Paleontologists have faced a tough challenge: figuring out how to tell male and female dinosaurs apart from their fossils. But recent research might finally offer some insights, especially for a group of dinosaurs known as hadrosaurs, or duck-billed dinosaurs.
Hadrosaurs thrived during the Late Cretaceous Period, around 100.5 to 66 million years ago. Fossils of these herbivores have been discovered all over the world. Some of these fossils have signs of healing from bone injuries in one specific area—near the base of their tails. While the fossil record is mostly silent on soft tissues that could reveal reproductive traits, scientists have speculated that differences in bones might simply be due to age or species, not sex. Finding fossilized eggs has proven difficult too.
A study published in the journal iScience suggests that these injuries may have occurred during mating. The lead author, Dr. Filippo Bertozzo, believes these signs could help identify female hadrosaurs. He remarked, “This will be a game-changer for understanding differences between male and female dinosaurs.”
Interestingly, Canadian paleontologist Darren H. Tanke noticed similar injuries in hadrosaurs back in the 1980s while examining fossils in Alberta’s Dinosaur Provincial Park. He hypothesized that males might have been mounting females when these injuries happened. His findings were largely based on fossils found in Canada.
Fast forward to recent years, when Bertozzo studied a hadrosaur fossil called Olorotitan arharensis in Russia. His PhD research focused on diseases in these dinosaurs. He suggested a new study to Tanke. This was significant because earlier methods of analysis lacked the advanced simulations available today to explore dinosaur behavior.
Bertozzo’s team examined nearly 500 tail vertebrae from various hadrosaur species housed in museums across North America, Europe, and Russia. They found that the injuries on the middle part of the tails were strikingly consistent among fossils from different locations and times.
The injuries, including broken tips and deformities of the vertebrae, appeared in multiple specimens. The patterns suggested a common cause—likely linked to mating behavior, as they ruled out other possibilities like fighting or accidental injuries from daily life.
In a fascinating twist, Bertozzo speculated that during mating, the males might press down on females’ tails if they were lying sideways, leading to the tail injuries. He stated, “The mating hypothesis is the one … best explained by our observations.”
An important dynamic in animal behavior is competition during reproduction, a phenomenon observed in many modern species, including sea lions and birds. Dr. Gareth Arnott, a co-author of the study, noted, “Reproductive competition is one of the most complex topics in animal biology.”
Experts have shown interest in the research. Dr. Albert Prieto-Márquez praised the consistent injury patterns as significant but emphasized the need for further evidence to solidify the findings. “To be sure, we’d need to find the same pattern in specimens known to be female, such as those with eggs,” he remarked.
Further, medullary bone—temporary tissue found in female birds and dinosaurs for egg production—would help validate the hypothesis. In modern chickens, this tissue appears just before egg-laying. Identifying medullary bone in dinosaur fossils would mean a real breakthrough in confirming sex.
While the study raises exciting possibilities about understanding dinosaur behavior, it remains just a starting point. There is still much to explore, including studying fossils from other regions and using advanced simulations to analyze more injury scenarios.
Bertozzo is eager to learn if these injuries appear in other dinosaur types. Some expectations include insights on sex differences in anatomical features and skull crests previously attributed to new species.
In the words of Dr. Yoshitsugu Kobayashi, one of the pioneering researchers in hadrosaur paleontology, “This study opens a fascinating window into the private lives of dinosaurs.” It hints at how even ancient bones can offer glimpses into their behavior, merging the fields of paleontology and biological sciences in exciting ways.
For more on the complex and emerging world of dinosaur biology, check studies like this one in iScience.
