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Turtle and Tortoise Newsletter, 2000, 6:28-30
© 2000 by Chelonian Research Foundation

Turtle and Tortoise Newsletter

Generic Revisions of Emydine Turtles

James Ford Parham1,2 and Chris R. Feldman3
1Department of Integrative Biology, 3060 Valley Life Sciences Building,
University of California, Berkeley, California 94720-3140, USA; E-mail: parham@socrates.berkeley.edu
2University of California Museum of Paleontology, 1101 Valley Life Sciences Building,
University of California, Berkeley, California 94720, USA
3Department of Biology, Utah State University, Logan, Utah 84322-5305, USA; E-mail: elgaria@biology.usu.edu

Emydine turtles (sister to Deirochelyinae within Emydidae) are represented by ten extant species, nine of which are restricted to North America. This charismatic and ecologically diverse group of turtles is relatively well studied (as turtles go) and is familiar to both amateur and professional chelonologists. Recent phylogenetic studies (Bickham et al., 1996; Burke et al., 1996; Lenk et al., 1999; Feldman and Parham, 2001, 2002), combined with the discovery of important new fossils (e.g., Hutchison, 1981; Holman, 1987, Holman and Fritz, 2001), have contributed to an emerging consensus on the major aspects of emydine evolutionary history. Based on this combined evidence, two independent studies (Holman and Fritz, 2001; Feldman and Parham, 2002) proposed contrasting generic revisions of emydine turtles. The purpose of this note is to briefly review these taxonomic changes and point out areas of agreement and disagreement.

Presently, the emydine species can be divided into four well-supported, monophyletic groups (Figure 1); listed in order of their date of authorship these are:

Emys Dumeril 1806 - The type species of Emys is the European pond turtle, Emys orbicularis (Linnaeus 1758). Using mtDNA data, Bickham at el. (1996) were the first to suggest that the western pond turtle, Emys marmorata Baird and Girard 1852, Blanding’s pond turtle, Emys blandingii (Holbrook 1838), and E. orbicularis form a monophyletic group. Given this arrangement, Bickham et al. (1996) suggested that all three species could be placed in the genus Emys, pending further support. Since that time, a monophyletic Emys has been strongly supported by two additional molecular-based studies (Lenk et al., 1999; Feldman and Parham, 2002) and an expanded Emys was adopted by Feldman and Parham (2002). However, Holman and Fritz (2001), based on the results of Lenk et al. (1999), suggested the Emys clade be divided into three separate genera: Emys, Actinemys Agassiz, 1857 (for E. marmorata) and Emydoidea Gray 1870 (for E. blandingii). They specifically avoided placing a species without shell kinesis (E. marmorata) into the same genus as taxa with shell kinesis (E. orbicularis and E. blandingii). We disagree with this typological approach, and provide the following arguments in support of a more inclusive Emys.

First, there are multiple examples of turtle genera that display varying degrees of shell kinesis. Two notable examples are mud turtles (Kinosternon) and Palearctic tortoises (Testudo). In fact, shell kinesis can be polymorphic within a single species. For example, the spider tortoise, Pyxis arachnoides, can have a plastron with a well developed hinge or an akinetic plastron (Siebenrock, 1906; Bour, 1981). Additionally, Harding (pers. comm. To JFP) has recorded E. blandingii with akinetic plastra in Michigan. Because shell kinesis is a character that can vary at several taxonomic levels, even within emydine species, we feel it should not be used to split Emys into separate genera.

Second, Feldman and Parham (2002) found that the amount of uncorrected sequence divergence among the three Emys species (5.66-6.33%) overlaps with the genetic distances seen between other congeneric emydines (4.22- 6.09%), but is less than that observed between emydine genera (7.01-9.26%). Although useful as a comparative example, we emphasize that genetic distance alone (i.e, without a phylogenetic justification) should not be an arbiter of taxonomy.

Figure 1. A phylogenetic tree of emydine species based on Feldman and Parham (2002), similar to Bickham et al. (1996) and Lenk et al. (1999). The four species groups are well supported, but the basal relationships (e.g., the relationships of Clemmys sensu stricto) are more ambiguous.”

Third, the taxonomy suggested by Holman and Fritz (2001) results in three closely related genera, each with a single living species. This would obscure the undeniably close relationships of E. marmorata, E. blandingii and E. orbicularis. Separate generic names are redundant because Emys species are already distinguished by their specific epithets. Extinct relatives of Emys species exist, but the bulk of Emys research and interest is focused on living taxa. To make the scientific names informative to the majority of workers, we suggest Actinemys and Emydoidea be reserved as subgeneric names for groups that include a living species and its close fossil relatives.

Terrapene Merrem 1820- No taxonomic revision is required for the well-known genus Terrapene. All analyses support the hypothesis that the species of Terrapene represent a natural group with a shared history that is independent of the other emydines.

