Cainotheriidae is an extinct family of

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 known from the

Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...

Middle Miocene The Middle Miocene is a sub-epoch of the Miocene epoch (geology), epoch made up of two Stage (stratigraphy), stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene. The sub-epoch lasted from 15.97 ± 0. ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

. They are mostly found preserved in

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

ic deposits. These animals were small in size, and generally did not exceed in height at the shoulders, ranging in size from those of

rabbits Rabbits are small mammals in the family Leporidae (which also includes the hares), which is in the order Lagomorpha (which also includes pikas). They are familiar throughout the world as a small herbivore, a prey animal, a domesticated form ...

to tragulids. For a long time, they were considered to have a similar lifestyle to hares and rabbits. The dentition was full and highly

selenodont Selenodont teeth are the type of molars and premolars commonly found in ruminant herbivores. They are characterized by low crowns, and crescent-shaped cusps when viewed from above (crown view). The term comes from the Ancient Greek roots (, ' ...

, i.e. the premolars and molars had curved and crescent-shaped cutting edges (as in today's ruminants). The skull was small, with a short snout and orbits closed posteriorly placed at the center of the skull. A peculiar characteristic of this group were the

auditory bulla The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic b ...

, protective structures of the bones of the ear : they were very large, like those that are found today in small mammals that live in open and dry environments. This evolved cranial anatomy was in stark contrast to the rest of the skeleton, rather primitive: the cainotheriids still possessed four non-reduced toes (an ancestral condition of the artiodactyls), even if the lateral fingers were shorter; they ended in long claws, as in modern rabbits. The hind legs were much longer than the front ones, and indicate a remarkable adaptation to running and jumping.

Classification

The bizarre anatomical features of the cainotheriids denote them as primitive artiodactyls. Previous research placed them near to

Tylopoda Tylopoda (meaning "calloused foot") is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camel ...

, more recent research places them closer to

Ruminantia Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, principa ...

. '' Robiacina'' of the middle/upper Eocene was previously classified as a member of this family, but has been more recently split into a separate family as the sister taxon to Cainotheriidae. In the course of the Upper Eocene primitive genera such as '' Oxacron'' and '' Paroxacron'' developed, considered the first true cainotheriids as sister taxa in the subfamily Oxacroninae. Subsequently, in the course of the Oligocene, the subfamily Cainotheriinae underwent a discrete evolutionary radiation, with the rabbit-sized genera '' Plesiomeryx'' and '' Caenomeryx''. The most specialized genus, '' Cainotherium'', was also the last to disappear, during the middle Miocene. Even at the beginning of the Miocene, these animals were quite common in various parts of Europe, with numerous species (e.g. ''C. laticurvatum, C. miocenicum, C. bavaricum''). The cainotheriids died out definitively when, during the Miocene, the climate became colder.

Paleoecology

These small ungulate animals possessed exceptionally long hind legs; this characteristic, combined with small size and large auditory bulla, has led many scholars to consider cainoterids a sort of ecological parallel of rabbits. It was therefore assumed that these animals proceeded to leap thanks to the long hind legs, but the discovery of fossil traces of the lower Miocene found in the locality of Salinas de Anana in Spain, clearly left by ''Cainotherium'', showed that the locomotion of these animals had to be very different from that of rabbits, and quite similar to that of the current small ruminants.

Classification

Paleoecology

References

Further reading