Australia: The Land Where Time Began

A biography of the Australian continent 

Teinolophos trusleri the earliest known platypus

This early platypus is known from the Aptian Stage of the Lower Cretaceous. The holotype is a partial dentary (lower jaw), found at Flat Rocks in Victoria. It has been dated to about 123 Ma, and is the oldest known relative of the platypus. It was originally thought to be a eupanthothere, but further study revealed similarities to Steropodon, but at about 10 cm it was smaller. The lower molar is broadly similar to the m2 of Steropodon. It has a compressed triconid and the talonid has no basin. The dentary of Steropodon is about 6 times the size of the Teinolophos dentary. An "orthal" occlusion with the upper molars is indicated by wear facet.

The lower jaw differs from that in living monotremes in that the condyl is well above the tooth row, and a higher ascending ramus. In modern monotremes the condyl is on the same level as the teeth. It is believed it also had a stronger bite than modern monotremes.

Sources & Further reading

1. Mary E. White, The Nature of Hidden Worlds, Reed, 1993
2. Long, John A, 1998, Dinosaurs of Australia and New Zealand, University of New South Wales Press.
3. Patricia Vickers-Rich, Thomas Hewitt Rich, Wildlife of Gondwana, Reed Australia, 1993