- Source: Sivasmilus
Sivasmilus is a fossil genus of barbourofelid (false saber-toothed cat) containing only a single species, Sivasmilus copei. It is known from only a single specimen, a partial mandible collected from the Chinji Formation in the Lower Siwaliks in Pakistan, estimated to be from the Miocene. The fossil was originally described in 1915 when it was assigned to the fossil feline Sivaelurus chinjiensis, but was used as the basis of a new genus and species in 1929 by Hungarian paleontologist Miklós Kretzoi. Sivasmilus copei was a relatively small, cat-like animal.
History and naming
The holotype and only specimen assigned to Sivasmilus, a partial left mandible labelled GSI-D 151, was collected from the Chinji locality in the Salt Range, same as the holotype specimen of Sivaelurus chinjiensis; that fact along with their similar size led paleontologist Guy Ellcock Pilgrim to provisionally assign GSI-D 151 to S. chinjiensis when he described the fossil in 1915.
In 1929, paleontologist W. D. Matthew considered the holotype of Sivaelurus to be distinctly feline, but the mandible fragment GSI-D 151 to be distinctly machaerodont (saber-toothed cat) based on features of the teeth; in that same year, Hungarian paleontologist Miklós Kretzoi reached the same conclusion in a wholly separate paper and erected the new genus and species Sivasmilus copei for it. In his 1932 paper on Siwalik carnivorans, Pilgrim acknowledged this reassignment and agreed with its machaerodont affinities, stating that he had sought to avoid establishing an ill-defined genus when he assigned it to Sivaelurus.
In 2018 a study noted that the mandible fragment seemed to fit the holotype of Sivaelurus (a near-complete right maxilla, or upper jaw bone) quite well.
Description
The holotype of Sivasmilus copei is a partial left mandibular ramus with the canine tooth and second, third, and fourth premolars. The mandible overall is small and relatively slender, with a moderately developed mental crest, and two mental foramina situated under the second and third premolars respectively. The ramus is broken off after the fourth premolar and any further teeth are unknown; additionally, the front part of the fourth premolar is broken off just above the root. It was noted by several authors that the chin formed a more obtuse angle with the lower edge of the ramus than was usual in "machaerodonts" (which at the time included the nimravids and barbourofelids).
The canine tooth is relatively large and somewhat elongated, situated above the level of the premolars, with an oval cross-section and missing or vestigial keels. The diastema between the canine and the third premolar is relatively long, with a vestigial second premolar (a primitive trait) situated at about the halfway point. The third premolar itself was small, low-crowned, with only a weak posterior (rear) accessory cusp and encircling cingulum (a shelf at the base of the tooth), and no anterior (front) accessory cusp or parastyle at all. The front edge of the third premolar, however, had a distinct series of very fine serrations. The fourth premolar was a longer tooth, with a large posterior accessory cusp and a broader cingulum than in the third premolar, a strong metastyle behind the principal cusp and room for a parastyle in front of the principal cusp, though Pilgrim could not say if a parastyle was present or not.
Kretzoi thought that Sivasmilus lies evolutionary between Afrosmilus africanus and Propontosmilus sivalensis [=Paramachaerodus orientalis]. Pilgrim, reviewing it in 1932, described it as a small and primitive species of machaerodont.
Classification
The genus Sivasmilus was originally assigned to the subfamily Machairodontinae in the family Felidae, though a 2021 study referred it without explanation to the Barbourofelinae. This was followed by other papers, though a 2022 study mentioned in passing that it bore a greater resemblance to machairodontines but that an inspection of the known material was needed.
