I’m reading The Song of the Dodo: Island Biogeography in an Age of Extinction by David Quammen. It’s an excellent book.
In what I’m reading now, Quammen spends some time discussing dwarfism and gigantism and the factors that cause it. (It’s complex, I won’t try to recap). In one of the most fascinating things I’ve come across in a while, he discusses the historical diet of Komodo Dragons (which are really just mind boggling huge monitor lizards).
The question, you see, is what would allow a Komodo Dragon to get so mind boggling huge. A problem arises. While they currently eat deer, goats, and pigs, these animals have only recently arrived to the islands on which Komodos live. Thus the lizards have been around much longer than their food.
One of the disadvantages to becoming as big as a Komodo Dragon is the amount of food needed. Lots and lots of food. Small birds, furry rodents, and buzzing insects just won’t cut it.
It seems there’s only one big animal in the fossil record worth eating if you’re a Komodo Dragon — pygmy elephants.
There are actually two species of small elephant known from the fossil record, occuring in the areas where Komodos now exist. The smaller of the two was only 5 foot high, around the size of a modern cow. The ancestral Komodo Dragons first arriving would likely already have been large monitor lizards. At first, juvenile elephants would have been their meal ticket to survival as the selective pressure to grow bigger pushed their gigantism.
The hypothesis on the historical food source of Komodo Dragons has been advocated by no less than Jared Diamond. (Yes, the ecologist and Guns, Germs, and Steel Jared Diamond). It was originally suggested by an earlier biologist named Walter Auffenberg, who conducted the landmark study on Komodo Dragons in the early ‘70s. Diamond reviewed the evidence and made a case for this hypothesis.
If this hypothesis is false, the fossil record has left no trace of what ancestral Komodo Dragons feasted on. But the idea is intriguing. To me it’s these little tantalizing wonders that make science so fun. I mean, whose heart doesn’t warm a little at the thought of a monstrously big monitor lizard crunching on the bones of a baby pygmy elephant?
And so of course that raises the next question. How did elephants arrive on an island in the first place?
The answer is just as worthy of it’s own post but in short, they swam. Quammen also devotes some discussion to this fascinating topic, including well documented accounts of modern elephants swimming at sea. There were a couple that were documented swimming from a small island to Sri Lanka in 1954. A few years later, a mother and her calf made the same swim in the opposite direction. Reports of elephants swimming to islands exist elsewhere in India, Cambodia, and Kenya.
A more sensational example, which may or may not be true, is an elephant which was reported to have been lost overboard from a ship approaching South Carolina in 1856, and to have swum the remaining 30 miles to shore.
But the best evidence comes from the fossil record. For example, the Channel Islands off the coast of California (I’ve been there to see Island Scrub-Jay by the way) sported a species of pygmy mammoth (yes, the irony is ripe). Scientists assumed that a land bridge was responsible for their presence, yet a closer look revealed that the water between the island and the mainland was deep and that no land bridge ever existed. Also telling is that many other species around during the Pleistocene which left good fossils on the mainland do not occur on the islands. If such a land bridge existed, their absence is not to be expected.
So there you have it. Two good hypothesis that Komodo Dragons ate pygmy elephants and that elephants colonized islands by swimming. See — science is fun!