ANIMAL SPECIES:Platypus
The Platypus is a unique Australian species. Along with echidnas, Platypuses are grouped in a separate order of mammals known as monotremes, which are distinguished from all other mammals because they lay eggs.
Fossils
The fossil record for monotremes is poor in comparison to that of other groups of mammals, and until recently little was known about their evolutionary history. Several fossil discoveries since the early 1970s have shed some light on the origins of monotremes. We now know that monotremes were present in Australia during the Mesozoic Era, when Australia was still part of the supercontinent, Gondwana. The fossil evidence suggests that monotremes originated and diversified in the Australian/Antarctic section of Gondwana, and that there was only a single dispersal to South America before the break up of Gondwana.
Four species related to Platypus have been found in fossil deposits from Australia, including a complete skull of Obdurodon dicksoni and an opalised jaw fragment of Steropodon galmani. The latter is 110 million years old and represents one of Australia's oldest mammals. The only evidence that Platypus ancestors were once present outside Australia came in 1991, when a 61 - 63 million year old fossil tooth was found in Patagonia, in southern Argentina.
Studies of these fossils indicate that the one remaining living species of Platypus is more specialised than its predecessors. It is smaller, its functional teeth have been replaced by horny pads and other aspects of its anatomy appear simpler. It also appears to have a more restricted distribution, being confined to the river systems of eastern Australia. Although Platypus remains widespread and reasonably common, this trend towards increasing specialisation suggests that it may be moving out onto an evolutionary 'limb' and that its current status should not be taken for granted.
Classification
- Species:
- anatinus
- Genus:
- Ornithorhynchus
- Family:
- Ornithorhynchidae
- Order:
- Monotremata
- Subclass:
- Prototheria
- Class:
- Mammalia
- Subphylum:
- Vertebrata
- Phylum:
- Chordata
- Kingdom:
- Animalia
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