Return to World Chelonian Trust Main Page for more Turtle and Tortoise Information
The Taxonomic Level Genus: Its definition and delineation. - Scott Thomson
Taxonomic designation of turtles and tortoises is an ongoing process, as years go by more tools become available to taxonomists studying exactly how the various species relate to each other. Among these tools are morphometric analyses, DNA analyses and the fossil record. The information these taxonomists discover can and does lead to a clearer understanding of the world we live in which is something for which we own them our thanks. Sometimes it also means that occasionally an animal we knew by one name needs to be referred to as something different. Usually these changes are with species that are recently discovered, seldom encountered or are a designation of subspecies status for a subgroup or area variant of a species that is judged sufficiently different to warrant such a designation.
We try to keep abreast of these changes whenever possible, and when they happen we change the names in our online galleries and articles to reflect the new accepted taxonomic name. Occasionally though, this happens with a species that is both commonly kept in captivity and is very well known by the old scientific name. In this situation if we merely changed the name we would be doing a disservice to the people needing assistance with the species. People searching the internet for help with a species are not likely to know of recent taxonomic shifts or every name their animal is known by. Most reptile keepers get their initial information from books and encyclopedias that only use the name accepted sat the time of publishing. However we cannot ignore the advances made by taxonomic researchers because there is the possibility that a visitor will search under the new name rather than the old.
Because of the above reasoning there are animals listed under more than one name on this web site in the galleries and occasionally in the articles section as well. Whenever possible we will make a note of the currently accepted name where ever we use an older one. As an example of the changing nature of chelonian taxonomy we highlight the proposed recent changes in the genus Clemmys and Emydoidea in the table below. Below the table are the abstracts of two recent articles that have led to this situation. As time allows we will update all articles dealing with these species to reflect the present names once any contradiction is resolved as well as still referring to the older ones so that people can find the assistance they seek.
|Common Name||Old Designation||New Designation*|
|North American Wood Turtle||Clemmys insculpta||Calemys insculpta1|
|North American Bog Turtle||Clemmys muhlenbergii||Calemys muhlenbergii1|
|Western Pond Turtle||Clemmys marmorata||Emys marmorata1|
|Blandings Turtle||Emydoidea blandingii||Emys blandingii1|
|Spotted turtle||Clemmys guttata||Clemmys guttata|
*It appears that the name Glyptemys will be accepted in preference over Calemys at this time.
The 10 extant species of emydine turtles represent an array of morphological and ecological forms recognizable and popular among scientists and hobbyists. Nevertheless, the phylogenetic affinities of most emydines remain contentious. Here, we examine the evolutionary relationships of emydine turtles using 2092 bp of DNA encoding the mitochondrial genes cyt b, ND4, and adjacent tRNAs. These data contain 339 parsimony informative characters that we use to erect hypotheses of relationships for the Emydinae. Both maximum parsimony and maximum likelihood methods yield a monophyletic Emydinae in which all but three nodes are well resolved. Emys orbicularis, Emydoidea blandingii, and Clemmys marmorata form a monophyletic clade, as do the species of Terrapene. Clemmys muhlenbergii and Clemmys insculpta form a third monophyletic group that may be sister to all other emydines. Clemmys guttata is problematic and probably related to Terrapene. Based on this phylogeny, and previous molecular work on the group, we suggest the following taxonomic revisions: (1) Clemmys should be restricted to a single species, C. guttata. (2) Calemys should be resurrected for C. muhlenbergii and C. insculpta. (3) Emys should be expanded to include three species: E. orbicularis, E. blandingii, and E. marmorata. Furthermore, our analyses show that neither kinetic-shelled nor akinetic-shelled emydines form monophyletic groups. Therefore, shell kinesis was either independently gained in Emys and Terrapene or secondarily lost in E. marmorata and C. guttata. Parsimony, paleontological evidence, and the multiple origins of shell kinesis in related turtle lineages (especially geoemydines) support the independent origin of plastral kinesis.
As there is convincing evidence for a paraphyly of the genus Clemmys sensu McDOWELL (1964), it is suggested that Clemmys RITGEN, 1828 be restricted to its type species, Clemmys guttata (SCHNEIDER, 1792). Clemmys marmorata (BAIRD & GIRARD, 1852), a species more closely related to emydine taxa with a hinged plastron than to other species with nonhinged plastra previously referred to Clemmys, is treated as a member of the monotypic genus Actinemys AGASSIZ, 1857. Clemmys insculpta (LE CONTE, 1830 (1829)) and Clemmys muhlenbergii (SCHOEPFF, 1801) are regarded as representing another distinct genus for which the name Glyptemys AGASSIZ, 1857 (species typica: Testudo insculpta LE CONTE, 1830 (1829)=Glyptemys insculpta) is given precedence over Calemys AGASSIZ, 1857, erected for Testudo muhlenbergii SCHOEPFF, 1801. - Based on a large amount of fossil material from Nebraska (USA), Glyptemys valentinensis n. sp. is described. With this new species, the genus Glyptemys is now known from the Middle Miocene (Medial to Late Barstovian: ca 14.5-11.5 Ma BP) to modern times. Glyptemys valentinensis is morphologically more similar to Glyptemys insculpta than to G. muhlenbergii. It is suggested that G. valentinensis gave rise to G. insculpta between Late Barstovian and Late Hemphillian times (11.5-5.5 Ma BP). As sequence data of the mitochondrial cytochrome b gene argue for a differentiation of G. insculpta and G. muhlenbergii exactly in Medial Barstovian times (ca 14.5 Ma BP), G. valentinensis could be the last common ancestor of G. insculpta and G. muhlenbergii.
Return to Conservation / Natural History
World Chelonian Trust
PO Box 1445
WCT Web Master