Australo-American sideneck turtles

(Chelidae)

Class Reptilia

Order Testudines

Suborder Pleurodira

Family Chelidae

Thumbnail description
Medium to large sideneck turtles with a nuchal scute (absent only in Elseya), zero to six neural bones, the pleural bones almost always meeting at the midline behind the neurals, mesoplastral bones absent, and the pelvis fused to the carapace and plastron

Size
6–19 in (14–48 cm)

Number of genera, species
16 genera; 50 species

Habitat
Swamps, marshes, seasonally flooded wetlands, ponds, lakes, streams, and rivers

Conservation status
Critically Endangered: 3 species; Endangered: 4 species; Vulnerable: 6 species; Lower Risk/Near Threatened: 8 species; Data Deficient: 2 species

Distribution
South America, Indonesia, New Guinea, and Australia

Evolution and systematics

Fossils of these turtles are known from the Miocene of Australia and South America. They are most closely related to the other pleurodiran families: the Pelomedusidae of Africa and the Podocnemididae of South America and Africa. Their subfamilial relationships remain poorly understood. Molecular evidence suggests that the Chelidae can be further divided into three subfamilies: the Hydromedusinae, containing only the genus Hydromedusa; the Chelidinae, containing all other South American chelids; and the Chelodininae, containing both the short- and long-neck species of Australia and New Guinea. This taxonomic relationship has yet to be diagnosed in terms of morphological characters. Genetic and morphological data support the revision of the genus Phrynops, which resulted in the erection of two new genera (Bufocephala and Ranacephala) and the resurrection of three previously recognized genera (Mesoclemmys, Batrachemys, and Rhinemys). The status of several morphologically distinct Australian "species" is debated among taxonomists because the species are virtually indistinguishable using genetic analysis.

Physical characteristics

Sideneck turtles are extremely diverse in size, shape, and coloration. Most species have four claws on the hind feet and five claws on the forelimbs, zero to six neural bones present, the pleural bones almost always meeting at the midline behind the neurals, mesoplastral bones absent, and the pelvis fused to the plastron. Neck elongation is extreme; in some species the length of the neck may exceed that of the carapace. While the carapace tends to be dark and cryptic, there are a few spectacularly colored chelids that may have bright red, pink, orange, and yellow on the plastron and/or soft parts.

Distribution

With the exception of Batrachemys dahli, all of the South American chelids are found east of the Andes and as far south as northern Argentina. The remaining species are found in tropical to temperate regions of Australia and New Guinea. This curious distribution may be the result of a common ancestor that dispersed across Antarctica before the southern continents separated and drifted apart. No fossils attributable to this family have been found outside the present-day range.

Habitat

Primarily aquatic, most species inhabit permanent freshwater rivers, streams, lakes, and ponds. Some species are found in seasonal wetlands that are dry for most of the year, while others expand their range into flooded forests during the rainy season. The New Guinea snakeneck turtle (Chelodina siebenrocki) may frequent estuaries and coastal waters.

Behavior

Several species estivate by burying themselves in the mud during periods of extreme drought. Steindachner's turtle (Chelodina steindachneri), an aquatic species that resides in the deserts of Western Australia, is well adapted to the extremely high temperatures and desiccating conditions prevalent for most of the year. This species is resistant to evaporative water loss and stores fluids in accessory bladders in order to survive while buried for the year or two until the rains return.

Feeding ecology and diet

Most species are omnivorous to totally carnivorous; however, the adult Elseya dentata may be completely herbivorous. Many diverse adaptations for specialized feeding are found in this family. The snakeneck turtles of Australia and South America have developed very similar modes of prey capture. Both groups have independently evolved a long neck that is adapted for striking at prey while suspended in the water column. The negative pressure generated by the rapid expansion of the mouth and neck pulls the head toward the prey while simultaneously pulling the prey item into the turtle's open jaws. Matamatas lie in wait on the murky bottom of their aquatic habitat and use a gape-and-suck method similar to that of the snakeneck turtles to capture their prey. Alternatively, some Australian chelids are specialized for feeding on mollusks. As they age, macrocephalic females of the genus Emydura develop enormous skulls that provide the force required for crushing larger prey.

