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Raoellidae

Raoellidae is a family of extinct semiaquatic artiodactyls from the middle Eocene closely related to cetaceans. They are known primarily from northern India and Pakistan, especially in the Subathu Group of India, although potential remains of the raoellid Khirtharia have been found in northern China. They are relatively small animals; on average, raoellids were the size of a red fox. However, Khirtharia major, at about twice the size of an average-sized raoellid, would have been approximately the size of a coyote. Meanwhile, the smallest raoellid, Metkatius, was roughly the size of a house cat.

Etymology
The family Raoellidae is named after the genus Raoella. Raoella itself was named after A. Ranga Rao, a geologist who worked extensively on raoellids. However, Raoella was synonymized with Indohyus by Kumar and Sahni (1985), which was reaffirmed by Thewissen, Gingerich, and Russel (1987). Due to the rules of taxonomic nomenclature, the name Raoellidae stayed despite Raoella no longer being valid. == Classification ==
Classification
'' Most raoellids were initially placed in clades of basal placental mammals, usually those within Artiodactyla. Indohyus was initially placed within choeropotamidae, which is the family including the most basal Ancodonts, Khirtharia and Kunmunella were first assigned to Helohyidae, and Raoella was initially placed within Anthracotheriidae. Orliac and Ducrocq (2012) recovered the same result except for not including Haqueina. Rajouria was added to Raoellidae in the paper describing it. == Characteristics ==
Characteristics
Raoellids are distinct for their semiaquatic nature, which is believed to represent a transitional form from basal artiodactyls to more derived forms like cetaceans. Raoellids were generally diminutive creatures that were primarily herbivorous, although similar to a modern day raccoon, would have likely been opportunistic and eat other animals on a somewhat regular basis, especially in the case of the more derived hyperbunodont forms of raoellids (Khirtharia and Metkatius). Raoellids would have almost certainly been furry, unlike their closest living relatives. As artiodactyls, raoellids would have been digitigrade and have hooves, but they would not have been as large as modern non-cetacean artiodactyls and raoellids other toes would have been visible in life. Raoellidae was initially defined based on relatively few characteristics. They were thought to be basal artiodactyls with moderately long snouts that were distinguished from other mammals primarily by bunolophodont molars and other dental features. It was also noted that the raoellids appeared similar to the perissodactyls of the same region. This was interpreted as raoellids having immigrated to the region, although they also said that Raoellidae was not very similar to Asian artiodactyls which could be interpreted that raoellids were, indeed, native to the Indian subcontinent. The definition of Raoellidae was again modified by Orliac and Ducrocq (2012). According to them, raoellids are distinguished as a family by absence of a paraconid along with the reduction of the hypoconulid and parastyle. The teeth contain a large basin and are specialized for shearing. The first to third premolars lost the paracone completely along with one of their roots. The fourth premolar, in contrast, is double rooted and has endocristae that form a transverse loph. == Phylogeny ==
Phylogeny
External phylogeny When Raoellidae was first named by Sahni et al. (1980), it was placed as a basal group of artiodactyl. Sahni et al. also noted that despite all being basal families of artiodactyls, Raoellidae was not close morphologically to Dichobunidae or Helohyidae. In 1987, Thewissen, Gingerich, and Russel maintained this stance, although stated that Raoellidae could be somewhat closely related to Dacrytheriinae. They found that Raoellidae was the sister group to Cetacea. Raoellidae and Cetacea were observed to be the only members of Cetaceamorpha (all Whippomorphs more closely related to Cetaceans than to Hippopotamuses). This result was due to the auditory bulla found in Indohyus's skull and the denser bones characteristic of an aquatic or semi-aquatic lifestyle. This study reaffirmed the monophyly of Raoellidae. Rajouria is the most basal member of the family. Kunmunella and Indohyus are both equally basal members of Raoellidae, and the exact relationship between them is uncertain. Metkatius and Khirtharia are most closely related to each other and are the most derived members of Raoellidae. ==Taxonomy==
Taxonomy
IndohyusIndohyus indiraeKhirthariaKhirtharia aureaKhirtharia dayiKhirtharia inflataKhirtharia major?KunmunellaKunmunella kalakotensisKunmunella transversaMetkatiusMetkatius babbiangalanensisMetkatius kashmiriensisRajouriaRajouria gunneli == See also ==
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