''Ukhaatherium'' is a now extinct species of mammal that lived during the upper Cretaceous about 84 to 72 million years ago in today's East Asia. It is known above all from the fossil locality Ukhaa Tolgod, Mongolia. An adult ''Ukhaatherium'' has an estimated weight of about 32g and bears several similarities to lipotyphlan insectivorans such as the

tenrec A tenrec is any species of mammal within the afrotherian family Tenrecidae endemic to Madagascar. Tenrecs are wildly diverse; as a result of convergent evolution some resemble hedgehogs, shrews, opossums, rats, and mice. They occupy aquatic, a ...

Characteristics

''Ukhaatherium'' ''nessovi'', the type and only species for the genus, is known from multiple near-complete specimens. The most notable feature of the species is the presence of epipubic bones in the pelvic girdle, which have been lost in extant eutherian mammals. The loss of epipubic bones is associated with the evolution of prolonged gestation in eutherian mammalian reproduction. This means that ''Ukhaatherium'' may have had a short gestation period resulting in the birth of

altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...

young, like monotremes, marsupials, and extinct Mesozoic mammals such as

multituberculates Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, ...

. This supports the hypothesis that the presence of epipubic bones is the primitive mammalian condition. Despite some primitive skull and dental traits, the skeletons of ''Ukhaatherium'' and two other asioryctitheres, ''Asioryctes'' and '' Kennalestes'', are classed as eutherians and show several similarities with the extant lipotyphlans. Derived eutherian characteristics include the restriction of the upper ankle joint to the parasagittal plane.

Fossil findings

Since the year 1990, joint expeditions of the

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inte ...

and the Mongolian Academy of Sciences have taken place in the Gobi desert of southern Mongolia in order to investigate upper Cretaceous and

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

vertebrates. More than 500 mammalian skulls (many of which with corresponding postcranial skeletons) were discovered at the Ukhaa Tolgod fossil field between 1993 and 1997, together with very well-preserved dinosaur skeletons, eggs, and embryos, birds, and

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...

s. Fossils of two species of basal eutherian mammal were found, including the first known ''Ukhaatherium'' specimens and a new '' Zalambdalestes'' specimen. These originate from the Djadochta Formation.

Paleobiology

Systematics

''Ukhaatherium'' is a genus from the family of the Asioryctitheria, which lived in the late Cretaceous. ''Ukhaatherium'' and ''Asioryctes'' form the subfamily Asioryctinae, while ''Kennalestes'' stands somewhat outside this group.

References

Late Cretaceous mammals Campanian life Cretaceous mammals of Asia Cretaceous Mongolia Fossils of Mongolia Fossil taxa described in 1997 Prehistoric mammal genera {{cretaceous-mammal-stub