Emydidae

(vertebrate zoology) A family of aquatic and semiaquatic turtles in the suborder Cryptodira.

(Emydidae)

Class: Reptilia

Order: Testudines

Suborder: Cryptodira

Family: Emydidae

Thumbnail description
Small- to medium-sized turtles; carapace may be depressed, domed, or strongly keeled; plastron may or may not be hinged; double articulation found between the fifth and sixth cervical vertebrae

Size
10–24 in (25–60 cm)

Number of genera, species
12 genera; 35 species

Habitat
Freshwater rivers, streams, lakes, and ponds; other species are semiaquatic to fully terrestrial; still other species frequent estuaries and coastal waters

Conservation status
Endangered: 6 species; Vulnerable: 7 species; Lower Risk/Near Threatened: 14 species

Distribution
Temperate and tropical regions of North and South America, Europe, western Asia, and northern Africa

Evolution and systematics

The oldest fossils are known from the Upper Cretaceous and Paleocene of North America. These modern cryptodires are most closely related to the Geoemydidae of South America, Europe, Africa, and Asia and the Testudinidae, which also are found in North America.

Morphological and molecular evidence suggests a close relationship among western pond turtles (Actinemys marmorata), European pond turtles (Emys orbicularis), and Blanding's turtles (Emydoidea blandingii). Some researchers consider them to be members of a single genus (Emys), while others recognize them individually as the sole representatives of monotypic genera. Two subfamilies are recognized: the Emydinae (palatine excluded from the triturating surface) and the Deirochelyinae (humeropectoral sulcus excluded from the entoplastron).

Physical characteristics

There are typically eight pleurals, five vertebrals, and 24 marginals on the carapace and 12 scutes on the plastron. The seam between the posterior marginal scutes and the last vertebral overlap the pygal bone. A double articulation is found between the fifth and sixth cervical vertebrae. Most species have at least some webbing between the toes, and some species have a hinged plastron.

Bog turtles (Glyptemys muhlenbergii) attain a maximum size of 5 in (12 cm), whereas adult Gray's sliders (Trachemys venusta grayi) may reach 24 in (60 cm) or more. Males are generally smaller than females in the aquatic emydids; however, among semiaquatic and terrestrial species this may be reversed.

Distribution

These turtles are found in the lowland temperate regions of North America, North Africa, southern Turkey, the Middle East, and throughout Europe to southern Russia. They were formerly more widespread in Europe, but the Scandinavian populations were extirpated during the Pleistocene.

Habitat

This extremely diverse family is found in many habitats. They occur in abundance in most permanent freshwater rivers, streams, lakes, and ponds. One species is only found in estuaries and coastal waters, and a few species are semi-aquatic to fully terrestrial.

Behavior

Whether fully aquatic or terrestrial, most emydids have a well-developed basking habit. Some species are active year-round; others are seasonally inactive (dry season or winter). Males of many species exhibit elaborate courtship displays. Among the temperate northern species, hibernacula are generally located in well-oxygenated areas; however, painted turtles (Chrysemys picta) and Blanding's turtles are tolerant of extremely hypoxic, or low oxygen, conditions. At least two aquatic species, the chicken turtle (Deirochelys reticularia) and the western pond turtle, are known to hibernate terrestrially. The eastern box turtle (Terrapene carolina) burrows beneath leaf litter and hibernates in shallow soil where it may experience subfreezing temperatures.

Feeding ecology and diet

This family includes species that are strictly herbivorous to those that are strictly carnivorous. Hatchlings of many species are highly carnivorous, but switch to a more omnivorous diet as they mature. Some species have diverse, generalized diets and others are highly specialized. In map turtles (genus Graptemys), the females may develop huge heads with broad palates that enable them to crush large mollusks. Chicken turtles and Blanding's turtles have independently evolved a long neck with a well-developed hyoid apparatus, an elaborate bony structure that rapidly expands the throat to suck in prey items. This feeding adaptation is frequently found in piscivorous (fish-eating) turtle species.

