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?
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.
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.
References:
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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