Sivasmilus

Sivasmilus is a fossil genus of machairodontine (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 medium-sized, cat-like animal that weighed between 30 and 50 kilograms (66 and 110 lb).

Sivasmilus Temporal range: Miocene PreꞒ Ꞓ O S D C P T J K Pg N
The holotype of Sivasmilus copei as depicted by Pilgrim (1915).
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Suborder:	Feliformia
Family:	Felidae
Subfamily:	†Machairodontinae
Genus:	†Sivasmilus Kretzoi, 1929
Type species
†Sivasmilus copei Kretzoi, 1929
Chinji locality Show map of Punjab, Pakistan Chinji locality Show map of Pakistan
Map showing the location of the Chinji locality in Punjab, Pakistan.

History and naming

The holotype and only specimen assigned to Sivasmilus, a partial left mandible labelled GSI-D 151, was collected from the Chinji type 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.^[1]

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;^[2] 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.^[3] 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.^[4]

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.^[5] A review of Siwalik carnivorans in 2025 discussed the species and mentioned another mandible in the collections of the Geological Survey of Pakistan that might also belong to Sivasmilus.^[6]

A 2025 study describing Siwalik carnivoran fossils discussed the taxonomic history of GSI-D 151 in some detail, then compared its mandibular flange to that of various machairodontines. The researchers concluded that GSI-D 151 did not represent a Pseudaelurus-grade felid and was likely a distinct taxon, but that its broken teeth precluded any classification more specific than "Smilodontini indet." (that is, indeterminate) based on the pictures and description provided by Pilgrim's 1915 paper and a 2021 study.^[7]

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.^[1][4] 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).^[4][8]

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.^[1][4]

Kretzoi thought that Sivasmilus lay evolutionarily between Afrosmilus africanus and Propontosmilus sivalensis [=Paramachaerodus orientalis].^[3] Pilgrim, reviewing it in 1932, described it as a small and primitive species of machairodontine.^[4] The 2025 review of Siwalik carnivorans summarized it as relatively small, with an estimated weight of 30–50 kilograms (66–110 lb) based comparisons to extant related species.^[6]

The book also briefly described another specimen, in the collections of the Geological Survey of Pakistan, a mandible with a broken canine showing a distinct posterior crest, a completely absent second premolar, a two-rooted third premolar, and a pronounced blade-like anterior accessory cusp on the fourth premolar. It suggested but did not outright assign this specimen to Sivasmilus copei.^[6]

Classification

The genus Sivasmilus was originally assigned by Pilgrim to the subfamily Machairodontinae in the family Felidae,^[4] though a 2021 study referred it without explanation to the Barbourofelinae.^[9] This was followed by other papers, though a 2023 study mentioned in passing that it bore a greater resemblance to machairodontines but that an inspection of the known material was needed.^[10][11] The 2025 review placed it back in Machairodontinae,^[6] while the 2025 study assigned GSI-D 151 to Smilodontini as a distinct but indeterminate taxon.^[7]

Paleoecology

Sivasmilus copei is estimated to have lived 14.1–11.4 million years ago, during the Miocene.^[6] The presence of multiple species of the mouse-deer Dorcatherium from the same locality indicates the environment of the time was a humid, swampy forest with a dense understory.^[12]