Paleontologists have uncovered evidence of previously unrecognized soft tissue structures in the cheek areas of various dinosaur species. This discovery deepens our understanding of dinosaur anatomy and underscores the limitations of current methods for reconstructing anatomical features that are not well preserved.

“Such examples of soft anatomy in dinosaurs are rare due to the degradation of muscles and tissue over time,” remarked Henry Sharp, a paleontologist from the University of Alberta.

“While bones can be excavated and assembled into semi-complete skeletons, for a long time, there was no effective way to discern the muscles and tissues present in dinosaurs.”

“In the 1990s, existing systematic brackets utilized the closest living relatives of dinosaurs—alligators and birds—to gain insight into their ’tissues and muscles.’

“However, this approach has its shortcomings: the muscles reconstructed in dinosaurs are those found in alligators and birds.”

“What if dinosaurs possessed their own unique muscles that aren’t present in their modern relatives, or if birds have lost or adapted their original musculature?”

“While examining a skull of Edmontosaurus, affectionately named Gary, I noticed a distinctive flange structure atop the bone near its prominent cheek.”

“As I delved deeper, I struggled to find answers.”

“There were large, corrugated sections of the skull. In a mammalian skull, I would interpret that as cheek muscle attachment. Yet, reptiles are not supposed to exhibit such muscle structures.”

“This sparked intrigue. What if this finding contradicted existing models of dinosaur musculature?”

To gain a clearer understanding of this aspect of dinosaur anatomy, Sharp and his colleagues from the University of Alberta, the University of Toronto, the Royal Museum of Ontario, and the University of New England began investigating similar regions in the skulls of other dinosaur species, uncovering evidence of analogous structures.

“The findings were consistently located in the same area. This strongly suggests that it represents a muscle or ligament,” Sharp explained.

To validate their hypothesis regarding this bone area being a site for some type of soft tissue structure, researchers meticulously cut thin sections of dinosaur bone.

“Soft tissues, such as muscles and ligaments, are anchored to the bone via collagen fibers,” Sharp stated.

“These fibers help secure the muscle or ligament, preventing detachment and potential injury to the animal.”

Once the soft tissue deteriorates, what remains are the collagen fibers, which can be examined through thin slices of bone under polarized light.

“It appears as if someone has fractured a bone at the surface and then scraped it with an X-acto knife,” Sharp noted.

The researchers employed a technique called sleepy to analyze various angles of the zygomatic and mandibular bone slices, enabling them to investigate the 3D orientation of the collagen fibers.

“These collagen fibers don’t insert haphazardly; they align with the angles where muscles attach,” Sharp added.

In all examined dinosaur species, collagen fibers manifested connections between the cheek and lower jaw, reinforcing the idea that the soft tissue structure resembles cheek muscles and ligaments.

Variation in the size and attachment angles across different dinosaur species suggests that this newly identified soft tissue played specialized roles, such as stabilizing the jaw and influencing feeding behavior.

“While we don’t fully understand its precise functions, it is evident that these soft tissues significantly impacted how these dinosaurs chewed.”

“This discovery underscores the importance of comparing dinosaur fossils with those of modern relatives for a more nuanced and accurate comprehension of extinct anatomy.”

“Dinosaurs exhibit considerable diversity, yet we often overlook significant aspects by attempting to interpret the past solely through the lens of contemporary conditions.”

Survey results were published in Journal of Anatomy.

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Henry S. Sharp et al. Skull morphology and histology reveal previously unexpected cheek soft tissue structures in dinosaurs. Journal of Anatomy, published on March 21, 2025. doi:10.1111/joa.14242

This article is a rendition of a press release provided by the University of Alberta.