259-6 Oh, Snap! Discovery of Predatory Alligator Snapping Turtle at Waco Mammoth National Monument Sheds Light on a Pleistocene Environment

Session: Science and Stewardship of U.S. National Park Service Paleontological Resources (Posters)

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Abstract:

Macrochelys spp., the Alligator Snapping Turtles (ASTs), are both the largest and most aquatic freshwater turtles in North America. In contrast to the Common Snapping Turtle (Chelydra serpentina), ASTs typically only leave the water to lay eggs. Because of this behavior, ASTs are confined to permanent bodies of water. Habitat fragmentation due to climate change, damming of rivers, and draining of wetlands has put both modern species of Macrochelys at risk of extinction.

A microsite at Waco Mammoth National Monument (WMNM) recently produced fossils of Macrochelys, fish, and amphibians.  The presence of Macrochelys is particularly interesting because ASTs do not live in the Brazos River watershed today, their modern range instead restricted to rivers east of the Brazos. Little is known about AST’s historical range, and only one specimen was known from the Brazos River watershed. O. P. Hay identified the first Brazos River Macrochelys, a nearly complete skull, which was dredged from the river in 1911. This presumably Quaternary specimen has been the only known Brazos River AST for over a century, expanding the historical range of the genus, but shedding no light on the timing of its extirpation from this watershed. The discovery of a second specimen is an opportunity to learn more about this enigmatic taxon.

Future work will focus on dating of the specimen, diagnosis of the specimen’s pathologies, geochemical and geochronological analyses of the outcrop that produced the specimen, and further exploration of the site’s micro-vertebrate fossils. In addition to providing new information about the extirpation of ASTs from the Brazos River watershed, the presence of Macrochelys and other aquatic taxa indicate a paleoenvironment with a perennial body of water. Interestingly, recent research of the Late Pleistocene fossil beds at WMNM indicate a sub-arid to sub-humid paleoclimate in central Texas ~66 kya. If the new microsite is coeval with other fossil beds at WMNM, this feature may have been a consistent water source on an otherwise dry landscape. It is plausible that this reliable water source drew the site’s megafauna, which includes approximately 29 Columbian mammoths (Mammuthus columbi), and may help explain the megafaunal fossil accumulation at WMNM.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9459

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