Texas. One of the most interesting specimens from this locality is a large lizard vertebra. Its morphology is consistent with the extinct glyptosaurine lizards that were common in the Eocene of North America.

Above the Reklaw Formation is the Queen City Formation with its well-known in vertebrate fossil record. No vertebrate fossils have been reported previously from this formation. However, an outcrop in Bastrop County in the upper part of the formation below its contact with the Weches Formation has produced one shark tooth of a triakid that is possibly Galeorhinus. Additional fieldwork likely will result in additional taxa being discovered.

The Eocene Weches Formation contains a rich and well-studied invertebrate fauna. Although marine vertebrate remains occur throughout the formation, the only published identified vertebrate remains are from the diverse fish otolith fauna (Frizzell and Dante, 1965). Examination of two outcrops in Nacogdoches County has produced shark and batoid teeth. The shark fauna includes teeth from Striatolamia, Galeocerdo, Cretolamna, Abdounia, and Carcharias. Other specimens still under study may represent Synodon taspis, Physogaleus, and the oldest record of Sphyrna in North America. The batoids include Rhinobatos and a specimen of Dasyatis or Rhinoptera.

Probably the best-known Eocene vertebrate fauna in eastern Texas is from the Crockett Formation. That formation includes the highly fossiliferous outcrops of the Stone City and Cook Mountain members. That middle Eocene formation contains a diverse fish otolith fauna (Frizzell and Dante, 1965) that has received the most study. Other marine vertebrates include sharks and batoids (Breard and Stringer, 1999). Our research has recovered the first record of the shark Cretolamna in the formation. A specimen of a new species of trionychine turtle also has been found. This specimen may be the same taxon previously reported as Trionyx (Breard and Stringer, 1999). How ever, Trionyx does not occur in the Eocene of North America (Meylan, 1987), and the Stone City Member taxon is likely a non-Trionyx trionychine. Other fossil specimens record the presence of lizards, crocodilians, mammals, and birds in the formation. The avian specimens are two partial carpometacarpi that appear to be from two new small sized neoavian taxa. These are the first avian specimens from the Eocene of eastern Texas, and fill a major gap in our knowledge of avian evolution on the Paleogene Gulf Coast.

With these additional vertebrate fossils, the record of vertebrate evolution in the western part of the Gulf Coast now extends back from the late Eocene into the late Paleocene. The lower Eocene Carrizo Sandstone and the middle Eocene Sparta Formation are the only remaining Eocene formations in eastern Texas that do not have known vertebrate fossils. The mixture of marine and terrestrial taxa in the Paleogene outcrops makes eastern Texas an excellent center for studying the changes in vertebrate evolution during the significant climatic changes during the Paleogene. Potentially that combination of sampled marine and terrestrial taxa will allow for correlation of interior terrestrial deposits with the marine record.

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