Identify the Main Point or Issue in the Following Passage

Essay

Identify the main point or issue in the following passage, and decide whether the rest of the passage offers reasons for the main point (such as, whether the passage contains an argument), whether it illustrates (provides examples for) the main point, whether it explains the point, is irrelevant to the point, and so on.
"Here's why big animals stay warm easier: An elephant is ten thousand times heavier than a rabbit and produces body heat one-tenth as rapidly. But still the elephant keeps warmer because it has much less skin area per pound and much more body heat per square inch of skin."
-Adapted from Robert Bakker, The Dinosaur Heresies