CANNIBALISM AMONG APEX PREDATORS:EARLY PERMIAN DIMETRODONTS COMPARED WITH CRETACEOUS DROMAEOSAURID DINOSAURS

Today, cannibalism among apex predators on land is ubiquitous, but paleontology has been slow to identify fossil cases. Recently, strong evidence for cannibalism has been cited for Permian amphibians and large dinosaurs. We examined cases among mid-sized (adult mass c. 80-150kg) Early Permian Dimetrodon and Cretaceous dromaeosaur dinosaurs.

We use the criteria employed to identify cannibalism in human excavations: the suspected victims of cannibalism must show butchering marks that match those for other prey species. Shed teeth document where carcass dismemberment was intense. In the pond mudstones at the Craddock Ranch, Baylor County, TX, shed Dimetrodon teeth are mingled with skeletons of young and adult secodontosaurs, a small-toothed relative of Dimetrodon; the secodontosaurs show a high frequency of damage inflicted on the ends of limb bones and in the broad plates of ilia, scapulae and pubo-ischiadic plates, all areas where major muscles attached. Juvenile and adult Dimetrodon carcasses also are buried with many shed Dimetrodon teeth. Carnivore-inflicted damage to dimetrodont limb bones agrees closely with that seen on secodontosaurs. Dimetrodont-on-dimetrodont cannibalism seems well established. We examined an adult dromaeosaur from the Early Cretaceous Dakota Group of Wyoming; this predator had a body mass close to that of the average Craddock Ranch dimetrodonts. Shed dromaeosaur tooth crowns mingled with the carcass suggest cannibalism. Tooth marks on the dromeosaur match those seen on herbivorous ornithopod skeletons found with shed dromaeosaur teeth in the same area: fine incisions along the edge of the ilium; massive excavations in the lower pubis and lower humerus, probably caused by concentrated blows of incisiform teeth and claws. This case reinforces previous suggestions of cannibalism among mid-sized dinosaurs.

The dimetrodont carcasses show, on average, far more severe damage than do the dinosaur carcasses, suggesting that the dimetrodont feeding style was more mammal-like, with more intense tooth preparation, while the dinosaurs employed more avian-style ingestion, with entire limb segments swallowed whole. Evidence is accumulating that cannibalism was, indeed, ubiquitous in the Deep Past.