Khirtharia is an extinct genus of raoellidartiodactyl that inhabited what is now northern India and Pakistan during the middle-upper Eocene (early Lutetian, 48 to 45 million years ago).[1] There are three species of Khirtharia: K. dayi,K. inflata, and K. aurea.[2][3] There is also a possible fourth species, K. major.[4]Khirtharia is found primarily from Jammu and Kashmir and Northern Pakistan.[2][3] More specifically, it is most commonly found in the Upper Subathu Group within Jammu and Kashmir.[5][6]Khirtharia is notable for a well preserved skull of K. inflata, which allowed for obtaining an endocranial cast of the brain cavity.[7]
The endocranial cast of K. inflata showed that the brain of Khirtharia was slightly smaller than that of the related Indohyus. The brain cavity had a volume of approximately 5.5 cubic centimeters, less than in contemporary artiodactyls, giving strong evidence that whales evolved from artiodactyls of relatively small brain sizes. It was also hypothesized that the small brain of Khirtharia could be an adaptation to a semi-aquatic life, supporting the position of Raoellidae as the sister group to whales (Cetacea).[7][8]
Discovery
The first remains of Khirtharia were unearthed by E.S. Pinfold, who then stored them in a museum.[2] He found the remains in the Khirthar fold belt, which is a foldbelt found in Pakistan created by the formation of the Himalayan mountains.[9]Khirtharia was then named by Guy Ellcock Pilgrim in 1940 after the fossils of Khirtharia were given to him by the museum they were stored at.[2][10] Guy Pilgrim named the type species K. dayi.[10] It was named from a fragmentary mandible and maxilla with some of their respective premolars and molars. In 1972, the new species Bunodentus inflatus was discovered by A. Ranga Rao, which was synonymized with Khirtharia as K. inflata.[2][11][12]Indohyus major was described by Hans Thewissen and colleagues (1978) from a single tooth.[13] Orliac and Ducrocq (2012) found that the tooth was more similar to Khirtharia, and thus assigned the species to it, as K. major.[4]K. aurea was named by Thewissen and colleagues (2001) from northern Pakistan.[3]
Classification
External classification
Drawing of closely related taxon Indohyus, the type genus of Raoellidae.
The placement of Khirtharia has varied throughout the history of the taxon. Generally, it has been assigned to basal groups of artiodactyls, although it is currently a member of Raoellidae. When Khirtharia was first discovered by Pilgrim (1940), it was assigned to Helohyidae.[10][13] However, Dehm and Oettingen-Spielberg (1958) moved Khirtharia, along with Haqueina, to Dichobunidae.[14] When Coombs and Coombs (1977) reevaluated Helohyidae, they determined that the remains of Khirtharia were not diagnostic of any particular family of artiodactyls, and therefore left Khirtharia as an artiodactyl of uncertain position.[12][13] In 1981, the family Raoellidae was created, with Khirtharia being one of the three genera included, along with Raoella (a junior synonym of Indohyus) and Kunmunella.[13][15] After the results of a phylogenetic analysis by Orliac and Ducrocq (2012), it was determined that Khirtharia, along with Metkatius, were the most derived members of Raoellidae.[4] This result was confirmed by a phylogenetic analysis performed by Rana et al. (2021) in their description of Rajouria.[16]
Internal classification
The first species of the genus Khirtharia to be named was K. dayi, which is also the type species. K. dayi was named in 1940 by Guy E. Pilgrim.[10] In 1980, Robert M. West suggested that Bunodentus, at the time known only from an isolated molar and fragmentary mandible, was synonymous with Khirtharia dayi, although this change was only officially enacted by Kumar and Sahni (1985) who believed B. inflatus was different enough from K. dayi to warrant being placed under a different species.[2][6] Since there was only one species of Bunodentus, B. inflatus, Khitharia gained the species K. inflata.[6] Likewise, Indohyus major was named by Thewissen et al. (1978) from a single molar in Pakistan. It was named I. major due to the size of the tooth, being approximately twice the size of other raoellid teeth.[13] Orliac and Ducrocq found that this tooth was more similar to Khirtharia, however, and assigned it to the new species K. major.[4]K. aurea was named by Thewissen et al. (2001) from the remains of a single molar in northern Pakistan.[3] The species name (meaning gold in Latin) refers to the color of the sediments which the fossil was found in.[3]
Description
Khirtharia is a raoellid that lived during the early Lutetian age. It is most similar to Metkatius in that it had bunodont teeth. As a raoellid, Khirtharia was relatively small, although there was large interspecific variety in size.[1]
Khirtharia dayi
Khirtharia dayi is the type and smallest species of Khirtharia, and one of the two smallest species of Raoellidae as a whole.[1] Within K. dayi, there are two similar but distinct morphs: a more common one with relatively small molars and the other, more rare, one with relatively large molars.[13]
