| Diarthrognathus | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Clade: | Cynodontia |
| Family: | †Tritheledontidae |
| Genus: | †Diarthrognathus Crompton, 1958[1] |
| Species: | †D. broomi |
| Binomial name | |
| †Diarthrognathus broomi Crompton, 1958 | |
Diarthrognathus ("Two joint jaw") is an extinctgenus oftritheledontidcynodonts, known from fossil evidence found inSouth Africa[2] and first described in 1958 by A.W. Crompton.[3] The creature lived during theEarly Jurassic period, about 200 million years ago.[4][3] It wascarnivorous and small, slightly smaller thanThrinaxodon, which was under 50 centimetres (20 in) long.[5]
Diarthrognathus possesses a jaw structure that is similar to both mammals and more basal synapsids. Its primitive jaw joint is located between thequadrate andarticular bones, and its derived, mammalian jaw joint is located between thesquamosal anddentary bones.[6]
The articular and quadrate bonesevolved to become two of the middle-ear bones in mammals.[4] The transition exemplified byDiarthrognathus suggests thatnatural selection favoured animals with a more powerful bite.[7]
At one time,Diarthrognathus was thought to be synonymous withPachygenelus. However, in 1980, newly discovered fossils revealed sufficient differences to warrant separate genera.[8]
The double jaw joint ofDiarthrognathus neatly bridges early synapsids and mammals, and thus rebuts a claim bycreationists, such asDuane Gish, who thought such a transition was impossible.[9] This "twin-jointed jaw" can also be seen in other derived cynodonts, such as earlymammaliaforms.[10]
