Early land animals had fewer skull bones than fish, restricted their evolution - study

Tetrapods had more complex connections between the bones inside their skull than fish, and that this impeded their evolution.

 Early tetrapod. (photo credit: Science Photo Library/Alamy Stock Photo Image)
Early tetrapod.
(photo credit: Science Photo Library/Alamy Stock Photo Image)

Researchers found that tetrapod skulls had fewer bones than fish, limiting their evolution for millions of years, according to a new study conducted by researchers from the University of Bristol, Barcelona’s Universitat Pompeu Fabra and University College London.

The researchers analyzed the fossilized skulls of animals across the transition from sea to land and found that tetrapods, who evolved from fish and were the earliest land animals with limbs, had more complex connections between the bones inside their skull than fish, and that this impeded their evolution.

The peer-reviewed study was published last week in the journal Science Advances.

“Tetrapod skulls generally have fewer skull bones than their fish ancestors, but simply counting the number of bones misses some important data," said lead researcher James Rawson from the University of Bristol. We used a technique called network analysis, where the arrangement of skull bones - which bones connect to which - is recorded in addition to the bone number.”

“Tetrapod skulls generally have fewer skull bones than their fish ancestors, but simply counting the number of bones misses some important data."

James Rowden, lead researcher

What other data did the study find?

The research took a close examination of skull bones of over 100 species comprised of both living and fossil animals. Researchers also concluded that the tetrapods' origins coincide with a drop in the variety of skull bone arrangements.

Students and visitors are seen walking around the main campus buildings of University College London (UCL), part of the University of London, Britain, April 24, 2017. (credit: REUTERS/TOBY MELVILLE)Students and visitors are seen walking around the main campus buildings of University College London (UCL), part of the University of London, Britain, April 24, 2017. (credit: REUTERS/TOBY MELVILLE)

“We also see a similar drop in structural variability for the limb bones in early tetrapods, but the drop in the limbs happens 10 million years earlier," Rawson concluded.