Hint: Ornithorhynchus, or duck-billed platypus, is the only living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), although the fossil record includes several related species.
A semi-aquatic, egg-laying mammal endemic to eastern Australia, including Tasmania, is the platypus (Ornithorhynchus anatinus), sometimes referred to as the duck-billed platypus. The platypus, although a number of related species appear in the fossil record, is the sole living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus).
It is one of the five existing species of monotremes, together with the four species of echidna, the only mammals that lay eggs instead of giving birth to live young. It senses prey, like other monotremes, through electrolocation. It is one of the few venomous mammal species, as there is a spur on the hindfoot of the male platypus that delivers a venom likely to cause serious pain to humans. When they first encountered it, the unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists, and the first scientists to examine a preserved platypus body (in 1799) judged it to be a fake, made of several sewn together animals.
Hence, the correct answer is an option (C) 'Mammal'.
One of the three species of monotremes is the Duck-billed platypus. Among mammals, these species are unique in that they retain the ancestral feature of egg-laying. They have a cloaca through which eggs are laid and they eliminate both liquid and solid waste. Stream-lined and elongated, Duck-billed platypuses have fur ranging from light brown to dark brown on the dorsal side and brown to silver-grey on the ventral side. They have bills that imitate those of ducks, and they have flat and wide tails that resemble those of beavers (Grant and Temple-Smith, 1998) Two nostrils are located on top of their bills and on either side of their heads are their eyes and ears. They have short arms, bare soles, webbed forefeet and hind feet that are partly webbed. There are five digits each for each foot, characterized by a large nail for the forefeet and sharp claws for the hind feet. There are mammary glands in females, but no breasts. The young have milk teeth when there are grinding plates for adults. Young people are smaller in size than adults.
In the study of evolutionary biology, the unusual characteristics of the platypus make it a significant subject, and a familiar and iconic symbol of Australia. For some Aboriginal tribes of Australia, who often used to kill the animal for food, it is culturally important. It has featured on the reverse of the Australian twenty-cent coin as a mascot at national functions and features, and the platypus is the New South Wales state's animal symbol. Humans hunted the platypus for its fur until the early 20th century, and it is now protected in its range. While only modest success has been attained through captive-breeding projects and the platypus is vulnerable to the effects of contamination, it is not under any imminent threat.