Paleontologists Probe ‘Apex’ the Stegosaurus for Its Secrets

There are no apparent predators in sight, but the 150-million-year-old Stegosaurus fossil now on display in the American Museum of Natural History still maintains a obstinately defensive posture, spiked tail held aloft. Measuring 11.5 feet (3.5 meters) tall and 27 feet (8.2 meters) long, the fossil, called Apex, is thought to be the largest and one of the most complete dinosaur remnants ever dug up from the earth, and visitors to the museum can admire it at the Gilder Center entrance for the next four years.

Apex was first unearthed in 2022 by a team led by commercial paleontologist Jason Cooper. It was found within the Morrison Formation, just outside of the aptly named town of Dinosaur, Colo. Ken Griffin, the billionaire owner of the financial firm Citadel, bought the fossil for $44.6 million in an auction last fall that shattered records; he agreed to lend it to the museum starting last December.

Some scientists have expressed concern that they are being priced out of their research field by private collectors, and have become too dependent on hopes of their generosity to conduct research. For now, the museum is happy to have obtained a fossil such as Apex, whose near-completeness is a boon not just for visitors but also for the museum’s Division of Paleontology, which will study the specimen’s life history with help from the data of existing collections.

To start, museum paleontologists are extracting samples from bones to find out more about the growth of the animal over time, “like how tree rings tell you more about the inside of a tree trunk,” according to paleontologist Roger Benson.

“We’ve had a huge amount of experience, both working in the field to discover new fossils, and then extracting the bones from the rock in the lab here, and also making what we call histological sections. That means taking samples that tell us about the evidence for growth inside of the bones, which is the microstructure of the bone,” he said.

More than 254 out of about 320 bone elements are from the original specimen, with the remaining, missing pieces substituted with 3D-printed and sculpted components. Each bone the paleontologists study can yield reams of information, but is also a test of patience and care.

The paleontologists first mount the specimen in a secure cradle, then extract the sample using a wire saw, a very fine wire that moves continuously and cuts very slowly. The extraction alone usually takes hours.

“Because it’s operating slowly, you can anticipate and deal with potential problems,” said Benson.

“After the extraction is done, we’ll cast the sample, and the place where we extracted the sample will replace that place with an exact cast of the missing portion, and that’ll continue to support the specimen. So, I mean, we’re confident that we can do that without serious issues, but it’s a very precise process.”

Through that process, museum paleontologists have already made some conclusions about the Stegosaurus now called Apex. One feature they noticed was that Apex had few, if any, bone pathologies, or bones that have been damaged or show signs of disease, such as abnormal growth, indicating that it led a relatively untroubled life despite its age and large size.

Many fossils that Benson has studied did not have such a clean slate, with some bearing as many as 10 injuries on their skull. Compared with those fossils, it’s far more likely that Apex died of old age, he said.

The Stegosaurus has long enjoyed status as an easily recognizable and popular dinosaur, with its fearsome spiked tail and splendid back-plates. But with the discovery of fossils like Apex and the advent of new technology, much more knowledge of these creatures are now accessible.

One emerging field in paleontology is geochemistry, which centers on analyzing the chemical composition of preserved fossils and the organic material within the bones. While it’s difficult to obtain non-degraded DNA from any fossil older than 2 million years, older fossils like Apex still retain some of the original biomolecules.

One startling hypothesis that can potentially be proven through geochemistry is that the Stegosaurus, unlike most other dinosaurs, is cold-blooded.

“It was from a really exciting paper that was published a couple of years ago,” said Benson. “If a Stegosaurus is in fact cold-blooded, that would mean it might have slower metabolic rates and slower growth and other aspects.”

Still, Benson cautioned, it’s a tentative hypothesis at the frontiers of scientific knowledge. And yet, it raises the possibility that there’s variation in the metabolism of dinosaurs. Given the apparently well-established knowledge about dinosaurs, it turns out we may not have understood them that well all along.