Turtles are reptiles of the Chelonia order of vertebrates. At some point in the evolution reptiles this order split from the main evolutionary line, according to the Oceanic Resource Foundation. The organization suggests that turtle-like creatures existed during the Triassic period, some 180 million years ago. Two families of sea turtle emerged over time: the Dermochelyidae and the Cheloniidae. Members of both families are among the world's endangered species.
The leatherback turtle is the only member of the Dermochelyidae family. Unlike other turtle species, it has a leathery carapace instead of a shell. Threats to the species start at birth when the mother lays eggs on sandy beaches. Despite her attempts to disguise the young, animal and human predators will try to steal the eggs. Many hatchlings are devoured by birds as they try to reach the sea, further reducing numbers. Another reason the species is on the critically endangered list is that the turtles frequently get caught in fishing nets. The hawksbill turtle, which predominantly lives in tropical waters is also critically endangered for similar reasons to those affecting the leatherback. The hawksbill population has decreased by 80 percent over three generations, according to the IUCN Red List. The IUCN also lists the Kemp's Ridley turtle, which is native to the U.S. and Mexico, in this category.
The green turtle inhabits tropical and sub-tropical waters. This is the only hebivore of the various turtle species. The species is endangered by loss of nesting sites, hunting the adults and over-harvesting eggs, according to the World Wildlife Federation. The IUCN Red List reports a decline of 48 to 67 percent in the mature female population, which has a direct bearing on overall decline. As with other turtle species, the impact of marine fisheries and damage to the turtles' habitat also contribute to the endangered status. The loggerhead turtle is one of the most common turtle species found in the Mediterranean, although that is not his only habitat. The development of tourism around nesting sites along the coasts of Greece and Turkey is a major cause of endangerment to the loggerhead, as is fishing activity.
The olive Ridley turtle has one of the most abundant populations yet it's listed as vulnerable. The WWF says this is because they have a limited number of nesting sites, so any disturbance to these can have major repercussions for the species. The IUCN Red List explains the difficulties involved in collecting accurate data for this species, but concludes that significant population declines are occurring in two main nesting sites in Mexico and Costa Rico.
The IUCN Red List placed the flatback turtle in the vulnerable category during the 1990s. It has now changed that listing to "data deficient." This species is native to Australian waters and has the most restricted habitat range of all turtle species. The IUCN marine turtle specialist group reported population declines due to loss of eggs to predators and a damage to the habitat. It estimated a 20 percent decline in the population. These claims were challenged by an unspecified petitioner. Consequently, the IUCN adjusted the listing.
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