The Platypus was first described in 1799 in Shaw’s naturalist’s Miscellany along with the koala, Kangaroo, wombat and emu. The most curious was the platypus. Since its first discovery there has been much debate as to whether it is a mammal and how it should be classified.
The platypus is a primitive mammal that has many features that separate it from other mammals-it lays eggs, there is an absence of true teeth and an absence of mammary glands, although it has special glands that secrete milk. It has fur like other animals, but it has a beak like the bill of a duck, webbed feet and a tail like a beaver.
A dried platypus skin has been sent to England in 1798 and was considered to be fake.
Up until 1884 there was uncertainty about how the platypus reproduced. In 1884 Caldwell solved the problem by capturing a female with eggs.
About 1904 the scientific American reported that there are many mammals that do not possess teeth when adults.
Up until 1973 there was uncertainty about the platypus being able to regulate its body temperature like other mammals. Recent research shows that it can regulate body temperature but the mechanism is underdeveloped.
There are two living groups: The platypuses and the echidnas. The only Cretaceous mammal known for Australia is also a monotreme, Steropodon galmani, a platypus-like animal that might be more appropriately placed in a family of its own.
Until 1971, an understanding of the history of Australia’s platypus was non-existent. Apart from the fact that it was a monotreme and only known from Australia, all else was mystery. Then three major discoveries were made: two molar teeth of Obdurodon insignis, a 25 million-year-old platypus from the Tirari desert; a jaw fragment with three teeth of sterepodan galmani a 110 million year old monotreme from opal deposits at Lightning Ridge, New South Wales; and, from 15-20-million-year-old Riversleigh deposits, a complete skull as well as a nearly complete dentition of a second species of Obdurdon.
In 1971, while one puzzled group of Palaeontologists stared in confusion at a strange tooth found in the late Oligocene deposits of Lake Frome Embayment. These were the first teeth of a fossil platypus to be found and were named Obdurodon insights.
Naturally, these central Australian discoveries caused a great deal of delight as well as anticipation but despite many tonnes of processed matrix later, central Australia has failed to produce more than a few isolated teeth, a fragment of a lower jaw and a portion of a pelvis.
Discovery of the opalised jaw of Steropodon galmani in the dinosaur rich early Cretaceous deposits of Lightning ridge was one of the most exciting moments in the history of Australian palaeontology. It was the first and so far only known Mesozoic mammal from Australia. It may also have been the largest Cretaceous mammal anywhere in the world, overlapping in size some of the smallest dinosaurs, although less than twice the size of the living platypus. It had well developed teeth whose shape indicates that even by this early date monotremes has achieved many of the distinctive dental features that distinguish them from other groups of mammals.
When we first discovered Ringtail Site at Riversleigh ,one of the system C localities in Ray’s Amphitheatre, apart from the ringtail possum jaw and some bats, we saw little in the way of mammals.
But in the lab we were delighted to find isolated molars of the first fossil platypus from riversleigh. In the 1985 expedition a whole, perfect skull, the first and only ornithorynchid skull known apart from that of the modern Platypus. It was spotted as a braincast, complete with fosslilsed blood vessels when pieces of the skull were broken away in the course of fracturing blocks of limestone. After recovery and restoration of the broken pieces and dissolution of the surrounding limestone in dilute acetic acid, the skull that emerged took their breath away.
The Riversleigh material has provided a great deal of new information about the structure, relationships and paleobiogeography of platypuses in general. At this point besides the complete skull there is a complete dentition and partial lower jaw.
So far, specimens of the riversleigh Obdurodon have come from the so called aquatic sites.
Discovery in 1991 and 1992 of Obdurodon like monotreme teeth in 61-63 million year old sediments in Patagonia, Southern Argentina, has shocked everyone who thought platypuses were uniquely Australian. Clearly they were once part of a Gondwanan fauna that must also have been present on Antarctica, but survives today only in Australia.
Because the living platypus, the only surviving descendant of Obdurodon, has become highly specialised with loss of its functional teeth, overall reduction in body size simplification of most of its cranial anatomy, we are concerned that all the lineage is in decline.
When a group looses its generalised body form and edges to far out on its evolutionary limb in terms of specialisation, that limb is in increasing danger of falling off. The fossil record of rapid decline over just the last 15% of its known history suggests a less optimistic view.
This is an animal just surviving in the twilight of a long and remarkable history.
To add to these concerns, today’s platypuses persist only in the permanent river systems of eastern Australia, sometimes in remnant rainforests but more often in the rivers that drain the open forests of the great divide. With humans abusing their the chemistry of the waterways with fertilisers and other noxious substances and deforestation and pollution of the rivers watersheds its candle may be in imminent danger of going out.