Reproductive biology

In sexually dimorphic aquatic species, the female is larger than the male. The size difference is most extreme among species of the genus Graptemys. Mating generally occurs in the spring; however, some species may store sperm from an earlier mating for several years. The male is brightly colored and may possess long thin claws on the forelimbs that are vigorously waved before the female during courtship. A unique pattern of head bobs also may be exchanged before the female allows the male to mount. This elaborate courtship suggests that females choose their mate. The elongate eggs, which may be flexible or brittle shelled, are generally laid in nests dug in the soil away from the water (sometimes more than 0.6 mi [1 km] away). Most species that have been investigated exhibit temperature-related sex determination.

Conservation status

Seven species are listed as Vulnerable and six as Endangered on the IUCN Red List; 14 others are listed as Lower Risk/Near Threatened. Human activities (e.g., pollution, habitat destruction, road mortality, and collecting for the pet trade) are responsible for declines in most species. No species demonstrates the destructive effect that human exploitation may have on a turtle population better than the diamondback terrapin (Malaclemys terrapin), which once faced extinction throughout its range due to overcollection for human consumption. This turtle recovered as it fell out of favor with the wealthy.

Significance to humans

Many species are prominent in the international pet trade; the red-eared slider (Trachemys scripta elegans) has been the world's pet turtle for several decades. The hatchlings are exported by the tens of thousands from ranching operations in Louisiana. This turtle has established breeding populations throughout the world and is considered an invasive pest because it may harm native species. A few species are consumed by humans locally.

Species accounts

Resources

Dodd, C. Kenneth, Jr. North American Box Turtles: A Natural History. Norman: University of Oklahoma Press, 2001.

Gibbons, J. Whitfield. Life History and Ecology of the Slider Turtle. Washington, DC: Smithsonian Institution Press, 1990.

Schmidt, Karl P. A Check List of North American Amphibians and Reptiles. 6th edition. Chicago: University of Chicago Press, 1953.

Buhlmann, Kurt A., and J. Whitfield Gibbons. "Terrestrial Habitat Use by Aquatic Turtles from a Seasonally Fluctuating Wetland: Implications for Wetland Conservation Boundaries." Chelonian Conservation and Biology 4 (2001): 115–127.

Costanzo, J. P., J. D. Litzgus, J. B. Iverson, and R. E. Lee. "Cold-Hardiness and Evaporative Water Loss in Hatchling Turtles." Physiological and Biochemical Zoology 74 (2001): 510–519.

Holman, J. Alan, and Uwe Fritz. "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)." Zoologische Abhandlungen (Dresden) 51 (2001): 331–353.

Pearse, D. E., F.J. Janzen, and J. C. Avise. "Multiple Paternity, Sperm Storage, and Reproductive Success of Female and Male Painted Turtles (Chrysemys picta) in Nature." Behavioral Ecology and Sociobiology 51 (2002): 164–171.

St. Clair, R. C. "Patterns of Growth and Sexual Size Dimorphism in Two Species of Box Turtles with Environmental Sex Determination." Oecologia 115 (1998): 501–507.

[Article by: Patrick J. Baker, MS]

The noun has one meaning:

Meaning #1: box and water turtles
  Synonym: family Emydidae

Emydidae Fossil range: Late Cretaceous - Recent
Graptemys nigrinoda hatchlings
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Reptilia Subclass: Anapsida Order: Testudines Suborder: Cryptodira Superfamily: Testudinoidea Family: Emydidae
Subfamilies
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).

Contents 1 Anatomy 2 Behavior 3 Threats to the Emydidae 4 Systematics and evolution 4.1 Fossil record 4.2 Classification 5 External links

Anatomy

Sizes are variable and range from only 11 centimetres (4.3 in) (Clemmys) to nearly 60 centimetres (24 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

Echmatemys wyomingensis

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

Wikispecies has information related to: Emydidae

Wikimedia Commons has media related to: Emydidae

• Emydidae at the Encyclopedia of Life
• University of Michigan Animal Diversity Web
• the European pond turtle (Emys orbicularis)
• Emydidae

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