Reproductive biology

Females are generally larger than males; however, the reverse is true in Pseudemydura and Elusor. Males of the latter genus possess an extremely long tail with a unique bony structure that may play a role in copulation. Breeding has been observed in the early spring for many species, but may be year-round in the Tropics. Nests are typically constructed in spring and early summer; however, some tropical species

nest during the winter as well. Clutch size ranges from one to 28 and two or more clutches may be produced per year. The brittle-shelled eggs may be elongate or spherical, 1.2–2.4 in (3–6 cm) in greatest diameter. Incubation may last more than 200 days in species that require a period of diapause (early developmental arrest) for proper development.

A variety of nest chambers are constructed. The gibba turtle may lay its elongate eggs in shallow nests beneath vegetation, whereas the western swamp turtle uses her forelimbs to dig a chamber, which she then enters to deposit her eggs. Researchers in Australia have discovered that, while completely submerged, the female northern snakeneck (Chelodina rugosa) lays her eggs in the muddy bottom of temporary ponds. Development is arrested until the water subsides during the dry season, but resumes in time for incubation to be completed before the pond fills again. Hatchlings may remain in the nest until rain softens the hardened soil plug with which most species seal the nest chamber. In extreme cases emergence may occur nearly two years after the eggs were laid. All species analyzed thus far exhibit genetic sex determination.

Conservation status

Thirteen species are listed as Threatened on the IUCN Red List: six are Vulnerable, four Endangered, and three Critically Endangered. Eight species are listed as Lower Risk/Near Threatened. The western swamp turtle (Pseudemydura umbrina), with known populations of fewer than 400 individuals, may be one of the world's most endangered turtles. Similarly, Hoge's sideneck (Ranacephala hogei) is known from just a few locales in Brazil, and is thought to be Critically Endangered. The major threat to most species is habitat destruction or degradation. Many of the threatened species are being bred in captivity, offering hope for future repatriations. However, active conservation efforts in nature are lacking for most species.

Significance to humans

Many species are consumed locally.

Species accounts

List of Species

Gibba turtle

Mesoclemmys gibba

subfamily

Chelidinae

taxonomy

Emys gibba Schweigger, 1812, locality unknown.

other common names

None known.

physical characteristics

This is a small to medium (up to 9 in [23 cm] maximum carapace length) sideneck turtle with a prominent medial keel on its oval carapace. The nuchal scute is long and narrow. The carapace and upper surfaces of the soft parts are uniformly dark in color. The bridge and underside of the marginals are mostly yellow with some dark mottling at the seams. With the exception of the gular and anal scutes, which are predominantly yellow, the plastral scutes are mostly dark with yellow markings at the edges. The relatively small head has wrinkles of skin that give a marbled texture and appearance. Two small, fleshy barbels are widely separated on the chin. Up to five rudimentary neural bones may be present.

distribution

This species is found in the Amazon basin in northeastern Peru, eastern Ecuador, southeastern Colombia, northern

Brazil, to the Rio Negro of southwestern Venezuela. The distribution is interrupted by the Sierra Nevada de Mérida, but resumes in northeastern Venezuela and continues through Guyana, Suriname, French Guiana, and northeastern Brazil.

habitat

The gibba turtle is found in marshy prairies and slow-moving creeks of lowland tropical rainforests.

behavior

In Trinidad this species is primarily nocturnal; however, basking may occur in the early morning. Although relatively docile, this species may emit a foul-smelling musk from the inguinal glands when handled.

feeding ecology and diet

The natural diet may be omnivorous; however, in captivity it is primarily carnivorous, feeding on small fish, frogs, and worms.

reproductive biology

The nesting season lasts from July to November. The female may nest in vegetation, among the roots of trees, or excavate a shallow chamber to deposit two to four elongate eggs. The small clutch size is offset by the relatively large size (up to 1.8 in [4.5 cm] long and 1.3 in [3.2 cm] wide) of the brittle-shelled eggs. A flexible connection between the carapace and plastron may allow the diminutive female to pass these enormous eggs successfully. Incubation may take up to 200 days under natural conditions.

conservation status

Not threatened. Unfettered habitat loss and degradation, however, may reduce or extirpate populations before they are ever recorded.

significance to humans

They are consumed locally by indigenous peoples, and are also gathered to supply the international pet trade.

