Evo­lu­tion­ar­ily Dis­tinct & Glob­ally Endan­gered (EDGE)

he Thy­lacine or Tas­man­ian Tiger (Thy­lac­i­nus cyno­cephalus) is one of the sad­dest exam­ples of how a species can become extinct due to irre­spon­si­ble human behaviour.

The thy­lacine was the largest mar­su­pial car­ni­vore and the last remain­ing rep­re­sen­ta­tive of an entire mam­mal fam­ily. Thy­lacines were once wide­spread across the Aus­tralian main­land, but became extinct there and sur­vived only on Tas­ma­nia. The rea­sons for its dis­ap­pear­ance in main­land Aus­tralia and its con­tin­ued sur­vival in Tas­ma­nia remain a mys­tery, although cli­mate change (Jour­nal of Bio­geog­ra­phy, 27.09.2017), an increase in human activ­ity and the pres­ence of din­goes are high on the list of cul­prits. Only when dri­ven to the brink of extinc­tion by human per­se­cu­tion in Tas­ma­nia as well, the species was finally awarded legal pro­tec­tion in 1936. Sadly, this action came too late for the thy­lacine. Hunted out of exis­tence by Aus­tralian farm­ers who feared that the striped, canine-​like mar­su­pi­als would kill their sheep, the last thy­lacine died in cap­tiv­ity in Hobart Zoo 75 years ago next week, on Sep­tem­ber 7, 1936 (although the species was not offi­cially declared extinct by inter­na­tional stan­dards in 1986). Even more sadly a recent study revealed that the preda­tor was prob­a­bly not a threat to sheep after all. Its notably long jaw, one of the animal’s most dis­tinc­tive fea­tures, could open to an amaz­ing 120 degrees but was too weak to kill sheep (Jour­nal of Zool­ogy, 31.08.2011)

Footage of the last known thy­lacine, and its strik­ing jaw, shot before its death in captivity:

EDGE of Exis­tence programme

The EDGE of Exis­tence pro­gramme is a con­ser­va­tion pro­gramme of the Zoo­log­i­cal Soci­ety of Lon­don (launched in Jan­u­ary 2007), and is the only global con­ser­va­tion ini­tia­tive to focus specif­i­cally on threat­ened species that rep­re­sent a sig­nif­i­cant amount of unique evo­lu­tion­ary his­tory. Using a sci­en­tific frame­work to iden­tify the world’s most Evo­lu­tion­ar­ily Dis­tinct and Glob­ally Endan­gered (EDGE) species, the EDGE of Exis­tence pro­gramme high­lights and pro­tects some of the weird­est and most won­der­ful species on the planet. EDGE species have few close rel­a­tives on the tree of life and are often extremely unusual in the way they look, live and behave, as well as in their genetic make-​up. They rep­re­sent a unique and irre­place­able part of the world’s nat­ural her­itage, yet an alarm­ing pro­por­tion are cur­rently slid­ing silently towards extinc­tion unnoticed.

(Moos)

The method­ol­ogy of iden­ti­fy­ing and rank­ing the EDGE animals

Every species in a par­tic­u­lar tax­o­nomic group (e.g. mam­mals or amphib­ians) has been given a score based on the amount of unique evo­lu­tion­ary his­tory it rep­re­sents, and its con­ser­va­tion sta­tus accord­ing to the IUCN Red List of Threat­ened Species, the world’s most com­pre­hen­sive assess­ment of the con­ser­va­tion sta­tus of plant and ani­mal species. These scores are used to iden­tify and rank EDGE species.

Each species is given an ‘Evo­lu­tion­ary Dis­tinc­tive­ness’ (ED) score, which is cal­cu­lated from a fam­ily tree or phy­logeny. In this phy­logeny (see fig­ure A), species A would have a higher ED score than either species B or C — it rep­re­sents a branch rather than a twig on the tree of life. If species A were to go extinct, there would be no sim­i­lar species left on the planet and a dis­pro­por­tion­ate amount of unique evo­lu­tion­ary his­tory would be lost forever.

A ‘Glob­ally Endan­gered’ (GE) score is then cal­cu­lated for each species based on the 2006 IUCN Red List. Species which are Crit­i­cally Endan­gered receive a higher score than less threat­ened species, which in turn receive a higher score than those not cur­rently in dan­ger of extinc­tion. The two scores are then com­bined to pro­duce an EDGE score for each species. EDGE species are species which have an above-​average ED score and are threat­ened with extinc­tion (Crit­i­cally Endan­gered, Endan­gered or Vulnerable).

A selec­tion of videos fea­tur­ing Evo­lu­tion­ar­ily Dis­tinct & Glob­ally Endan­gered species

Please go to the EDGE pages for fur­ther infor­ma­tion and donation.

Most of the above text is reprinted from mate­ri­als avail­able at EDGE. Orig­i­nal text may be edited for con­tent and length.