Specimen of the Week: Week 134
By Jack Ashby, on 5 May 2014
For the past 133 weeks your weekly Specimen of the Week was lovingly delivered to you by our Curatorial Assistant Emma, who left the Grant Museum on Friday for an exciting new job. The show must go on, however, and from now on the rest of Team Grant will take it in turns to select and serve the treasures we find in our collections.
As you may predict, it could be very tempting for someone with the power to select which Specimens of the Week are featured to highlight with bias the species they are most interested in (shark expert Emma gave you a ridiculous THIRTY-THREE blog posts featuring sharks in her reign). I frown upon such prejudice, and will stay well away from Australian mammals, my own field of zoological nerdery. This week’s Specimen of the Week is…
The Taxidermy Platypus
Well I bet you didn’t see that coming. It is a well-known fact that platypuses are the most interesting animals in the world. It is for this reason, and definitely not because they are my favourite animal, that the Grant Museum can confidently claim to have more specimens of platypus on display than any other museum in the world.
1) Platypuses are one of five species of mammal to lay eggs. The other four species are the almost-as-interesting echidnas. Together, platypuses and echidnas form the order Monotremata, so named for the single (monos) urogenitary opening (trema (meaning hole)) or cloaca (meaning sewer) that they have, doing all their defacating, urinating and birthing through one single opening. Other mammals, like us, have two holes – one at the front and one at the back.
2) I have regular conversations about platypuses, and one thing that seems to throw people is that some mammals lay eggs, when many people are under the impression that all mammals give birth to live young. There are a few unique defining characteristics of all mammals*; live-birthing is not one of them. They include three inner-ear bones, a specialised ankle joint, a single bone forming either side of the jaw, the ability to produce milk (mammary is the root of the word mammal), and the presence of hair. Interestingly platypuses do not truly suckle their young as they don’t have nipples. They do have mammary glands, though, the milk kind of sweats out of them and the babies lap it up.
3) Platypuses are an evolutionary biologist’s dream. Mammals evolved from reptiles at the end of the Triassic about 210 million years ago. As such, mammals should show a lot of characteristics they inherited from their reptilian ancestors. Monotremes arose early in mammal history – around 200 million years ago (the oldest platypus fossils are 63-61 million years old from Patagonia**). In many respects, platypuses show a larger number of the “primitive” reptilian characters than other mammals – they lay eggs, they walk with bent elbows and knees (rather than straight legs) and although homeothermic, their body temperature has a wider range of stability. But platypuses are not primitive…
4) On top of this more-reptiley “primitive” frame, they have added some of the most advanced characteristics of all mammals. A) Male platypuses are among the only poisonous mammals. They have a horny spur on their heels attached to a venom gland, used during sexual competition (and said to be excruciating and long-lasting to humans). B) They are the only mammals capable of electro-reception – they can detect electricity through their bills…
5) Platypuses are restricted to the lakes and rivers of Tasmania and eastern Australia, where they are pretty common. They use the amazing power of electro-reception to hunt their invertebrate prey. Muscular movement in animals (including heartbeats, so a platypus can find you if you lay still) is controlled by electrical impulses. Little is known about platypus feeding, but it is assumed that platypuses can locate their prey buried under silt by sensing these electrical impulses with their bills. They gather food up in little pouches at the base of the bill, and then mash it up (for adult platypuses have no teeth) with their not-at-all-bird-like rubbery bills when on the surface.
Jack Ashby is the Manager of the Grant Museum of Zoology.
*naturally this doesn’t work for species which have through evolution lost these characters – whales have no ankles, let along specialised ones, and no hair. It also doesn’t work for boys.
** this shows that platypuses existed before the break up of Gondwana (the giant southern landmass). The oldest Australian platypuses are less than 26 million years old.