Matamata

Chelus fimbriatus

subfamily

Chelidinae

taxonomy

Testudo fimbriata Schneider, 1783, Approuague River, Guisanbourg, French Guiana.

other common names

French: Matamata; German: Fransenschildkröte.

physical characteristics

A medium to large turtle (up to 18 in [45 cm] in carapace length), the matamata is probably the most distinctive of all turtles. This species is recognized by its flattened yet rugged shell, and the rough skin with fringelike appendages that gives the head a triangular appearance when viewed from above. The raised conical knobs on each scute form three keels on the dark carapace to enhance the cryptic appearance of this bottom-walking species. Furthermore, the skin on the broad flat head forms small flaps that are most pronounced above the tympana and waver gently in a slow current. The tiny eyes are set forward and may be of little use in the turbid waters this species inhabits. The tubelike proboscis is used to breathe without fully surfacing.

distribution

Northern South America, including the Amazon and Orinoco Rivers.

habitat

This highly aquatic freshwater species prefers the still waters of oxbow lakes and ponds. Anecdotal evidence suggests that this species survives extended periods in brackish water, but it is not known whether it enters these habitats freely or is deposited there by flooding rivers.

behavior

These turtles are poor swimmers and spend the majority of their time walking along the bottom. When found in rivers, matamatas avoid the current by moving beneath cut banks and submerged logs.

feeding ecology and diet

This carnivorous turtle feeds mainly on small fishes. The matamata lies in wait at the murky bottom of its aquatic habitat where fish may be attracted to the fringelike skin on its head. After locating the fish via vibrational cues detected by the skin and enlarged tympana, it uses a gape-and-suck method to violently draw the prey and a large volume of water into the mouth. The water is then expelled and the fish swallowed.

reproductive biology

Courtship and mating have not been described; however, nesting generally takes place between October and December. In Venezuela, nests are often constructed in the clay soil of steep riverbanks. Eight to 28 spherical (1.4–1.6 in [3.5–4.0 cm] diameter), brittle-shelled eggs are produced annually. The long incubation (200 or more days) suggests that embryos require a diapause or estivation before hatching occurs.

conservation status

Not threatened.

significance to humans

The grotesque appearance of this species discourages consumption, even in regions where other turtle species are readily eaten. Matamatas are frequently available in the pet trade where the adults and juveniles may command high prices.

Common snakeneck turtle

Chelodina longicollis

subfamily

Chelodininae

taxonomy

Testudo longicollis Shaw, 1794, Australasia.

other common names

English: Long-neck turtle; French: Chélidés; German: Schlangenhalsschildkröten.

physical characteristics

This is a medium-sized (to 10 in [25 cm] carapace length), long-neck species. The oval shell is brown and has a shallow central groove that may be pronounced in some specimens. The wide, cream-colored plastron has a dark pattern that follows the seams of the scutes. In contrast to the wide shell, the neck is relatively thin and the small head is distinctly pointed.

distribution

Eastern Australia from Adelaide, South Australia, to Victoria, New South Wales, and Queensland.

habitat

This species prefers slow-moving backwaters, especially weedy lagoons, swamps, and billabongs. It may occasionally be found in the swift currents of streams and rivers.

behavior

When the seasonal wetlands dry up, this species is known to make long overland migrations to the nearest water hole or to estivate terrestrially. It may lie dormant for portions of the summer and winter in shallow burrows beneath vegetation. However, in some regions the snakeneck turtle has been observed to hibernate communally in aquatic sites. This species emits a foul-smelling musk from the inguinal and axillary glands which may serve to deter would-be predators.

feeding ecology and diet

This species is an opportunistic carnivore, mostly feeding on aquatic invertebrates, fish, tadpoles, and crustaceans. It may also feed upon terrestrial insects and carrion if available.

reproductive biology

In the temperate portion of its range, mating has been observed in April and May. Nesting occurs from late September to December. The female deposits eight to 24 brittle-shelled, elongate eggs (up to 1.3 in [34 mm] in length and 0.8 in [20 mm] wide) in nests constructed near the water's edge. A diapause or embryo estivation occurs during development; therefore, incubation may take up to 185 days, although 120 to 150

days are more usual. The observed sex ratio of the resulting hatchlings is independent of incubation temperature.

conservation status

Not threatened. This species is still quite common.

significance to humans

Although many snakenecks are consumed by Aborigines, this "smelly" snakeneck turtle is generally avoided.

