EPOW - Ecology Picture of the Week

Two Tortoises, One Scute

left:  Seychelles or Aldabra Giant Tortoise, Dipsochelys dussumieri, Seychelles Islands
right:  Galapagos Giant Tortoise, Geochelone vandenburgi, Isabela Island, Galapagos Islands, Ecuador

Explanation:  QUICK, can you tell the difference between these two tortoises?  Are they the same?  

Well, if you moused-over the above image, you saw the difference highlighted.  One key difference is the presence of a "scute" just above the head on the tortoise on the left, and its absence on the tortoise on the right.  

Scutes are plates or shields that comprise the covering of a turtle's shell.  The one highlighted is called the nuchal scute which is the plate just over the turtle's head in some species.  In this case, its absence is one of the diagnostic features of the set of giant tortoises that inhabit the Galapagos Islands, even though both of these species belong to the same family of land tortoises, Testudinidae.  

I encountered the tortoise on the left -- a Seychelles or Aldabra Giant Tortoise -- along the shores of Lake Baringo in the Rift Valley of Kenya in eastern Africa.  This tortoise was immense in size, and likely immensely old, and obviously had been transported here at one time from its home in the Seychelles, an archipelago of some 115 islands in the western Indian Ocean off the shore of Kenya, north of Madagascar.  This species is a native of Aldabra Atoll in the Seychelles.  

I found the tortoise on the right -- one of the Galapagos Giant Tortoises -- at Urbina Bay on Isabela Island of the Galapagos Island archipelago in the eastern Pacific Ocean off the mainland of Ecuador.  

So here is a small lesson in paying attention to what may seem to be very minor differences when observing wildlife.  
  

These individuals represent the last two species of giant tortoises remaining in the wild.  Six other giant tortoise species have gone extinct, and two other species are extinct in the wild but apparently still occur in captivity.  

How amazing and incredible it is to see these rarities, and how important it is to ensure their persistence in the wild, given the fate of most of their giant cousins.  

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