Giant extinct vampire bats: bane of the Pleistocene megafauna

In the previous post we looked at the biology and behaviour of vampire bats. This time we're going to take things a little bit further...

Prior to the spread of people and domestic livestock, it is thought that vampires (here we're mostly talking about the Common vampire Desmodus rotundus) most likely fed on capybaras, tapirs, peccaries, deer and birds, though we also know that they sometimes feed on fruit bats and reptiles. Populations that live on islands off the Peruvian and Chilean coasts feed on seabirds and sealions. Now that the Americas are full of millions of cattle, horses, donkeys, pigs and chickens however, vampires have largely switched to these domestic prey, and it is said that the majority of modern colonies now feed entirely on the blood of livestock, particularly cattle, horses and donkeys [image at top from here].

Vampires have done well thanks to this modern influx of domestic animals: it is estimated that between 500,000 and two million head of livestock are lost each year due to vampire bats, equal to between 50 million and a quarter billion dollars (Brown 1994). Deaths are not caused by the bat's feeding activities, but by the diseases they transmit, most notably rabies, murrina and Venezuelan equine encephalomyelitis (VEE). During the 20th century, Common vampire bats appear to have increased in numbers as the numbers of livestock ranches grew, and it also seems that vampires have been moving northwards since the 1950s: in 1967 a Hairy-legged vampire Diphylla ecaudata was shot dead in Texas (Reddell 1968), making it the only vampire yet reported from the USA in modern times.

If vampires do so well when confronted with abundant big mammalian prey, it is tempting to speculate that vampires were more abundant, and perhaps taxonomically more diverse, in the past than they are today. As we all know, the Americas are largely devoid of the megafaunal assemblage that characterized them until just a few tens of thousands of years ago. Could this speculation be true?

It seems that this in fact was the case: vampires were more diverse taxonomically, morphologically and ecologically in the Pleistocene than they are today. To start with, we can say with certainty that two of the three living species - the Common vampire and Hairy-legged vampire - were alive in the Pleistocene: Common vampire fossils are known from Venezuela and Brazil while Hairy-legged vampire fossils have been reported from Mexico and Brazil. To date, fossils of the third living species, the White-winged vampire Diaemus youngi, are unknown, but because phylogenetic studies show that Diaemus is equally as old as Desmodus (Honeycutt et al. 1981, Wetterer et al. 2000, Jones et al. 2002), and because fossils show that Desmodus has been around since the late Pliocene at least, Diaemus must have a ghost lineage going back this far as well. Diphylla diverged before Diaemus and Desmodus did, so it must be even older [adjacent Diaemus image from here].

While we presently lack fossil species of Diaemus and Diphylla, we do have several fossil species of Desmodus. The oldest of them is D. archaeodaptes Morgan et al., 1988 from the late Pliocene of Florida. It was similar in size to the Common vampire but differed in many details, including in having a less rounded cranium, and in possessing a more flexible jaw joint. The braincase of D. archaeodaptes is in fact less modified (compared to the normal phyllostomid condition) than that of the Common vampire, perhaps indicating that it was less specialized for the enhanced terrestrial locomotion practiced by the Common vampire (Morgan 1991).

Stock's vampire D. stocki Jones, 1958 was the most northerly-occurring vampire, and occurred in California and West Virginia as well as Mexico and elsewhere. In being about 15-20% bigger than the Common vampire, it introduces us to the interesting fact that a few extinct vampires were rather bigger than the living species. A species named from Florida, D. magnus Gut, 1959, is regarded nowadays as a synonym of D. stocki. Jones' 1958 paper on D. stocki was submitted for publication 11 days prior to Gut's 1959 paper on D. magnus, and while D. stocki was first named for crania, D. magnus was first named for lower jaws. While writing their descriptive papers, both authors were unaware of the other's work, and subsequent study has shown the bats they named to be the same species. D. stocki had relatively larger and broader cheek teeth than the Common vampire, its upper incisors were different in shape, and its hindlimbs were shorter and more robust. The adjacent image is a D. stocki humerus [borrowed from here].

A species endemic to Cuba, D. puntajudensis (Woloszyn & Mayo, 1974), was first described in 1958 but wrongly identified as referable to the living Common vampire subspecies D. r. murinus, then regarded as an extinct D. rotundus subspecies, and only awarded specific status this century (Suarez 2005). Though similar in size to the Common vampire, D. puntajudensis differed in having a more rounded cranium and shorter face, and it also differed in the anatomy of its jaw joint and in having more robust hindlimb bones. Today there are no vampire bats on Cuba.

Better known than any of these species is the sensationally-named D. draculae Morgan et al., 1988, first described from Venezuela's Cuevo del Guacharo (this is the same cave where Alexander von Humboldt first discovered the remarkable Oilbird Steatornis caripensis in 1799). D. draculae has more recently been reported from Belize and Brazil, and an even bigger giant vampire that represents either a population of D. draculae or a closely related species is also known from Buenos Aires Province in Argentina (Pardinas & Tonni 2000) - a surprisingly southerly record for any vampire. D. draculae is often described as a 'giant vampire'. In relative terms this is true, as its remains are about 25% bigger than those of the Common vampire. Was it really a 'giant' when compared with other bats? At most its wingspan was 60-75 cm and it perhaps weighed about 60 g, so it was about on par with a large horseshoe bat or a small fruit bat. This makes it bigger than the vast majority of microbats, most of which weigh between 10 and 20 g. [adjacent image from here].

Intriguingly, the morphology of some of these vampires suggests that they differed in ecology and behaviour from the living vampire species. Furthermore, of particular interest is the fact that some of these vampires survived until very, very recently. Very recently. Check back soon: all will be revealed....

Refs - -

Brown, D. E. 1994. Vampiro: the Vampire Bat in Fact and Fantasy. High-Lonesome Books (Silver City, New Mexico).

Honeycutt, R. L., Greenbaum, I. F., Baker, R. J. & Sarich, V. M. 1981. Molecular evolution of vampire bats. Journal of Mammalogy 62, 805-811.

Jones, K. E., Purvis, A., MacLarnon, A., Bininda-Emonds, O. R. P. & Simmons, N. B. 2002. A phylogenetic supertree of the bats (Mammalia: Chiroptera). Biological Reviews 77, 223-259.

Morgan, G. S. 1991. Neotropical Chiroptera from the Pliocene and Pleistocene of Florida. Bulletin of the American Museum of Natural History 206, 176-213.

PARDINAS, U., & TONNI, E. (2000). A giant vampire (Mammalia, Chiroptera) in the Late Holocene from the Argentinean pampas: paleoenvironmental significance Palaeogeography, Palaeoclimatology, Palaeoecology, 160 (3-4), 213-221 DOI: 10.1016/S0031-0182(00)00067-5

Reddell, J. R. 1968. The hairy-legged vampire, Diphylla ecaudata, in Texas. Journal of Mammalogy 49, 769.

Suarez, W. 2005. Taxonomic status of the Cuban vampire bat (Chiroptera: Phyllostomidae: Desmodontinae: Desmodus). Caribbean Journal of Science 41, 761-767.

Wetterer, A. L., Rockman, M. V. & Simmons, N. B. 2000. Phylogeny of phyllostomid bats (Mammalia: Chiroptera): data from diverse morphological systems, sex chromosomes, and restriction sites. Bulletin of the American Museum of Natural History 248, 1-200.