Ice Age Animal Fossils Hidden in Texas Water Cave, Including the Giant Ground Sloth

A hidden source of Ice Age history has been discovered in a water-filled cave in Texas, where a paleontologist discovered dozens of ancient fossils. Water caves across the state, home to active underground rivers and streams, have been touted as fossil treasure troves, but their paleontological potential has yet to be fully explored — until now.

A new study published in Quaternary Research details an unprecedented study of fossilized remains in a Texas water cave, identifying fossils that have never been seen before in Central Texas. Among the fossils discovered are those of a giant tortoise and an armadillo as big as a lion; These fossils, and many others, could date back to a warm period in Texas, about 100,000 years ago.

“This site shows us something different, and it’s really important because of all the work that’s been done in this area,” paleontologist John Moretti of the University of Texas at Austin said in a news release. “If it is interglacial in age, it is a new window into the past and into a landscape, environment and animal community that we have never observed in this part of Texas before.”

Texas Caves and Fossil Discoveries

Regional aquatic caves in Central Texas contain the remains of many Pleistocene vertebrates, but according to the new study, these fossils are poorly documented. The caves’ reputation for rich fossils comes from anecdotal descriptions of the state’s cavers.

However, Moretti saw first-hand how this reputation was born. While exploring an underground stream at Bender’s Cave, a water cave located on private property, Moretti snorkeled in search of fossils and encountered an impressive number of fossils.

“There were fossils everywhere, just everywhere, in a way that I have never seen in any other cave,” Moretti said in the release. “There were just bones all over the floor.”

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Extinct megafauna galore

Moretti and study co-author John Young, a local caver, made six trips to Bender Cave from March 2023 to November 2024, collecting fossils from 21 different areas of the cave. During their travels, the depth of the stream from which they took samples was often only a few feet. Fossils were also easy to obtain, since there was no need for intensive excavations: it was enough to take the samples from the bed of the river.

The remains of Bender Cave, which entered the cave through sinkholes during erosion and flooding thousands of years ago, include specimens of extinct megafauna commonly found in the area, including North American mammoths and camels. Conversely, other remains at the cave, of Jefferson’s ground sloth (Megalonyx jeffersonii) and proboscideans (the family that includes mastodons), are rarely seen in central Texas.

The new study also established the first regional records of Holmesina septentrionalisa species of pampathere (an extinct armadillo-like mammal) and a species of giant Hesperotestudo (an extinct genus of turtle).

A new look at the Texas Ice Age

Moretti thinks the fossils from Bender Cave could date back to the last interglacial, a period of warm climate that occurred 100,000 years ago during the last ice age. But the lack of geological material that can be reliably dated in the cave makes it difficult to confirm the true age of the fossils.

The habitat and temperature preferences of animals that once lived in central Texas provide some clues, however. The ground sloth and mastodon lived in forests, while the giant tortoise and pampatheres needed warm temperatures to live. The Last Interglacial fits these preferences, as central Texas might have been temporarily more forested during this period (whereas during the Cool Glacial Interval it would have shifted toward sprawling grassland with dry, cold conditions).

Moretti also determined that Bender’s Cave fossils share similarities with fossils closer to the Dallas area and Gulf Coast that originate from the last interglacial; Interestingly, they are not as closely related to the fossils from the 17 Late Pleistocene sites on the Edwards Plateau, the region where the cave is located.

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