Forelimbs of the Short-beaked Echidna (Tachyglossus aculeatus)

This wonderful old display specimen from the UNE Natural History Museum is a teaching tool that has allowed generations of students to see the forelimb structure and pectoral girdle of the short-beaked echidna – Australia’s only echidna species, and one of two monotremes (egg-laying mammals) that occur here – the other one of course is the platypus.

The forelimbs are really interesting for a number of reasons – first, you can see that great excavating machinery – robust claws and chunky bones for muscle attachment – that allows echidnas to tear into termite mounds and underground ant galleries. Indeed, echidnas are myrmecophagous, a term which means they a specialist diet almost entirely of ants and termites. But most interesting of all, this specimen shows how monotremes move with limbs splayed out to the side like a lizard, rather than limbs under the body, such as in a cat and most other mammals.

Monotremes provide other examples of the ancient reptilian ancestry of all mammals. Although they are very definitely mammals, echidnas (and platypus) have a number of reptilian features, such as the laying of soft, leathery eggs, and possession of a single opening – the cloaca – that is used to expel all bodily waste, and to mate. Indeed, the Latin name for the order ‘Monotremata’ literally means ‘one hole’ – perhaps an unfortunate scientific name for such a wonderous and attractive animal!