From: University of Bristol Newsroom
Published May 7, 2014 11:02 AM

A dinosaur's evolution of the claw

How did the evolution of the dinosaur claw evolve into the current bird form? A new University of Bristol study into the claws of a group of theropod dinosaurs, known as therizinosaurs, has revealed a great versatility in their usage. Theropod dinosaurs, a group that includes such famous species as Tyrannosaurus rex and Velociraptor, are often regarded as carnivorous and predatory animals, using their sharp teeth and claws to capture and dispatch prey.  However, the detailed look at forelimb claws demonstrates that these claws were very likely to have been used for other tasks.

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Inspired by this broad spectrum of claw morphologies, Dr. Stephen Lautenschlager from Bristol's School of Earth Sciences studied the differences in claw shape and how these are related to different functions.

His research focused on the therizinosaurs, an unusual group of theropods, which lived between 145 and 66 million years ago. Therizinosaurs were very large animals, up to 7m tall, with claws more than 50cm long on their forelimbs, elongated necks and a coat of primitive, down-like feathers along their bodies.  But in spite of their bizarre appearance, therizinosaurs were peaceful herbivores.

Dr. Lautenschlager said: "Theropod dinosaurs were all bipedal, which means their forelimbs were no longer involved in walking as in other dinosaurs.  This allowed them to develop a whole new suite of claw shapes adapted to different functions."

In order to fully understand how these different claws on the forelimbs were used, detailed computer models were created to simulate a variety of possible functions for different species and claw morphologies.

The dinosaur claws were also compared to the claws of mammals, still alive today, whose function (that is, how and for what the claws are used) is already known.

In the course of evolution, several theropod groups, including therizinosaurs, changed from being carnivores to become plant-eaters.  This new study reveals that, during this transition, theropod dinosaurs developed a large variety of claw shapes adapted to specific functions, such as digging, grasping or piercing.

Dr. Lautenschlager said: "It's fascinating to see that, with the shift from a carnivorous to a plant-based diet, we find a large variety of claw shapes adapted to different functions.  This suggests that dietary adaptations were an important driver during the evolution of theropod dinosaurs and their transition to modern birds."

Read more at the University of Bristol.

Tyrannosaurus Rex image via Shutterstock.

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