Dinosaur Cannibal: Fossil Evidence Found in Africa
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"Eat or be eaten" may have been the mantra for Majungatholus atopus, a large, two-footed carnivorous dinosaur with a bump on its head that roamed Madagascar, the island off the southeast coast of Africa, about 65 million years ago.
Analysis of bones scored by tooth marks suggests Majungatholus was a cannibal that regularly dined on members of its own species and other dinosaurs. The rare, tooth-marked bones are the best evidence to date for a behavior probably common among dinosaurs but difficult to prove.
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Recent analysis of fossils indicates that Majungatholus practiced cannibalism, quite possibly as a result of environmental stress. |
"I don't think this should be unexpected, but because of the nature of the fossil record we get such a limited window on this type of phenomenon. We have such a small sample of what really went down," said Raymond Rogers, a geologist at Macalester College in Saint Paul, Minnesota.
Rogers; together with his wife Kristina Curry Rogers, a curator of paleontology at the Science Museum of Minnesota; and David Krause, a professor of anatomy at Stony Brook University in New York; report their finding in the April 3 issue of Nature.
The trio analyzed hundreds of bones collected in Madagascar since 1993. Unlike most dinosaur fossils, many of these bones exhibit tooth marks. All of the tooth marks and many of the bones were identified as belonging to Majungatholus.
"When you ponder how difficult it is to find conclusive evidence at modern-day crime scenes, it's pretty amazing for us to realize that we have such direct evidence for animal interactions that occurred over 65 million years ago," said Krause, who helped to methodically sift through the evidence to rule out other potential suspects.
The wealth of material collected during the Madagascar expeditions, which are funded in part by a grant from the National Geographic Society Committee for Research and Exploration, is also giving scientists unprecedented detail on the lifestyle of Majungatholus.
"It is really exciting," said Kristina Curry Rogers. "It is a rare window into the world of dinosaurs whose behavior and biology were poorly known. Now we know it was a rabid meat-eater anxious to rip into the flesh of whatever it found."
Dinosaur Cannibalism
Scientists believe that cannibalism was as common among dinosaurs as it is among modern animals. Lions, komodo dragons, foxes, and even pet dogs are among the animals that practice cannibalism today. But evidence for the behavior in the fossil record remains scarce.
Edwin H. Colbert, a former paleontologist with the American Museum of Natural History in New York who died in 2001, presented the first evidence for dinosaur cannibalism 1989. Colbert described two adult specimens of Coelophysis bauri, found with the skeletons of young Coelophysis in their rib cages. The small meat-eating dinosaur lived in North America during the Late Triassic period 228 to 208 million years ago.
Colbert's find was questioned, however, when Robert Gay, a paleontology student at Northern Arizona University in Flagstaff, presented evidence at a conference in October 2002 suggesting the larger animals were merely lying on top of the younger ones, casting evidence of cannibalism into doubt.
Several bones of carnivorous dinosaurs with tooth marks on them from other meat-eating dinosaurs have been found in Alberta, Canada. But scientists have yet to narrow down who was eating who, said Rogers.
The latest find suggests cannibalism owing to bones found with distinctive sets of tooth marks that match both the size and spacing of teeth in Majungatholus' jaws and similar grooves that match the sharp serrations on Majungatholus' blade-like teeth.
The researchers were careful to compare the tooth-scored Madagascar bones to the teeth of other animals living on the island 65 to 70 million years ago. One two-footed, meat-eating dinosaur named Masiakasaurs was ruled out because of its small size: It only grew to one-fifth the size of 30-foot (9-meter) Majungatholus.
Other possible candidates include two large crocodiles (Mahajangasuchus insignis and Trematochampsa oblita). But both animals had teeth too variable in size, spacing, and location to have made the evenly-spaced tooth marks observed on the fossils, said Krause. Nor did the ancient crocodiles have tooth serrations of correct size and spacing to have made drag marks observed on some of the best-preserved bones.
"With these other candidates eliminated, Majungatholus atopus stands accused of cannibalism and is presumed guilty until proven innocent, which, in my opinion, is unlikely to happen," said Krause.
Hans-Dieter Sues, associate director for science and collections and curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, originally described Majungatholus in 1979. He said he was not the least bit surprised to learn of new evidence pointing to cannibalistic behavior by Majungatholus.
"I fail to see what the big deal is," he said. "Cannibalism is very common among reptiles and Coelophysis has long been established as eating small members of its own species—the unpublished recent claims of a student from Arizona notwithstanding."
Rogers agrees that finding evidence for cannibalism among dinosaurs is no big surprise. The behavior is common among living reptiles and mammals, fish, birds, even insects. "But I would certainly like to see comparable evidence presented for Coelophysis," he said.
Hard Life
More than making the case for cannibalism, the evidence collected by Rogers and colleagues helps paint a picture of Majungatholus' life as a hard and stressful venture that caused it eat its own kind—not out of dietary preference but out of a bid to stay alive.
According to Rogers' analysis of rocks and soils where the fossils were found, Late Cretaceous Madagascar was marked by a seasonal and semi-arid climate, much like that of Madagascar today. Flooding occurred periodically. In addition, times of severe drought forced animals to gather around the few remaining sources of water.
"There might have been times of plenty for Majungatholus, but there also might have been times of need, and these stressful episodes could have led to this behavior," he said.
Many of the fossils collected in Madagascar came from large bone beds, where in addition to Majungatholus, the researchers found frogs, turtles, and the remains of long-necked sauropods called titanosaurs that were also a staple in Majungatholus' diet.
The beds suggest to Rogers an oasis, perhaps the remaining source of water and forage that a variety of animals migrated towards in a hard scrabble effort to survive. Such a lean environment can push animals that might not regularly practice cannibalism to seek sustenance in the flesh of their neighbors.
"I think that periodically in this ecosystem animals were pushed to feed on whatever was remaining to feed on," said Rogers. "They were hard times. Majungatholus had to strip all remaining flesh from bones."
This intense feeding behavior, Rogers said, would account for the unusual concentration of tooth-marked bones and suggests that the dinosaurs were so hungry they sought every available bit of flesh.
"The evidence indicates that Majungatholus was a methodical carnivore, capable of focusing on particular behaviors," said Curry Rogers. "It worked long and hard to procure a meal."
