Wednesday 19 November 2008

Thylacoleo and Thylacosmilus

“Thylacoleo and Thylacosmilus”
Graphite pencil illustration, November 2008

Thylacoleo carnifex Owen, 1859
Thylacoleonidae; Diprotodontia; Mammalia; Chordata
Pleistocene Australia

Thylacosmilus atrox Riggs, 1933
Thylacosmilidae; Sparassodonta; Mammalia; Chordata
Miocene to Pleistocene South America

Thylacoleo carnifex means “executioner pouched lion”. The “pouched” part of its name refers to the fact that it is a marsupial, just like the Tasmanian devil (Sarcophilus harrisi) and Tasmanian wolf (Thylacinus cynocephalus), also known as the Tasmanian tiger or thylacine (the last name itself deriving for the Greek for “pouched dog”). But unlike those famous marsupial carnivores, it belongs to the same marsupial order as the koala, kangaroos, wombats and their kin (an exclusively Australasian group), the Diprotodontia, while the devil and wolf belong to the Dasyuromorphia, a group of mostly carnivorous and insectivorous marsupials from Australia and New Guinea. There were also carnivorous kangaroos in times gone.

Thylacosmilus atrox means “fierce pouched sabre”. Again a marsupial, but also in a different order containing uniquely South American beasts, which were able to become the dominant mammalian carnivores there because at the time (mid-Tertiary to early Quaternary), South America was an island continent, not connected to North America by the Central American land-bridge. The large carnivores of today’s South America, the jaguar, puma, maned wolf and zorros, had not yet reached the continent, so the niche for large carnivore was available to the sparassodontans.

The name Thylacosmilus also alludes to its similarity to northern hemisphere true sabre-toothed cats of the subfamily Machairodontinae (family Felidae), which are completely unrelated to the marsupials (as distant as you and I are to the kangaroo). In fact, enlarged canine teeth have evolved separately in at least 6 different mammalian lineages: the sparassodontans (like Thylacosmilus), the creodonts (like Machaeroides), the machairodontines (like Smilodon, the sabre-toothed “tiger”), the barbourofelids (family Barbourofelidae, order Carnivora; close relatives of the cats), the nimravids (family Nimravidae, order Carnivora; distant relatives of the cats), and also the walrus (Odobenus rosmarus). Also, it has been noted that the clouded leopards (genus Neofelis) have enlarged canines, and may either be close relatives of the true sabre-teeth, or they represent another convergence of this trend.

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