Monday, 25 January 2016

Sexual Selection In Dinosaurs

In recent years our knowledge of the sexual aspects of dinosaur evolution has taken several leaps forward. It has recasts these creatures as organisms with clear anatomical physiology and evolutionary links to animals we see around us today, rather than as distant memories in the fossil record. Among the discoveries driving this is the first conclusive identification of sexual dimorphism in stegosaurus last year, and just a few weeks ago, the remains of fossilised marks produced during mating rituals.

An artist's impression of Protoceratops's
frill based mating display
The study examined here is the latest contribution to the reconstruction of ancient sexual paradigms, identifying the first conclusive case of sexual selection, specifically in Protoceratops, perhaps the most abundant dinosaur species known. The great wealth of available specimens allowed researchers, led by Dr David Hone from the School of Biological and Chemical Sciences at Queen Mary's University, London, to gather enough data to demonstrate the development of sexually selected characteristics during growth.

'Palaeontologists have long suspected that many of the strange features we see in dinosaurs were linked to sexual display and social dominance but this is very hard to show. The growth pattern we see in Protoceratops matches that seen for signalling structures in numerous different living species and forms a coherent pattern from very young animals right through to large adults,' said Dr Hone.

Allometric studies, focusing on the length and width of the neck frill, were conducted on the skulls of 37 individuals from the Djadochta Formation in the Gobi desert. The sample covered a range of individuals from four developmental categories: hatchlings, juveniles, sub-adults and adults. The data showed a trend in the frill becoming proportionally wider as the dinosaur became older, while the hatchlings lacked the frill altogether, before its sudden acquisition and rapid growth in later developmental stages. - a characteristic of sexual display. And while hard to prove, it is possible that the network of blood vessels in the frill may have been used to give a red coloration, adding to the mating ritual.

'Biologists are increasingly realising that sexual selection is a massively important force in shaping biodiversity both now and in the past,' said Dr Rob Knell, also from QMUL's School of Biological and Chemical Sciences, Not only does sexual selection account for most of the stranger, prettier and more impressive features that we see in the animal kingdom, it also seems to play a part in determining how new species arise, and there is increasing evidence that it also has effects on extinction rates and on the ways by which animals are able to adapt to changing environments.'