Last week I gave you this mystery object from the Grant Museum of Zoology to try your hand at identifying:

Not the best photos, but they do show some of the key features I used to work out what it is.

There were a lot of comments with a variety of different groups of animal being mentioned, although everyone recognised this as a mammal immediately. The large broad tail was recognised by Allen Hazen as an adaptation to swimming, but its unusual proportions threw some people into thinking this was something quite basal, like a marsupial or member of the Pilosa. The presence of a clavicle supported that to some extent as many of the more recent mammal orders, like the Carnivora, have a reduced or absent clavicle.

The hind feet were also recognised as an adaptation to swimming by palfreyman1414, but he was sceptical that this specimen represented just one species, suggesting it might be a chimera. However, I wouldn’t do that to you (unless it was an April Fool prank) so the real animal remained to be identified.

Hiroto Nakatsubo raised the possibility of it being a rodent, but commented that it was on the big side. This could have pointed at Beaver, as many people suggested, except the specimen lacks the distinctive tail morphology. All of this followed my own though path for working out what it is – a medium large aquatic rodent that isn’t a Beaver.

That narrowed it down to Capybara, Muskrat, Coypu or monster Water Vole. Of these, only one has the size difference between fore and hind limbs, plus the distinctively weird acromion process on the shoulder – the Coypu Myocastor coypus Kerr, 1792. So Isaac Krone was the first to get the correct identification, which he hinted at with reference to the Coypu’s alternative common name Nutria and the genus name which means “mouse-beaver” in Greek. Well done to Isaac!

Coypu showing off its weird discrepancy in limb lengths. Image by José Reynaldo da Fonseca, 2006