“They fight! And bite! They fight and bite and fight! Fight fight fight! Bite bite bite!”
That’s the theme from “The Itchy and Scratchy Show” – the ultra-violent riff on Tom and Jerry regularly featured on The Simpsons – but it could be easily applied to almost any documentary about prehistoric animals that you care to name. Just look at the titles alone ; Prehistoric Predators, Jurassic Fight Club, Monsters Resurrected, Clash of the Dinosaurs, Prehistoric Assassins. Even with all our abilities to place computer-generated flesh on virtual bones, we can’t really think of anything better to do than pit prehistoric monstrosities against each other as if we were back in the preschool sandbox with our favorite dinosaur toys. I can’t say I blame modern artists for bringing long-dead creatures to life only to have them tear each others throats out, though. The genre has a very long tradition. Some of the earliest restorations of dinosaurs and marine reptiles by the 19th century artist John Martin were apocalyptic spectacles of antediluvian combat where scavengers waited to pick at the remains of the losing contestant.
Prehistoric monsters and reenactments of violent encounters sell, and that’s true for news sources, too. During the past week multiple headlines have popped up saying “Sabertooth Cats May Have Feasted on Early Humans” (LiveScience, FOX News), “Sabretooth cats threatened most ancient human ancestor” (BBC), and “Were our earliest hominid ancestors hunted by saber-toothed tigers?” (io9). At first these titles recall the plots of z-grade horror films, but the truth of the matter is that sabercats existed for almost the entirety of human evolution. By the time the earliest humans originated about six million years ago, sabercats had already been around for more than 14 million years, and the last of the sabertooths only disappeared around 10,000 years ago. Given their prominent dentition it is difficult not to wonder about how swiftly they could have destroyed the humans they lived alongside, but what spurred the recent spurt of sabercat headlines?
Back in September of 2010 a team of paleontologists led by Louis de Bonis and Stéphane Peigné published a description of two sabertoothed cats in the obscure journal Comptes Rendus Palevol. Both animals were known from only partial skeletal material and belonged to genera of sabercats known from elsewhere, but what made them noteworthy, at least as highlighted by the later reports, was that they lived alongside one of the potential candidates for the earliest-known member of the human family. From the very start, humans had to worry about long-fanged predators stalking through the forest primeval.
The cats and their prey were not found in Africa’s eastern Rift Valley – a narrow stretch of the continent where many early humans have been discovered – but far to the west, among the 7 million year old rock of Chad’s Djurab Desert. No one expected to find early humans here, but in 2002 Michel Brunet and a squad of co-authors described the crushed skull and accompanying fragments of what they believed to be the oldest known member of our lineage. They named it Sahelanthropus tchadensis, and the distorted skull was given the popular name Toumai.
Whether Sahelanthropus is actually a human or an ape peripheral to human ancestry remains a matter of debate among paleoanthropologists. Scientists are still piecing together the story of human evolution during the critical window of 6-8 million years ago when the first humans are predicted to have originated, and the general paucity of material makes identifying any species as the ancestor of all later humans very tricky business. (Not to mention the fact that Toumai’s skull was found on the surface and not in a rock layer, meaning that its exact geologic date has not yet been determined. In fact, Toumai has been surrounded by a great deal of scientific gossip, including the idea that the fossils may have been transported or reburied by modern people crossing the desert. I will refer you to John Hawks for the details.) Sahelanthropus could represent the root of the human family tree, or it could have been a collateral relative that lived alongside our early human ancestors. As ever, we need more fossils to be sure.
Regardless of whether Toumai was a human or a human-like ape, however, it did not have the prehistoric jungle all to itself. Paleontologists have found the bones of many other creatures which composed an ecosystem both alien and familiar. The jackal-sized hyena Hyaenictitherium minimum, the prehistoric giraffe Bohlinia adoumi, the three-toed horse Hipparion, and other mammals have all been described from the same area since excavations began in the 1990’s. Together the lot seem to indicate a mixed environment where permanent sources of water existed near patches of woodlands and grasslands, although, because of our removed position in time, it is difficult to be sure about this.
When paleontologists look at a fossil site, they must always ask themselves how that site formed and how long a time span it might represent. Were all the fossils lumped together by a single event, or does the site represent an accumulation over thousands or even millions of years? In the case of the area where Toumai was found, it appears that the fossils all come from a single, thin slice of rock which accumulated over 360,000 years. That’s quite a long time when considering the way local habitats might change over time, and while we can say that the different mammal species were contemporaries it is difficult to tell whether individuals of those species lived alongside each other at this place at any one point in time.
The same goes for the three large, saber-toothed cats found there. The first was described in 2005 under the name Machairodus kabir. Estimated as being slightly larger than the largest known Amur tiger, this cat was big enough to take on juvenile hippos and elephants. The other two were announced together in the 2010 study. One, represented by a partial skull and a few lower jaw pieces, was presented as a new species of an already-known genus and given the name Lokotunjailurus fanonei. (Say that ten times fast.) The other was rather poorly-preserved – only a toothless lower jaw was found – and referred to the widespread genus Megantereon.
