Dark Banquet - Bill Schutt [14]
Sadly, of the thirty-four recognized genera in the family Equidae, only one survives. What does remain, however, from this once diverse and widespread group, is a transitional fossil record that is unsurpassed in its ability to shed light on the relationship between environmental change and the accompanying structural modifications that can accumulate in generations of creatures living in those changed environments.
Unfortunately, no such easy-to-interpret transition exists for vampire bats or many other organisms, for that matter. Compounding the fact that bat bones are extremely delicate, fossils from creatures that inhabited tropical regions are relatively rare. This is primarily because the remains of the newly dead in such environments are usually dismantled, eaten, and destroyed—with little chance of preservation in the fossil record. The vast majority of vertebrate fossils come from creatures that lived near shorelines—beaches, rivers, or even ponds. Here, rapid sediment deposition could give the dead at least a small chance at becoming fossilized.
Regrettably, this phenomenon, along with the fact that most fossilized creatures had hard parts like shells or bones, led some paleontologists to describe the fossil record as “biased.” Not a bad description, really. But problems arose when deceptively named creation scientists intentionally took the term (and others) completely out of context in an effort to discredit the theory of evolution and insert their own faith-based beliefs.*24
So how do scientists think vampire bats evolved? In cases like this one, where the fossil record isn’t very helpful, researchers often rely on knowledge of what works for organisms living today—preferably those that are closely related to the ancient creatures in question. Prehistoric environments are also important since they provide information on the climate and surroundings in which the ancient critters existed. For the most part, this technique has led to the following hypotheses on the origin of blood feeding in bats.
In one scenario, protovampires fed on blood-engorged ectoparasites like ticks that were feeding on large mammals. Seemingly, the ectoparasite hypothesis was founded upon the knowledge that roughly 70 percent of bats are insectivores (although ticks are certainly not insects), combined with purely anecdotal reports that vampire bats consume parasitic moths. During my graduate studies, I added a modification to this hypothesis by suggesting that if protovampires had in fact gotten their first blood meal by dining on ectoparasites, then blood feeding might actually have originated during mutual grooming behavior. Vampire bats are extremely social animals and studies have shown that they spend approximately 5 percent of their time grooming each other. During such behavior, protovampires may have obtained their first taste of blood from the very same tick and bed bug species that commonly parasitize modern vampire bats (and, indeed, most bats).
Bat biologist Brock Fenton suggested that the small size of ectoparasites, combined with the difficulty of locating them on another animal, made the ectoparasite hypothesis improbable. He was also troubled by the fact that ectoparasites have a worldwide distribution, yet vampire bats are restricted to three New World species. In other words, if ectoparasites were found pretty much everywhere, feeding on all sorts of vertebrates, then why weren’t there more species of vampire bats in existence? I’ll address this question momentarily.
Another hypothesis on the origin of vampire bats was proposed by Fenton, who suggested that blood feeding might have evolved from protovampire bats feeding on insects and their larvae present in and around wounds on large mammals. These wounds,