Sinoconodon

Sinoconodon is an extinct genus of mammaliamorphs that appears in the fossil record of the Lufeng Formation of China in the Sinemurian stage of the Early Jurassic period, about 193 million years ago.[1] While sharing many plesiomorphic traits with other non-mammaliaform cynodonts, it possessed a special, secondarily evolved jaw joint between the dentary and the squamosal bones, which in more derived taxa would replace the primitive tetrapod one between the articular and quadrate bones. The presence of a dentary-squamosal joint is a trait historically used to define mammals.[2][3]

Sinoconodon Temporal range: Sinemurian ~193 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Restoration of S. rigneyi
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Therapsida
Clade:	Cynodontia
Clade:	Mammaliamorpha
Order:	†Sinoconodontiformes Kinman, 1994
Family:	†Sinoconodontidae Mills, 1971
Genus:	†Sinoconodon Patterson & Olson, 1961
Species:	†S. rigneyi
Binomial name
†Sinoconodon rigneyi Patterson & Olson, 1961
Synonyms
List Genera Lufengoconodon Young 1982a Species Lufengoconodon changchiawaensis Young 1982a Sinoconodon changchiawaensis (Young 1982) sensu Crompton & Sun 1985 Sinoconodon parringtoni Young 1982 Sinoconodon youngi Zhang 1983

Sinoconodon closely resembled early mammaliaforms like Morganucodon, but it is regarded as more basal,[4] differing substantially from Morganucodon in its dentition and growth habits. Like most other non-mammalian tetrapods, such as reptiles and amphibians, it was polyphyodont, replacing many of its teeth throughout its lifetime, and it seems to have grown slowly but continuously until its death. It was thus somewhat less mammal-like than mammaliaforms such as morganucodonts and docodonts.[2][5] The combination of basal tetrapod and mammalian features makes it a unique transitional fossil.[6]