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Image of Madagascar Big-headed Turtle
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Madagascar Big Headed Turtle

Erymnochelys madagascariensis (Grandidier 1867)

Biology

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This turtle occurs in freshwater areas and, like most other side-necked turtles, it is highly aquatic - rarely venturing onto land except to lay eggs, and preferring to bask on logs, rocks or banks surrounded by water (8). It is mainly herbivorous, feeding on plants and the fruits, flowers and leaves of plants overhanging the water. It has also been known to opportunistically feed on small vertebrates (7). Hatchlings and juveniles are predominantly carnivorous (8). Females produce eggs that are spherical to elongate shaped, with leathery shells (7). Normal clutch sizes are in the region of 10 to 25 eggs for a mature female (8).
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Conservation

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The Madagascar big-headed turtle is protected from international trade by its listing on Appendix II of the Convention on International Trade in Endangered Species (CITES) (3). In May 2003 the Turtle Conservation Fund (TCF) released the first ever list of the world's top 25 endangered turtles, which included the Madagascar big-headed turtle (5). The TCF intends to cover a five year 'Global Action Plan' that includes captive breeding and reintroduction projects, trade monitoring, and establishment of rescue centres, local conservation plans and educational programs (5). The Durrell Wildlife Conservation Trust is also independently involved in the conservation and protection of this species (9). It is hoped that these measures will provide the protection that this species needs to survive in its natural habitat.
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Description

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Tortoises and turtles are among the oldest of all living reptiles having appeared about 250 million years ago. They have evolved little since then and their ancient appearance and unique biology fascinates biologists (4). The Madagascar big-headed turtle is, however, one of the most endangered turtles in the world, and is included on the Turtle Conservation Fund's (TCF) top 25 endangered turtles list (5). This species has a hard, dark-brown coloured shell enclosing the soft parts of the body and, as its name suggests, a distinctively large head. Juvenile turtles have a delicate pattern of fine black lines on the shell, but these disappear with age. Its other common name, the Madagascar side-necked turtle also reveals a feature shared by other species in the Pleurodira sub-order: when the head is withdrawn into the shell, the neck bends sideways rather than straight back as in other turtles and tortoises (6). The neck is also long, and allows the turtle to draw breath at the surface of the water without exposing the rest of the body to potential predators (7).
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Habitat

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Inhabits large, freshwater areas such as permanent slow moving rivers, backwaters and lakes (2). Many hatchlings and juveniles move into smaller rivers and even rice paddy-fields where they grow quickly before returning to larger bodies of water to breed when mature (8).
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Range

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This turtle is endemic to Madagascar and occurs in the western lowland areas of the island (2).
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Status

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Classified as Endangered (EN) on the IUCN Red List 2007 (1), and listed on Appendix II of CITES (3).
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Threats

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This species is heavily exploited for food in Madagascar, where it is easily caught in nets, fish traps and by hook and line (8). It is also caught and exported illegally from Madagascar to Asia for the traditional medicine market. Furthermore, land development on Madagascar is a serious threat to this turtle, as it destroys its natural habitats. Clearing forests for agriculture and timber opens up Madagascar's untouched habitat and leads to terrible erosion. Subsequent siltation of rivers and lakes renders the turtles even more susceptible to trapping (5).
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Distribution

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Continent: Indian-Ocean
Distribution: Madagascar
Type locality: "Mouroundava (=Morondava) Tsidsibouque flumina in occidentali insulae Madagasacar littore.
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Madagascan big-headed turtle

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The Madagascan big-headed turtle (Erymnochelys madagascariensis)[1] 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 endangered turtle in the world by a 2018 review.[3] Due to its ancient origins and threatened status, it is ranked as #1 on the EDGE of Existence programme's list of priority reptiles.[4]

Taxonomy

It is a highly evolutionary distinctive species, the only member of the ancient family Podocnemidae found outside of South America. It diverged from its closest relative, Podocnemis, during the Late Cretaceous, about 78 million years ago, possibly following the submergence of a land bridge connecting South America and Antarctica with Madagascar.[5]

