The 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 possesse ...

, are an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

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 (metatarsals) touching the groun ...

artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...

s in the clade

Whippomorpha Whippomorpha or Cetancodonta is a group of animals that contains all living cetaceans (whales, dolphins, etc.) and hippopotamuses, as well as their extinct relatives, i.e. Entelodont, Entelodonts and Andrewsarchus. All Whippomorphs are descendan ...

. Fossils of raoellids are found in

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

strata of South and Southeast Asia. An exceptionally complete skeleton of ''

Indohyus ''Indohyus'' is an extinct genus of digitigrade artiodactyls known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is one of the earliest known non-cetacean ancestors of whales. Discovery The fossils were di ...

'' from

Kashmir Kashmir () is the 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 Panjal Range. Today, the term encompas ...

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

Cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

). All other

Artiodactyla The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...

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

raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...

-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 ''Indohyus'' and later fully adapted to aquatic life.

Taxonomy

*'' Raoella'' **''Raoella dograi'' *'' Haqueina'' **''Haqueina haquei'' *''

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

Taxonomy

References

Further reading