Raoellidae, previously grouped within

Helohyidae Helohyidae were a group of artiodactyl mammals. They were most prominent in the mid-to-upper Eocene (~50 to 39 million years ago). Description Helohyidae share vague similarities to present-day pigs, though were slimmer in build. They possessed ...

, are an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of semiaquatic

digitigrade In terrestrial vertebrates, digitigrade ( ) locomotion is walking or running on the toes (from the Latin ''digitus'', 'finger', and ''gradior'', 'walk'). A digitigrade animal is one that stands or walks with its toes (phalanges) on the ground, and ...

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

s in the clade

Whippomorpha Whippomorpha or Cetancodonta is a suborder of artiodactyls that contains all living cetaceans (whales, dolphins, and porpoises) and the hippopotamids. This makes it a crown group. Whippomorpha is a suborder within the order Artiodactyla (even-t ...

. Fossils of Raoellids are found in

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

strata of

South Asia South Asia is the southern Subregion#Asia, subregion of Asia that is defined in both geographical and Ethnicity, ethnic-Culture, cultural terms. South Asia, with a population of 2.04 billion, contains a quarter (25%) of the world's populatio ...

and

Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

. An exceptionally complete skeleton of ''

Indohyus ''Indohyus'' (Meaning "India's pig" from the Greek words ''Indos'', "from India" and ''hûs'', "pig") is an extinct genus of artiodactyl known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is among the clo ...

,'' the best preserved Raoellid, from

Kashmir Kashmir ( or ) is the Northwestern Indian subcontinent, northernmost geographical region of the Indian subcontinent. Until the mid-19th century, the term ''Kashmir'' denoted only the Kashmir Valley between the Great Himalayas and the Pir P ...

suggests that Raoellids are the " missing link" sister group to whales (

Cetacea Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

). All other

Artiodactyla Artiodactyls are placental mammals belonging to the order (biology), order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof ...

are relatives of these two groups. δO¹⁸ values and osteosclerotic bones indicate that the

raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the North American, northern or common raccoon (also spelled racoon) to distinguish it from Procyonina, other species of raccoon, is a mammal native to North America. It is the largest ...

-like ''Indohyus'' was habitually aquatic. However, it is still unclear if ''Indohyus'' primarily fed on land or in water. It is hypothesized that cetaceans evolved from ancestors similar to Raoellids and later fully adapted to aquatic life.

Taxonomy

*'' Rajouria'' **''Rajouria gunnelli'' *'' Haqueina?'' **''Haqueina haquei'' **''Haqueina haichinensis'' *''

'' **''Indohyus indirae'' **''Indohyus major?'' *'' Kunmunella'' **''Kunmunella kalakotensis'' **''Kunmunella transversa'' *'' Metkatius'' **''Metkatius kashmiriensis'' *'' Khirtharia'' **''Khirtharia aurea'' **''Khirtharia dayi'' **''Khirtharia inflata'' **''Khirtharia major?''

Phylogeny

In 2011 a study was published examining the remains of a possible raoellid from China. After a

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

, they found it to be most closely related to previously named species of ''Khirtharia'', placing it under this genus as the new species ''K. major''. The phylogenetic tree that resulted from their analysis placed ''Haqueina'' outside of Raoellidae in the clade Dichobunidae, a group of artiodacyls not closely related to

ns. The study did not include ''Rajourna'' due to ''Rajouria'' only being described after this study was published. It found that Raoellidae is

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

. ''Kunmunella'' is the most basal member of Raoellidae, followed by ''Indohyus'', and then ''Metkatius'' and ''Khirtharia''.

References

Sources

* * * * * * * * {{Taxonbar, from=Q135753 Whippomorphs Eocene Artiodactyla Prehistoric mammals of Asia Eocene first appearances Eocene extinctions Prehistoric mammal families