By being in the same genus, K. dayi's skull is probably similar to the better-preserved skull of K. inflata. The snout is broad. There is a prominent preorbital foramen above the third premolar. The orbits are open posteriorly and there is no postorbital bar, showing that Khirtharia was likely omnivorous. The jugal bone connects to the maxilla above the second molar. The internal nares connect to the throat just after the third molar. There is a large parietal crest, although a relatively minor sagittal one.[2][7] There is a specimen of K. dayi where the entire mandible is preserved except for the most posterior portion of the coronoid. Symphysis occurs before the first premolar in one specimen, although in another it ends at the seconds premolar. The mandible is shallow for the first two premolars, but it quickly grows in height by about 20% with the last two. The ramus begins immediately after the third molar. It is tall and vertical. The angle is enlarged, especially posteriorly so that it extends bast the head of the mandible.[2]
For the upper dention of K. dayi, the first premolar is single-rooted, while the second is double-rooted. The second premolar is narrow and non-molarized; in life it would have appeared similar to a canine. The tooth is widest posteriorly because of a relatively large postero-lingual (tongue-side) shelf. The third premolar is similar to the second; it is non-molarized and has a postero-lingual shelf. However, the third molar was slightly larger and there were large vertical grooves. The fourth premolar represents a transition from the canine-like first to third premolars to the molars. There are only two cones on the tooth, both situated in the front portions. Because of this, the posterior section of the tooth is low and flattened. The cone on the labial (lip) side of the tooth is larger than the protocone, which it is connected to by a ridge. The first lower molar is square-shaped. There are four large cusps which are rounded; they were likely used for crushing plant matter. The paracone is the largest cusp while the hypocone is the smallest. The first molar is very transverse. The second lower molar is significantly larger than the first and, as opposed to being square in shape, is trapezoidal. Cingulum are less apparent than the first molar. The second molar is has bulbous cusps. As with the first molar, the paracone is the largest of the cusps.While the first and second premolars were not preserved, Ranga Rao postulated that the first lower premolar was single-rooted while the second premolar was double-rooted. The third premolar is large and triangular, with prominent cingulum. The fourth premolar is slightly larger than the third. It is more premolariform than the upper fourth premolar.[2] The lower molars of Khirtharia lack the paraconid. The lower molars are highly bunodont. There is a large ridge connecting the protoconid and metaconid and a large ridge connecting the hypoconid and entoconid. The largest molar is the third.[2]
Khirtharia inflata
Khirtharia inflata differs from K. dayi in terms of size in that it is between the size of the two morphs and slight dental differences.[6][13] The premaxilla is elongated and the maxilla is tall.[17] The incisors are caniniform and raptorial, likely adapted to seizing prey.[8][17] Compared to K. dayi, K, inflata has more bunodont and squarish upper molars; the upper molars of K. inflata are similar to the lower molars of K. dayi. The lower molars are also more bunodont and the hypoconid is the largest cusp (in K. dayi the metacone is the largest cusp). The lower molars are also longer than in K. dayi. All molars have cusps separated from each other by valleys.[6] The skull is relatively rectangular, with the height staying of the skull slowly decreasing anteriorly until the beginning of the nostril openings, where it is about half of its maximum height. While there is a sagittal crest, it is minor.[7][8]
Khirtharia aurea
Khirtharia aurea is known from relatively sparse remains. Depending on the validity of K. major as a species of Khirtharia, K. aurea is either the largest or second largest species of Khirtharia.[3][13] The molars of K. aurea have more prominent cingulum than in both K. dayi and K. inflata. Unlike K. inflata, the hypocone is reduced to the point of being smaller than the protocone and the cusps are (unsurprisingly) less inflated than in K. inflata. The two known upper molars are large and bunodont. In the left first molar, the metacone is taller and narrower than the protocone, which is the largest cusp overall. The hypocone is much smaller than the protocone and shifted labially. In the third molar, the paracone being the largest cusp. The protocone is less tall than the paracone, although roughly the same in the other dimensions.[3] In 2007, a study came out stating that the holotype specimen, previously identified as a third molar, could possibly be a second molar.[18]
Khirtharia major
Khirtharia major is a possible species of Khirtharia known only from two molars. It is the largest species of Khirtharia and the largest raoellid as a whole; it is twice the size of Indohyus indirae. It is different from all other species of Khirtharia in that it has an elongated third molar, larger hypocone, and a variety of other small morphogical differences.[4][13]
Paleobiology
Khirtharia was most similar to Metkatius in terms of its paleobiology due to the shared bunodont nature of their teeth, although Khirtharia's teeth were even more bunodont than those of Metkatius.[1] The incisors of Khirtharia were caniniform, which is an adaptation for catching and holding onto potential prey.[17] The molars are bunodont, which is a characteristic of omnivorous taxa. Since Khirtharia also had the most bunodont teeth of any raoellid, this suggests it had the most carnivorous diet of any raoellid.[19] Due to being a raoellid, Khirtharia was almost certainly semi-aquatic.[20] Therefore, Khirtharia was probably an omnivorous semi-aquatic chevrotain-like creature.
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