Fossil Skull Reveals Tetrapods' Transition from Water to Land

A fossil skull recently discovered in East Greenland is helping to reveal a bit more about tetrapods - creatures dating back millions of years ago - and their transition from water to land, a new study says.

The skull belongs to Acanthostega gunnari, one of "four-footed" vertebrates known as tetrapods that emerged from the ocean and first stepped on land 380-360 million years ago. Tetrapods evolved from lobe-finned fishes, but various adaptations allowed them to make the move to land.

Acanthostega gunnari is crucial for better understanding this chapter in animal evolution.

However, scientists have failed to gain more insight into the creature because fossils are often damaged and deformed from spending millions of years in the ground. And until now, a complete, 3-D skull from this species has ever been discovered.

Now, using special software, scientists from the Universities of Bristol and Cambridge have created the first 3D reconstruction of the skull of 360 million-year-old Acanthostega specimens. By "digitally preparing" the specimens, they were able to reveal several bones deep within the skull, including some that had never before been seen or described.

"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," lead author Dr. Laura Porro said in a statement.

Not only that, but the size, shape and distribution of its teeth indicate that 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," concluded co-author Emily Rayfield.

The findings are described in more detail in the journal PLOS ONE.

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