''Ashoroa'' (named after its type locality Ashoro, Hokkaido) is an extinct genus of

desmostylia The Desmostylia (from Greek δεσμά ''desma'', "bundle", and στῦλος ''stylos'', "pillar") are an extinct order of aquatic mammals native to the North Pacific from the early Oligocene (Rupelian) to the late Miocene (Tortonian) (). Desmos ...

n, aquatic, herbivorous

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

. Fossils of ''Ashoroa'' have been found in the Morawan Formation on

Hokkaido is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

(, paleocoordinates ) and were dated to the late

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Description

''Ashoroa'' is the smallest and one of the oldest desmostylians with an estimated body length of . It is known from a rib, a humerus, a femur, and three vertebrae of the single species and holotype, ''Ashoroa laticosta''. ''Ashoroa'' had pachyosteosclerotic (large and dense) bones. The ribs are broader than in other desmostylians, similar to

sirenia The Sirenia (), commonly referred to as sea cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise two distinct famili ...

n ribs, and very dense, like those of '' Behemotops'' and '' Paleoparadoxia''; and extant, semi-aquatic mammals such as

Eurasian beaver The Eurasian beaver (''Castor fiber'') or European beaver is a species of beaver widespread across Eurasia, with a rapidly increasing population of at least 1.5 million in 2020. The Eurasian beaver was hunted to near-extinction for both its fur ...

and

hippopotamus The hippopotamus (''Hippopotamus amphibius;'' ; : hippopotamuses), often shortened to hippo (: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Sahar ...

, but not as dense as in sirenians. The recovered long bones lack inner cavities, like in ''Paleoparadoxia'' and ''

Desmostylus ''Desmostylus'' is an extinct genus of herbivorous mammal of the family Desmostylidae living from the Chattian stage of the Late Oligocene subepoch through the Late Miocene subepoch (28.4 mya–7.250 Mya) and in existence for approximately .. ...

'', and the

trabecula A trabecula (: trabeculae, from Latin for 'small beam') is a small, often microscopic, biological tissue, tissue element in the form of a small Beam (structure), beam, strut or rod that supports or anchors a framework of parts within a body or ...

r pattern is different from that in ''Behemotops''. interpreted ''Ashoroa'', together with ''Behemotops'' and ''Paleoparadoxia''. as a "shallow water swimmer, either hovering slowly at a preferred depth, or walking on the bottom".

References

Bibliography

* * {{Taxonbar, from=Q4805827 Desmostylians Chattian life Prehistoric placental genera Oligocene mammals of Asia Fossils of Japan Fossil taxa described in 2000