Biology Preliminary Assessment

The Platypus (Ornithorhynchus anatinus) Class: Mammalia Order: Monotremata Family: Ornithorhynchidae Genus Species: Ornithorhynchus anatinus First Discovered: by the first European settlers in the late eighteenth century. The first platypus specimen was sent back to England for identification in 1798 by Captain John Hunter. When he first saw the specimen, English naturalist George Shaw, thought the animal was a hoax, confessing that it was “impossible not to entertain some doubts as to the genuine nature of the animal, and to surmise that there might have been practised some arts of deception in its structure.” He even checked the area around the animal's bill for any sign of stitches, believing the animal to be a fake. Why it baffled scientists: the platypus baffled scientists due to its peculiar physical characteristics. It had a furry body like mammals, duck-like bill, and webbed feet. Due to its strange physical features and behaviour, the early European settlers named the strange animal duckbill, water mole or duck mole. They were not sure whether the animal was a mammal, a bird or a reptile since it seemed to have features from each of those groups. The platypus had the characteristics of a reptile (laid eggs), bird (its duck bill), beaver (tail and waterproof fur) and otter (webbed feet), as well as being a mammal (has fur, lungs, warm blood, secretes milk for young). The platypus’s unique reproductive system also made it Figure 1- The Distribution of the Platypus difficult for scientists to classify. It challenged the ideas at that time about taxonomic classification. Much controversy broke out between the leading scientists in Europe. The classification system that they used was based on Aristotle’s method, established in 334BC, of arranging animals into classes according to their reproductive organs1. It was widely accepted that mammals gave birth to live young (viviparous), reptiles and sharks hatched their young from eggs inside their body (ovoviviparous) and birds hatched their young from eggs laid outside their body (oviparous). However, the platypus was observed to lay two to four eggs from which its young hatched, and was thus oviparous like a bird. But unlike a bird, it suckled its young. Scientists were also confused as they could not see the platypus’s mammary glands and it was only confirmed in the early 1830s by Richard Owens, an English biologist who worked at the Royal College of Surgeons in London that the female platypus actually secreted milk from its skin. 1 http://www.abc.net.au/rn/science/ockham/stories/s332655.htm The female platypus digs a long burrow, lined with grass and leaves. She lays two to four leathery eggs, less than 2cm long, which have already developed for about four weeks in the platypus’s uterus. After about 10 days, the young platypus hatch out of the eggs. They obtain nutrients from suckling their mother’s mammary glands. How its unique features were understood: Scientists finally classified the platypus as a monotreme- an egg laying mammal. The platypus’s scientific name is Ornithorhynchus anatinus from ornithorhynkhos, meaning “bird snout” in Greek and anatinus, meaning “duck-like” in Latin. Monotreme also has Greek origins, with monos meaning single and trema meaning hole. This name refers to the fact that monotremes have one hole from which they urinate, defecate, and reproduce- called the cloaca. This is unlike placental female mammals which have a separate opening for each. The platypuses unique features were slowly understood with the development of new technology and information: Clearly the development of the electron microscope has helped scientists to be able to study the platypus in greater detail. Up until the 1930’s, scientists observed the platypus searching for food underwater – with its eyes, ears and nostrils closed. So they wondered how the platypus actually found its food. By using the electron microscope to take a closer look at the platypus, they discovered thousands of sensors in its beak, accounting for why the platypus did not have to use its eyes, ears or nose to forage for food. New technology has allowed scientists to discover more about this unique creature. In 1944, the first platypus – named Corrie – was bred in captivity at Healesville by David Fleay. This allowed a closer study of the platypus, but was only made possible due to the development of the platypusary- a home for platypuses that mimicked their natural habitat. It incorporated an elaborate network of pumps and filters, a life-like flowing stream, and natural flora that enabled the Platypus to be bred in captivity. The platypusary was developed by Dr. David Fleay, an Australian, in the late 30’s and early 1940’s. The platypusary also allowed scientists to monitor the behaviour of platypus’ in an environment as close to their natural habitat as possible. Developments in biotechnology have allowed scientists