UK: Huge prehistoric 'accessories' attracted mates

Fins, crests and sails - various species of dinosaur displayed intriguing accessories. Now research suggests many of these adaptations grew extra large in order to attract mates.

Scientists at the universities of Hull and Portsmouth in the UK, and the University of Western Australia, studied the head-crests of pterosaurs and the back-sails of pelycosaurs. Such features are generally believed to have served to regulate body temperature.

But the researchers have found that in the case of pterosaur and pelycosaur the features were much bigger than required for temperature regulation. They used the laws of physics to predict the scaling relationships.

Animal metabolism - the process behind heat generation - can be plotted against body size. The researchers found that in each case the scaling of the crests and the sails was too extreme to have a dedicated body temperature control function.

They suggest bigger crests and sails were more attractive to prospective mates, so they became more exaggerated over successive generations.

Some pterosaurs had crests five times bigger than their skulls. Other species with apparently exaggerated structures include the plate-backed stegosaurus, head-crested hadrosaurs, pterosaurs such as pteranondon and the sail-backed eupelycosaurs dimetrodon and edaphosaurus.

Dr Joseph Tomkins, from the University of Western Australia's Centre for Evolutionary Biology, said the sails of the eupelycosaurs were among the earliest known examples of exaggerated secondary sexual traits in the history of vertebrate evolution.

"Indeed the sail of dimetrodon is one of the largest secondary sexual traits of any animal."

As for pterosaurs, Tomkins said the analysis suggested that male pteranodon either fought each other using their crests or that females assessed males on the size of their crests.

Dr Dave Martill, from the University of Portsmouth, said pterosaurs put even more effort into attracting a mate than peacocks whose large feathers are considered the most elaborate development of sexual selection in the modern day.

"Peacocks shed their fantastic plumage each year, so it's only a burden some of the time, but pterosaurs had to carry their crest around all the time."

The paper is published in The American Naturalist.