Trachemys haugrudi: New Fossil Turtle Species Discovered in Tennessee
University of Pennsylvania paleontologist Steven Jasinski has announced the discovery of a previously unknown species of fossil turtle in the Gray Fossil Site, an area rich with fossils in eastern Tennessee, the United States.
Named Trachemys haugrudi, the ancient reptile was a fairly small turtle, not more than 10 inches (25 cm) in total shell length, smaller than the extant red-eared slider turtle (Trachemys scripta elegans).
The Gray Fossil Site represents an ancient sinkhole surrounded by a forest from which dozens of fossil animal species have been characterized, including new species of red panda, Eurasian badger, kinosternid turtle, and colubrid snake.
Thorough examination of the dozens of turtle fossils from the site revealed important differences between Trachemys haugrudi and other known fossil and living species.
“Turtles are best known for their shells, and indeed it is this feature of their anatomy that is commonly found as fossils. Yet the fossil shells are typically found in broken pieces,” Jasinski explained.
“Often gaps or holes remain, or only single small pieces are found, and the whole must be inferred from other information, including other fossil and living creatures.”
“It is extremely rare to get more complete fossils, but Trachemys haugrudi, commonly called Haugrud’s slider turtle, provides me with dozens of shells, and several are nearly complete.”
As part of the study, Jasinski sought to determine where Trachemys haugrudiwas positioned in the evolution of similar turtles both within the genus and in related genera.
The scientist found Trachemys haugrudi to be most closely related to a group of fossil Trachemys turtles from Florida and next most closely related to a distinct group of fossil Trachemys from the Midwestern United States.
Together, these fossil Trachemys form a closely related group situated within other still-living species of Trachemys.
Today, distinct, closely-related groups of Trachemys species dwell in Mexico, Central and South America, and the Caribbean. Jasinski’s investigation, along with other information from previous studies, indicates that one group evolved in Mexico and Central and South America and evolved into different species within this geographic area, and another group evolved separately in the Caribbean.
Species from the United States, including the red-eared slider turtle, are found near the base of their ‘branch’ of the Trachemys family tree; their fossil ancestors are still waiting to be discovered.
The fossil Trachemys species in this study are on a distinct part of the Trachemys tree, and current understanding suggests that they did not give rise to the modern species living today.
The findings imply that there was once much greater diversity in Trachemysturtles than exists today.
It seems that many of the ancient slider species died out without leaving any direct descendents, perhaps because they lacked the ability to adapt to different environments.
“While Trachemys turtle species are considered plastic, implying they can adapt to and live in many environments, this adaptive lifestyle may be a relatively newer characteristic of these turtles,” Jasinski explained.
“More fossils are needed to better understand if this aspect of their evolution is a recent addition.”
“To get a handle on invasive turtles, understanding more about their ancient relatives could only be helpful.”
A paper reporting this discovery is published in the journal PeerJ.
S.E. Jasinski. 2018. A new slider turtle (Testudines: Emydidae: Deirochelyinae: Trachemys) from the late Hemphillian (late Miocene/early Pliocene) of eastern Tennessee and the evolution of the deirochelyines. PeerJ 6: e4338; doi: 10.7717/peerj.4338