Teinolophos

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Teinolophos Temporal range: Late Barremian ~123 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Monotremata
Family:	†Teinolophidae
Genus:	†Teinolophos
Species:	†T. trusleri
Binomial name
†Teinolophos trusleri Rich et al., 1999

Teinolophos is a prehistoric species of monotreme, or egg-laying mammal, from the Teinolophidae. It is known from four specimens, each consisting of a partial lower jawbone collected from the Wonthaggi Formation at Flat Rocks, Victoria, Australia. It lived during the late Barremian age of the Lower Cretaceous.

The species name honours the artist Peter Trusler. The genus name, Teinolophos, means "extended ridge", a reference to its tooth structure.

Originally, Teinolophos was thought to be a eupantothere. Further research revealed similarities to Steropodon, except in size: the animal was around 10 cm long. It is often listed as a steropodontid, though it may be more basal.^[1] Teinolophos is deeply divergent within monotreme evolution, so in 2022 it was proposed to move it into its own family, Teinolophidae. Stirtodon may be a close relative of Steropodon within Teinolophidae.^[2]

The holotype is a partial left dentary known as NMV P208231. An age of approximately 123 million years makes this the earliest known monotreme. The lower molar is broadly similar in morphology to the m2 of Steropodon. The trigonid is compressed and the talonid has no basin. The dentary is about one sixth the size of Steropodon's, and wear facets indicate an "orthal" occlusion with the upper molars.