Yanoconodon
{{Short description|Extinct family of mammals}}
{{automatic taxobox
|fossil_range = Early Cretaceous, {{fossilrange|122}}
|image = Yanoconodon BW.jpg
|image_caption = Yanoconodon allini
|image_upright = 1.15
|taxon = Yanoconodon
|authority = Chen, Chen, Li & Luo, 2007
|type_species = {{extinct}}Yanoconodon allini
|type_species_authority = Chen, Chen, Li & Luo, 2007
}}
Yanoconodon is a monotypic genus of extinct early mammal whose representative species Yanoconodon allini lived during the Mesozoic in what is now China. The holotype fossil of Yanoconodon was excavated in the Yan Mountains about 300 kilometres from Beijing in the Qiaotou member of the Huajiying Formation (which the original authors considered part of the Yixian Formation) of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, 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, a group composing most taxa once classified as "triconodonts" which lived during the time of the dinosaurs. These were a highly ecologically diverse group, including large sized taxa such as Repenomamus that were able to eat small dinosaurs,Hu, Y., Meng, J., Wang, Y. & Li, C. (2005). Large Mesozoic mammals fed on young dinosaurs. Nature. Vol 433, 12 January 2005, Number 7022, pp91-178, {{doi|10.1038/nature03102}}. [https://www.newscientist.com/channel/life/dn6874.html See commentary on this article (Retrieved 25/6/2007)]. the arboreal Jeholodens, the aerial volaticotherines and the spined Spinolestes. 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. {{doi|10.1080/02724634.2017.1315425}}.
Yanoconodon's name is composed of two elements: 'Yan' is taken from the Yan Mountains in the north of the Hebei Province near where the holotype 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, who was notable for his research on the mammalian middle ear.Luo, Z., Chen, P., Li, G., & Chen, M. (2007). [http://carnegiemnh.net/assets/science/vp/Luo_et_al_2007_Yanoconodon.pdf A new eutriconodont mammal and evolutionary development in early mammals]. Nature. Vol 446, 15 March 2007, {{doi|10.1038/nature05627}}.[http://www.physorg.com/news93110526.html Paleontologists Discover New Mammal from Mesozoic Era] at [http://www.physorg.com/ 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,Meng Chen, Gregory Philip Wilson, A multivariate approach to infer locomotor modes in Mesozoic mammals, Article in Paleobiology 41(02) · February 2015
DOI: 10.1017/pab.2014.14 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.{{cite web | title = Yanoconodon, a transitional fossil | date = March 16, 2007 | author = PZ Myers | url = http://scienceblogs.com/pharyngula/2007/03/yanoconodon_a_transitional_fos.php | work = Pharyngula: Evolution, development, and random biological ejaculations from a godless liberal}} The closely related eutriconodont Jeholodens lacks these lumbar ribs, and it has been suggested that this morphological difference is due to changes in the Hox genes, 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, Vol. 301, 18 July 2003, no. 5631, pp. 363 - 367, {{doi|10.1126/science.1085672}}. supporting the theory that these genes have evolved the ability to repress the ancestral lumbar morphology seen in the Eutriconodonts.
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. 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 of Yanocodon is said to be a "Rosetta Stone" of mammalian middle ear evolution.
References
{{Reflist}}
External links
- [http://www.sciam.com/article.cfm?id=fossil-reveals-ear-evolution-in-action From Jaw to Ear: Transition Fossil Reveals Ear Evolution in Action] by David Biello, Scientific American
- [http://www.smm.org/buzz/image/yanoconodon_allini Artist's impression of Y. allini].
{{Mammaliaformes|T.}}
{{Taxonbar|from=Q2418217}}
Category:Early Cretaceous mammals of Asia
Category:Fossil taxa described in 2007
Category:Taxa named by Meng Chen (paleontologist)
Category:Taxa named by Peiji Chen
Category:Taxa named by Gang Li