''Anachlysictis gracilis'' is an extinct carnivorous mammal belonging to the group

Sparassodonta Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now thoug ...

, which were

metatherian Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as we ...

s (a group including

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s and their close relatives) that inhabited

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

during the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...

. ''Anachlysictis'' is the first record of such borhyaenoids in northern

, and also the most primitive known member of the family

Thylacosmilidae Thylacosmilidae is an extinct family of metatherian predators, related to the modern marsupials, which lived in South America between the Miocene and Pliocene epochs. Like other South American mammalian predators that lived prior to the Great Am ...

, 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. This species was found in the Villavieja Formation in the area of

La Venta La Venta is a pre-Columbian archaeological site of the Olmec civilization located in the present-day Mexican state of Tabasco. Some of the artifacts have been moved to the museum "Parque - Museo de La Venta", which is in nearby Villahermos ...

in Colombia, a famous fossil deposit in the Middle Miocene (

Laventan The Laventan ( es, Laventense) age is a period of geologic time (13.8 to 11.8 Ma) within the Middle Miocene epoch of the Neogene, used more specifically within the SALMA classification in South America. It follows the Colloncuran and precedes the ...

; 13.8-11.8 million years ago),''Anachlysictis gracilis''
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.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.

Description

''Anachlysictis'', was smaller than its better-known relative ''

Thylacosmilus ''Thylacosmilus'' is an extinct genus of saber-toothed metatherian mammals that inhabited South America from the Late Miocene to Pliocene epochs. Though ''Thylacosmilus'' looks similar to the "saber-toothed cats", it was not a felid, like the w ...

'', 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, giving the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

a flattened profile. Otherwise their

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

was not as specialized as that of later relatives. It had

carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified ...

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 In human anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it ...

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 Borhyaenidae is an extinct metatherian family of low-slung, heavily built predatory mammals in the order Sparassodonta. Borhyaenids are not true marsupials, but members of a sister taxon, Sparassodonta. Like most metatherians, borhyaenids and o ...

, or even a specialized member of the same, having emerged in the Late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

. The primitive characteristics and age of ''Anachlysictis'' suggest an earlier origin of the thylacosmilids at the base of the superfamily

Borhyaenoidea Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now thou ...

, whose

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

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

. This was originally considered to be a species of

opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered Nort ...

, but is now considered a primitive sparassodont, so ''Hondadelphys'' could well represent the sister clade of Thylacosmilidae.

References

External links

Marsupial 'bears' and marsupial sabre-tooths in Tetrapod Zoology
{{Taxonbar, from=Q4750667 Sparassodonts Miocene mammals of South America Laventan Neogene Colombia Fossils of Colombia Honda Group, Colombia Fossil taxa described in 1997 Prehistoric mammal genera