Paleontologists have introduced a new genus and species of stem cell turtles, based on complete fossil shells discovered in the early Ale Holocene Denver Formation in Colorado.
Reconstruction of Tavachelydra stevensoni in a water environment with logs. Image credit: Andrey Atuchin.
Tavachelydra stevensoni existed in present-day US during the late Ale Holocene, approximately 66-65 million years ago, shortly after the mass extinction event.
The species is part of the Chelydridae family of freshwater turtles, which includes at least seven extinct species and two extant genera.
“The clade of extant Chelydrid turtles (Chelydridae) comprises five species native to the New World,” stated Dr. Tyler Lyson from the Denver Museum of Natural Sciences and his team.
“Though not a varied clade, Chelydrid turtles are commonly found in most North American freshwater ecosystems.”
“The broader group of Chelydrids (i.e., Pan-Chelydridae) is present throughout Laurasia, but their fossil records are notoriously fragmented.”
Fossilized shells and two skulls of Tavachelydra stevensoni were found in the Corral Bluffs survey area in El Paso County, southern Colorado, east of Colorado Springs.
“The straight shell measures nearly 50 cm in length, making Tavachelydra stevensoni one of the larger turtles from the early Ale (Puercan) of the Denver Basin,” remarked the paleontologist.
“Interestingly, two Pan-Chelydrid turtles coexisted during the early Middle Age of this formation: Tavachelydra stevensoni and Denverus middletonii.
“The size difference is significant, with Tavachelydra stevensoni being at least four times larger than Denverus middletonii, which may have reduced competition between the two species in overlapping geographical ranges.”
Although little is known about the paleoenvironment of the single known specimen of Denverus middletonii, the yellow sandstone of fine to medium grain was initially interpreted as channel fill.
In contrast, the two specimens of Tavachelydra stevensoni suggest that they were likely found in ponded waters or sediments, indicating they lived in sediment-rich areas such as overbank deposits.
“While little can be said about the diet of Denverus middletonii due to the lack of skull preservation, the skulls of Tavachelydra stevensoni show large, wide, flat surfaces, likely used to consume hard-shelled organisms such as corals, shelled mollusks, and crabs,” noted the researchers.
“Thus, it seems plausible that Denverus middletonii and Tavachelydra stevensoni occupied distinct ecological niches, with Tavachelydra stevensoni preferring a pond habitat and a durophagous diet.”
“Remarkably, turtle species with a durophagous diet have shown higher survival rates during mass extinction events compared to those with softer diets.”
In addition to the presumed dietary habits of Tavachelydra stevensoni, other common reptiles from the same sedimentary formation include the button-toothed crocodile Cf. Wangonacosuchus and Baenid turtles such as Paratabena nerrellum, Succersies gilberti, and Cedrobaena putrius.
“This indicates that durophagy was a significant life history trait for the earliest Ale-Holocene freshwater vertebrates in North America.”
The discovery of Tavachelydra stevensoni is detailed in a paper published in the Swiss Journal of Palaeontology.
____
TR Lyson et al. 2025. New pan-chlydrid turtle, Tavachelydra stevensoni gen. et sp. from the Coral Bluffs area, Lower Aleapione (early Danian, Puercan), Denver Basin, Colorado. Swiss J Palaeontol 144, 46; doi:10.1186/s13358-025-00375-4
Source: www.sci.news
