27 March 2015

Smiley Smilodon

...Meow? [photo by the author]
If there is one animal that could be considered the living (or, ah, once-living) emblem of the Ice Age, that animal is undoubtedly the woolly mammoth. But second place is nothing to sneeze at, and second place is firmly defended by a pair of 20-centimetre-long canine teeth. Yes, in the popular imagination, the second-most iconic animal of the Ice Age is the ferocious sabretooth tiger.

It's rather shame that there's not really such a creature as a sabretooth tiger.

Smilodon Was a Cool Cat

Sabretooth cat is the correct name, for these animals belong to their own unique branch of the cat family tree, bearing little relation to tigers, or to any other cats, for that matter. Although the name sabretooth cat can be applied to any of the members of this group, Machairodontinae, it is most commonly meant to refer to the genus Smilodon. Three species of Smilodon are generally recognised.

Smilodon gracilis is the oldest species, appearing at the start of the Pleistocene Epoch, about 2.5 million years ago; it is also the smallest species, at about 55-100 kilograms (121-220 pounds), comparable to a cougar or a leopard. This species evolved in North America, likely from a species of the earlier sabretooth Megantereon, and spread to northern South America in the Great American Biotic Interchange. S. gracilis is believed to be the direct ancestor of the two better-known Smilodon species of the mid Pleistocene-early Holocene.

Smilodon populator, from eastern South America, was the largest Smilodon species and one of the largest cats of all time, weighing in at a whopping 220-400 kilograms (485-882 pounds) and standing some 120 centimetres (47 inches) at the shoulders. S. populator evolved about one million years ago, and went extinct around 10,000 years ago.

The species that is probably the most familiar in the public consciousness and that will be the focus of the rest of this post is the North American Smilodon fatalis. Although smaller than its South American congener, S. fatalis was still a very big cat: 160-280 kilograms (353-617 pounds) and up to 100 centimetres (39 inches) at the shoulder. Some North American Smilodon are assigned to separate species S. californicus (as the one in the Beneski Museum is labelled) and S. floridanus, but these are generally considered to be junior synonyms of S. fatalis. S. fatalis first appeared about 1.6 million years ago, and like S. populator, survived until as recently as 10,000 years ago.

Smilodon fatalis, drawn by the author.
The Beneski's beautiful Smilodon specimen was an exchange from Chicago's Field Museum of Natural History, and it clearly shows the animal's anatomy. Though it isn't as tall or as long as a tiger or lion, especially with its stumpy bobtail, its sturdy legs and barrel-chested physique more than compensate for the smaller dimensions by making it an exceptionally burly cat. Clearly, the stocky sabretooth was not a pursuit predator, but an ambush hunter that would have had to sneak up on prey to within a close range and then attack. Despite their fearsome appearance, the cat's sabres are actually pretty delicate and likely wouldn't have been used for wounding prey; instead, they would have used their strength to overwhelm a prey animal and once it was pinned down and exhausted, cut the animal's throat with the sabres. This method of hunting seems more likely in light of evidence that sabretooth cats lived in groups; we can tell this because of healed injuries some cats incurred that would have prevented hunting or even walking, with the fact that they actually were healed being taken as pretty strong support that these animals lived in a social structure that would have allowed a seriously wounded cat to still get fed and eventually recover from damage that would probably proved fatal without the care of other cats.

Smilodon fatalis (left) with the author (right, poorly photographed).

Trapped In Tar

The Smilodon in the Beneski was collected from Rancho La Brea in Los Angeles. Rancho La Brea is probably the world's best-known tar pit. More accurately called asphalt pits or lakes, tar pits occur where subterranean asphalt seeps up to the surface, creating a natural asphalt pool. Upon being exposed, the lighter components vaporise and only a very thick, very stick asphalt remains.

Smilodon, represented by the remains of some 2,100 individuals, is the second-most common animal found at the La Brea Tar Pits, after the dire wolf Canis dirus. This is unusual; carnivores are rarely the most abundant animals in an environment, so why are there so many of them at Rancho La Brea?

These ground sloths are in a sticky situation, wading into a tar pit where
carnivores hope for an easy meal. Sabretooth cats lurk at left, while
condor-like teratorns
Teratornis merriami sit wating in the trees.
[art by Charles R Knight, image in the public domain]
The La Brea site is what is known as a predator trap, and here's how it works: a herbivore like a bison, camel, or ground sloth comes to drink the water pooling on top of the asphalt. Wading in, the animal finds itself stuck in the goopy substance. It tires itself struggling to get free, and dies of exhaustion, starvation, or overheating in the sun. Any predators in the district think they've found an easy meal: a nice, juicy bison, just lying dead in the shallows of a pond. Coming in to feed on the fresh carcass, they too become mired, and similarly expire in their attempts to break away. As this process repeated over thousands of years, it created one of the world's richest fossil sites, giving palaeontologists an unbeatable treasure trove of information about Pleistocene North America and the Ice Age's poster-child predator, the mighty sabretooth cat.

-- M

 - Page Museum
 - Florida Museum of Natural History
 - Switek, Brian. 'The Rise and Fall of the Great Sabercats.' Aeon
 - Christiansen, Per, and John M. Harris. 'Body size of Smilodon (Mammalia: Felidae).' Journal of Morphology 266.3 (2005): 369-384.

No comments:

Post a Comment