Khirtharia () is an extinct genus of raoellid artiodactyl that inhabited what is now northern India and Pakistan and potentially China during the middle-upper Eocene (Ypresian to Lutetian, 53 to 45 million years ago). There are three species of Khirtharia: K. dayi, K. inflata, and K. aurea and a possible fourth species, K. major. Khirtharia is found primarily from Jammu and Kashmir and Northern Pakistan and is most commonly found in the Upper Subathu Group within Jammu and Kashmir of northern India. Khirtharia is notable for a well preserved skull of K. inflata, which allowed for obtaining an endocranial cast of the brain cavity. 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). As a raoellid, Khirtharia would be a relatively small, omnivorous, semiaquatic mammal. Khirtharia had the highest level of carnivory out of all raoellids. Khirtharia as a whole is relatively normal sized for a raoellid, but it had the largest variation in size within its genus. It had hooves and a large tail. Khirtharia was a good swimmer, and likely used this advantage to escape from predators.
Discovery The first remains of Khirtharia were unearthed in 1940 by Ernest Sheppard Pinfold while working for the Attock Oil Company, who stored the remains in the British Museum. He found the remains in the Khirthar fold belt, which is a foldbelt found in Pakistan created by the formation of the Himalayan mountains. Khirtharia was then named by Guy Ellcock Pilgrim in 1940 after he was invited to the museum by the head of geology and the fossils of Khirtharia were given to him by Pinfold, including remains found by other geologists in the Attock district of Punjab At the time, all of the remains of Khirtharia were extremely fragmentary. Guy Pilgrim named the first and type species K. dayi. It was named from a fragmentary mandible and maxilla with some of their respective premolars and molars. In 1972, the new species Bunodentus inflatus, named for its "inflated" teeth, was discovered by A. Ranga Rao. 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 in 1985 by Kumar and Sahni who believed B. inflatus was different enough from K. dayi to warrant being placed under a different species (K. inflata). In 1978, Indohyus major was described by Hans Thewissen and colleagues 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. In 2012, Orliac and Ducrocq found that the tooth of I. major was more similar to Khirtharia, and thus assigned the species to Khirtharia as K. major. In 2001, K. aurea was named by Thewissen and colleagues from material in the Chorgali formation of northern Pakistan. It was named after the golden color (aurea is Latin for golden) of the sediment the fossils were found in. K. aurea is the oldest species of Khirtharia and the oldest raoellid.
Classification
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 named by Pilgrim, it was assigned to Helohyidae. However, in 1958, Richard Dehm and Therese zu Oettingen-Spielberg moved Khirtharia, along with Haqueina, to Dichobunidae which was corroborated by Sahni and Khare in 1972 and Gingerich in 1977. Later in 1977, when Coombs and Coombs 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. In 1980, Robert West reaffirmed Khirtharia's initial placement within Helohyidae. 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. After the results of a phylogenetic analysis in 2012 by Orliac and Ducrocq, it was determined that Khirtharia, along with Metkatius, were the most derived members of Raoellidae. This result was confirmed by a phylogenetic analysis performed by Rana and colleagues in 2011 in their description of Rajouria. Raoellidae is widely considered to be the sister group to Cetacea (whales), and thus Khirtharia is closely related to cetaceans, but not a cetacean itself.
Description
Raoellids were a group of mammals closely related to cetaceans. They were generally small and semiaquatic. In life, they would appear similar to the modern day chevrotain, but with a more dog-like snout and large, robust, tail. All members of Raoellidae had denser bones than average for an artiodactyl, hinting at their semiaquatic nature. Denser bones are characteristic of aquatic and semiaquatic animals, such as hippopotamuses and whales, because it counteracts the buoyancy of their lungs and thus enables the organism to maintain a neutral buoyancy more efficient for swimming. Khirtharia is a raoellid that lived during the early Lutetian age. It is most similar to Metkatius in that it had bunodont (bumpy and rounded cusped) teeth. As a raoellid, Khirtharia was relatively small, although there was large interspecific variety in size. Khirtharia's canines differ from Indohyus; in Indohyus the cingulum and styles are reduced while in Khirtharia they are not. The upper canines of Khirtharia show a much larger difference between crown and root compared to Indohyus. The upper incisors of Indohyus are separated by small gaps, while they are not in Khirtharia.
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