Identifying the distinguishing traits among male and female dinosaurs has been a persistent challenge for scientists. Despite previous assertions, a new study led by Queen Mary University of London suggests that it is too difficult to positively recognize the sex of a dinosaur based on a skeleton alone.
The researchers analyzed the skulls of modern-day gharials, large crocodiles with narrow snouts that widen at the nostrils, to gauge whether their sex can be determined using only fossil records.
Male gharials are larger than females and have a fleshy growth on the end of their snout, known as a ghara. Although the ghara is comprised of soft tissue, it is supported by a bony hollow near the nostrils that is visible in the skull.
The study was focused on 106 gharial specimens stored in museums all over the world. The experts found that aside from the presence of the bony hollow, the narial fossa, the males and females were strikingly similar.
“Like dinosaurs, gharials are large, slow growing reptiles that lay eggs, which makes them a good model for studying extinct dinosaur species,” explained study co-author Dr. David Hone.
“Our research shows that even with prior knowledge of the sex of the specimen, it can still be difficult to tell male and female gharials apart. With most dinosaurs we don’t have anywhere near that size of the dataset used for this study, and we don’t know the sex of the animals, so we’d expect this task to be much harder.”
Across many species, males and females have extremely different appearances, which is known as sexual dimorphism. For example, with the exception of reindeer, antlers are only found in male deer.
Sexual dimorphism is very common throughout the animal kingdom and is likely present in dinosaurs, but the gender differences may be too difficult to spot on skeletal remains.
“Some animals show extraordinarily high levels of sexual dimorphism, for example huge size differences between males and females,” said Dr. Hone.
“Gharials sit somewhere in the middle as they do possess these large narial fossa that can help with identification. Our study suggests that unless the differences between the dinosaurs are really striking, or there is a clear feature like the fossa, we will struggle to tell a male and female dinosaur apart using our existing dinosaur skeletons.”
The findings challenge previous studies that have proposed specific gender differences in popular dinosaur species, such as the Tyrannosaurus rex.
“Many years ago, a scientific paper suggested that female T. rex are bigger than males. However, this was based on records from 25 broken specimens and our results show this level of data just isn’t good enough to be able to make this conclusion,” said Dr. Hone.
The study is published in the journal PeerJ.