In this episode we discuss the interesting extinct and extant mammals that Darwin collected in South America during his voyage on the Beagle. James makes an argument that it was the mammals that Darwin collected that stimulated his idea that species evolve. Sarah talks about why there are so many large mammals in Africa and not in South America, which Darwin thought was odd since vegetation growth is much more dense and thick in the rain forest of South America compared to the plains of Africa.
Some of Darwin's unique species he collected on his voyage.
|From Darwin's journal where he realizes species transmutate|
"In July opened first note book on 'transmutation of Species'—Had been greatly struck from about month of previous March on character of S. American fossils—& species on Galapagos Archipelago. These facts origin (especially latter) of all my views."
From Darwin's Journal July 1837.
Darwin was struck by two interesting aspects of the mammals of South America. The first was that there was a strong correspondence between the mammals that he shot, collected and ate in South America with the fossils he collected in the same area. Three major kinds of mammals intrigued Darwin during his exploration of South America. The first is the sloths, a slow moving herbivore mammal that are adapted to feeding on leaves and fresh buds of the cecropia tree. The first mammal Darwin collected was giant bones from the megatherium, an extinct species of giant ground sloth.
The other mammal type that intrigued Darwin was the fossil giant Glyptodont which looks similar to the extant armadillo still found in from South America up through Central America into the southern regions of North America.
Follow this link to a wonderful National Geographic article that discusses some of these amazing prehistoric mammals.
During the discussion Sarah mentioned the diversity of form prehistoric mammals exhibited in the fossil record. The image below collects some of the various forms of elephants that have evolved over the past 65 million years. Note how diverse the tusks, modified teeth, have developed in the various species.
Josh mentioned how impressive it is to watch vampire bats feed. Here is a link to cool video from National Geographic that shows interesting bat behavior but the narrator tries to hard to be cute.