What did the earliest skulls on land look like?

As one of the earliest tetrapods, Acanthostega gunnari can tell us a lot about the anatomy and ecology of the vertebrates which moved onto land. Unfortunately, none of the fossil specimens includes an intact, articulated skull, which makes it hard to figure out exactly how the jaw fit together and what the mandibular muscles looked like.

To get a better picture of this ancient skull, a team of researchers in the UK turned to X-ray computer tomography (CT), which enabled them to digitially separate the bones from each other and build a 3D reconstruction of a skull from East Greenland. Their analysis revealed that A. gunnari had a more strongly hooked lower jaw than earlier 2D reconstructions had suggested.

"Because early tetrapods skulls are often 'pancaked' during the fossilization process, these animals are usually reconstructed having very flat heads," said lead author Dr. Laura Porro, in a press release. "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."

The team also explored the biomechanical implications of their reconstruction. Based on the contact between the different bones that make up the skull, they inferred that Acanthostega probably seized prey with the front of its jaw and then used the smaller, hook-shaped teeth further back to restrain the prey while it was swallowed. According to the study, the morphology of the skull "is more consistent with an aquatic mode of feeding."

In addition to what it reveals about A. gunnari, this study also demonstrates the insights that CT scans can offer in studies of fossils that have been badly deformed. The researchers are planning to use this method to study other flattened early tetrapod fossils to learn more about the anatomical changes vertebrates underwent in their migration onto land.

space

Ref

Porro, LB, Rayfield, EJ, and Clack, JA. Descriptive Anatomy and Three-Dimensional Reconstruction of the Skull of the Early Tetrapod Acanthostega gunnari Jarvik, 1952. PLOS One 10(3): e0118882. doi:10.1371/journal.pone.0118882

space

Image credit
The image is Figure 8 from the paper and is distributed under a CC-BY license by PLOS.

0 Comment