Fearful scimitars

Sabertooth by Mauricio Anton (2013) Bloomington. Indiana University Press. 243 pp.

This is the natural history of an ecological niche: an ambush predator that captures prey by a throw and pin, with powerful forelimbs and a long, strong back, followed by a bite to the neck, using greatly elongated canine teeth, made possible by jaw adaptations that permit a huge gape and a long, strong neck. The bite results in bleed out and death of the victim. It is argued that this leads to quicker and safer kills than the suffocation method employed by modern big cats on large prey. The author does a remarkable job of tracing the paleontology of successive groups of species that have occupied this role since the Permian, although there seem to have been no dinosaurs that did so.

The illustrations of fossils, reconstructed animals and landscapes are beautifully done, in loving detail. The painstaking anatomical analyses to show how these killing machines worked are clear and persuasive, at least to a non-expert. There are interesting accounts of the constantly changing nomenclature of the fossils.

It would be useful to see similar accounts of modern large cats, hyaenids and other carnivores to get a sense of how the sabertooths fit into the big picture of carnivore evolution and why it is they went extinct instead of the others.

The extinction happened several times, as the successive groups of sabretooths disappeared, and they were not quickly replaced. Sometimes millions of years seem to have elapsed before a new lineage appeared to fill the niche. Indeed, sometimes there were no large felids of any kind for extended periods, if we can trust the fossil record. At other times, a new group may have out-competed the current occupants of the sabertooth niche. One might say that there is room at the top of the food web, but it is a precarious position that isn’t always filled.

Perhaps the most recent occupants of the niche went extinct with the megafauna of the old and new worlds, but could they have been done in by more efficient pantherids? Was their technique only suitable for very specific types of prey that got replaced by more wary and evasive herbivores or did vegetation change doom their hunting methods? Did their very specialized anatomy and techniques simply run out of room for improvement against ever more challenging prey? Anton thinks that their very specialized niche may have left them relatively more vulnerable to shifts in prey abundance. This would be a major factor in the late Pleistocene, along with competition from lions and humans, among others. As the least flexible group, they may have been the first to go.

Does it mean there’s an unoccupied niche now, or are those habitats and resources simply gone?

What other convergences in form and behavior has natural selection produced across time and biogeographic realms? We all know at least a few ecological equivalents, like pangolins and armadillos, or moles, marsupial moles and mole crickets. There’s an interesting one involving modern beetles’ and early rodents’ mandibles, but it isn’t clear what the functional significance is (John Acorn in American Entomologist, Summer 2014, p 128). Thanks to Mauricio Anton for presenting this story so beautifully.

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