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Palaeontology

Skull reconstruction sheds new light on tetrapod transition from water to land

360 million-year-old tetrapods may have been more like modern crocodiles than previously thought, according to 3D skull reconstruction.

The results publish March 11, 2015 in the open-access journal PLOS ONE by Laura Porro from University of Bristol, UK, and colleagues.

Acanthostega gunnari was a ‘four-footed’ vertebrate, also known as a tetrapod, that invaded land during one of the great evolutionary transitions in Earth’s history, 380-360 million years ago. This species is crucial for understanding the anatomy and ecology of the earliest tetrapods; however, after hundreds of millions of years buried in the ground, fossils are often damaged and deformed.

To try to reconstruct the skull of this species from numerous skull pieces, the authors of the study applied high-resolution X-ray computed tomography (CT) scanning to several specimens of Acanthostega gunnari from East Greenland.

Researchers found that the reconstructed skull had a longer postorbital region and a more strongly hooked lower jaw than previously thought. They also found clues as to how the species fed. The size and distribution of its teeth and the shape of contacts between individual bones of the skull (called sutures) suggest Acanthostega may have initially seized prey at the front of its jaws using its large front teeth and hook-shaped lower jaw.

     

The researchers plan to apply these methods to other flattened fossils of the earliest tetrapods to better understand how modifications to these early animals’ bones and teeth helped them meet the challenges of living on land.

Dr. Laura Porro added, “Because early tetrapods skulls are often ‘pancaked’ during the fossilization process, these animals are usually reconstructed having very flat heads. Our new reconstruction suggests the skull of Acanthostega was taller and somewhat narrower than previously interpreted, more similar to the skull of a modern crocodile.”

Header Image : The articulated cranium and lower jaws shown in oblique right lateral view (A). Right facial skeleton and skull roof shown in “exploded” view to illustrate the nature of sutural contacts (B); the left side of the cranium (braincase omitted) is shown in internal view (C). The right lower jaw in “exploded” view to illustrate sutural morphology. Individual bones shown in various colors. Credit : Porro et al.

PLOS

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