That’s a lot of sabercats for just one site! In fact, it is a bit puzzling. Multiple large, carnivorous mammals live alongside each other in Africa today – lions, leopards, cheetahs, wild dogs, and spotted hyenas – but no two are alike and each employs different strategies in capturing prey. These differences are what allow them to coexist. While a pride of lions has the brute strength to bring down a water buffalo, leopards are solitary ambush predators that rely on a range of smaller fare. This kind of partitioning may not have existed among the sabercats.
Although saber-tooths differed in build and the anatomy of their teeth, they have generally been reconstructed as specialists of large prey. If the three species of sabercat from Chad all lived alongside each other, they almost undoubtedly would have come into competition for food and territory. That each species lived during the same time is likely, but did all three really occupy the same habitat all at once? Can we be sure that these fossils don’t represent a succession of occupation by different species at different times?
We can’t. All three species of sabercat obviously lived in this area around seven million years ago, but, for the moment, there is insufficient information to know whether they shared that habitat or switched out with each other over the course of generations. This creates problems for the “Sabercat bites man” headline. Since the Sahelanthropus bones were found on the surface, not in the actual fossil layer, we can’t precisely pinpoint when the ape lived. There is little doubt that the date is around seven million years ago – it likely came out of the nearby fossil layer that has yielded so many other mammals – but this is a squishy estimate that makes it difficult to determine the cast of creatures that were actually present at the site at the same time .
This may sound like nitpicking, though. There were three species of sabercat known from the area, and at least one probably lived next to Sahelanthropus. Could sabercats have killed and eaten the apes as reported? Yes – they certainly had some formidable cutlery at their disposal! – but there is not much reason to think that Sahelanthropus was a regular part of the sabercat diet. We don’t have a full skeleton to come up with a body estimate, but, based upon the available skull, Toumai and kin were not very big – smaller than chimpanzees, but a little bigger than gibbons. To a sabercat, they would have made relatively difficult meals. The teeth of sabercats were suited to stripping large amounts of flesh from prey carrying large amounts of soft tissue. To a Machairodus or a Lokotunjailurus, Toumai would have been a rather paltry and bony meal that would not have provided much reward for the effort. There is no reason to be dogmatic and say that these sabercats never, ever ate prehistoric apes, but, if they did, it was probably a relatively rare event.
Yet, in both the popular reports and a final note in the paper, de Bonis suggests another type of relationship between the sabercats and Sahelanthropus. For years it has been argued that early humans benefited from the messy eating habits of saber-toothed predators. Hindered by their large canines, sabercats may have left a good deal of meat on carcasses, therefore allowing enterprising humans to pick up a little take-out. “The remains of the killed big herbivores left a large amount of food for some scavengers”, de Bonis and co-authors state, “or occasionally scavengers like the abundant jackal sized Hyaenictiherium minimum or even like the primitive hominids.”
I don’t think sabercats were as sloppy as has been supposed. From Smilodon to Lokotunjailurus, many saber-tooths had batteries of incisor teeth which jutted out far in front of their impressive canine teeth. This arrangement allowed them to scrape the maximum amount of meat from the skeletons of their prey, and the well-worn incisors of the sabercat Homotherium serum from a Texas cave indicates that they did just that. Sabercats could not entirely obliterate a skeleton like bone-crushing spotted hyenas can, but they could have very effectively defleshed a carcass. There likely would not have been much left for Sahelanthropus, and, even if there was, sabercat leftovers were not necessarily a safe dinner choice. The predators would likely have opened up the internal organs of the prey animal, allowing the spread of internal bacteria that could have made a scavenging Sahelanthropus quite sick.
The only reason that we are hearing anything at all in the press about the two recently-described sabercats is because they were found at a site that has also yielded an ape with a controversial bid as the earliest known human. There is not terribly much to say about them – one cannot be positively identified, and the other is primarily of interest to fossil mammal specialists – but their proximity to one of our potential ancestors ushered them into the spotlight. Maybe a few of the sabercats snagged apes for a light snack, but when we start to reconstruct these scenarios we are entering the realm of scientific storytelling. We don’t have any positive evidence, nor is there any reason to say that such interactions never happened. In these cases, though, I think we would do well to keep in mind what is known and what remains unknown. Stories are beautiful and powerful things, and there is perhaps no window into the past so influenced by stories as the study of our own origins.
Top Image: A restoration of the sabercat Homotherium serum – on display at the Liberty Science Center – gets ready for its close up. Photo by author.
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de BONIS, L., PEIGNE, S., LIKIUS, A., MACKAYE, H., VIGNAUD, P., & BRUNET, M. (2005). Hyaenictitherium minimum, a new ictithere (Mammalia, Carnivora, Hyaenidae) from the Late Miocene of Toros-Menalla, Chad Comptes Rendus Palevol, 4 (8), 671-679 DOI: 10.1016/j.crpv.2005.09.020
de Bonis, L., Peigné, S., Taisso Mackaye, H., Likius, A., Vignaud, P., & Brunet, M. (2010). New sabre-toothed cats in the Late Miocene of Toros Menalla (Chad) Comptes Rendus Palevol, 9 (5), 221-227 DOI: 10.1016/j.crpv.2010.07.018
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