Steropodon

Steropodon
Status Fossil

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Monotremata
Family:
Genus:	*Steropodon*
Species:	*galmani*

Information

Steropodon was a prehistoric monotreme, or egg-laying mammal. It lived during the middle Albian era, in the Lower Cretaceous period, and is the earliest known platypus-like creature.

Steropodon is known only from a single opalised jaw with three molars, discovered at the Griman Creek Formation, Lightning Ridge, New South Wales, Australia. It was a large mammal for the Mesozoic, being 40-50cm long. The lower molars are 5mm-7mm in length, with a width of 3mm-4mm. A length of 1mm-2mm is more typical for Mesozoic mammals.

The molars "bear striking resemblance to the tribosphenic pattern characteristic of living therians..." (Pascual). However, there are also differences: there is no entoconid, and an absence of wear seems to suggest that the upper molars (as yet unknown) did not have a protocone.

Woodburne, 2003 (p.212) reports that the holotype is a right mandible named AM F66763, which seems to work at the Australian Museum, Sydney. The preserved molars are m1-m3. Page 237 includes: "In Steropodon, the madibular canal suggests the presence of a bill, with a bill also known in Obdurodon dicksoni and Ornithorhynchus anatinus."

Links and references

Archer et al. "First Mesozoic mammal from Australia -- an early Cretaceous monotreme". Nature 318, 1985. Pages 363-366.

Fossil Monotremes

BBC, Walking With Dinosaurs

Australia’s Lost Kingdoms

Lost Sea Opals An array of fossils from the Lightning Ridge location. Many animal groups are represented.