It might be easier to “mummify” dinosaurs than scientists thought.
Unhealed bite marks on fossilized dinosaur skin suggest that the carcass of the animal was cleaned before being covered with sedimentresearchers report Oct. 12 in PLUS ONE. The find challenges the traditional view that burial very soon after death is required for dinosaur “mummies” to form naturally.
The new investigation focuses on Dakota, a Edmontosaurus fossil discovered in North Dakota in 1999. About 67 million years ago, Dakota was an approximately 40-foot-long duck-billed dinosaur that ate plants. Today, Dakota’s fossilized limbs and tail still contain large areas of well-preserved, fossilized scaly skin, a striking example of dinosaur “mummification.”
The creature is not a true mummy because its skin has turned to rock, instead of being preserved as real skin. Researchers have come to refer to those fossils with exquisitely preserved skin and other soft tissues as mummies.
In 2018, paleontologist Clint Boyd of the North Dakota Geological Survey in Bismarck and colleagues began a new phase of cleaning and examining the dinosaur fossil. The team found what appeared to be skin tears on the tail and puncture holes in the animal’s right front leg. To investigate what might have caused the skin markings, the researchers teamed up with Stephanie Drumheller, a paleontologist at the University of Tennessee at Knoxville, to remove additional rocky material around the markings.
The holes in the skin, particularly those on the forelimb, are much like the bite wounds of prehistoric relatives of modern crocodiles, the researchers say. “This is the first time it’s been seen in dinosaur soft tissue,” says Drumheller.
Because the markings on the tail are larger than those on the forelimb, the team believes that at least two carnivores chewed the Edmontosaurus corpse, probably as scavengers because the wounds did not heal. But scavenging doesn’t fit the traditional view of mummification.
“This assumption of rapid burial has been built into the explanation of mummies for a while,” says Drumheller. That clearly wasn’t the case for Dakota. If the scavengers had enough time to eat her carcass, then the deceased dinosaur had been out in the open for a while.
Looking at Dakota’s deflated skin envelope, wrapped down to the underlying bone with no muscles or other organs, Drumheller had an unexpected “eureka moment,” he says. “I had seen something like this before. It just wasn’t in the paleontological literature. It was in the forensic literature.”
When some smaller modern scavengers, such as raccoons, feed on the internal organs of a larger carcass, the scavengers cut open the body of the carcass. Forensic investigation showed that this hole provides an escape route for gases and fluids from further decomposition, allowing the remaining skin to dry out. The burial could happen later.
The researchers “have a very good point,” says Raymond Rogers, a researcher at Macalester College in Saint Paul, Minn., who studies how organisms break down and fossilize and was not involved in the research. “It would be highly unlikely for a corpse to reach advanced stages of desiccation and also experience rapid burial. These two generally assumed prerequisites for mummification appear to be somewhat incompatible.”
Fossilization of soft tissues, such as skin or brains either fleshy head combs – is rare, but not unheard of (Serial number: 8/20/21; Serial number: 12/12/13). “Yes [soft tissue] it requires a spectacular confluence of strange events for it to fossilize, it’s much more common than you’d expect if that were the case,” says Drumheller. Perhaps, then, mummies originating from common cadaver destinations could explain this.
But while the dry, “jerky-like” skin might survive long enough to be buried, the conditions involved aren’t necessarily common, says Evan Thomas Saitta, a paleontologist at the University of Chicago who wasn’t involved in the study.
“I still suspect that this actual process is a very precise sequence of events, where if you get the timing wrong, you end up without a dinosaur mummy,” he says.
Understanding that sequence of events, and how common it is, requires discovering how fossilization proceeds after a mummy’s burial. This is an area of research that Boyd says he is interested in looking into next.
“Is it just the same fossilization process as for bones?” he asks. “Or do we also need a different set of geochemical conditions to fossilize skin?”