|Evolutionary Lessons from Pterosaurs|
|SciMed - Biology|
|TS-Si News Service|
|Wednesday, 06 July 2011 14:00|
Bristol, UK. A new study shows the unusual evolutionary development of the pterosaurs (flying reptiles), becoming more and more specialized throughout their 160 million years on Earth.
Palaeontologists routinely speculate about the rise and departure of species through time, but the new study provides a set of objective measurements of the relative success and breadth of adaptation of pterosaurs through their time on the Earth.
New work by Katy Prentice, who performed the research as part of her undergraduate degree (MSci in Palaeontology and Evolution) at the University of Bristol, significantly advances population studies in paleontology, but the application of rigor to her studies can have broad implications across a variety of other fields. "We're delighted to see a student mastering some tough mathematical techniques, and coming up with such a clear-cut result," said Professor Michael Benton at Bristol.
Extremes in Pterosaur Morphology
The giant and possibly flightless Quetzalcoatlus from the Late Cretaceous of Texas was as tall as a giraffe. The small insectivorous Anurognathus from the Late Jurassic of Germany is seen flying above the artist's head.
The drawings are courtesy of Mark Witton. You can see more of the artist's work on his his web sites: Mark Witton's photostream on flickr, and Pterosaurs: dragons of the air
Click Pic for DetailsUsually, when a new group of animals or plants evolves, they quickly try out all the options. "When we did this study, we thought pterosaurs would be the same", said Prentice. Pterosaurs were the first flying animals — they appeared on Earth 50 million years before Archaeopteryx, the first bird — and they were very successful. "But the amazing thing is that they didn't really begin to evolve until after the birds had appeared."
Katy Prentice did the study in conjunction with her supervisors, Dr Marcello Ruta and Professor Michael Benton. The findings appear in the Journal of Systematic Palaeontology.
They looked at 50 different pterosaurs that ranged in size from a blackbird to the largest of all, Quetzalcoatlus, with a wingspan of 12 metres, four times the size of the largest flying bird today, the albatross.
"Pterosaurs were at the height of their success about 125 million years ago, just as the birds became really diverse too," said Dr Marcello Ruta. "Our new numerical studies of all their physical features show they became three times as diverse in adaptations in the Early Cretaceous than they had been in the Jurassic, before Archaeopteryx and the birds appeared."
Pterosaurs dwindled and disappeared 65 million years during the mass extinction that killed the dinosaurs. In their day they had been a fair match for the birds, and the two groups divided up aerial ecospace between them, so avoiding conflict.
CitationEvolution of morphological disparity in pterosaurs. Katherine C. Prentice, Marcello Ruta, Michael J. Benton. Journal of Systematic Palaeontology 2011; ePub ahead of print. doi:10.1080/14772019.2011.565081
Pterosaurs were important flying vertebrates for most of the Mesozoic, from the Late Triassic to the end of the Cretaceous (225–65 Ma). They varied enormously through time in overall size (with wing spans from about 250 mm to about 12 m), and in features of their cranial and postcranial skeletons. Comparisons of disparity based on discrete cladistic characters show that the basal paraphyletic rhamphorhynchoids (Triassic–Early Cretaceous) occupied a distinct, and relatively small, region of morphospace compared to the derived pterodactyloids (Late Jurassic–Late Cretaceous). This separation is unexpected, especially in view of common constraints on anatomy caused by the requirements of flight. Pterodactyloid disparity shifted through time, with different, small portions of morphospace occupied in the Late Jurassic and Late Cretaceous, and a much larger portion in the Early Cretaceous. This explosion in disparity after 100 Ma of evolution is matched by the highest diversity of the clade: evidently, pterosaurs express a rather ‘top heavy’ clade shape, and this is reflected in delayed morphological evolution, again an unexpected finding. The expansion of disparity among pterodactyloids was comparable across subclades: pairwise comparisons among the four pterodactyloid superfamilies show that, for the most part, these clades display significant morphological separation, except in the case of Dsungaripteroidea and Azhdarchoidea. Finally, there is no evidence that rhamphorhynchoids as a whole were outcompeted by pterodactyloids, or that pterosaurs were driven to extinction by the rise of birds.
Keywords: pterosaurs, disparity, diversity, rhamphorhynchoids, pterodactyloids, morphospace.
|Last Updated on Wednesday, 06 July 2011 14:07|