Fossils Show Some Dinosaurs Used Feathers for Courtship

An analysis of fossilized dinosaur tail bones suggests some feathered dinosaurs used tail plumage to attract mates.

Artist’s impression of Similicaudipteryx using its tail feathers in a mating display (Sydney Mohr)

A team of paleontologists, led by Scott Persons of the University of Alberta, followed a chain of fossil evidence that started with a peculiar fusing together of vertebrae at the tip of the tail of four different species of dinosaurs, some separated in time and evolution by 45 million years.

“The final vertebrae in the tails of a group of dinosaurs called oviraptors were fused together, forming a ridged, blade-like structure,” Persons said. “The structure is called a pygostyle. Among modern animals, only birds have them.”

Fossils of the early oviraptor Similicaudipteryx reveal feathers radiating from the fused bones at the tail tip. Similicaudipteryx was not known to be a flying dinosaur, and its tail feathers evolved as a means of waving its feathered tail fans.

No direct fossil evidence of feathers has been found with the fossils of the oviraptors that followed Similicaudipteryx, but Persons explained “there is still strong evidence they had a feathered tail.” The study appears in the journal Acta Palaeontologica Polonica.

“Because the later oviraptor had the same tail structure as the feathered Similicaudipteryx, the tails of later oviraptors still served the same purpose,” Persons said. “The hypothesis of oviraptor tail-waving is supported by both the bone and muscle structure of the tail.”

Individual vertebrae at the base of an oviraptor’s tail were short and numerous, indicating great flexibility. Based on dissections of modern reptile and bird tails, the reconstruction of the dinosaur’s tail muscles revealed oviraptors had what it took to really shake their tail feathers. Large muscles extended far down the tail and had a sufficient number of broad connection points to the vertebrae to propel oviraptors’ tail feathers vigorously from side to side and up and down.

Oviraptors were two-legged dinosaurs that had already gone through major diversifications from the iconic, meat-eating dinosaur family. They were plant-eaters that roamed parts of China, Mongolia and Alberta during the Cretaceous period, the final age of the dinosaur.

“By this time, a variety of dinosaurs used feathers for flight and insulation from the cold,” Persons said. “This shows that by the late Cretaceous, dinosaurs were doing everything with feathers that modern birds do now.”

In addition to feathered-tail waving, oviraptors also had prominent bone crests on their head, which the dinosaurs also may have used in mating displays.

“Between the crested head and feathered-tail shaking, oviraptors had a propensity for visual exhibitionism,” Persons concluded.

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Bibliographic information: Persons WS et al. Oviraptorosaur tail forms and functions. Acta Palaeontologica Polonica, published online 04 Jan, 2013; doi: 10.4202/app.2012.0093