By studying the intertwined fossil remains of two turkey-sized, egg-stealing dinosaurs—nicknamed Romeo and Juliet—paleontologists claim they have a way of determining the sex of a specimen, a notoriously difficult trait to nail down. The secret lies in the size and shape of two bones at the very base of the tail.
Determining dinosaur sex is notoriously difficult. Sexual characteristics in dinos likely manifested themselves in soft tissues, just like in many animals. Unfortunately, soft tissue is usually lost in the fossilization process, leaving behind bone and occasionally feathers.
Working within those constraints, Scott Persons, a vertebrate palaeontologist at the University of Alberta in Edmonton, Canada, and his colleagues set about quantifying the differences between the remains of Romeo and Juliet, two adult oviraptorosaurs. Any significant differences, they hypothesized, could be the distinguishing marks of males and females.
The differences they found were in the bones that made up the base of the tail. Here’s Sid Perkins, reporting for Nature News:
A number of chevrons in one of the fossils were longer and had broader tips than those in the other specimen. The differences do not seem to be due to injury or disease, says Persons. Nor do they seem to be the result of changes in the bones during fossilization.
Instead, the researchers suggest that the variations are a sign of sex differences. The bones might be shorter in females to ease the process of laying eggs. In males, a set of longer, broad-tipped chevrons could have offered a better anchor for a penis-retracting muscle that the creatures are presumed to have had.
But the most tantalizing explanation might be that males needed larger chevrons to anchor the muscles that controlled their flexible, feather-tipped tails. The researchers suspect that male oviraptorosaurs shook their tail feathers in intricate displays to woo potential mates, akin the the behaviour of modern-day peacocks.
Other paleontologists are urging caution, though. Importantly, this study was only conducted on two specimens. The differences seen could just boil down to intraspecific variation. Also, we don’t know if this same technique would apply to larger dinosaurs. (Remember, these were just turkey-sized.)
But if the tail-bone measuring technique does work, being able to determine dinosaur sex just by measuring a few bones offers tantalizing possibilities, potentially revealing previously unknowable behaviors and population patterns, changing our understanding of the ancient world.