Sunday, June 12, 2016

Tracking the Mighty Sabertooths

This is a modern Tiger print.
By Aiwok, via Wikipedia.
Did you hear about those newly-discovered saber-toothed cat footprints? If not, check it out over at Science (there’s an awesome picture). The tracks are apparently up to 19cm across – bigger than a Bengal tiger’s! They were discovered in Argentina (because some countries have all the luck these days), and presented at a conference in May. These tracks probably belonged to a species of Smilodon, the most famous saber-toothed cats of them all.

Sabertooth tracks are rare, but these aren’t the first. I’ll get more into that later, but first: what exactly is a saber-toothed cat? Are they really cats anyway? 

The answer is complicated because saber-teeth were surprisingly common. Those dagger-like canines evolved several times in several different carnivore lineages. The saber-toothed cats people normally think of, like Smilodon, were true cats, members of the Felidae family called machairodonts. But there were also the Nimravids and the Barbourofelids, two lineages of animals similar to cats but not-quite-cats, sometimes called the “false sabertooths.”

Calling Nimravids and Barbourofelids “false” is a bit unfair, especially considering that they both evolved long before the “true” sabertooths, and stalked the planet for a much longer time. It is true that they were not true felids, and alas both groups went extinct by the end of the Miocene Period, around the time the earliest machairodonts were evolving their own saber-toothed forms.

Thylacosmilus, a marsupial sabertooth.
Look how weird that skull is.
Those teeth are rooted above the eyes.
Image: Claire Houck via Wikipedia
Saber-teeth are not unique to cats and their relatives. There were even saber-toothed, cat-like marsupials, such as the Thylacosmilus, whose dagger-teeth had roots that extended above its eyes, and were ever-growing like the incisors of rodents. Weird. Marsupials are weird.

Anyway, the “true” saber-toothed cats were the machairodonts. There were many species in this group, but probably the three most famous genera are the three that lived alongside Homo sapiens: Machairodus, which went extinct early on in our own species’ history, and Homotherium and Smilodon, which both lived right up to the end of the Ice Age, disappearing along with the woolly mammoths, ground sloths, and others.

As I said, sabertooth tracks are rare, but not unheard of. The tracks found in Argentina belong to Smilodon populator, a relative of the North American species Smilodon fatalis, famously known from the La Brea Tar Pits. About a decade ago, tracks were reported from Mexico, likely belonging to Homotherium (for images of those tracks, check out the original paper). Tracks known from Coffee Ranch in Texas, from around 3 or 4 million years ago, are probably from Machairodus, and even older tracks have been found in Iran, though which cat they belong to is uncertain.

Probably the most famous footprint site in the world is the Laetoli site in Tanzania. Discovered in the 1970s, this site hosts the earliest evidence of bipedalism in early human ancestors: footprints that probably belonged to Australopithecus (you know, Lucy) that were clearly walking on two legs. That fame overshadows the fact that the site also hosts footprints of ancient elephants, giraffes, pigs, rabbits, birds, rhinos, and more, including some felid tracks too large to have belonged to anything but the site’s resident sabertooth, Homotherium.

Isn’t it cool that there's a place where you can see 3.6 million year-old footprints of a massive dagger-mouthed predator in the same site as footprints of our own human ancestors?

Cast of the famous Laetoli hominin footprints, the earliest evidence of bipedal walking in our ancestors.
The same site has footprints of tons of other animals, including true saber-toothed cats.
Image by Wolfgang Sauber via Wikipedia.
You may have noticed that I keep saying these footprints “probably” belonged to this or “likely” came from that. This is because it's nearly impossible to say definitively what animal left a footprint. For this reason, most footprints are given their own scientific names. The new footprints from Argentina aren’t called Smilodon populator, but instead the much less pronounceable Smilodonichnum miramarensis, honoring their similarity to Smilodon, as well as Miramar, the city nearby the fossil site.

You can learn a lot from fossil prints and tracks (called ichnofossils). Paleo-artists are often particularly interested in trackways, since they can provide insight into an ancient animal’s gait and posture, important info for creating accurate representations. Mauricio Anton discussed this exact topic a few years ago on his blog, Chasing Sabretooths. Just the other day, Mark Witton wrote a post about dinosaur resting posture, including what evidence we can glean from tracks.

This is one of the most famous art pieces by one of the most famous paleo-artists,
Charles R. Knight's Smilodon. Footprints complement bones nicely in providing
information artists can use to create accurate artwork of ancient creatures.
Image from Wikipedia.
Ichnofossils are often overshadowed by the inspiring and photogenic skeletons that make up most of vertebrate paleontology studies, but they are no less important. It's nice to visit the Science website and see a big picture of a fossil footprint on the home page.


Abbassi and Shakeri 2006. Vertebrate Footprints from the Miocene Upper Red Formation, Shokorchi Area, Zanjan Province, NW Iran [Here, paywalled]

Johnston 1937. Tracks from the Pliocene of West Texas. The American Midland Naturalist. [Paper here, but also discussed here]

Leakey and Hay 1979. Pliocene Footprints in the Laetoli Beds at Laetoli, northern Tanzania. Nature. [PDF]

Rodriguez-de la Rosa et al. 2007. Footprints of Machairodontid Felids from the Late Tertiary of Central Mexico. [PDF]

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