Clemmys Ritgen 1828- The only species in the genus Clemmys is the type species, Clemmys guttata (Schneider 1792). Although monotypic genera are generally undesirable, it is necessary here because the phylogenetic affinities of C. guttata to other emydine genera are uncertain (Bickham et al., 1996; Burke et al., 1996; Feldman and Parham, 2002). None of the analyses suggest a close affinity to Emys marmorata or Glyptemys.

Glyptemys Agassiz 1857- All analyses agree that the wood turtle, Glyptemys insculpta (LeConte 1829), and bog turtle, Glyptemys muhlenbergii (Schoepff 1801), are each other’s closest relative and are not closely related to Clemmys. Two groups working in parallel (Holman and Fritz, 2001; Feldman and Parham 2002) revised the taxonomy of these species. Unbeknownst to one another, they chose different names for this clade. Feldman and Parham (2002) chose Calemys Agassiz 1857 while Holman and Fritz (2001) chose Glyptemys. The generic revision of Holman and Fritz (2001) was published three months before Feldman and Parham (2002) so Glyptemys is the appropriate, valid name. We would like to thank James Harding, Phillip Spinks and Patricia Holroyd for providing helpful suggestions.

Literature Cited
Agassiz, L. 1857. Contributions to the Natural History of the United States of America. Boston: Little, Brown and Co., 452 pp.

Baird, S.F. and Girard, C. 1852. Descriptions of new species of reptiles collected by the U.S. exploring expedition under the command of Capt. Charles Wilkes, U.S.N. Proc. Acad. Nat. Sci. Philadelphia 6:174-177.

Bickham, J.W., Lamb, T., Minx, P. and Patton, J.C. 1996. Molecular systematics of the genus Clemmys and the intergeneric relationships of emydid turtles. Herpetologica 52:89-97.

Bour, R. 1981. Étude systématique du genre endémique Malagache Pyxis Bell, 1827 (Reptilia, Chelonii). Bulletin Mensuel de la Société Linnéenne de Lyon 50(4):132-176.

Burke, R.L., Leuteritz, T.E. and Wolf, A.J. 1996. Phylogenetic relationships of emydine turtles. Herpetologica 52:572-584.

Duméril, A.M.C. 1806. Zoologie analytique ou Méthode naturelle de classification des animaux, rendue plus facile à l’aide de tableaux synoptiques. Paris: Allais, 344 pp.

Feldman, C.R. and Parham, J.F. 2001. Molecular systematics of emydine turtles. Chelonian Conservation and Biology 4(1):194-198.

Feldman, C.R. and Parham, J.F. 2002. A molecular phylogeny for emydine turtles: taxonomic revision and the evolution of shell kinesis. Molecular Phylogenetics and Evolution 22(3):388-398.

Gray, J.E. 1870. Supplement to the catalogue of Shield Reptiles in the collection of the British Museum. Part 1. Testudinata (Tortoises). London: Taylor and Francis, 120 pp.

Holbrook, J.E. 1838. North American Herpetology; or a description of the reptiles inhabiting the United States. Ed. 1 Vol. 3. Philadelphia: J. Dobson and Son, 122 pp.

Holman, J.A. 1987. Herpetofauna of the Egelhoff site (Miocene: Barstovian) of north-central Nebraska. J. Vert. Paleo. 7:109-120.

Holman, J.A. 1995. A new species of Emydoidea (Reptilia: Testudines) from the late Barstovian (medial Miocene) of Cherry County, Nebraska. J. Herp. 29:548-553.

Holman, J.A. and Fritz, U. 2001. A new emydine species from the Middle Miocene (Barstovian) of Nebraska, USA with a new generic arrangement for the species of Clemmys sensu McDowell (1964) (Reptilia: Testudines: Emydidae).
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Hutchison, J.H. 1981. Emydoidea (Emydidae, Testudines) from the Barstovian (Miocene) of Nebraska. PaleoBios. 37:1-6.

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Lenk, P., Fritz, U., Joger, U. and Winks, M. 1999. Mitochondrial phylogeography of the European pond turtle, Emys orbicularis (Linnaeus 1758). Mol. Ecol. 8:1911-1922.

Linnaeus, C. 1758. Systema naturae per regna tria naturae secundum classes, ordines, genera, species cum characteribus diferentiis, synonymis, locis. 10th ed. Vol. 1. Stockholm: Salvii, 824 pp.

Merrem, B. 1820. Versuch eines Systems der Amphibien. Tentamen Systematic Amphiborum. Marburg: Kreiger 199 pp.

Ritgen, F.A. 1828. Versuch einer natürlichen eintheilung der Amphibien. Nova Acta Physico-Medica Acad. Caes. Leopold.-Carol. Natur. Curio. 14:246-284.

Schoepff, J.D. 1801. Historium Testudinum iconibus Illustrata. Erlangen: Palmii 160 pp.

Siebenrock, F. 1906. Schildkröten von Ostafrika und Madagaskar. In: Voletkow, A. (Ed.). Reise in Ostafrika 2. Stuttgart: E. Schweizerbart’sche Verlagsbuchhandlung, Nägele & Dr. Sproesser, pp. 1-40.