Steropodon galmani was a prehistoric monotreme, or egg-laying mammal species that lived during the middle Albian stage, in the Lower Cretaceous period. It 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 5 - 7mm in length, with a width of 3 - 4mm. A length of 1 - 2mm is more typical for Mesozoic mammals. Also from Lightning Ridge is Kollikodon ritchiei.

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."

See also

• Fossil Monotremes

External links

• 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.

References

• Archer, M., Flannery, T.F., Ritchie, A., Molnar, R.E. (1985). "First Mesozoic mammal from Australia — an early Cretaceous monotreme". Nature 318: 363-366.