| Asiavorator | |
|---|---|
 | |
| Holotype limb bones ofA. gracilis | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Genus: | †Asiavorator Spassov & Lange-Badré, 1995 |
| Species: | †A. gracilis |
| Binomial name | |
| †Asiavorator gracilis Matthew & Granger, 1924 | |
| Synonyms | |
List
| |
Asiavorator (meaning "Asian devourer") is an extinctgenus ofcivet-like carnivoran belonging in the familyStenoplesictidae. It was endemic toAsia and lived during theEocene andOligocene epochs.[1]
The teeth ofAsiavorator suggest that it wasomnivorous or more precisely, ranged fromhypercarnivorous tomesocarnivorous.[2][3]
The first remains ofAsiavorator to be found were collected in the 1922 field season of the Central Asiatic Expeditions near the Loh campsite inÖvörkhangai Province, Mongolia. This locality is part of theHsanda Gol Formation. The specimens, designatedAMNH19123, included limb bones and lower teeth.Matthew andGranger (1924) described AMNH 19123 as the type specimen of a new carnivoran species they namedPalaeoprionodon gracilis.[4]
The genusAsiavorator was erected by Spassov and Lange-Badré in 1995 as a monotypic genus for their new speciesA. altidens, with the type specimen ofA. altidens being amandible (FM 487-95) from the Hsanda Gol Formation.[5] Dashzeveg (1996) described a new species of stenoplesictid,Stenoplesictis simplex, based on a mandible (PSS 27-25) from theErgilin Dzo Formation of Mongolia.[6] In 1998, Hunt reassignedS. simplex to the genusShandgolictis, renaming itShandgolictis simplex and assigning it toAeluroidea.[7]
Later authors found thatAsiavorator altidens andPalaeoprionodon gracilis weresynonymous and represent a distinct genus, thus the two were synonymized asAsiavorator gracilis, retaining thespecific name of the latter and thegeneric name of the former. A re-examination by Egiet al. (2016) found that the tooth measurements of PSS 27-25 are not notably different from those of AMNH 19123, thus concluding thatStenoplesictis simplex andShandgolictis simplex arejunior synonyms ofAsiavorator gracilis. Currently,A. gracilis is the only accepted species in the genus.[8]
Using the carnivoranregression on the specimen PSS 21-25,Asiavorator has been estimated to have a body mass of 3.6 to 5.6 kg. This is larger thanAlagtsavbaatar, a feliform known to have beensympatric withAsiavorator, whose body mass has been estimated at 2.6 to 3.6 kg.[8]
Like many other carnivorous mammals,Asiavorator has long and sharp-pointedcanine teeth, presumably used in killing prey. The upper and lower canines were approximately equal in length. Thecarnassial resembles that of a cat, being compressed and possessing a vestigial heel and reducedmetaconid. The first upper molar is very elongated, measuring 10 mm long and 4.5 mm wide in the specimen PSS 27-25. An obtuse angle is formed by the shearing edges of theprotoconid and paraconid, while the well-developed metaconid is placed against the internal posterior side of the protoconid. The base of the crown has acingulum on the external side. The second molar isbunodont, and possesses two roots and a flattenedtrigonid of three low cusps and a trenchant heel. The fourthpremolar is large and compressed, similar to the condition seen in domestic cats.[4][6]
Asiavorator had a well-developedmasseteric fossa and a thinmandible. The mandibular corpus has a prominent lower edge below the molars. Below the first molar, themandibular ramus of the specimen PSS 27-25 measures 13.4 mm in height and 5.6 mm in width.[6]
The limb bones ofAsiavorator were slender and long. At itsdistal end, thehumerus expanded transversely with a strong epicondylar bridge. Theulna was wide, and at theproximal half of the shaft it was flattened, whereas the distal half was triangular, though significantly less so than the slenderradius in sectional area.Asiavorator had long and slender metatarsals, and thefirst metatarsal bone was vestigial or absent. Thecalcaneum lacks a fibular facet. Thetalus bone possessed deep and narrow trochlea, with a well-developed inner crest.[4]
In the original description of the holotype, Matthew and Granger (1924) assigned the species to the genusPalaeoprionodon asP. gracilis, referring it to the European genus based on similarities in the dentition and proportions of the limbs, though they did clarify that this referral is provisional until the dentition is better known.[4]
The referred mandible PSS 27-25 was described as a new species,Stenoplesictis simplex, by Dashzeveg (1996). The author placedS. simplex in the familyViverridae following Hunt (1989), which listed the Stenoplesictinae as a probable subfamily of viverrids.[6][9] This subfamily would later be elevated to family level and renamedStenoplesictidae. The placement ofS. simplex in the genusStenoplesictis was refuted by Peigné and de Bonis (1999) based on the dentition, though they did not assign the species to another genus. However, they did note that the type specimens of"Palaeoprionodon" gracilis and"Stenoplesictis" simplex were very similar, and that this species likely belonged in the same lineage as"Stenoplesictis" indigenus (later renamedAlagtsavbaatar indigenus).[10]
Spassov and Lange-Badré (1995) did not assignAsiavorator to any family in their description of the genus, placing it asFeliformiaincertae sedis.[5] Egi et al. (2016) made the same taxonomic placement for the genus, though they do state that the Mongolian small feliforms (Asiavorator,Alagtsavbaatar andShandgolictis) appear to form amonophyletic clade relative to the European generaStenoplesictis,Palaeoprionodon andHaplogale, which independently evolved hypercarnivory. They state this clade is a sister taxon to the extantFeliformia excluding theNandiniidae.[8]
The oldest known fossils ofAsiavorator originate from thelate Eocene-agedErgilin Dzo Formation of Mongolia, suggesting the genus first evolved during theErgilian age. Sedimentary analyses suggest the Ergilin Dzo Formation was afloodplain environment with abraided stream network formed by fluvial systems.[11] In this environment,sympatric predators included the nimravidsNimravus andEofelis, the entelodontidEntelodon, and the related stenoplesictidAlagtsavbaatar.[8][12]
Most known specimens ofAsiavorator were found in theHsanda Gol Formation, which is dated to around 33.4 to 31 million years ago (early Oligocene). This formation is believed to have been deposited in an open,semi-aridsteppe environment withplaya lakes andephemeral rivers.[13] Many types of small mammals would have coexisted withAsiavorator in this habitat, such as severalrodent species, the lagomorphDesmatolagus and the erinaceidPalaeoscaptor.[14][15] Sympatric predators included several species ofHyaenodon, the feliformsShandgolictis,Nimravus andPalaeogale, the amphicynodontidsAmphicynodon andAmphicticeps, and the didymoconidsDidymoconus andErgilictis.[16] Herbivorous mammals were also present, such as the gelocidPseudogelocus, the largest of these being the hornless rhinocerotoidParaceratheriumtransouralicum.[17][18]
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