to sequence the entire platypus genome, which was published in 2008. By studying the genome of the platypus, scientists have been able to account for the platypuses unique features. Scientists from all around the world gathered at Washington University in the US to decode the genome of the platypus. By comparing the genome of the platypus to the genome of mammals, scientists were able to make conclusions about the evolution of the platypus. Scientists have been able to compare the genomes of the human, mouse, dog, opossum and chicken and they have discovered the platypus shares 82% of its genes with these species, possibly accounting for its strange mix of features. Also, scientists have been able to account for the venom producing capabilities of the platypus through studying its genome. They have found that the gene for venom production in its genome actually originated from the genome of reptiles. The genome explains the unique features of the platypus. Certain genes of the platypus are related to similar reptilian and mammalian genes. Also, the platypus gene that is responsible for the production of casein, a protein in milk, is the same gene that is found in mammals. In 2004, scientists at the Australian National University discovered that the platypus X chromosome (sex chromosome) is very similar to the ‘Z’ sex chromosome of birds, perhaps establishing an evolutionary relationship between the bird and the platypus, & accounting for its unique features. In 1985, a team from the Australian National University, led by Dr. Henning Scheich, proved that the platypus’s bill was sensitive to electric currents. This was done by exposing the bills to low electric currents –both underwater and above water – and measuring the level of brain activity that this generated. Although it has been suspected for centuries that the platypus contained sensors in its bill, its exact nature had never been determined. In the 1988, a group from Monash University, led by Dr. Uwe Proske, confirmed that the platypus contained electro receptors in its bill. This sensory system could detect electrical charges as small as those discharged by the flick of the tail of a shrimp. This new information explained how the platypuses foraged for food underwater when its eyes, ears and noses were shut. They dubbed this the platypuses ‘sixth sense’. Until recently, scientists have believed the platypus to be a ‘primitive’ creature, and inferior evolution of the mammal. However, recent information and technology has shown that the platypus is actually a highly evolved animal with unique & advanced features. Scientists have concluded that it was Australia’s isolation (as an island) which allowed its animals and plants to develop unique characteristics. Australian Fossils Name of fossil: Diprotodon (Diprotodon opatum) Where it was found- Its fossils have also been found in Darling Downs in south-eastern Queensland; Wellington Caves, Tambar Springs and Cuddie Springs in New South Wales; Bacchus Marsh in Victoria; and Lake Callabonna, Naracoorte Caves and Burra in South Australia. The Diprotodon's habitat was that of semi arid plains, Figure 2- An artist's impression of the Diprotodon opatum savannahs and open woodland. Diprotodon opatum fossils have also been found in coastal areas, but scientists attribute this to the lower sea levels during the Pleistocenic, meaning that these areas were probably more inland. Description: the Diprotodon was a native Australian marsupial that lived during the Pleistocene, about 1.6 million years ago. It was the last of the herbivorous diprotodontids (animals with “two front teeth”) and went extinct 45 000 to 25000 years ago, perhaps due to human hunting and climate change. Palaeonologists have been able to recover complete skulls & skeletons of the Diprotodon opatum, as well as hair and foot impressions. From this fossil evidence, they have been able to ascertain that the Diprotodon was the largest marsupial that ever lived, weighing 2500 kg and averaging a height of 1.8m and a length of 3.8m. It is part of Australia’s mega-fauna, which are very large animals like the elephant and whale. Its body was stout, heavily built, large bellied and it had four sturdy, pillar like legs. Although its head was large in proportion to its body size, it was relatively light as it was filled with many air spaces. The Diprotodon had a small trunk due to its nasal bone structure. The Diprotodon had small, in turned feet, similar to the wombat. The Diprotodons were herbivores, eating up to 100-150kg of shrubs, forbs and bushes a day. Like all diprotonotids, they had two distinctive incisors which were used to unearth the vegetation. The skeletons of female diprotodons have been found with babies where there would usually be a pouch. Like the wombat, the pouch probably opened at the rear of the animal. Its closest living relative is the wombat.

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