It's been over two years (!) since I travelled down with my colleagues Manuel Domínguez-Rodrigo, Lucía Cobo-Sánchez, and Enrique Baquedano to the Florida Museum of Natural History to examine the fossils from a site called Haile 21A. What initially drew our interest was the co-occurrence of two partial skeletons of the sabertooth cat Xenosmilus hodsonae with over two thousand peccary bones within the sediments of an ancient sinkhole. I returned home from that trip just days before much of the country shut down because of the COVID-19 pandemic. What a two years it has been...but I am happy to report that we have completed our analysis, and the results appear in the journal Nature Scientific Reports. The study has enjoyed some modest media attention from both Rice University and my own institution.
Sabertooth cats—named for their imposing upper canines—roamed the landscapes of Asia, Europe, and the Americas for several million years before the last species went extinct ~10,000 years ago at the end of the last Ice Age. As apex predators, sabertooth cats played an important role in regulating ancient ecosystems. While they are fascinating in their own right, what draws me to these remarkable predators is the fact that they shared the landscape with, and often came into contact with, our early ancestors. The invention of sharp-edged stone tools ~2.6 million years ago allowed early humans to butcher the meat, organs, and other soft tissues from the carcasses of large animals. This change in diet no doubt would have increased the chances of running into a sabertooth. The question is: what were those interactions like? We know that some unlucky australopithecines fell victim to large cats like leopards, so it is likely that sabertooths too preyed upon our ancestors. Some researchers also argue that the abandoned kills of sabertooths would have provided scavengers, including early humans, with a ready meal. This is not an unreasonable idea. The enormous canines of sabertooths, while no doubt efficient killing weapons, were relatively narrow and thus prone to breakage. So, the idea goes, sabertooths intentionally avoided tooth-on-bone contact in order to protect their delicate teeth but, in so doing, left significant chunks of flesh and all the goodies inside of bones (marrow, grease, and the like) behind for others to eat.
Researchers have devised ingenious methods to reconstruct the killing and feeding behavior of sabertooths by analyzing the shape and chemical make-up of their teeth and bones. This information provides a wonderful window onto the adaptations of these animals. In order to directly infer what they ate and how they ate it, however, we really need to look at the bones of their prey. There are many sites around the world where sabertooth fossils are found in association with the bones of potential prey animals. The problem is that it's very difficult to be sure that sabertooths were the culprit. After all, lots of other animals and even geological processes can accumulate bones. So, it is only in very rare circumstances that we can be reasonably sure that sabertooths were responsible for the bones found at a site. It so happens that Haile 21A is just such a place: we can say with a good deal of confidence that the sabertooth cat Xenosmilus consumed about sixty peccaries there some million-and-a-half years ago.
That's not to say this whole thing is straightforward. In fact, there are three carnivores in addition to Xenosmilus at Haile 21A, and one or more of them could reasonably be considered as suspects: a coyote-sized canid called Canis edwardii, a wolf-sized canid called Canis armbrusteri, and the sabertooth cat Smilodon gracilis. So why do we think the peccaries were eaten by Xenosmilus? The clues lie in the tooth marks left on the peccary bones. The marks are too big to have been created by Canis edwardii, so that's one suspect eliminated. We know, too, that modern wolves tend to gnaw on and break open bones, which results in lots and lots of individual tooth marks (try this at home with your dog). The peccary fossils, when they do preserve tooth marks, often only preserve a single, or perhaps a few, individual marks—quite unlike a large canid but very similar to what we see among modern big cats like lions and leopards. Another suspect down. That leaves us with the two sabertooth cats. To untangle this, we impressed the teeth from fossils of each species into clay in order to determine if the shape of their tooth marks could distinguish them. It turns out that yes, they can, and in most cases the tooth marks match up very well with Xenosmilus. In fact, the teeth of a Xenosmilus fossil from Haile 21A fit snuggly inside several tooth marks, which is about as close to a smoking gun as you can get.
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| Impressions of Haile 21A sabertooth teeth in clay (photo: Manuel Domínguez-Rodrigo) |
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| Xenosmilus tooth placed inside a tooth mark (photo: Manuel Domínguez-Rodrigo) |
Now that we've identified our culprit, we can proceed with reconstructing how sabertooths consumed their prey. The peccary bones from Haile 21A show evidence for nibbling on or near muscle attachments, so much so that parts of the bone itself was chewed away completely. This is not what you would expect if Xenosmilus was afraid to graze the bone with its teeth. Nor would you see this if large hunks of meat were being left on the bones. The patterns of damage on the Haile 21A fossils in fact match well what we see on the bones of prey consumed by modern lions, who we know leave very little flesh behind. This means that little, if any, meat would be left on the peccary carcasses for a would-be scavenger. What Xenomsmilus did not do, or did not do very often, is break open the peccary bones. This, too, is consistent with observations of modern lions, who can gnaw off the softer parts of bones but typically do not crush or fragment them. So, a scavenger might have been able to scrounge some marrow and grease from the abandoned peccaries at Haile 21A. Our findings from Haile 21A do not appear to be a one-off, either. The 20,000-year-old fossils of juvenile mammoths at Friesenhahn Cave in Texas show that another species of sabertooth cat, Homotherium serum, also stripped clean the carcasses of their prey.
That's all well and good, but it's important to point out that the fossils from Haile 21A and Friesenhahn Cave were deposited before humans ever set foot in the Americas. How, then, can we use these findings to test the idea that early humans scavenged from the remains of sabertooth kills? Importantly, the teeth and skeleton of Xenosmilus and Homotherium are very similar to those of other species of sabertooth cats that shared the landscape with humans in Africa, Eurasia, and the Americas between 2.5 million years ago and 10,000 years ago. We therefore think it is plausible that most of these cats consumed their prey in a similar fashion. If that is the case, an abandoned sabertooth kill would probably have been an insignificant and irregular source of meat. A scavenger hoping for a more substantial meal would need to be willing and able to drive these big cats from a kill, a strategy referred to as "confrontational scavenging." Cut marks left by sharp-edged stone knives indicate that early humans were indeed fully capable of gaining quick access to carcasses, either as confrontational scavengers or hunters in their own right. In fact, it has been suggested that early humans not only were major competitors but may in fact have contributed to the extinction of some species of sabertooths. I look forward to seeing more research on these iconic predators...there certainly are many more questions to answer.
References:
Domínguez-Rodrigo, M, Egeland, CP, Cobo-Sánchez, L, Baquedano, E, Hulbert, RC (2022). Sabertooth carcass consumption behavior and the dynamics of Pleistocene large carnivoran guilds. Nature Scientific Reports. doi.org/10.1038/s41598-022-09480-7
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