Giant Snappers, Take 3

There aren't many pictures of very large Common Snapping Turtles (Chelydra serpentina) - let alone with decent angles or objects that can be used for scale - so I feel obliged to share a series of photos taken in Rhode Island's Blackstone River in May, 1986:

I have no prior experience with gun identification, but this appears to be a Ruger MK II with a 4 in (10 cm) bull barrel; this scale gives realistic measurements of the man in the photograph, who is roughly the same size I am. Thus, the strait carapace length is approximately 16.5 inches (42 cm), which isn't record size (49.4 cm/19.4 inches), but then, the same body of water reportedly holds numerous other individuals which are even larger. The weight was estimated to be around 80 pounds (36 kg).

The carapace appears to have three low keels, which seems remarkable for a turtle of this size. Supramarginals are obviously not present, so this cannot be an out of place Alligator Snapping Turtle (Macrochelys temminckii). The head:carapace ratio is difficult to determine, but appears to be larger than 1:3, judging by the last photo. The tail is rather short and slender for a snapping turtle - could this individual be female? The record for that gender is an SCL of only 36.6 cm (14.4 inches) - in which case this individual would be quite remarkable (Ernst and Lovich 2009 - citing Gibbons and Lovich 1990)

Small (8 inch/20 cm SCL) female Snapping Turtle finishing up a nest. Photo by me.

Snapping turtle with ~40 cm (15.7 inch) SCL - note how the tail has a post-carapace 'bulge' and is overall much thicker than that of the Blackstone Specimen. Taken from Flickr user Karim Rezk. Similar photos can be found here and here.

Males snappers have an anal vent past the carapace rim and a pre-anal tail length of over 120% the length of the posterior lobe; females have a vent beneath or slightly under the rim and have a pre-anal tail length under 110% of the lobe (Ernst and Lovich 2009 - illustrated here). Males also have longer and thicker tails, a smaller plastron, and narrower bridge (see Chelydra.org). Unfortunately, most of these traits are not observable in the specimen and I am uncertain if the tail morphology is within the range of variation for males.  Still, it is a remarkable animal, and it certainly isn't every day that a turtle has a shell the size of a human torso.

Since this is such an interesting topic, I will start on a sub-page of this blog that focuses on snappers which are potentially larger than record size. If anyone reading has any stories, I will be highly interested.

Many thanks to the source for the photograph!

References:

Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland. ISBN 13:978-0-8018-9121-2

Gibbons, J., and Lovich, J. (1990). Sexual dimorphism in turtles with emphasis on the slider turtle (Trachemys scripta). Herpetol. Monogr. 4, 1-29.

Giant Snappers, Take 2

At the Audubon Society of Rhode Island's Environmental Education Center, I couldn't help but notice an enormous Common Snapping Turtle (Chelydra serpentina) skull when I was placing a complete Corn Snake shed into a specimen drawer. All I could determine about this specimen is that it's from Auburn, Maine and rivals my prior giant snapper in size.

Ventral view of the skull. Using ImageJ, I calculated the distance from the tip of the premaxilla (i.e., the beak) to the end of the supraoccipital to be 14.74 cm or 5.8 inches. The currency - which refused to smoothen out - is there to establish rough scale.

Dorsal view of skull. These measurements slightly exceed the ventral view, probably due to the highly raised supraoccipital. The bill has somehow become even more crinkled.

Note the enormous temporal/otic notches and damage to the prefrontal.

Frontal view. The posterior portion of the head was probably considerably wider in life.

Data from Herrel and O'Reilly (2006) indicates their largest Chelydra had a 11.8 cm (4.65") head corresponding with a carapace length of 38.6 cm (15.6"), giving a head:SCL ratio of 1:3.27. This implies that the Auburn Specimen (head length ~14.7 cm) has an SCL of at least 48 cm (19") - as snapping turtle heads appear to get proportionally smaller with increased SCL. So how does Gamera stack up?

The specimens appear to be nearly identical in size - and somehow, angle. 

The official maximum size* of Chelydra serpentina, as given by Ernst and Lovich (2009), is an SCL of 49.4 cm (19.4") (Ernst and Lovich 2009) - a length both of these specimens appear to have approached, or slightly exceeded. Considering just about everybody has a story about giant snappers, this seems to imply that such lengths are not uncommon; the ease in which I found the two very large specimens appears to support this. Ferri (2002) claims the "normal" maximum for Chelydra is 47 cm SCL, but specimens may reach 60 cm (2 feet); while this claim was not substantiated as far as I can tell, it seems plausible.

* One wild specimen with a 47 cm (18.5") SCL weighed 34 kg (75 pounds)... and was known for attacking horses! (Ernst and Lovich 2009) - presumably the specimens I ran across are/were similarly massive and potentially traumatogenic.

More on this subject soon.

References:


Ernst, C. H., and Lovich, J. E. (2009). Turtles of the United States and Canada. John Hopkins University Press: Baltimore, Maryland. ISBN 13:978-0-8018-9121-2

Ferri, Vincenzo. (2002). Turtles and Tortoises. Firefly Books: Buffalo, New York. ISBN 978-1552096314

Herrel, A. and O'Reilly, J. (2006). Ontogenetic Scaling of Bite Force in Lizards and Turtles. Physiological and Biochemical Zoology 79(1), 31–42. DOI: 10.1086/498193