GEOG 235. Biogeography

The Elephant Family: An Exercise in Interpeting Cladograms

Introduction: Elephants and most other proboscideans derived from a group called gomphotheres during the Miocene. Changes in skull and tusk architecture that led to modern elephants are first apparent in Stegotetrabelodon. During the Pliocene elephants radiated to become the dominant giant herbivores of Africa, Eurasia, and North America. Large-brained and highly intelligent, elephants are also good swimmers and dispersed to offshore islands. E. celebensis inhabited the island for which it is named (known now as Sulawesi); E. falconeri inhabited Sicily, Malta, and Cyprus. (Although they do not appear on the cladogram below, dwarfed mammoths are known form the Channel Islands off California.)

Elephants, like hominids, may owe their success to their evolutionary capacity to leave tropical forests and adapt to the spreading grasslands of the Pliocene and Pleistocene. Many taxa only disappeared in the late Pleistocene or early Recent. Still surviving are the African elephant, Loxodonta africana, and the Asiatic elephant, Elephas maximus.

Simplified Cladogram of the Elephantidae

Questions. (Answer in complete sentences. Early in the semester you will only be responsible for those questions assigned in class. However, by the end of the semester you should be able to provide answers to all. )

1. Interpret the cladogram for Elephantidae only in terms of the evolutionary relationships of the five genera represented. (Ignore geography for now.) What is the phylogeny of the elephants suggested by the above cladogram?
2. There are two species of elephant extant today (see introduction). How closely related are they?
3. Consider the area cladogram depicted by the colors in the above diagram. Describe the implied origins and dispersal history of the Elephantidae.
4. Combine the patterns of phylogeny and geography you described in questions 1 and 3. Reconstruct a probable biogeographic history of the the species of the Pleistocene and those surviving today. Include what you know about Pleistocene physical geography to describe probable dispersal routes.
5. Which is the only species that indicates elephants crossed Wallace's Line?
6. Which genus was most successful (in evolutionary terms)? Why do you say that?
7. E. falconeri and E. celebensis were both pigmy forms. E. falconeri measured a mere one meter at the shoulder. Why is not surprising that these two species were so small?