Last week I gave you this gnarly looking skull from the Dead Zoo to identify:
I didn’t think it would be a difficult one, especially since it is a critter I’ve used as a mystery object before (although that was over 10 years ago!)
As I suspected, everyone figured out that this is the skull of an Alligator Snapping Turtle, but things have become a bit more complicated than they used to be over the last decade, since the single species that used to be in the genus Macrochelys has since been split.
The amount of splitting has varied, but at the moment it seems to have settled on two species being recognised; Macrochelys temminckii (Troost, 1835) and Macrochelys suwanniensis Thomas et al., 2014.
One of the key diagnostic features identified to differentiate between them is the angle of the squamosal (the bit of bone with the arrow pointing it above). In M. temminckii the angle is greater than 90° whereas in M. suwanniensis it’s less than 90°.
That suggests to me that the Dead Zoo specimen is probably the Suwannee Snapping Turtle Macrochelys suwanniensis Thomas et al., 2014. The only problem with this identification is that the collection locality is simply “Mississippi”, which doesn’t fit with the Suwannee river distribution of the species.
I’ll need to go back and look at a few other skeletal characters to confirm the identification once I’m back in the Dead Zoo, but my guess is simply that the collection locality wasn’t accurately recorded, since the specimen came from the natural history supplier Edward Gerrard rather being collected and properly documented by a researcher.
It certainly wouldn’t be the first time a representative locality has been given for a specimen meant for display or teaching rather than research!
Zygoma 
I didn’t notice there was two species.
It was well worth the rewrite after the WordPress delete glitch!
These species were the bugbears of my childhood. Not this particular one, because I didn’t grow up anywhere near the Suwanee. But various Snappers are found throughout the South, in swampy areas. I lived near the Dismal Swamp in Va. We were warned when we went out without an adult to look out for them and for Cotton-mouth Moccasin snakes. I saw plenty of dead Snappers. But never a living one. And I never saw the Cottonmouth, alive or dead. Such is the power of folk myth. In California where I now live, my neighbors frantically kill rattlesnakes on sight. Nothing I say seems to make a dent in this automatic response of fear and revulsion.
And the irony is that released “pet” snappers are just one more introduced species beginning to infest California waters (joining the bullfrogs and the capybaras).