Yanoconodon

Taxobox
name = "Yanoconodon"

---

image_caption = "Yanoconodon allini"
image_width = 250px
fossil_range = Early Cretaceous
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Eutriconodonta
familia = Jeholodentidae
genus = "Yanoconodon"
genus_authority = Chen, Chen, Li & Luo, 2007
species = "Y. allini"
binomial = "Yanoconodon allini"
binomial_authority = Chen, Chen, Li & Luo, 2007

"Yanoconodon" is a monotypic genus of extinct early mammal whose representative species "Yanoconodon allini" lived 125 million years ago during the Mesozoic in what is now China. It is considered to be a transitional fossil due to the formation of its middle ear, which is a cross between those of modern mammals and their nearest relatives, the mammaliaformes. "Yanoconodon" was a Eutriconodont, a group synonymous to the Triconodonts which lived during the time of the dinosaurs. Indeed, some such as "Repenomamus" grew so large that they were able to eat small dinosaurs in some cases. 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. [http://www.newscientist.com/channel/life/dn6874.html See commentary on this article (Retrieved 25/6/2007)] .] In particular, "Yanoconodon" is considered to be closely related to "Jeholodens".Luo, Z., Chen, P., Li, G., & Chen, M. (2007). "A new eutriconodont mammal and evolutionary development in early mammals". Nature. Vol 446, 15 March 2007, doi:10.1038/nature05627.]

"Yanoconodon"'s name is comprised 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 in the Yixian Formation; '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." [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, although at the time of its existence, it was significantly longer than most other animals due to a number of extra vertebrae the animal possessed. It was lightly-built and fed on insects, worms and other invertebrates. Like other Eutriconodonts, "Yanoconodon" probably hunted at night out of the danger posed by predatory dinosaurs during the day. Like most early mammals, "Yanoconodon" had short, sprawling legs and claws that were most likely used for burrowing underground or digging.

"Yanoconodon" is the first Mesozoic mammal to be found in China to date. The holotype of "Yanoconodon" excavated from the fossil-rich Yixian Formation, about 300 kilometres from Beijing, was brilliantly preserved and allowed scientists to discover what the creature is most notable for, the transitional stage of its middle ear. This is said to be the "Rosetta Stone" in regard to the development of the mammalian middle ear and the evolution of complex anatomic features over time. In addition to this discovery, scientists also discovered the presence of lumbar ribs, a particularly rare feature in mammals today.

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" paralogues 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.

References

External links

* [http://www.smm.org/buzz/image/yanoconodon_allini Artist's impression of "Y. allini"] .