Family Emydidae is a large and diverse group of turtles comprised of 50 – 60 extant species. After a long history of taxonomic revision, the family is presently recognized as a monophyletic group defined by unique skeletal and molecular character states. Emydids are believed to have originated in the Eocene, 42 – 56 million years ago. They are mostly native to North America, but one genus, Trachemys, occurs in South America and a second, Emys, ranges over parts of Europe, western Asia, and northern Africa. Some of the species are threatened and their future survival depends in part on understanding their systematic relationships and habitat requirements. The present treatise provides a synthesis and update of studies which define diversity and classification of the Emydidae. A review of family nomenclature indicates that Rafinesque, 1815 should be credited for the family name Emydidae. Early taxonomic studies of these turtles were based primarily on morphological data, including some fossil material. More recent work has relied heavily on phylogenetic analyses using molecular data, mostly DNA. The bulk of current evidence supports two major lineages: the subfamily Emydinae which has mostly semi-terrestrial forms ( genera Actinemys, Clemmys, Emydoidea, Emys, Glyptemys, Terrapene) and the more aquatic subfamily Deirochelyinae ( genera Chrysemys, Deirochelys, Graptemys, Malaclemys, Pseudemys, Trachemys). Within subfamilies, some generic relationships have become well defined, supporting sister group relationships (e.g. Emydoidea + Emys, Malaclemys + Graptemys, and Trachemys + Graptemys/ Malaclemys). There is also strong evidence that Glyptemys and Deirochelys are outgroups (early sister lineages) to all of the other taxa in their respective subfamilies. The phylogenetic position of other genera (e.g. Clemmys, Chrysemys, Actinemys) remains enigmatic or controversial. Similarly, many species relationships have been clarified within recent decades, but several remain poorly resolved such as those belonging to Pseudemys, Trachemys, and Terrapene. Overall, our systematic knowledge of emydid turtles has rapidly progressed and ongoing studies are targeting broader and more comprehensive sampling of populations.

Emydidae, Turtles, Systematics, Phylogeny, Taxonomy, Actinemys, Chrysemys, Clemmys, Deirochelys, Emydoidea, Emys, Glyptemys, Graptemys, Malaclemys, Pseudemys, Terrapene, Trachemys.