Anachlysictis gracilis is an extinct carnivorous mammal belonging to the group Sparassodonta, which were (a group including and their close relatives) that inhabited South America during the Cenozoic. Anachlysictis is the first record of such borhyaenoids in northern South America, and also the most primitive known member of the family Thylacosmilidae, a group of predators equipped with "saber teeth". It was also the only confirmed record of a thylacosmilid that did not belong to the genus Thylacosmilus until the official publication of Patagosmilus in 2010.[Forasiepi A. & Carlini A. A new thylacosmilid (Mammalia, Metatheria, Sparassodonta) from the Miocene of Patagonia, Argentina. Zootaxa 2552: 55–68 (2010)]
This species was found in the Villavieja Formation in the area of La Venta in Colombia, a famous fossil deposit in the Miocene (Laventan; 13.8–11.8 million years ago),[ Anachlysictis gracilis at Fossilworks.org] based on fragments that include a front portion of the lower jaw, with an incipient molar tooth and a piece of carnassial from the front of the maxilla.[Goin, F. J. (1997). New clues for understanding Neogene marsupial . In: Vertebrate Paleontology in the Neotropics. The Miocene Fauna of La Venta, Colombia, R. F. Kay, R. Cifelli, R. H. Madden, and J. Flynn, eds., pp. 185-204, Smithsonian Institution Press, Washington, DC.]
Description
Anachlysictis, was smaller than its better-known relative
Thylacosmilus, weighing around .
[Wroe, S., Argot, C., & Dickman, C. (2004). On the rarity of big fierce carnivores and primacy of isolation and area: tracking large mammalian carnivore diversity on two isolated continents. Proceedings of the Royal Society B Biological Sciences, 271(1544), 1203-1211.] The specialized features of
Thylacosmilus such as the flanges on the lower jaw, were smaller (due to the upper canines not being proportionately as long). It also lacked a rim around the eye socket, resulting in a more flattened shape of the
skull. Otherwise their
anatomy was not as specialized as that of later relatives. It had
carnassial teeth to effectively process meat and flat fangs, located just below the nose, that were not cross-rounded as in unspecialized mammal carnivores, while the accommodation area of the
masseter muscle (involved in the movements of the jaw) was reduced.
[Goin, F.J. 2003. Early marsupial radiations in South America. En: M. Jones, C. Dickman y M. Archer (eds.), Predators with Pouches, The Biology of Carnivorous Marsupials, CSIRO Publishing, Australia, pp. 30–42.] This is because, as in other predatory saber-toothed species, this muscle is reduced, leaving more space for the jaw joint to increase its opening angle and letting the well-developed neck muscles bring down the skull and allow the fangs to bite into the flesh of their prey.
Taxonomy
Until the discovery of
Anachlysictis, it was supposed that
Thylacosmilus was a close relative of the family
Borhyaenidae, or even a specialized member of the same, having emerged in the Late
Miocene. The primitive characteristics and age of
Anachlysictis suggest an earlier origin of the thylacosmilids at the base of the superfamily
Borhyaenoidea, whose
monophyly needs review. The pattern of the molars of
Anachlysictis is very similar to that of the little-known methatherian
Hondadelphys, also from the Honda Group at the Konzentrat-Lagerstätte La Venta. This was originally considered to be a species of
opossum, but is now considered a primitive
Sparassodonta, so
Hondadelphys could well represent the sister clade of Thylacosmilidae.
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