The June 2025 General Meeting was held on June 13th, 2025 via Zoom. Our speaker was John A. Moretti of the Jackson School of Geosciences at The University of Texas at Austin. His topic was "New discoveries in Inner Space Cavern reveal the animals of Ice Age Texas".
Summary from John Moretti
New discoveries in Inner Space Cavern reveal the animals of Ice Age Texas.
John A. Moretti
Jackson School of Geosciences, The University of Texas at Austin (UT)Summary: Since its discovery in 1963, Inner Space Caverns has been famous for its rich abundance of Ice Age fossils. Those fossils represent mammoths, extinct horses, saber-tooth cats, and other animals that went extinct over 11,000 years ago. I am exploring the Ice Age archive preserved in Inner Space Cavern for lessons about how animal communities change over time and how changes in the past led to the animal community of today. My investigations have recovered new fossils of bats, giant jaguars, and tiny antelope-like pronghorn. Research and analysis of those fossils are providing new insights about the origins of the native fauna of Texas and revealing that Inner Space Caverns contains one of the oldest, longest, and most important troves of Ice Age fossils anywhere in Texas. Come learn more about this famous cave and the ancient history of the Texas Hill Country!
Expanded Summary: Fossils from the Ice Age were found in Inner Space Cavern in Williamson County, Texas, soon after its discovery in 1963. Cavers from Dallas-Ft. Worth and from Austin soon began exploring the cave and made the first fossil discoveries. Those cavers invited paleontologist Dr. Bob H. Slaughter at Southern Methodist University to come and see what they had found.
When we talk about the Ice Age, we are referring to a formal period of geologic time, known as the Pleistocene Epoch. The Pleistocene spanned from 2.588 million years ago to 11,700 years ago. The fossils in the cave here are at the young end of that range, within the Late Pleistocene (~125,000 to 11,700 years ago).
Most of the animals we find as fossils in Inner Space Cavern would have never voluntarily entered a cave. Individual bones from many individual animals were likely accumulating in the cave in a variety of ways. Bones from carcasses decomposing on the surface could be washed or blown into the cave. Owls like to roost around cave mouths and often will deposit the remains of their prey (in the form of owl pellets) into caves. Other animals, like peccaries, big cats, and bats use caves as shelter and some of those animals end up dying in caves as a result.
There are many caves on the Edwards Plateau that contain Pleistocene fossils, but Inner Space Cavern is really special. One of my older colleagues at UT, Ernest L. Lundelius, Jr. studied Inner Space Cavern in the late 1960s. Ernie taught us that the Ice Age record preserved in Inner Space Cavern may span tens of thousands of years and may extend back beyond the last cold, glacial interval of the Pleistocene. Such a record would be longer and reach further back in time than nearly any other cave in Texas. Such an expansive window into the past could help us better understand how and why animal communities change over time and why things like saber-tooth cats and mammoths went extinct while jaguars and white-tailed deer did not. Still, Ernie was not entirely sure about his conclusions, and we really needed more evidence to understand the natural archives in Inner Space. I took on that task because it was an exciting opportunity to learn a lot and have a real impact on what we know about the natural history of Texas. I am writing up my findings now and I am pleased to report that Ernie was mostly correct!
I designed my investigation to help me learn more about Inner Space Cavern specifically and, more broadly, how animal communities change over time. I excavated in five different locations throughout the cave, anywhere that had Pleistocene deposits. Those excavations gave me amazing samples of fossils from all different types of animals. I used those fossils to determine what types of animals were present in the past. I also used some fossils and other materials to obtain radiocarbon dates. Together, those samples allowed me to build a chronology for the Ice Age deposits in the cave and understand what species were present and when were they alive.
In my talk on 13 June, I described some of the many fossil animals that we have discovered in Inner Space Cavern, including glyptodonts, Jefferson’s ground sloth, jaguar, saber-tooth cats, and extinct peccaries. But most exciting discoveries were finding answers to big picture questions. For example, using fossil identifications, stratigraphic patterns, and a suite of radiocarbon ages, I was able to demonstrate that some of the fossils and deposits in the cave date to the last warm period of the Pleistocene, over 29,000 years ago. This is the first glimpse of that warm period from any cave in central Texas. More than just a new fossil or two, this finding opens a window into a part of central Texas history that we have never seen before.
Studying sites like Inner Space Cavern is the only way for us to learn about natural history in deep time. The archives in places like Inner Space Cavern are unique records of the past and if we know how to read those records we can learn about the past, about why the present-day is the way it is, and about what the future could be like. Its history class for the natural world. Inner Space Cavern preserves portions of Texas’s prehistoric history that may not be recorded anywhere else in central Texas. Those portions of prehistoric history fill in gaps in our understanding, kind of like finding long lost chapters to a history book. As we gain a clearer picture of the past, we gain a better understanding of the world we live in. Why do we have raccoons and rattlesnakes and not mammoths and saber-tooth cats? Why don’t we have deep soils in the region? What came before us? Bit by bit, fossil by fossil, rare and special places like Inner Space Cavern teach us about how nature works.
