'It blew my mind': Long-lost ice-age ecosystem, including fossils of lion-size armadillo and giant ground sloth, discovered in Texas 'water cave'

While exploring a cave in central Texas, scientists unearthed a long-lost ice-age ecosystem, including the remains of a giant tortoise and a lion-size armadillo relative, among a trove of fossils in an underground stream.

In a study published March 19 in the journal Quaternary Research, researchers say the cave may preserve the remains of animals that lived during a relatively warm period of the last ice age. If the findings are validated, the site would offer a rare look at an animal community that was missing from central Texas' fossil record.

"It blew my mind," lead author John Moretti, a vertebrate paleontologist in the University of Texas at Austin's Jackson School of Geosciences, told Live Science. "Just the abundance of fossils and the animals those fossils represent were really exciting."

Moretti and John Young, a local caver, were exploring Bender's Cave, near San Antonio, in 2023, when they came across the fossils. The cave is difficult to access and has a subterranean stream running through it, so it had largely been ignored by paleontologists. However, they suspected fossils were present, as amateur cavers had previously brought in their finds, Moretti said.

It was Moretti and Young who found the ice-age fossils simply lying in the mud.

"We have bags attached to our waists, and we're picking up fossils as we go," Moretti said. Over six trips between 2023 and 2024, Moretti and Young discovered fossils from 21 areas in the cave. Among the finds were a claw from a giant sloth (Megalonyx jeffersonii), mammoth teeth, and bones of camelids (Camelops), the long-legged ancient relatives of modern day llamas.

But what really intrigued them was the discovery of fossils of two ice-age beasts: a pampathere (Holmesina septentrionalis), a giant armadillo relative that lived during the middle to late Pleistocene (781,000 to 126,000 years ago) ; and an extinct genus of giant tortoise (Hesperotestudo).

The discovery of these two fossilized animals puzzled Moretti and Young because these ice-age giants were not known to have lived in this area. For more than a century, researchers have studied ice-age fossil sites in central Texas and built a picture of the region during that time as a dry grassland dominated by grazing animals. According to Moretti, this climate would not have been suitable for the tortoise or the pampathere.

Moretti and Young suggested that the animals' remains washed into the cave system from the surface through sinkholes during floods and then settled on the streambed. If this is the case, the animals may have lived during a warmer interglacial period, roughly 100,000 years ago, when temperatures rose and animals that favored milder conditions moved into the region, the researchers proposed.

Moretti said they have not been able to accurately date the bones because the collagen proteins often used as the biomarker in fossils were completely eroded by the mineral-rich water. This water also contaminated many of the fossils, as the bones absorbed carbon and other minerals after being deposited. This means a test may measure this contamination rather than the fossils' true ages.

To overcome this challenge, the team is now trying to date the calcite crusts that formed on the bones after they entered the cave. Although these results won't provide exact dates for the fossils, they can set a minimum age for when they were deposited. With these dates, the researchers hope to narrow down whether the cave fossils represent a warmer interglacial chapter of Texas' history.

"We still don't know everything about the natural world," Moretti said. "There's still a lot to discover out there."

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