The first 3D reconstruction of the skull of a 360 million-year-old near-ancestor of land vertebrates shows such creatures were more like modern crocodiles than previously thought.
The 3D skull, created by scientists from the Universities of Bristol and Cambridge, England, differs from earlier 2D reconstructions.
The researchers applied high-resolution X-ray computed tomography (CT) scanning to several specimens of Acanthostega gunnari - one of the 'four-footed' vertebrates known as tetrapods - which invaded the land during one of the great evolutionary transitions in earth's history, 380-360 million years ago.
Because early tetrapods skulls are often 'pancaked' during the fossilisation 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," said lead author Laura Porro.
Tetrapods evolved from lobe-finned fishes and display a number of adaptations to help them survive on land.
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An iconic fossil species, Acanthostega gunnari is crucial for understanding the anatomy and ecology of the earliest tetrapods.
However, after hundreds of millions of years in the ground fossils are often damaged and deformed.
No single specimen of Acanthostega preserves a skull that is complete and three-dimensional which had limited scientists' understanding of how this key animal fed and breathed.
Using special software, the researchers 'digitally prepared' a number of Acanthostega specimens from East Greenland, stripping away layers of rock to reveal the underlying bones.
They uncovered a number of bones deep within the skull, including some that had never before been seen or described, resulting in a detailed anatomical description of the Acanthostega skull.
Once all of the bones and teeth were digitally separated from each other, cracks were repaired and missing elements duplicated.
Using information from other specimens, the bones were fitted together like puzzle pieces to produce the first 3D reconstruction of the skull of Acanthostega, with surprising results.
The researchers also found clues which suggest Acanthostega may have initially seized prey at the front of its jaws using its large front teeth and hook-shaped lower jaw.
"These new analyses provide fresh clues about the evolution of the jaws and feeding system as the earliest animals with limbs and digits began to conquer the land," said study co-author professor Emily Rayfield.