Galapagos Tortoises
The Galapagos Islands are home to giant tortoises that feed on green vegetation.
Originally, tortoises lived only on Albemarle Island and had dome-shaped shells (see
figure 1and Videodisc pictures 16112 and 16113). Albemarle has a fairly wet climate and
more different kinds of plants than other islands. (see videodisc picture 17370 of plants.)
Today tortoises are found on the other islands as well. On the small islands such as Hood,
there are tortoises that have a ‘saddleback’ shell (see figure 2 and videodisc picture
16115). The ‘saddleback’ shell is above the neck and is big above the hind feet. On the
small islands the climate is drier and there are almost no plants that live on the ground.
Prickly pear cactus (a major source of food and water for these tortoises) has a tree-like
form; the woody trunk holds fleshy green parts of the plant high off the ground.(See
videodisc 17178, 17298 (flower), 17369 (fruit),18407)
Using the information provided here, please answer the question on the next page.
Dome shaped shell
Figure 2
Saddleback shell
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Explanation for Galapagos Tortoises
How would a scientist explain how tortoises with the ‘saddleback’ shell came to be?
Please give a detailed explanation.