Victoria river snapper

Elseya dentata

subfamily

Chelodininae

taxonomy

Chelymys dentata Gray, 1863, upper Victoria River, Northern Territory, Australia.

other common names

English: Northern Australian snapping turtle, northwest snapping turtle.

physical characteristics

This is a medium to large (up to 13 in [34 cm] maximum carapace length) sideneck turtle. The crown of the head has a prominent scale and the thick neck is covered with rough tubercles. The nuchal scute is absent. The posterior rim of the carapace is deeply serrated in juveniles; however, it may become relatively smooth in adults.

distribution

This mostly tropical species is found throughout the Victoria River and nearby drainages of Western Australia and the Northern Territory.

habitat

Rivers, fast-moving creeks, and flooded forests of tropical Australia.

behavior

Adults, especially the larger females, are strong swimmers. Cloacal respiration is well developed in this species. In fast-moving currents the adults may rarely surface.

feeding ecology and diet

These turtles are mostly herbivorous, consuming bark, fruits, pandanus roots, and the seeds and blossoms of flowering plants found along riverbanks.

reproductive biology

In the Daly River nesting occurs in February and March. At least one clutch of 10 brittle-shelled eggs is laid each season. The elongate eggs (2 × 1 in [51 × 28 mm]) hatch after 120 days.

conservation status

Not threatened. Although this species is not on the IUCN Red List, its populations in several river drainages have been negatively affected by pollution.

significance to humans

None known. These highly aquatic turtles live in remote regions of the country and therefore have little direct interaction with humans.

Western swamp turtle

Pseudemydura umbrina

subfamily

Chelodininae

taxonomy

Pseudemydura umbrina Siebenrock, 1901, Australia.

other common names

None known.

physical characteristics

This is a very small sideneck turtle (to 6 in [15.5 cm] carapace length). The primitive skull is nearly roofed over with a slight ventral emargination of the temporal region. The intergular scute is large and completely separates the gulars. A dark border is present at the seams of the plastral scutes. The rough skin of the neck is covered with conelike projections.

distribution

Known only from a few wetlands near Perth, Western Australia.

habitat

Seasonally inundated swamps and marshes.

behavior

The wetlands inhabited by this species experience seasonal periods of intense drought that cause them to dry up completely. Although ambient temperatures may be as high as 104°F (40°C), the turtle survives by burrowing into the sandy soil under decaying plant matter and estivating until the rains return to fill the pools.

feeding ecology and diet

This species is carnivorous, feeding on tadpoles, crustaceans, and the adults and larvae of aquatic insects.

reproductive biology

Mating has been observed in wild populations during June and August. Nesting occurs in October and November. The female digs a large cavity in a sandy bank with her forelimbs and then enters the chamber to lay her eggs. A single clutch of three to five elongate, brittle-shelled eggs (1.4 × 0.8 in [35 × 20 mm]) is laid annually. Although it is unclear when they hatch, neonates appear after 170–220 days. They may be stimulated to emerge by the onset of winter rains that fill the wetlands and signal the beginning of a period when food is abundant.

conservation status

Listed as Critically Endangered by the IUCN. The population has stabilized due to an effective captive breeding program; however, fewer than 400 individuals are known to inhabit the protected wetlands.

significance to humans

The rarity, limited distribution, and cryptic coloration and reclusive behavior of this species have limited their interactions with humans.

Resources

Books

Cann, John. Australian Freshwater Turtles. Singapore: Beaumont Publishing, 1998.

Pritchard, Peter C. H., and Pedro Trebbau. The Turtles of Venezuela. Athens, OH: Society for the Study of Amphibians and Reptiles; Oxford, OH, 1984.

Periodicals

Georges, Arthur, et al. "A Phylogeny for Side-Necked Turtles (Chelonia: Pleurodira) Based on Mitochondrial and Nuclear Gene Sequence Variation." Biological Journal of the Linnean Society 67 (1999): 213–246.

McCord, William P., Mehdi Joseph-Ouni, and William W. Lamar. "A Taxonomic Reevaluation of Phrynops (Testudines: Chelidae) with the Description of Two New Genera and a New Species of Batrachemys." Revista de Biologia Tropical 49 (2001): 715–764.

Patrick J. Baker, MS