''Yanoconodon'' is a monotypic genus of extinct early mammal whose representative species ''Yanoconodon allini'' lived during the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

in what is now China. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

fossil of ''Yanoconodon'' was excavated in the

Yan Mountains The Yan Mountains, also known by their Chinese name Yanshan, are a major mountain range to the north of the North China Plain, principally in the province of Hebei. The range rises between the Chaobai River on the west and the Shanhai Pass on ...

about 300 kilometres from

Beijing } Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...

in the Qiaotou member of the

Huajiying Formation The Huajiying Formation is a geological formation in Hebei, People's Republic of China. Known for its fossils including feathered dinosaurs, the age of the formation is uncertain. It may represent an early portion of the Jehol Biota, dating to s ...

(which the original authors considered part of the

Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its exq ...

) of

Hebei Hebei or , (; alternately Hopeh) is a northern province of China. Hebei is China's sixth most populous province, with over 75 million people. Shijiazhuang is the capital city. The province is 96% Han Chinese, 3% Manchu, 0.8% Hui, and 0 ...

Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous

, and so probably dates to around 122 Ma ago.Jin, F., Zhang, F.C., Li, Z.H., Zhang, J.Y., Li, C. and Zhou, Z.H. (2008). "On the horizon of ''Protopteryx'' and the early vertebrate fossil assemblages of the Jehol Biota." ''Chinese Science Bulletin'', 53(18): 2820-2827. ''Yanoconodon'' was a

eutriconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the p ...

, a group composing most taxa once classified as "

triconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the p ...

s" which lived during the time of the

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s. These were a highly ecologically diverse group, including large sized taxa such as ''

Repenomamus ''Repenomamus'' (Latin: "reptile" (reptilis), "mammal" (mammalis)) is a genus of opossum- to badger-sized gobiconodontid mammal containing two species, ''Repenomamus robustus'' and ''Repenomamus giganticus''. Both species are known from fossils ...

'' that were able to eat small dinosaurs,Hu, Y., Meng, J., Wang, Y. & Li, C. (2005). ''Large Mesozoic mammals fed on young dinosaurs''.

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...

. Vol 433, 12 January 2005, Number 7022, pp91-178,
See commentary on this article (Retrieved 25/6/2007)
the arboreal '' Jeholodens'', the aerial volaticotherines and the spined ''

Spinolestes ''Spinolestes'' is an extinct mammal genus from the Early Cretaceous of Spain. A gobiconodontid eutriconodont, it is notable for the remarkable degree of preservation, offering profound insights to the biology of non-therian mammals.Thomas Marti ...

''. ''Yanoconodon'' is inferred to be a generalized terrestrial mammal, capable of multiple forms of locomotion.Chen, M., Z.-X. Luo, and G. P. Wilson. 2017. The postcranial skeleton of Yanoconodon allini from the Early Cretaceous of Hebei, China, and its implications for locomotor adaptation in eutriconodontan mammals. Journal of Vertebrate Paleontology. . ''Yanoconodons name is composed of two elements: 'Yan' is taken from the

in the north of the

Hebei Province Hebei or , (; alternately Hopeh) is a northern province of China. Hebei is China's sixth most populous province, with over 75 million people. Shijiazhuang is the capital city. The province is 96% Han Chinese, 3% Manchu, 0.8% Hui, and 0 ...

near where the

of ''Yanoconodon'' was found; 'Conodon' is an often used as a mammalian taxonomic suffix meaning 'cuspate tooth'. Its species name, "allini," is derived from mammalian researcher

Edgar Allin Edgar is a commonly used English given name, from an Anglo-Saxon name ''Eadgar'' (composed of ''wikt:en:ead, ead'' "rich, prosperous" and ''Gar (spear), gar'' "spear"). Like most Anglo-Saxon names, it fell out of use by the later medieval per ...

, who was notable for his research on the mammalian middle ear.Luo, Z., Chen, P., Li, G., & Chen, M. (2007).
A new eutriconodont mammal and evolutionary development in early mammals
'.

. Vol 446, 15 March 2007, .
Paleontologists Discover New Mammal from Mesozoic Era
' a
www.physorg.com
- Retrieved 25/6/2007.

Description

''Yanoconodon'' was a small mammal, barely 5 inches (13 centimetres) long. It had a sprawling posture, and although previously inferred to be semi-aquatic, direct study of its postcrania indicates that ''Yanoconodon'' was likely a terrestrial mammal, and that it has features in common with digging, arboreal, and semiaquatic mammals. ''Yanocodon'' had lumbar ribs, a feature not seen in modern mammals. The closely related

''Jeholodens'' lacks these lumbar ribs, and it has been suggested that this morphological difference is due to changes in the

Hox genes Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the co ...

, specifically in the ''Hox10'' group. In mice, a triple mutation knocking out all ''Hox10'' genes leads to the presence of lumbar ribs,Deneen M. Wellik and Mario R. Capecchi. (2003). ''Hox10 and Hox11 Genes Are Required to Globally Pattern the Mammalian Skeleton''.

Science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...

, Vol. 301, 18 July 2003, no. 5631, pp. 363 - 367, . supporting the theory that these genes have evolved the ability to repress the ancestral lumbar morphology seen in the

Eutriconodonts Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the p ...

. The ''Yanoconodon'' holotype is so well preserved that scientists were able to examine tiny bones of the middle ear. These are of particular interest because of their "transitional" state: ''Yanoconodon'' has fundamentally modern middle ear bones, but these are still attached to the jaw by an ossified

Meckel's cartilage In humans, the cartilaginous bar of the mandibular arch is formed by what are known as Meckel's cartilages (right and left) also known as Meckelian cartilages; above this the incus and malleus are developed. Meckel's cartilage arises from the fir ...

. This is a feature retained from earlier stem mammals, and illustrates the transition from a basal tetrapod jaw and ear, to a mammalian one in which the middle ear bones are fully separate from the jaw. Despite this feature ''Yanoconodon'' is a true mammal''.'' It is thought that the feature was retained during early embryo development, whereas it is lost in most other mammal groups. The intermediate anatomy of the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...

of ''Yanocodon'' is said to be a "

Rosetta Stone The Rosetta Stone is a stele composed of granodiorite inscribed with three versions of a decree issued in Memphis, Egypt, in 196 BC during the Ptolemaic dynasty on behalf of King Ptolemy V Epiphanes. The top and middle texts are in Ancien ...

" of mammalian middle ear

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

References

External links

From Jaw to Ear: Transition Fossil Reveals Ear Evolution in Action
by David Biello, Scientific American
Artist's impression of ''Y. allini''
{{Taxonbar, from=Q2418217 Eutriconodonts Early Cretaceous mammals of Asia Transitional fossils Fossil taxa described in 2007 Taxa named by Meng Chen (paleontologist) Taxa named by Peiji Chen Taxa named by Gang Li Taxa named by Zhe-Xi Luo Prehistoric mammal genera