Evolution & Names

Platypus 11.4.16 Tidbinbilla River (Photo John Bundock) 10%In this section you can read about:

  • Names for the platypus (including “What is the plural of platypus?”)
  • The platypus’s fossil history
  • Echidnas – the other modern monotremes

Names for the platypus

 Aboriginal people had many different regional names for the platypus, including “boondaburra”, “mallingong” and “tambreet”. According to Aboriginal legend, the platypus originated when a young female duck mated with a lonely and persuasive water-rat. The duck’s babies had their mother’s bill and webbed feet and their father’s four legs and handsome brown fur.

A British scientist, Dr George Shaw, published the first scientific description of the platypus in 1799. His initial reaction was that this very unusual looking animal was an elaborate hoax. He even took a pair of scissors to the preserved specimen, expecting to find that the bill had been attached to the rest of the body with stitches.

plat 1790s drawing (Shaw)

When the specimen proved to be genuine, Shaw named it Platypus anatinus, from the Greek words “platys” (meaning flat or broad) and “pous” (meaning foot) and a Latin word meaning duck-like (“anatinus”). When it was later found out that the word “Platypus” had already been applied to a group of beetles, the specimen was renamed Ornithorhynchus anatinus, with the first word meaning “bird-like snout”.

Because the word “platypus” is derived from Greek, its plural should (strictly speaking) be “platypodes” However, this has never caught on for some reason (we can’t imagine why not). Instead, the preferred plural is either “platypus” or “platypuses”, depending on which dictionary you consult. The term “platypi” – a Latin plural – is definitely incorrect.

Photo courtesy of John Bundock; drawing by Frederick Nodder, used to illustrate Shaw’s (1799) paper

Fossil history

Based on fossil evidence, the earliest known ancestors of the modern platypus date from the early Cretaceous Period (100-146 million years ago). At that point in time, the world was still dominated by dinosaurs. None of these early fossils can definitely be said to have been platypus-like, though the remains of Steropodon galmani (a lower jaw fragment containing three teeth, dated to more than 100 million years ago) show some distinctly platypus-like features and suggest that a bill may have been present.

The oldest known animal that is definitely believed to have been a member of the platypus family (based on fossilised teeth and some pieces of leg bone) is Monotrematum sudamericanum. It lived in Patagonia (in southern South America) about 61-63 million years ago – at a time when Australia, Antarctica and South America were joined together as part of a single land mass known as Gondwana.

Capture skullSeveral other former members of the platypus family have been described, based on fossils found at various sites in Australia. These animals are estimated to have lived between about 4 and 26 million years ago. They are all believed to have had a bill, though bill size and shape (as shown at left) were not necessarily the same as that of a modern platypus. The fossil remains dating from about 4 million years ago (a leg bone and part of a lower jaw) are similar to corresponding structures in the modern platypus, and may possibly represent the earliest known record of the living animal.

Photo of skull of Obdurodon dicksoni courtesy of T. Rowe (U. of Texas)

Echidnas – the other modern monotremes

0003The platypus’s closest living relatives are four species of echidna: three species of long-beaked echidna found in Papua New Guinea, and the short-beaked echidna found in both Australia and Papua New Guinea (as shown at right). At first sight, echidnas seem to be very different from the platypus – stocky, rounded animals that feed on land (mainly on insects or worms) and are more or less spiny.

However, the platypus and echidnas share a number of features that collectively distinguish them from all other mammals:

  • Both groups have a single opening in their body that is used to excrete solid and liquid waste as well as for reproduction (causing them to be classified as monotremes, meaning “one opening”).
  • Both groups lay eggs (though, unlike the platypus, echidnas incubate their eggs in a pouch).
  • Both groups lack teeth as adults and have an unfurred bill or beak that (at least in the platypus and short-beaked echidna) contains receptors capable of detecting electrical fields produced by their prey.
  • Both groups have a lower active body temperature than most other mammals.
  • In both groups, pointed spurs are present on the ankles of adult males (connected to functional poison glands in the case of the platypus but not echidnas).
  • The skeletons of both groups have many reptilian features that are not present in other mammals.

Reflecting the fact that the earliest known echidna fossils are no more than 15 million years old, the evolutionary relationship between echidnas and the platypus remains poorly understood. However, it’s currently believed that echidnas developed from a platypus-like ancestor rather than vice-versa, with a number of lines of evidence suggesting that the two groups may have begun to diverge as recently as about 18 million years ago (though possibly as much as 90 million years ago).

Photo: APC