By Mari Hansen The image of a paleontologist in a wetsuit, snorkel in mouth, crawling along the dark floor of an underground stream and reaching down to pick up a mammoth tooth like someone picking up a coin from a sidewalk has a subtle surreal quality. There were just bones lying there, waiting, as if they had given up hiding, without any drilling, brushes, or months of meticulous excavation.
That’s essentially what happened when local caver John Young and vertebrate paleontologist John Moretti descended more than thirty feet into Bender’s Cave, a water cave in Comal County, Central Texas, and discovered something that, in their own words, “blew their minds.”
| Detail | Information |
|---|---|
| Discovery Site | Bender’s Cave, Comal County, Central Texas |
| Location Type | Water cave / underground stream system on private property |
| Lead Researcher | John Moretti, vertebrate paleontologist |
| Institution | University of Texas at Austin, Jackson School of Geosciences |
| Co-Author / Explorer | John Young, local caver |
| Exploration Period | March 2023 – November 2024 |
| Total Trips | Approximately 6–8 expeditions |
| Fossils Collected From | 21 distinct zones inside the cave |
| Estimated Fossil Count | Approximately 1,000 fossils recovered |
| Estimated Age | 70,000 to 130,000 years old — likely from the last interglacial period (~100,000 years ago) |
| Key Animals Found | Giant tortoise (Hesperotestudo), pampathere (Holmesina septentrionalis), giant ground sloth (Megalonyx jeffersonii), mammoth, mastodon, saber-toothed cat, camelids |
| Publication | Quaternary Research, published March 19 |
| Dating Challenge | Mineral-rich water eroded collagen; carbon contamination complicates precise dating |
| Current Dating Approach | Calcite crusts formed on bones after cave deposition |
| Exploration Method | Snorkeling and crawling along submerged streambed — no excavation required |
According to a century’s worth of paleontological research, the remains of animals that had no business being in Central Texas were found on the bed of a subterranean stream, dispersed throughout 21 different zones inside the cave.
Two in particular were the most remarkable discoveries. The first was a pampathere, Holmesina septentrionalis, a massive, armadillo-like animal that was about the size of a lion and could grow up to seven feet in length and three feet in height. The second was Hesperotestudo, an extinct giant tortoise that would have appeared almost cartoonishly large against the barren Texas scenery.
Fossil sites farther east, along the Gulf Coast, and up close to Dallas provided information about both animals. In Central Texas, neither had ever been recorded. Never once. Not in all the decades that scientists had been exploring this area.
“We thought we knew so much,” Moretti remarked. He wasn’t acting overly dramatic. For almost a century, Central Texas has been the subject of extensive research. Researchers had developed a reasonably certain image of what the area looked like during the Ice Age: a wind-blown, dry grassland that was dominated by grazers and most likely not warm or moist enough to support armor-plated giants or slow-moving reptiles that required milder temperatures. This cave implies that the image was not complete. Perhaps considerably so.
Between March 2023 and late 2024, Moretti and Young visited the cave six or eight times, each time wading through a stream whose depth varied greatly based on recent rainfall. They discovered an almost embarrassing amount of stuff there. Mammoth fangs. A massive ground sloth’s claw. bones from baby mammoths, mastodons, saber-toothed cats, and ancient camels.
They most likely entered the cave at the same time, swept in through sinkholes during ancient floods, and settled on the streambed where they would remain undisturbed for between 70,000 and 130,000 years. This is indicated by the fact that everything was polished smooth and stained a similar rusty red. The weight of that number is difficult to ignore. There has been no sound for a hundred thousand years.
According to the theory put forth by Moretti and his colleagues, there was a warmer phase of the last Ice Age, or what geologists refer to as the last interglacial period, which occurred about 100,000 years ago.
During this time, temperatures increased and Central Texas’s landscape may have changed from open grassland to something more humid and forested. Mastodons and ground sloths favored trees. Pampatheres and giant tortoises required warmth to survive.
A whole community of animals that have never been found in this region’s fossil record may have existed here, flourished for a while, and then vanished once more as temperatures dropped, leaving their bones in a cave that no one bothered to investigate if the climate momentarily permitted both.
Proving it is the difficult part. The fossils’ dating was not aided by the mineral-rich water that flowed through Bender’s Cave. It contaminated the bones with absorbed carbon and other minerals and weakened the collagen proteins that are normally used to determine age.
In this instance, a standard carbon date may measure the water chemistry in the cave rather than the animals’ true ages. Currently, the research team is attempting to date calcite crusts that developed on the bones after the animals entered the cave.
While this method is not perfect, it can determine a minimum age and help identify which historical period these animals belong to.
Even from the outside, all of this seems genuinely exciting, like a sort of geological detective work. The Bender’s Cave fossil assemblage consistently clustered with interglacial sites near Dallas and the Gulf Coast, not with the younger glacial-era sites that predominate Central Texas, according to Moretti’s statistical analysis comparing it to other Ice Age sites throughout Texas. Even though it’s circumstantial, it’s difficult to ignore.
The finding was truly unexpected, according to David Ledesma, an assistant professor at St. Edwards University who researches how small animals reacted to previous climate changes. His response carries a little more weight because he was not involved in the study.
“Some of the fossils that John has come across are species that we didn’t think would occur in this part of Texas,” he stated. A scientist acknowledging that there are still surprises in a place they thought they understood has a satisfying quality.
This discovery also subtly highlights the fact that a large portion of Texas’s natural history is located on private property, making it impossible for researchers to access it without landowners’ permission. Bender’s Cave is located in Comal County on private land.
Moretti has been candid about the fact that this type of science depends solely on collaboration and trust. Where they are not welcome, paleontologists cannot dig. The bones simply remain there, beneath the water, in the dark, for an additional 100,000 years if they aren’t being dug.
Whether the Bender’s Cave site will be verified as an interglacial deposit or whether the dating will ultimately indicate something different is still up in the air. However, the possibility itself is noteworthy. Due to the length of time that Central Texas has been studied, the majority of researchers believed that the major surprises were over. The fossil record seemed solid enough to be trusted, if not comprehensive.
At the conclusion of one interview, Moretti stated, “We still don’t know everything about the natural world,” despite the presence of a lion-sized armadillo and a giant tortoise in an underground stream that was ignored for decades. It sounds like a platitude until you imagine him reaching down to retrieve a saber-toothed cat tooth from the mud while submerged in the dark. Then it sounds just right.