Extinct ice age giants in Bender's Cave challenge existing climate records for the Edwards Plateau - Biology - Paleontology & Fossils

Fossilized claw of a ground sloth found at Bender's Cave. Credit: Moretti and Young 2026

A recent study by Dr. John Moretti of the University of Texas and local caver John Young uncovered the remains of Ice Age megafauna, revealing an entirely new ecosystem that once thrived on the Edwards Plateau. Among the finds were a genus of giant tortoise (Hesperotestudo) and a large armadillo-like pampathere (Holmesina septentrionalis). The work is published in the journal Quaternary Research.

Snorkeling in Bender's Cave

Bender's Cave is located in Comal County, Texas, and has been explored and mapped by cavers from as early as the 1990s to the present. However, the cave has thus far never undergone scientific investigation.

The cave is one of many so-called "water caves" found in Texas, meaning it contains active underground rivers and streams. "There are many more water caves here in central Texas alone, and none of them have been formally investigated by paleontologists," explained Dr. Moretti.

Bender's Cave has three known sinkhole entrances, of which the first is plugged by natural debris and historic garbage. Meanwhile, sinkholes #2 and #3 had been cleared by other cavers; sinkhole #2 served as the primary entrance.

Descending around 11 meters below the surface, the sinkhole widens into elongated fissures underground, from which one can then navigate to a crawlspace that eventually intersects the flowing underground stream passage. Once inside, Moretti and Young were able to collect fossils, including some that required them to use masks and snorkels to retrieve.

With a wet suit and goggles, paleontologist John Moretti searches for fossils in the stream that flows through Bender's Cave. Credit: John Moretti

The fossils of Bender's Cave

Among the Pleistocene fauna recovered were mammoths, bison, horse, and camel (Camelops), all species relatively common in the surrounding region. However, two fossil fauna remains were particularly intriguing, belonging to a group of megafauna not thought to occur in this region due to unsuitable habitat or climate.

These two fossils included the extinct giant tortoise (Hesperotestudo) and a pampathere (Holmesina septentrionalis). According to previous studies on the megafauna of central Texas, the region was characterized by dry, cool, open grasslands, habitats unsuitable for either tortoise or pampatheres.

"The fossils of the novel taxa exhibit the same patterns of preservation as the more common taxa (e.g., bison, horse, camel). Fossils of the novel taxa also appear to overlap with those of common taxa in terms of their spatial distribution through the cave system. Both lines of evidence offer some support that the overall assemblage of common and novel taxa may represent a contemporaneous fauna," explained Dr. Moretti, saying that the dating of these faunal remains is still tentative.

An attempted radiocarbon date (17,330–17,030 cal BP) taken from a fossil linked to Marine Isotope Stage (MIS) 2 is likely incorrect, possibly due to geochemical contamination that altered the date, making it appear younger/older than it actually is.

Additionally, the occurrence of novel taxa such as pampatheres and giant tortoise would suggest a wet, warm, and forested environment, which is in disagreement with all other climate records for the region at the time.

Using a statistical technique called hierarchical cluster analysis, the megafauna species found in Bender's Cave were compared against those identified in other late Pleistocene sites across Texas. The findings indicate that the fossils likely date to MIS 3 or MIS 5, with the latter being the more likely candidate.

"Marine Isotope Stage 5 is commonly referred to as the last interglacial. This was an interval characterized by a warm global climate between about 71,000 to about 130,000 years ago. The warmest portion of this interval (MIS 5e), from about 112,000 to 130,000 years ago, was one of the warmest moments in the past 200,000 years," Dr. Moretti explained.

"We understand that North America would have been warmer during this interglacial, relative to colder glacial intervals. That would have allowed animals that prefer warm temperatures to be more widespread, relative to glacial intervals. Those animals would include giant tortoises, alligators, giant armadillos, and their glyptodont and pampathere relatives."

The researchers stress that the cluster analysis is an exploratory tool, not a definitive answer. However, if proven, the Bender's Cave fossil assemblage would represent one of only a handful of sites dated to this period, explained Dr. Moretti, "Sites of that age are relatively uncommon, and the entire period is beyond the reach of radiocarbon dating, meaning that even when we do find these sites, it is hard to date the associated fossils.

"Bender's Cave is exciting because it gives us a new impetus to explore this time period and test ideas about the geographic and temporal distribution of animals, habitats, and associated temperature and moisture patterns."

Going forward

"I am working in multiple other water caves in the Texas Hill Country, and they exhibit similar patterns—both in terms of fossil preservation and the occurrence of novel taxa. Those similarities in taphonomy and biodiversity suggest that what we learn from Bender's Cave is going to help us understand fossil assemblages in water caves broadly, at least within the Edwards Plateau of central Texas," Dr. Moretti elaborated.

Additionally, the team is hoping to refine the dates of Bender's Cave, possibly with U-Th dating of speleothems associated with the fossils and U-series and electron spin resonance dating of mammal teeth, which would provide a clearer picture of the age of the remains. 

by Sandee Oster, Phys.org

edited by Sadie Harley, reviewed by Robert Egan 

Source: Extinct ice age giants in Bender's Cave challenge existing climate records for the Edwards Plateau