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Zoological Society of London

12 April 2018

Turtles that breathe through their genitals and chameleons the size of a human thumbnail are amongst the weird and wonderful reptiles heading for extinction unless urgent action is taken, according to the latest ranking from international conservation charity ZSL’s pioneering EDGE of Existence programme

Roti Island snake
© Ben Tapley

Backed by a study published in journal PLOS ONE, ZSL’s EDGE Reptiles List uses a complex formula to highlight species that are particularly Evolutionarily Distinct and Globally Endangered (EDGE), providing wildlife scientists worldwide with a scientifically rigorous way of focusing their conservation efforts on those animals that effectively represent their own distinct branches of the Tree of Life. 

What is the purpose of EDGE lists?

First established in 2007, EDGE Lists have previously been published for Amphibians, Birds, Corals and Mammals. Now the spotlight has turned to reptiles, resulting in a list of the top 100 conservation priorities for a class of animals that includes turtles, crocodilians, snakes and lizards. Each species is given an EDGE score, which combines extinction risk with how isolated (or unusual) that species is on the Tree of Life, providing an at-a-glance guide to both its evolutionary uniqueness and conservation status. 

Commenting on the launch, EDGE Reptiles co-ordinator Rikki Gumbs, (who led the PLOS ONE paper as part of his PhD studies at ZSL and Imperial College London) said:

“Reptiles often receive the short end of the stick in conservation terms, compared with the likes of birds and mammals. However, the EDGE Reptile List highlights just how unique, vulnerable and amazing these creatures really are. From the world’s largest sea turtles to a blind species of snake found only in Madagascar, the diversity of EDGE Reptiles is breath-taking.” 

The rankings

Iconic species featuring on ZSL’s EDGE Reptiles List include the world’s largest sea turtle, the leatherback (Dermochelys coriacea) which weighs in at #85, and the Mary River turtle (Elusor macrurus), which can stay underwater for up to three days by breathing through its reproductive organs and sits at #30. These turtles are also commonly known as 'punk turtles' due to their distinctive  green Mohican-style hair.

Other stand-outs include the gharial (Gavialis gangeticus), a freshwater crocodile once common across much of Asia but now confined to a handful of rivers in northern India and Nepal. Classified as Critically Endangered by the IUCN Red List of Threatened Species, fewer than 235 are believed to survive in the wild, contributing to its EDGE ranking of #16. 

The Mary river turtle
© Chris Van Wyk

Topping the list overall, with an EDGE score higher than that of any amphibian, bird or mammal, is the Madagascan big-headed turtle (Erymnochelys madagascariensis), while various geckos, chameleons and snakes also feature, including the Round Island keel-scaled boa (Casarea dussumieri), ranked #23 on the list. This strange species, whose closest relative on the Tree of Life was declared extinct less than 30 years ago, can change colour over a 24-hour period, and is also the only vertebrate with a joint in its upper jaw, used to capture and eat its lizard prey. 

Gumbs adds: “Just as with tigers, rhinos and elephants, it is vital we do our utmost to save these unique and too often overlooked animals. Many EDGE Reptiles are the sole survivors of ancient lineages, whose branches of the Tree of Life stretch back to the age of the dinosaurs. If we lose these species there will be nothing like them left on Earth. Using ZSL’s EDGE methodology to create the world’s first EDGE Reptile List, not only are we providing conservation scientists with a quantitative tool to prioritise species for conservation, but we also hope to bring the plight of these weird and wonderful creatures to the public’s attention before they disappear.”

As well as highlighting the world’s most Evolutionarily Distinct and Globally Endangered species, ZSL’s EDGE of Existence programme also works with partners including the National Geographic Society and Fondation Segré to fund early-career conservationists working on the front-line to conserve these animals around the world, through the EDGE Fellowship scheme. 

Commenting on the publication of the EDGE Reptiles ranking, ZSL’s EDGE of Existence Programme Manager Dr Nisha Owen said: “When EDGE launched in 2007, our vision was to shine a light on those species that, if they were allowed to go extinct, would effectively take an entire branch of the Tree of Life with them. Over the intervening decade, our EDGE Fellows have worked to save everything from pangolins and echidnas, to the Chinese giant salamander and Philippine Eagle. We’re delighted to now be expanding the programme to embrace reptiles as well, highlighting a whole additional class of Evolutionarily Distinct and Globally Endangered wildlife while also empowering a new generation of field conservationists striving worldwide to secure their protection.”

See ZSL's EDGE reptiles list in full