The floor of Bender’s Cave looked like a graveyard. Fossils strewn in either direction of the flooded river, packed so tightly that archaeologist John Moretti could not move them without disturbing them. He was wearing a snorkel mask.
“There were fossils everywhere, just everywhere, like I’ve never seen in any other cave,” said Moretti, who recently completed his doctorate at the UT Jackson School of Geosciences. It was just bones on the ground.
What Moretti pulled from an underground stream in Comal County turned out to be more unusual than the usual Ice Age bone haul. Among the finds were giant tortoise shells and armor plates from the pampathera, a related armadillo about the size of a lion. Neither species has been recorded in Central Texas before. The research is published in the journal Quaternary Research.
Texas and the Edwards Plateau with suitable Late Pleistocene sites indicated. (CREDIT: Quaternary Research)
The cave itself sits beneath private land and has an active underground stream connected to the Trinity Aquifer system. Moretti and co-author John Young, a local caver, made six trips into the cave between March 2023 and November 2024, dividing the stream channel into 21 sampling points and collecting fossils by hand from the underwater gravel. Excavation is not necessary. The bones were just lying there.
A Different Type of Fossil Site
Caves are common throughout the limestone karst of the Edwards Plateau, which spans much of Central Texas. But despite nearly a century of archaeological work in the area, no one had formally studied the fossils that lie in these underground rivers. Water caves are, in some ways, difficult places to do science. The water level changes when it rains. Access requires repeated sinkholes. And without stable sediment layers, dating the bones is very difficult.
Moretti estimates that the remains in Bender’s Cave are late Pleistocene, possibly more than 20,000 years old. A more remarkable possibility, which he carefully explains, is that they could have experienced the last ice age, a warm period that reached its peak about 125,000 years ago and is known in geological terms as Marine Isotope Stage 5. If so, they would fill an obvious gap.
“This site shows us something different, and that’s very important because of all the work that has been done in this area,” Moretti said. “If it’s different in age, it’s a new way to get to know the past and the environment, the environment and the community of animals that we haven’t seen in this part of Texas.”
Escape to Bender’s cave. (A) Low ceiling and shallow water; (B) collecting fossils underwater in one of two large chambers; (C) snorkel test in deep water; note the plaster covering on the ceiling and walls (All dimensions are in millimeters). (CREDIT: Quaternary Research)
Other notable finds in the cave include fossils from Jefferson’s ground sloth, teeth of saber-tooth cats, bones of camels, horses, bison and mammoths, and fragments of mastodon. The bones are polished, reddish-brown, and highly mineralized, suggesting that they entered the cave almost together, drilled through holes during floods. Two bone samples sent for radiocarbon dating lacked usable collagen, and one that came back was almost entirely contaminated with carbonated groundwater.
What Animals Explain
The real argument for an ice age comes from the animals themselves. Pampathere and the giant tortoise needed warm temperatures to survive. The ground sloth and mastodon were forest foragers, dependent on woody plants. Central Texas during the last ice age, about 20,000 years ago, was an open grassland in a cool, relatively dry climate. There would have been little room for them.
During the warm ice ages, this area may have had forests, a warm climate, and animals that came from both. It’s exactly the same combination seen at sites on the north Texas coast, such as Ingleside and Moore Pit, which are described as interglacial in age and contain four of the same types found at Bender’s Cave.
To put the numbers behind this intuition, Moretti conducted a hierarchical cluster analysis comparing the composition of fossils at 43 sites in Texas from the Late Pleistocene. The algorithm linked Bender’s cave to sites from the last ice age, not to the smaller caves in Central Texas that share its location.
Fossils of Megalonyx jeffersonii and Holmesina septentrionalis. (CREDIT: Quaternary Research)
David Ledesma, an assistant professor at the University of St. Edward, who was not part of the research, says the results were truly surprising. He said: “Some of the fossils that John has seen are species that we didn’t think could exist in this part of Texas. It’s exciting that we’re learning new things and finding new things.”
Practical Effects
Educational gaps are real. Fossils in a cave stream are not encased in mud like those in a dry cave environment. They can merge across time, and without reliable radiometric dates, ages remain uncertain. Moretti believes that an assemblage can represent many moments rather than a single photograph. New dating techniques, including speleothem uranium-thorium dating and uranium series and electron spin resonance of fossil teeth, are in progress.
But even before those results arrive, the caveat is important. If the four story species really lived in Central Texas during the warm ice age, the fossil record has a huge gap in it, which the existing sites have not been able to see. That has direct implications for how scientists understand Pleistocene Texas environmental variation, and perhaps for how they model the relationship between climate and the distribution of large mammals.
It also has an instant message for land management. Most caves in Texas are located on private land. Moretti was able to conduct this research only because local landowners donated artifacts to the Jackson School Museum.
“These connections and collaborations make a lot of the natural science that is done in Texas possible,” he said. “It takes contributions from everyone, not just university scientists, to learn about the natural world we live in and depend on.”
The research findings are available online in the journal Quaternary Research.
The first story “Lion-sized armadillo, ancient turtles: Ancient ice creatures found in Central Texas” was published in The Brighter Side of News.
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