On Friday the mystery object was provided by Mark Carnall, the curator of the newly reopened Grant Museum of Zoology:

It’s not been an easy one to work out – I thought it was part of a fish skull when I first saw it and comments have ranged from a squashed frog to Yoda’s foot.

The closest suggestions came from Jamie Revell, Steven D. Garber, PhD and Helen (sort of…), this is the plastron (the shell on the underside) of a turtle. That’s the easy bit(!?) – the next question has to be ‘what species of turtle?’.

This has kept me busy for much longer than I thought it would – I have no reference to hand that shows plastron shape for different species and the plastron of turtles can vary during development and appear very different in living specimens, making an image search unhelpful. However, there is the Turtles of the World (TotW) website which provides a fantastic resource for this kind of thing – as long as you have the time to go through an awful lot of text descriptions.

Thanks to the TotW, I’m pretty sure that this is from a softshell turtle of some sort (from the family Trionychidae) since it has a big gap (or lacuna) in the middle of the plastron, which is characteristic of the family. It also has quite distinctive fused hyo-hypoplastra (the boomerang-shaped bits at the top and bottom of the image) and there appear to be seven thick bony bits (callosities) – fewer than you normally get in a turtle from this family.

This suggests that it comes from the Indian Flapshell Turtle Lissemys punctata (Bonnaterre, 1789) going by the description in TotW:

There is a hinge on the plastral forelobe which allows it to partially close the anterior opening, thus protecting the head and forelimbs. This hinge lies at the point of attachment of the epiplastra to the entoplastron. The hyo- and hypoplastra are fused, and posterior extensions are absent from the entoplastron. Seven plastral callosities occur in adults, but none in juveniles.

As it turns out, this identification was confirmed by Mark, who also pointed me in the direction of the Grant Museum’s online catalogue to check.

Plastron of live Indian Flapshell turtle

The weird looking Indian Flapshell Turtle (image by L. Shyamal)

Alas I had hoped to write more about the humble plastron, touching on topics ranging from their function to the ancient Chinese art of plastromancy, I had also hoped to make more mention of the newly reopened Grant Museum of Zoology, but identifying what species this object came from has left me short of time (albeit much more knowledgeable about turtles). At least you can read more about the Grant on their very own blog and here’s a video about the move – well worth a watch!