Macrochelys suwanniensis, Thomas, Travis M., Granatosky, Michael C., Bourque, Jason R., Krysko, Kenneth L., Moler, Paul E., Gamble, Tony, Suarez, Eric, Leone, Erin, Enge, Kevin M. & Roman, Joe, 2014

Thomas, Travis M., Granatosky, Michael C., Bourque, Jason R., Krysko, Kenneth L., Moler, Paul E., Gamble, Tony, Suarez, Eric, Leone, Erin, Enge, Kevin M. & Roman, Joe, 2014, Taxonomic assessment of Alligator Snapping Turtles (Chelydridae: Macrochelys), with the description of two new species from the southeastern United States, Zootaxa 3786 (2), pp. 141-165 : 150-151

Macrochelys suwanniensis sp. nov.

Common name. Suwannee Alligator Snapping Turtle

Holotype. UF 166146, adult male skeleton from Santa Fe River and State Road 235, Alachua County, Florida (29.87872o N, 82.33619o W, datum WGS84, elev. 23 m), found dead, apparently from gunshot wounds, in very low water in 2003 by Jason R. Bourque (see Figures 10 , 11 , 12 ). (Suwannee lineage; Figure 9 ).

Paratypes. UF 22267, partial skeleton from Santa Fe River, near Town of Santa Fe, Alachua County, Florida, on 9 April 1962 by George R. Zug; UF 12694, partial skeleton from Fletcher Spring, Lafayette County, Florida (29.84672o N, 82.89256o W, elev. 9 m), on 19 November 1961 by B. Sites, D. Desautels, and D. Young.

Diagnosis. Macrochelys suwanniensis is distinguished by the following: carapacial caudal notch very wide and lunate ( Figure 10 ), usually comprising the pygal and peripheral set 11 (shared with Chelydra ); pygal sutured medially (composed of two bones) often with no serrations; Peripheral 11 with 1–2 serrations; distal rib end of costal 1 enters posterior third of peripheral 3; pleural scute set 1 with broad overlap onto the nuchal; dermal scale on the frontals very wide; processus trochlearis oticum with developed proximal and distal protuberances; squamosal contacts opisthotic anteriorly when viewed in dorsal aspect; mandible broad with expanded triturating surfaces and developed labial rugosity just anterior to the coronoid; posterior projection of the squamosal acutely angled in lateral aspect, dorsally straight or downwardly directed, and posteriorly extensive past the plane of the quadrate ( Figure 11 ).

Comments. Most carapaces of Macrochelys suwanniensis exhibited a medially sutured pygal. This feature is significant when considering caudal notch width and is likely at least part of the reason this species possesses the widest caudal notch amongst congeners. The extra suture may allow the caudal notch to expand as the turtle grows larger. This is in contrast to M. temminckii , which possesses a single unsutured pygal bone and consequently the narrowest caudal notch of extant Macrochelys . Peripheral 11 is usually doubly serrated; i.e., the serrations that are typically contained on the pygal bone in the western and central species have migrated onto the 11th peripheral set in M. suwanniensis .

Distribution. Restricted to the Suwannee River drainage in Florida and Georgia.

Etymology. Specific epithet refers to combination of the new Latin suwanni– (referring to the Suwannee River) and the Latin –ensis (belongs to the) to form the composite noun suwanniensis .

Specimens examined. See Appendix.

Figures

FIGURE 9. Bayesian inference phylogeny for extant chelydrids (Chelydra and Macrochelys). Note that representative skeletal synapomorphies in skull and carapace (above and below, respectively, next to lineage name) are provided for each lineage of Macrochelys; values above major nodes represent posterior probabilities (≥ 95 %); values below major nodes represent the mean divergence time estimation of the most recent common ancestor (MRCA); and bars at major nodes represent 95 % Highest Posterior Density (HPD).

FIGURE 10. Photograph of Macrochelys suwanniensis holotype (UF 166146) demonstrating external (A) and internal (B) carapace morphology.

FIGURE 11. Photograph of Macrochelys suwanniensis holotype (UF 166146) demonstrating a superior view of plastron morphology.

FIGURE 12. Photograph of Macrochelys suwanniensis holotype (UF 166146) demonstrating a superior (A), inferior (B), cranial (C), caudal (D), and left (E) and right (F) lateral view of skull morphology.