The Big-headed Amazon River turtle (''Peltocephalus dumerilianus''),"''Peltocephalus dumerilianus'' "
The Reptile Database. also known as the big-headed sideneck, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Podocnemididae Podocnemididae is a family of pleurodire (side-necked) turtles, once widely distributed. Most of its 41 genera and 57 species are now extinct. Seven of its eight surviving species are native to South America: the genus '' Peltocephalus'', with tw ...

Taxonomy

An additional, much larger species of ''Peltocephalus'' is known, the extinct '' Peltocephalus maturin''. ''Peltocephalus'' is the most basal podocnemidid genus, splitting off in the Cretaceous around 86 million years ago.

Etymology

The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''dumerilianus'', is in honor of French

herpetologist Herpetology (from Ancient Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is a branch of zoology concerned with the study of amphibians (including frogs, salamanders, and caecilians (Gymnophiona)) and reptiles (in ...

André Marie Constant Duméril André Marie Constant Duméril (1 January 1774 – 14 August 1860) was a French zoologist. He was professor of anatomy at the National Museum of Natural History (France), Muséum national d'histoire naturelle from 1801 to 1812, when he became pr ...

Description

Peltocephalus dumerilianus female and male tails

The largest specimen recorded possessed a long carapace and weighing . However,

Alfred Russel Wallace Alfred Russel Wallace (8 January 1823 – 7 November 1913) was an English naturalist, explorer, geographer, anthropologist, biologist and illustrator. He independently conceived the theory of evolution through natural selection; his 1858 pap ...

recorded coming across a remarkably large ''Peltocephalus'' specimen that eight people fed on with enough for leftovers for the next day. The exact size of this specimen is unknown.

Sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

is present like in most turtles, with males being larger with wider heads and longer tails. It is considered morphologically similar to another podocnemidid, the

Madagascan big-headed turtle The Madagascan big-headed turtle (''Erymnochelys madagascariensis'') is a turtle native to the waters of permanent slow moving rivers and lakes in western Madagascar. These turtles are critically endangered and have been evaluated to be the most ...

, which is similarly omnivorous unlike the herbivorous genus ''

Podocnemis ''Podocnemis'' is a genus of aquatic turtles, commonly known as South American river turtles, in the Family (biology), family Podocnemididae. The genus consists of six Extant taxon, extant species occurring in tropical South America.

Geographic range

''P. dumerilianus'' is found in

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

( Amazonas,

Pará Pará () is a Federative units of Brazil, state of Brazil, located in northern Brazil and traversed by the lower Amazon River. It borders the Brazilian states of Amapá, Maranhão, Tocantins (state), Tocantins, Mato Grosso, Amazonas (Brazilian st ...

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

, and possibly in

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

Habitat

The preferred natural

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s of ''P. dumerilianus'' are rivers and freshwater swamps, preferring

igapó (, from Tupi language, Old Tupi: "root forest") is a word used in Brazil for Blackwater river, blackwater-flooded forests in the Amazon biome. These forests and similar swamp forests are seasonally inundated with freshwater. They typically occur ...

and other

blackwater river A blackwater river is a type of River#Classification, river with a slow-moving channel flowing through forested swamps or wetlands. Most major blackwater rivers are in the Amazon Basin and the Southern United States. The term is used in fluvial ...

systems.

Behaviour

While not territorial, its strong jaws have been recorded severely injuring a child's knee, and

ribeirinhos The Ribeirinhos are a traditional rural population in the Amazon rainforest, who live near rivers. Their main activities are fishing and farming on a small scale, for their own use. They usually live in pile dwellings and travel by motor boats ...

often report them mutilating the fingers of adults. Even juveniles have bites powerful enough to tear chunks off a conspecific's plastron. Captive specimens can be highly aggressive towards other turtle species, even killing them. Less agile swimmers than other podocnemidid turtles, they are generally thought to not disperse across long distances; one 19-year-old male was captured in the same stream where he was first tagged as a hatchling.

Diet

Like all extant podocnemidids, ''P. dumerilianus'' is a plant-based omnivore, though includes the largest proportion of animal matter in its diet among its family. Nevertheless, fruits and seeds can represent up to 85% of its diet. It has a preference for apple snails when available. As undigested seeds have been observed in the intestines, it may be an important seed disperser. It is an opportunistic predator, usually crawling around the bottom of water bodies searching for mollusks, fish, insects, and even scavenged carrion from other reptiles and mammals. Adults have been observed sitting immobile underwater with their jaws open, possibly trying to catch prey with a sit-and-wait approach also seen in alligator snapping turtles.

Reproduction

Like all other turtles, ''P. dumerilianus'' is

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

. Unlike other members of its group which lay their eggs on sandy beaches, the Big-headed Amazon River turtle prefers concealed nests.

Conservation

Although listed as Vulnerable by the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

, the assessment was made in 1996. This may no longer be reflective of the level of threat against this species, as there has been

habitat degradation Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...

through river contamination by mining activities and pesticides, deforestation, and the construction of hydroelectricity infrastructure. Additionally, illegal gold mining evicts over 1000 of the turtles per year (although this may be an underestimate), and may then be sold on the market at a price of up to USD $50 per turtle. The species is hunted for consumption in its range. During Alfred Russel Wallace's expedition along the

Negro In the English language, the term ''negro'' (or sometimes ''negress'' for a female) is a term historically used to refer to people of Black people, Black African heritage. The term ''negro'' means the color black in Spanish and Portuguese (from ...

and

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers approximately 1 million km2, with 65% of it in Venezuela and 35% in Colombia. It is the List of rivers by discharge, f ...

rivers, he and his team often fed on it. He records that while indigenous people in the upper Rio Negro often hunted the species, and penned them when there was scarcity of food, they also told him that the species was getting rarer.