A gaping hole in the bony steering wheel of a triceratops nicknamed “Big John” may be a battle scar from one of his companions.
The steering wheel that haloes the head of triceratops it’s an iconic part of her look. Equally iconic, at least to paleontologists, are the holes that mar the hull. For more than a century, researchers have debated various explanations for the holes, called fenestrae, from battle scars to natural aging processes. Now, a microscopic analysis of Big John’s partially healed injury suggests that could be a traumatic injury from a fight with another triceratopsresearchers report April 7 in scientific reports.
In the summer of 2021, Flavio Bacchia, director of Zoic LLC in Trieste, Italy, was reconstructing the skeleton of Big John, the largest known triceratops to date, when he noticed a keyhole-shaped fenestra on the right side of his steering wheel. Bacchia then contacted Ruggero D’Anastasio, a paleopathologist at the “G. D’Annunzio” of the University of Chieti-Pescara in Italy, who studies injuries and diseases in human and other ancient animal remains.
“When I first saw the opening, I realized there was something strange about it,” says D’Anastasio. In particular, the jagged edges of the hole were strange. He had never seen anything like it.
To analyze the fossilized tissues around the fenestra, he obtained a piece of bone the size of a 9-volt battery, cut from the bottom of the keyhole. The rest of Big John sold at auction for $7.7 million, the most expensive non-tyrannosaurus rex dinosaur fossil ever.
Looking at the bone under a scanning electron microscope, D’Anastasio and his team found evidence consistent with new bone formation processes typically seen in mammals. New bone growth is usually supported by blood vessels, and in the bone near the edge of the hole, the tissue was porous and strewn with vascular channels. Further from the fenestra, the bone showed little evidence of vessels.
The team found that the irregularity of the hole margins that D’Anastasio had observed was also present at the microscopic level. The rim was dotted with microscopic dimples called Howship’s lacunae, where, in one of the first steps of bone healing, bone cells eroded existing bone to replace it with healthy bone. The researchers also looked at primary osteons, formations that occur during the growth of new bone.
Furthermore, a chemical analysis revealed high levels of sulfur, indicative of proteins involved in the formation of new bone. In mature bone, sulfur is present only in trace amounts.
Taken together, it was clear that this particular fenestra was a partially healed wound. “The presence of healing bone is typical of the response to a traumatic event,” says D’Anastasio.
Scientists can only hypothesize about what happened so long ago. But the location and shape of the wound suggest that Big John’s steering wheel was impaled from behind by a triceratops rival, adding evidence to the idea that triceratops they fought each other (Serial number: 01/27/09). It was probably an initial puncture that was pulled down to create the keyhole shape, the researchers say.
“Pathology is a great tool for understanding dinosaur behavior,” says Filippo Bertozzo, a dinosaur paleontologist at the Royal Belgian Institute of Natural Sciences in Brussels who was not involved in the study. Dinosaur behavior has long been the realm of speculation, he says, but analyzes like these can give insight into the lifestyle of these animals.
He adds that this particular wound “is not a Rosetta stone”, because it is unlikely that all fenestrae are war wounds. “The fenestration remains a great mystery.”
Also a mystery, D’Anastasio says, is why the bone remodeling seen in this triceratops sample was more similar to the healing seen in mammals than in other dinosaurs. And Big John himself might have more secrets.
“We published an aspect, a paleopathological case,” says D’Anastasio. “The complete skeleton of Big John must be studied.”