Evolution and systematics

Fossil records for echidnas are scarce. The first tachy-glosssid fossil, a long-beaked echidna (Zaglossus robusta = Megalibgwilia), found in a gold mine at Gulgong, New South Wales in 1895 was about 15 million years old. Tachyglossus remains have been found in Pleistocene sediment (about 100,000 years old) at Mammoth Cave, Western Australia and in the Naracoorte Caves of South Australia. Fossil records show that long-beaked echidnas became extinct on mainland Australia in the late Pleistocene.

The divergence of present day echidnas and their relationship to other fossil monotremes from the Cretaceous (120 million years ago), are unknown.

The family Tachyglossidae is divided into two genera. Tachyglossus, the short-beaked echidna, consists of one species, T. aculeatus, and five subspecies. Zaglossus, the long-beaked echidna, has three species, with four subspecies of Z. bartoni. Zaglossus taxonomy is based on world museum collections.

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