Friday mystery object #432 answer

Last week I gave you a mystery object from the Grant Museum of Zoology, UCL, with this old photo from my time as the Curator there:

This is one of those species that I have a bit of a soft spot for, due to the general weirdness of the skull. That does however make it quite recognisable as a specimen, even in a photo that hasn’t been taken for the purposes of identification – like this one.

Everyone who commented recognised that this is some sort of turtle, and thanks to that very flat skull with all the features towards the very front end, most people worked out that it’s a from a Mata-mata Chelus sp. Duméril, 1806.

Illustration of Chelus fimbriatus, by R. Mintern, 1885

Back in 2016, when I took the photo of the specimen, that would have been enough for a species identification (which would have been Chelus fimbriata), but today it’s simply not good enough, since molecular taxonomists determined a species level split in populations from the Amazon and Orinoco basins in 2020. Darn.

Fortunately, morphological differences between Mata-mata from different basins have been recognised for a while (link opens a pdf of ), reflecting the molecular split between species. Unfortunately, the main area of morphological difference is in the carapace, which isn’t in the photo I provided (if only I’d known that the species was going to split back in 2016…).

But fear not – back in 2018 Hannah Cornish did a Specimen of the Week blogpost about this very specimen, with some more useful images. The overall outline of the Grant specimen seems more rectangular than oval, which may indicate that it is an Amazon Mata-mata, making the original identification of Chelus fimbriata (Schneider, 1783) still correct – although a proper examination of the specimen would be needed to confirm that.

So a hearty congratulations to everyone who figured out what this was – and I would suggest taking a look through the comments from the mystery object, as there are some very interesting observations and discussions about that strange skull which are well worth a read. That’s the kind of thing that I love most about running this blog!

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