Emydidae

Taxobox
name = Emydidae
fossil_range = Late Cretaceous - Recent


image_width = 200px
image_caption = "Graptemys nigrinoda" hatchlings
regnum = Animalia
phylum = Chordata
classis = Reptilia
subclassis = Anapsida
ordo = Testudines
subordo = Cryptodira
superfamilia = Testudinoidea
familia = Emydidae
subdivision_ranks = Subfamilies
subdivision =
Emydinae
Deirochelyinae

The Emydidae are the largest and most diverse family of Testudines.

The family Emydidae includes more than 40 species in 12 genera. Members are distributed throughout North America, northern South America, Europe, northwestern Africa, and Asia. Emydids are primarily freshwater species, though some species inhabit brackish waters "(Malaclemmys terrapin)" or are terrestrial (Terrapene, except "T. coahuila").

Anatomy

Sizes are variable and range from only convert|11|cm|in "(Clemmys)" to nearly convert|60|cm|in "(Kachuga)" in carapace length. Coloration is also quite variable. The family does not have a distinguishing suit of superficial characters, although they all have well-developed limbs with webbed feet. In most species, the carapace is low-arching, but some have a higher dome. The plastron is hinged and movable in some, while fixed in others. There are few distinctive skeletal features, but there is a lack of contact between the squamosal and parietal bones in the skull, and the the frontal bone forms part of the orbit.

Behavior

Food habits range from strictly carnivorous to strictly herbivorous. The carnivores feed on annelids, crustaceans, and fish. In several species, there is a shift from carnivory in juveniles to herbivory in adults. Small mammals, especially raccoons, are responsible for the destruction of many Emydid nests. Members of all vertebrate classes predate eggs and hatchlings. The wide range of sizes in mature animals leads to an assortment of predators. While snapping turtles are responsible for predation in some smaller species (e.g., "Clemmys muhlenbergii"), they cannot eat larger species. Alligators pose a risk to adults of several species, but humans are chiefly responsible for the deaths of adults either through collection for food or the senseless shooting of basking animals.

Knowledge of reproductive behavior ranges from some of the most detailed, long-term study of any taxa ("Chrysemys picta" in Michigan) to a total lack of information. In many species, dimorphisms include elongated foreclaws or a concave plastron in the male. The longer claws are used in a courtship routine in which the male faces the female and fans her face. The concave plastron allows the male to mount females in species with more domed carapaces (e.g., Terrapene). Reproduction is on an annual cycle, and multiple clutches may be produced in a single season. Clutch size is quite variable, ranging from as few as two to more than 30 eggs.

Threats to the Emydidae

Emydids are the principle turtles sold through the pet trade. The pond slider "(Trachemys scripta)" has expanded its range through the careless release of pets into the wild. Many Asian species are threatened by over-collection of animals for sale in markets and into the pet trade. The North America species "Clemmys muhlenbergii" is listed as an Appendix II species by CITES and is considered threatened or endangered in many states. This status is the result of habitat degradation and over-collection.

Systematics and evolution

The Emydidae are most closely related to the tortoises (Testudinidae) and are included along with that family in the Testudinoidea. Shared features include a lack of inframarginal scutes, the shape and muscle attachment of the ilium, and the shape of the eighth cervical vertebra (biconvex). Within the Emydidae, two subfamilies were recognized along biogeographic lines. The Emydidae as understood today contain New World species (except "Emys"), while the former Batagurinae, today a separate family Geoemydidae, contain Old World species (except "Rhinoclemmys"). Osteological characters, such as the construction of the mandible and articulations of the cervical vertebrae distinguish the two families.

The enigmatic Big-headed Turtle ("Platysternon megacephalum") was for some time considered a specialized but still very primitive early offshoot of the Emydidae. But with the geoemydidae being split off it is better reinstated as its own family Platysternidae, though it seems very close to the emydid-geoemydid group.

Fossil record

Presumed emydids are well-represented in the fossil record. "Gyremys sectabilis" and "Clemmys backmani" are both North American species that date from the Upper Cretaceous and Paleocene, respectively. These are the two oldest fossil species. Many other extinct species traditionally placed in the Emydidae are known from the Eocene of North America, Asia and Europe, but the Old World taxa are likely to be more properly Geoemydidae. The North American genus "Palaeochelys" and probably the trans-Atlantic "Echmatemys" too would seem to be Emydidae, but their precise relationship to the living genera are indeterminate.

Classification

*Subfamily Emydinae
**Genus "Emys"
**Genus "Emydoidea"
**Genus "Actinemys"
**Genus "Clemmys"
**Genus "Glyptemys"
**Genus "Terrapene"
*Subfamily Deirochelyinae
**Genus "Deirochelys"
**Genus "Chrysemys"
**Genus "Graptemys"
**Genus "Malaclemys"
**Genus "Pseudemys"
**Genus "Trachemys"

External links

*eol|16099925
* [http://animaldiversity.ummz.umich.edu/site/accounts/information/Emydidae.html University of Michigan Animal Diversity Web]
* [http://www.emys-home.de the European pond turtle ("Emys orbicularis")]