''Microdocodon'' is a genus of docodontan

mammaliaform Mammaliaformes ("mammalian forms") is a clade that contains the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts. It is defined as the clade originating from the most recent com ...

from the Late Jurassic

Yanliao Biota The Yanliao Biota is the name given to an assembly of fossils preserved in northeastern China from the Middle to Late Jurassic.Xu, X., Zhou, Z., Sullivan, C. and Wang, Y., 2017. The Yanliao Biota: a trove of exceptionally preserved Middle-Late Jur ...

. It contains only a single species, ''Microdocodon gracilis'', known from the

Daohugou The Haifanggou Formation (), also known as the Jiulongshan Formation (), is a fossil-bearing rock deposit located near Daohugou () village of Ningcheng County, in Inner Mongolia, northeastern China. The formation consists of coarse conglomerates ...

locality. It is unique for preserving the

hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebr ...

, which is almost unknown in the early mammal fossil record.

Anatomy

The species is notable for providing insight into the evolution of the ability to chew and suckle in early relatives of mammals, by preserving a nearly intact

hyoid The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebra. ...

in the throat. This bone is important in mammals because it allows them to suckle, and move their tongue with precision. The complexity of the structure in ''Microdocodon'' suggests that chewing and suckle evolved before in the precursors to Mammalia, the mammaliaforms, but after their split with the earlier

cynodonts The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

. This supports previous conclusions that an important feature that marks crown mammals (Mammalia) from the mammaliaforms is the evolution of the middle ear, and the way in which it disconnected from its previous position in the mandible. ''Microdocodon'' is an especially small early mammal, thought to have been a shrew-like insectivore weighing about 9 grams. It was probably capable of climbing and living in trees. ''Microdocodon'' lived at the same time as semiaquatic ''

Castorocauda ''Castorocauda'' is an extinct, semi-aquatic, superficially otter-like genus of docodont mammaliaforms with one species, ''C. lutrasimilis''. It is part of the Yanliao Biota, found in the Daohugou Beds of Inner Mongolia, China dating to the M ...

'', the subterranean mammaliaform ''

Docofossor ''Docofossor'' is an extinct mammaliaform (a docodont) from the Jurassic period. Its remains have been recovered in China from 160 million years old rocks. It appears to have been the earliest-known subterranean mammaliaform, with adaptations re ...

'', and the arboreal ''

Agilodocodon ''Agilodocodon'' was a genus of shrew-sized docodont from the Middle Jurassic, believed to be the earliest known tree-climbing mammaliaform. It contains one species, ''A. scansorius''. Appearance ''Agilodocodon'' measured approximately from he ...

'', all known from the

References

Docodonts Fossil taxa described in 2019 Taxa named by Chang-Fu Zhou Taxa named by Bhart-Anjan Bhullar Taxa named by April I. Neander Taxa named by Thomas Martin (paleontologist) Taxa named by Zhe-Xi Luo Prehistoric cynodont genera {{Paleo-Therapsid-stub

Anatomy

See also

References