Emydidae

Emydidae Temporal range:Upper Cretaceous–Recent
Black-knobbed map turtle
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Testudines
Suborder:	Cryptodira
Superfamily:	Testudinoidea
Family:	Emydidae (Rafinesque,1815)
Subfamilies and genera
See text.
Synonyms
EmidaniaRafinesque, 1815 EmydesSchmid, 1819 EmydidaeThomas Bell,1825 EmydaeSwainson,1839

Emydidae(Latinemys(freshwater tortoise) +Ancient Greekεἶδος (eîdos,“appearance, resemblance” )) is afamilyoftestudines(turtles) that includes close to 50speciesin 10genera.Members of this family are commonly calledterrapins,pond turtles,ormarsh turtles.Several species ofAsian box turtleswere formerly classified in the family; however, revisedtaxonomyhas separated them to a different family (Geoemydidae). As currently defined, the Emydidae are entirely aWestern Hemispherefamily, with the exception of two species ofpond turtle.

Description

Thisbog turtledisplays the keeled carapace, large bridge, and small head found in most emydids.

The upper shell (carapace) of most emydids is the shape of a low arch, although in some species, it is domed. The upper shell may have one or two ridges that run from front to the back of the animal (a projection commonly called a "keel" ), or such a feature may be absent. A prominent bridge often connects the top shell to the bottom shell (plastron). Emydids have large bottom shells, and some members of the family have a movable hinge that separates pectoral and abdominal segments (scutes). The skull is small.

The limbs of these turtles are adapted for swimming, with every member having some level of toe webbing.

Most species exhibittemperature-dependent sex determination,as is typical of turtles; however, one species (thewood turtle) is known to have genetic sex determination.

Behavior

Food habits range from strictlycarnivorousto strictlyherbivorous.The carnivores feed onannelids,crustaceans,and fish. In several species, a shift from carnivory in juveniles to herbivory in adults occurs. Small mammals, especiallyraccoons,are responsible for the destruction of many emydid nests. The wide range of sizes in mature animals leads to an assortment of predators. Whilesnapping turtlesare responsible for predation in some smaller species (e.g.,Glyptemys muhlenbergii), they cannot eat larger species.Alligatorspose a risk to adults of several species.

Knowledge of reproductive behavior ranges from some of the most detailed, long-term study of anytaxon(Chrysemys pictain 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

Emydids are the turtles most commonly sold through the pet trade. Thepond 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 American speciesClemmys muhlenbergiiis listed as an Appendix II species byCITESand is considered threatened or endangered in many states. This status is the result ofhabitat degradationand over-collection.

Systematics and evolution

Echmatemys wyomingensis

The Emydidae are most closely related to thetortoises(Testudinidae) and are included along with that family in theTestudinoidea.Shared features include a lack of inframarginal scutes, the shape and muscle attachment of theilium,and the shape of the eighthcervical vertebra(biconvex). Within the Emydidae, two subfamilies were recognized along biogeographic lines. The Emydidae as understood today contain New World species (exceptEmys), while the former Batagurinae, today a separate familyGeoemydidae,contain Old World species (exceptRhinoclemmys). Osteological characters, such as the construction of themandibleand articulations of the cervical vertebrae distinguish the two families.

The Enigma ticbig-headed turtle(Platysternon megacephalum) was for some time considered a specialized, but still very primitive early offshoot of the Emydidae. With the Geoemydidae being split off, though, it is better reinstated as its own family, the Platysternidae, though it seems very close to the emydid-geoemydid group.

Fossil record

Presumed emydids are well represented in thefossilrecord.Gyremys sectabilisandClemmys backmaniare both North American species that date from theUpper CretaceousandPaleocene,respectively. These are the two oldest fossil species. Many other extinct species traditionally placed in the Emydidae are known from theEoceneof North America, Asia, and Europe, but the Old Worldtaxaare likely to be more properly Geoemydidae.The North American genusPalaeochelysand probably the trans-AtlanticEchmatemys,too, would seem to be Emydidae, but their precise relationships to the living genera are indeterminate.

Classification

The two subfamilies and genera are arranged as follows:

• SubfamilyEmydinae
  • Clemmys
  • Emys
  • Actinemys
  • Emydoidea
  • Glyptemys
  • Terrapene
  • †Wilburemys
    • †Wilburemys yakimensis
• SubfamilyDeirochelyinae
  • Chrysemys
  • Deirochelys
  • Graptemys
  • Malaclemys
  • Pseudemys
  • Trachemys
• Subfamilyincertae sedis
  • †Acherontemys
    • †Acherontemys heckmani
  • †Psilosemys
    • †Psilosemys wyomingensis

References

Bibliography

• Ernst, Carl H.; Barbour, Roger William; Lovich, Jeffery E. (1994). Dutro, Nancy P. (ed.).Turtles of the United States and Canada.Washington and London: Smithsonian Institution Press. pp. 203–204.ISBN1-56098-346-9.
• Rhodin, Anders G.J.; van Dijk, Peter Paul; Iverson, John B.; Shaffer, H. Bradley (2010-12-14)."Turtles of the World 2010 Update: Annotated Checklist of Taxonomy, Synonymy, Distribution and Conservation Status"(PDF).pp. 000.89–000.138. Archived fromthe original(PDF)on 2011-07-17.Retrieved2010-12-15.