Despite Madagascar's long isolation and extensive number of endemic species, the Madagascan big-headed turtle is among the only terrestrial vertebrates whose isolation on Madagascar is thought to be due to Gondwanan vicariance during the Cretaceous; the only other extant Malagasy land vertebrates with this evolutionary history are two genera of blindsnakes (Madatyphlops and Xenotyphlops). All other Malagasy land vertebrates dispersed from the mainland to an already-isolated Madagascar from the latest Cretaceous to the present.[6]

Description

The Madagascan big-headed turtle is one of the most endangered turtles in the world, and is also included in the Turtle Conservation Funds (TCF) top 25 endangered. It has a hard dark brown shell enclosing all the soft parts of the body and, as its name indicates, a very large head. Young turtles have a soft pattern of fine black lines on their shells, but they disappear with age.[7]

Habitat

This species inhabits large areas with freshwater such as permanent slow streaming rivers, backwaters and lakes. Many of the hatching and juvenile turtles move into smaller rivers, where they can grow quickly and safely before going into deeper and larger bodies of water.

Range

It can be found in the western lowland areas of Madagascar.[8]

Threats

The main threat for this species is that they are heavily exploited for food, caught in nets, fish traps and by hooks and lines. It is also hunted for illegal export to Asia for the traditional medicinal market. Another threat is land development as it destroys its natural habitat.

Despite their vulnerability to extinction, they are commonly eaten for food and they are still commonly shipped from Madagascar to Asia to help meet the demand of Asia's traditional medicine market. A captive breeding program has also been started to prevent the species from becoming extinct. The Turtle Conservation Fund (TCF) intends to raise US$5.6 million to cover a five-year 'Global Action Plan' which includes captive breeding and reintroduction projects, trade monitoring, new rescue centers, local conservation plans, and educational programs.

References

  1. ^ a b c Rhodin, Anders G.J.; van Dijk, Peter Paul; Inverson, John B.; Shaffer, H. Bradley (2010-12-14). "Turtles of the world, 2010 update: Annotated checklist of taxonomy, synonymy, distribution and conservation status" (PDF). Chelonian Research Monographs. 5: 000.136. doi:10.3854/crm.5.000.checklist.v3.2010. ISBN 978-0965354097. Archived from the original (PDF) on 2011-07-17.
  2. ^ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  3. ^ Gumbs, Rikki; Gray, Claudia; Wearn, Oliver; Owen, Nisha (2018). "Tetrapods on the EDGE: Overcoming data limitations to identify phylogenetic conservation priorities" (PDF). PLOS ONE. 13 (4): e0194680. Bibcode:2018PLoSO..1394680G. doi:10.1371/journal.pone.0194680. PMC 5894989. PMID 29641585.
  4. ^ "Species". EDGE of Existence. Retrieved 2023-06-07.
  5. ^ Vargas-Ramírez, Mario; Castaño-Mora, Olga V.; Fritz, Uwe (2008-12-20). "Molecular phylogeny and divergence times of ancient South American and Malagasy river turtles (Testudines: Pleurodira: Podocnemididae)". Organisms Diversity & Evolution. 8 (5): 388–398. doi:10.1016/j.ode.2008.10.001. ISSN 1439-6092.
  6. ^ Ali, Jason R.; Hedges, S. Blair (2023-05-04). "The colonisation of Madagascar by land‐bound vertebrates". Biological Reviews. doi:10.1111/brv.12966. ISSN 1464-7931.
  7. ^ "Madagascar big-headed turtle videos, photos and facts - Erymnochelys madagascariensis". Arkive. Archived from the original on 2011-11-09. Retrieved 2012-08-20.
  8. ^ "Madagascar big-headed turtle videos, photos and facts - Erymnochelys madagascariensis". Arkive. Archived from the original on 2011-11-09. Retrieved 2012-08-20.
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Madagascan big-headed turtle: Brief Summary

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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 endangered turtle in the world by a 2018 review. Due to its ancient origins and threatened status, it is ranked as #1 on the EDGE of Existence programme's list of priority reptiles.

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