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Turtles and their land-based relatives, the tortoises, comprise a unique group of reptiles collectively called chelonians (in the Order Testudines). These animals are distinguished by a hard oval shell, or carapace, covering the internal organs. The turtles are aquatic and have flippers adapted to propelling them through water as opposed to the stumpy legs of the land-based tortoises which are best suited for moving across terrain.

NOTE on terminology: In most-English speaking countries, turtles refer to those species live in the sea or in fresh water, whereas tortoises live on land. In the U.S., turtles refer to both aquatic and terrestrial species; e.g., the box turtle Terrapene carolina carolina would, in England, be called a tortoise. (For more details, see the Wikipedia article on turtles). In this account, we will use the standard English convention.

Among Amazonian aquatic turtles most attention has been given to the giant river (or arran) turtle because of its commercial value. Here we will discuss the small species of turtles found in Amazonia.

Amazon species belong in a relatively primitive group, Sidenecked Turtles (the aquatic kind), belonging in the family Pelomedusidae (some authorities place them in a different family, Podocnemididae). Unlike most chelonians that retract their head into the shell in a vertical motion, the side-neck turtles swing their heads to the side, to rest in a gap between the upper and lower halves of the shell. A number of unique skeletal adaptations are associated with this mechanism. Taxonomists consider this to be the more primitive condition, and date early species as far back as the Cretaceous, the Age of the Dinosaurs.

These turtles vary mostly in the ornamentation of the carapace (shell) with most measuring about 10 to 15 inches when fully grown. The Podocnemis genus has a smooth gently rounded shell often greenish brown, whereas the matamata bears protuberances and horns on its black-brown carapace, presumably affording it some kind of protection.

The commonest species is the yellow-spotted river turtle Podocnemis unifilis (see photo), which has yellow-orange spotting on the head and a single barbel, or feeler, on the lower jaw. The spots are brighter and larger on juveniles. It grows from 1 to 2 feet in length, with the female up to twice the size of the male.

Unlike so many other groups of animals in the Amazon, the turtles are relatively few in species, about 20 according to John Kricher (1997), many fewer than are found in the smaller Mississippi River basin.

The turtle prefers swampy areas, lakes and the margins of slow-moving rivers. It likes areas where plenty of vegetation lines the water's edge. Here there is plenty of food and a chance to head for cover if needed.

Turtles like areas where they can come out of the water to bask, and slip back in just as easily. While feeding or avoiding predators, they roam the bottom of the water body, propelling themselves across the mud.

The commonest species, the yellow-spotted river turtle, ranges across northern South America, but the extent of its range is not well documented.

Most Amazon aquatic turtles are at least partly carnivorous, feeding on slow-moving invertebrates such snails, freshwater crabs, worms and aquatic insects. Some species may prey on fish and amphibians, or may even take floating fruit, water plants or carrion. The yellow-spotted river turtle feeds primarily on leaves, flowers and fruits that drop from overhanging vegetation into the water.

Little is known about the breeding habits of these turtles. Females lay eggs in burrows or under nests of vegetation, producing clutches of up to 100.

Courtship among the yellow-spotted side-necked turtle begins when the male nips at the female's tail. Still in the water he swims on top of her and maneuvers his tail underneath the edge of her shell. His mating organ then moves to toward the cloaca of the female and mating thereby takes place.

Nesting of the yellow-spotted river turtle has been recorded as nesting year-round, although it may have seasonal preferences. For example, in areas of flooded forest (varzea) it would make sense to nest after high water so the nest was safe from accidental flooding. Hence the female lays eggs at the height of the dry season so that the nest is not washed away by rainy season floods.

The females scoop out shallow nests in sandy river banks. This species has a recorded clutch size of up to 40, whereas the average 15-20. From 60 to 160 days after they are laid, the eggs hatch. About the size of a quarter when they hatch, the hatchlings must fend for themselves and fall prey to herons, caimans, and large fish.

Turtles are at risk of extinction from a variety of causes. The most widespread species, the yellow-spotted river turtle, is listed on CITES Appendix II, due to heavy hunting pressure. People eat the adults and the eggs. Fishermen may use them as bait. Egg-hunting is particularly damaging to the population as it does not give the population a chance to recover.

Scientists have proposed farming turtles but most efforts have focused on the giant river turtle, whereas the pressure on smaller species continues unabated. Other causes of turtle mortality from human activity are loss of habitat due to urbanization and hydroelectric projects, and ending up as bycatch in fishermen's nets. In one protection program, guards in Brazil are appointed to protect river banks where turtles are expected to lay eggs.

Kricher J. 1997. A Neotropical Companion. Princeton University Press.


Wikipedia: Turtle
Animal Diversity Web: Pelomedusidae
EMBL Reptile Database: Family Pelomedusidae (African Mud Terrapins) Pelomedusidae
World Chelonian Trust: Podocnemis unifilis (Yellow-spotted Amazon River Turtle) Care
Sedgewick County Zoo: Yellow-Spotted Amazon River Turtle
Wikipedia: Yellow-spotted river turtle
Fundación Peruana para la Conservación de la Naturaleza: Threats and Conservation Status
Turtles of the World: Yellow-spotted river turtle
Woodland Park Zoo: Yellow-spotted Side-necked Turtle
EMYSystem Species Page: Podocnemis unifilis
ITIS Standard Report: Podocnemis unifilis

Mainly photos
World Chelonian Trust: Podocnemis Gallery
Dr. Peter Uetz: Podocnemis_sextuberculata.jpg
Amazon River Turtle (Podocnemis sextuberculata)
Fundacion Peruana para la Conservación de la Naturaleza: Taricaya
ARKive: Yellow-headed sideneck turtle - Podocnemis unifilis
Digimorph: Skull of Podocnemis unifilis, Yellow-spotted Amazon River Turtle
Discover Life - Podocnemididae: Podocnemis unifilis
NAS - Nonindigenous Aquatic Species Podocnemis unifilis

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