This week I’ve decided to delve back into the depths of my phone’s memory to offer up a mystery object from the Grant Museum of Zoology:
Any idea what this might be?
Enjoy your Easter!
Friday mystery object #432
Zygoma
Adventures in natural history collections
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I think it someone’s mother, twice over. I’m guessing its the typical species but can’t really tell if it comes from the Orinocco
Turtle. No peccary. No…
Turtle – snapping? Matamata, as Allen Yates suggests? too flat for loggerhead?
looks a lot like my snapper, but might that be too common for easter quiz?
Can’t be much other than a turtle of some kind (but, if you want to see something strange, look for an SEM photo of an embryonic star-nosed mole… try NOT to see the nostrils as eyes!), but I don’t know what kind. It doesn’t seem quite right for a snapper (either Common or Alligator): in the photos I found of snapping turtle skulls taken from dead ahead, the crest over the brain case is visible, giving the rear of the skull a “single-peaked” appearance. That could be just a matter of the precise angle of view, but this one doesn’t look as if it has such a sharp-edged crest.
And I think sea turtles would look more convex on top. I’d be sympathetic to a Matamata identification, but, honestly, the only feature I can see uniting the two is … weirdness!
Umm… Instead of a single median crest, as in Snapping Turtles, the rear end of this skull looks as if it has two “horns”: the skull roof goes back and then rises in two outward-angled prominences, very roughly as far apart from each other as the orbits are.
Looking at “Skulls Unlimited”‘s ad for replica Matamata skulls, I think (though, given camera angle it’s hard to tell) that this might be a second feature (after weirdness) that Paolo’s object has in common with Matamata skulls.
But there are a lot of species of turtle.
It does seem to have a lower jaw, which rules out a lot of weird Paleozoic things!
OK since everyone is giving up on the cryptic answer thing this gets a little easier. I am certain this is a matamata skull in front view. the extreme flatness of the anterior skull, the really large lateral cranial embayments behind the orbits, the rugose dorsal surface, and the way the skull roof bends upwards towards he back all fit matamata perfectly. Even the enlarged hyoid elements can be seen poking up behind the skull (the living matamata uses these to expand the throat for suction feeding). I just don’t know if this is Chelus fimbriata or C. orinoccoensis.
spelling corrections: that should be Chelus fimbriatus and C. orinocensis
Adam Yates–
Sorry. I should have tried to stay a bit more cryptic. Sallie Reynolds picked up your mother-mother reference (I’m slow: I didn’t get it.) and used the “plain text” name, and then I just fixated on that kind of turtle.
The centered crest I referred to seems to be typical of most turtles: I take it that its absence is part of the “syndrome” you refer to. It certainly is characteristic of mm: is it unique to them among (extant) turtles?
Hi Allen,
That central crest you speak of is partly the result of a pair of embayments, or emarginations as they are called, that excavate the skull roof from the posterior margin, either side of the midline, leaving a central ‘isthmus’ (ie. the crest) between the two emarginations. Not all turtles excavate the skull roof in this manner, some like the mm, have emarginations that excavate from the side, often leaving a broader dorsal stripe of the skull roof through the middle (not unique to mm). Others, like sea turtles, don’t have much in the way of emarginations of either sort, but nonetheless can have the appearance of a central crest by the posterior projection of a spine from the supraoccipital bone located in the center of the posterior margin.
Hi Adam,
Thanks for the details. (Which I’ll try to remember while looking at a selection of turtle skulls.)
Is there any correlation between the from the back and the from the sides styles of margination and the crypto dire/pleurodire split?
Hi,
To my knowledge, the emargination style does not neatly map to the cryptodire/pleurodire split. There is quite a diversity of emargination styles (many have both, some even merge them, effectively erasing the dorsal skull roof) with lots of convergence and reversal. We’re at the limit of my memory now, and I have to start researching, to answer this more clearly.
cheers
Thanks Adam!
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