Fossil research reveals new species of turtles a

image: Map of North America in Cenomanian times (96 million years ago) showing the four families of turtles newly discovered at the Arlington Archosaur (AAS) site. The AAS fossil assemblage includes a diverse combination of turtle lineages native to North America alongside those that migrated from Asia or the Southern Hemisphere. One of these species, “Trinitichelys” maini is a new species to science, described here for the first time.
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Credit: Brent Adrian, MAE

The Arlington Archosaur Site (AAS) of Texas preserves the remains of an ancient Late Cretaceous river delta that once existed in the Dallas-Fort Worth area. Known for its finds of fossil crocodiles and dinosaurs, a multi-agency research team has described four species of extinct turtles, including a new river turtle named after AAS paleontologist Dr Derek Main and the oldest side-necked turtle in North America. These new turtles include an intriguing combination of native North American forms alongside Asian and Southern Hemisphere immigrants, suggesting a significant intercontinental migration of turtles during this time.

Originally discovered by amateur fossil hunter Art Sahlstein in 2003, the AAS is a prolific fossil locality found in the middle of a suburban subdivision. The AAS preserves the remains of an ancient Late Cretaceous river delta about 96 million years ago in what is now the Dallas-Fort Worth area. It maintains a record of a freshwater wetland located near the shore of a large peninsula, including a diverse assemblage of relatives of crocodiles, dinosaurs, amphibians, mammals, fish, invertebrates, and of plants, several of which are also new species awaiting description. “Until this discovery, there were very few turtle fossils from this period found in Appalachia,” says Dr. Heather Smith, one of the paper’s authors. The research team describing these findings includes Brent Adrian, MFA, Heather F. Smith, Ph.D., and Ari Grossman, Ph.D., of Midwestern University in Glendale, Arizona, and Christopher Noto, Ph.D. ., from the University of Wisconsin-Parkside.

“The AAS turtle assemblage informs a growing understanding of mid-Cretaceous Appalachian ecosystems, most of which have been obscured by subsequent erosion along coasts and extensive continental river drainages,” said Brent Adrian, the lead author of the study, published in the current issue of the online journal Electronic paleontology. A new species – “Trinitichelys” maini – is a baenid turtle, an extinct lineage of North American aquatic turtles that persisted from the Lower Cretaceous to the Eocene. These turtles were medium-sized (about the size of a modern snapping turtle), had heavily fused bones and carapaces, and occupied freshwater riverine habitats. “Trinitichelys” maini is the oldest member of the group found in the North American Appalachian subcontinent, which at the time was separated from Laramidia, the western subcontinent of North America.

“T.” maini pays tribute to the late Dr. Derek Main, the first director of the AAS project, who recognized the scientific potential of the site. “Derek’s incredible work with the community has led to the creation of one of the largest and most diverse collections of mid-Cretaceous fossils known in Texas,” says Dr. ‘AAS in 2013, “He was an inspiration to everyone who worked with him, and it’s only fitting that this new species be named after him.”

Alongside T. maini, the study describes three more intriguing new AAS turtles. One species represents the oldest side-necked (pleurodire) turtle discovered in North America. Side-necked turtles are native to the Southern Hemisphere, and the AAS marks the first time they’ve been found in North America. Another surprise is an early softshell turtle (trionychid), which belongs to a line that immigrated from Asia. Added to this unusual mix is ​​Naomichelys sp., a large semi-aquatic turtle with unusual tubercles (raised bumps) on its shell which is a North American relict species usually found in much older rocks. This combination of turtle species in one location is unique, as it includes Asian, Southern Hemisphere, and native North American forms, as well as young and older relict taxa.

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Work at the Arlington Archosaur site is supported in part by the National Geographic Society, which provided a grant to complete fieldwork at the site, and the Perot Museum of Nature and Science in Dallas, which preserves the fossils found on the site and organizes the many volunteers who work there. Electronic paleontology is the oldest professional peer-reviewed electronic journal of paleontology and is sponsored by the Palaeontological Association, the Paleontological Society, and the Society of Vertebrate Paleontology.


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