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Dinosaur Horns May Have Been Lopsided

Analysis by Dr. Karen Shaw Becker

Styracosaurus

Story at-a-glance -

  • Images of horned dinosaurs often depict them as being symmetrical — an assumption made by paleontologists after discovering only partial pieces of dinosaur skulls
  • The discovery of a well-preserved Styracosaurus skull by a University of Alberta graduate student suggests the horns were asymmetrical
  • The variations in the skull were extreme enough that if halves of it had been found in isolation, paleontologists may have believed they came from different species, raising questions about how other dinosaur species have been classified
  • The horns on the left side tended to be larger than those on the right, and the dinosaur’s left side showed evidence of injury
  • New discoveries are continually shedding new light on long-held assumptions regarding dinosaurs and other ancient creatures

Images of horned dinosaurs often depict them as being symmetrical, an assumption made by paleontologists after discovering only partial pieces of dinosaur skulls. The discovery of a Styracosaurus skull by a University of Alberta graduate student may change this assumption, however, as it turns out the horns may not have been symmetrical after all.

Styracosaurus is a horned dinosaur that lived in what is now Alberta, Canada and Montana in the U.S. Its name means "spiked lizard" and it was an herbivorous dinosaur thought to have six long horns that extended from its neck frill, a smaller horn above each eye and single horn protruding from its nose. Size wise, styracosaurus was a large dinosaur that could reach 18 feet long and six feet tall.1

Many styracosaurus bones have been uncovered in Alberta, Canada, in an area now known as the Dinosaur Provincial Park. During a 2015 expedition in the badlands northwest of the park, Scott Persons discovered the well-preserved skull, which he nicknamed Hannah, after his dog.

Dinosaur Skull Gives Clues About Asymmetrical Horns

The skull is unique in that it shows facial imperfections that suggest dinosaur horns were not always symmetrical, much like deer or moose horns of the modern day.2 In a news release, Persons explained:

"When parts of one side of the skull were missing, paleontologists have assumed that the missing side was symmetrical to the one that was preserved. Turns out, it isn't necessarily. Today, deer often have left and right antlers that are different in terms of their branching patterns. Hannah shows dramatically that dinosaurs could be the same way."3

The variations in the skull were extreme enough that if halves of it had been found in isolation, paleontologists may have believed they came from different species, raising questions about how other dinosaur species have been classified.

"The skull shows how much morphological variability there was in the genus," Robert Holmes, University of Alberta professor in the department of biological sciences, noted.4 In a partnership with researchers in the faculty of engineering, a 3D laser scan of the skull was performed, revealing even more details that will be accessible via a 3D model for scientists worldwide.

Striking details have been revealed from the skull, which was airlifted by a helicopter out of the field because it was so large. The horns on the left side tended to be larger than those on the right, and the dinosaur's left side showed evidence of injury. Persons told ABC News:

"It looks like Hannah suffered from some kind of old wound or infection, or both. Something happened to the left side of the face, probably when Hannah was young and the skull was still growing. It wasn't lethal, Hannah lived through it, but afterward the skull bones grew in a strange way."5

Ultimately, "The parietosquamosal frill of Styracosaurus albertensis is highly variable," the researchers wrote in the journal Cretacious Research. "This variability questions taxonomic distinctions based on morphology of the frill."6 In short, other new dinosaur species may actually be one and the same, mistakenly identified due to incomplete dinosaur skulls.

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Dinosaurs May Have Been Faster Than Believed

New discoveries are continually shedding new light on long-held assumptions regarding these fascinating creatures. Just as images often show dinosaurs with symmetrical horns, they also depict them as slow and plodding. But research by Tai Kubo, Ph.D., a postdoctoral researcher affiliated with the University Museum at the University of Tokyo, suggests otherwise.

By studying the fossilized footprints of Marasuchus, an ancient Dinosauriforme, or ancestor of dinosaurs, that lived during the Triassic Period and measured only about half a meter in length (1.6 feet), they found that it likely walked on two feet with an average stride of 1.15 meters (3.7 feet).7

"Given how high their hips stood, they probably walked very quickly," Kubo told Nikkei Asian Review.8 On the other hand, Archosaurs, ancestors of crocodiles, were about 2 to 3 meters (6.5 to 9.8 feet) in length but walked with an average stride of just 0.77 meter (2.5 feet), a short stride that suggests a slower, clumsier gait. 

"The fact that Dinosauriformes could walk fast is probably one reason they flourished instead of becoming extinct," Kubo said.9 New findings like this, and those uncovered via the skull of Hannah, suggest there's much more to be learned about ancient reptiles, not only regarding their behaviors but also in terms of their appearance.

It's becoming more common knowledge, for instance, that many dinosaurs likely had fluff, fuzz or feathers — a characteristic that's slow to be adopted in current images.10 One day, dinosaurs may turn out to be far different than we once imagined, complete with full feathers and horns of different shapes and sizes.