The monotypic Alligator Snapping Turtle is now three species

The Alligator Snapping Turtle, Macrochelys temminckii, has gone from being a monotypic species of southeastern North American rivers and the main ingredient in turtle soup to an endangered species that is now three distinct species. This transformation took less than 50 years. Thomas et al. (2014) note previous molecular analyses using mitochondrial and nuclear DNA suggested Macrochelys exhibited significant genetic variation across its range and includes three distinct genetic assemblages (western, central, and eastern = Suwannee).

However, no taxonomic revision or morphological analyses have been conducted previously. Thomas et al.  tested previous hypotheses of geographic assemblages by examining morphology, reanalyzing phylogeographic genetic structure, and estimating divergence dating among lineages. They reviewed the fossil record and discuss phylogeographic and taxonomic implications of the existence of three distinct evolutionary lineages. They found morphological and molecular data suggest significant geographical variation and suggest three species-level breaks among genetic lineages that correspond to previously hypothesized genetic assemblages. The holotype of Macrochelys temminckii is from the western lineage. They describe two new species: Macrochelys apalachicolae sp. nov. from the central lineage and Macrochelys suwanniensis sp. nov. from the eastern lineage (Suwannee River drainage). Their estimates of divergence times suggest that the most recent common ancestor (MRCA) of M. temminckii (western) and M. apalachicolae (central) existed 3.2–8.9 Ma during the late Miocene to late Pliocene, whereas M. temminckii-M. apalachicolae and M. suwanniensis last shared a MRCA 5.5–13.4 Ma during the mid-Miocene to early Pliocene. Examination of fossil material revealed that the fossil taxon Macrochelys floridana is actually a large Chelydra. 

Citation

Thomas, TM, Granatosky, MC, Bourque JR, Krysko, KL, Moler, PE, Gambel, T, Suarez, E., Enge, KM, and Roman, J. 2014.  Taxonomic assessment of Alligator Snapping Turtles (Chelydridae: Macrochelys), with the description of two new species from the southeastern United States. Zootaxa 3786 (2): 141–165