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By Root 786 0

blood feeding would have evolved again. As Stephen J. Gould explained in his outstanding book Wonderful Life, if we could somehow rewind the tape of the earth’s history and then allow it to replay, there would be no guarantee that evolutionary outcomes would turn out exactly the same. Gould’s point was that contingency (i.e., chance occurrences) had a great deal to do with which organisms survived to evolve over historical time. If, for example, the climate shifts that led to a reduction of North American forests had never occurred (or differed in some slight way), then, quite possibly, the modern horse as we know it would never have evolved. Similarly, if a meteor had missed the earth some sixty-five million years ago instead of slamming into an area near the current Yucatán Peninsula—maybe small, bipedal ostrich dinosaurs (Ornithomimosaurs) would now be trashing the earth’s resources, instead of humans. With regard to the evolution of vertebrate vampires, far more subtle changes might have produced Old World vampire bats, vampire birds, or even blood-feeding rodents. For whatever the reasons, though, in the conditions that actually existed, a single group of New World leaf-nosed bats underwent the evolutionary changes that would ultimately result in the only obligate mammalian sanguivores.

As an alternative to previous speculation on vampire bat origins, I proposed the arboreal-feeding hypothesis. Basically, this suggests that protovampires may have been foraging in much the same manner as several species of vampire bat relatives do today, that is, by feeding in the trees on small vertebrates like birds, bats, lizards, rodents, and marsupials.

In that regard, Diaemus youngi and the hairy-legged vampire bat, Diphylla ecaudata, both hunt in trees—feeding primarily on perching birds. There are, however, significant anatomical and behavioral differences between them that provide hints about the evolution of their feeding behavior. While a number of primitive anatomical features indicate that Diphylla originated as an arboreal blood feeder, evidence points to a recent return to the trees for Diaemus, where its ability to prey on birds would have reduced competition with the wildly successful, terrestrial hunter Desmodus rotundus.*27

While the fossil record for bats is scanty, it does indicate that there were carnivorous members of the Neotropical bat family Phyllostomidae present ten million years ago, right around the time vampire bats are thought to have evolved. There were also major climactic changes occurring in South America at this time, with evidence suggesting that formerly vast tracts of forest became isolated islands (refugia) surrounded by grassland. Similar to the horse evolution story in North America, these forest refugia and their surroundings may have become perfect staging grounds for evolutionary change—this time among the phyllostomids.*28

Evidence indicates that at least one phyllostomid alive at this time was a carnivore. Because of its size, Notonycteris may have stalked its prey through the branches before subduing it with bites, in much the same manner as its oversized modern counterpart, Vampyrum spectrum. It is very likely that Notonycteris and other ancient phyllostomid relatives would have encountered an increasingly diverse arboreal fauna, as marsupials like opossums, as well as primates, sloths, and larger forms of birds, took up residence in the trees during this time. Some of these new inhabitants would have been too large for carnivorous bats to stalk and kill using previously existing attack strategies. Over time, isolated populations of some carnivorous phyllostomid may have undergone a behavioral shift that allowed them to exploit these larger animals as a food source.†29 Maintaining a stealthy approach to their potential prey, these protovampires might have started biting larger species as they slept in the branches at night. Similar to Brock Fenton’s wound-feeding hypothesis, these early protovampires may have supplemented their normal diets with flesh and blood, in this case from