Saturday, May 4, 2013

Readers Write In: Did I Find An Alligator Snapping Turtle In a Cenote?


Hello:

I am an avid diver and lay scientist.  I took the attached photo at Rock Lake, NM which I hypothesize is the world's highest cenote at 4,600 ft. above sea level...I would prefer to know a bit about the subject of my photo, so I may give it due credit and hopefully bring positive attention to them. In this quest I came upon your name and therefore duly appreciate the offer given in your website for help.   

After positive identification I would ask if there is a known altitude range of these turtles?   Is this turtle a predator or is it grazing on grass? 

Thank you,
Francisco Z.


The first thing I had to do after receiving this e-mail was Google "cenote" and I found out that they were, "a deep natural pit, or sinkhole...resulting from the collapse of limestone bedrock...cenotes were sometimes used by the ancient Maya for sacrificial offerings."

Cool.

Now that I knew what a cenote was, I was able to focus on the task at hand, that is, identifying the turtle hanging out within the ancient Mayan sacrificial altar. I knew before looking at the picture that the animal was unlikely to be an Alligator Snapping Turtle (Macrochelys temminckii) because these animals are most closely linked to the streams and rivers of the southeastern United States far from New Mexico (although they can also be found in some states best characterized as Midwestern).

But Francisco's tentative identification was close. The large and broad carapace (shell) of the turtle, together with the long tail and head, reveal it as a Snapping Turtle (Chelydra serpentina). Both Snapping Turtles and Alligator Snapping Turtles are within the same family (Chelydridae) but are representatives of two different genera. Although they aren't too closely related, they are often confused for each other.

Alligator Snapping Turtles typically have three distinct ridges running down their shell and a relatively broad head, when compared to Snapping Turtles (here's a useful picture comparing the two). The differences between these species may seem subtle at first but telling them apart will become second nature after you look at and compare a few dozen of them.

Snapping Turtles are generalists, which means they eat a wide variety of things and can be found in just about any wet habitat. But, I was still surprised to know that one was in New Mexico, it seemed too far west for this species. However, after a little digging I discovered that the natural range of Snapping Turtles does in fact reach the eastern portions of New Mexico, including Rock Lake. 

Because Snapping Turtles are generalists, altitude is not a big concern for them and they can be found at elevations well above where Francisco found his turtle. As to Francisco's question about whether the animal was grazing, probably not. Snapping Turtles have a reputation as a voracious predator but this is a bit of an exaggeration. Although small fish, frogs and other assorted creatures would do well to avoid the area around Snapping Turtle mouths, the species is content to scavenge carrion and eat the roots of various aquatic plants. I've never heard of one grazing though; this animal was just probably hanging out and saving its energy (that is to say, relaxing).

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