Earliest land animals had fewer skull bones t


picture: Early tetrapod
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Credit: Science Photo Library / Alamy Stock Photo
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Original artist: Mark Garlick

The skulls of tetrapods had fewer bones than extinct and dwelling fish, limiting their evolution for tens of millions of years, in accordance with a modern examine.

By analysing fossil skulls of animals throughout the transition from an aquatic to terrestrial surroundings, researchers from the University of Bristol, Barcelona’s Universitat Pompeu Fabra and University College London found that tetrapods had extra complicated connections between their cranium bones than fish. And, slightly than selling the diversification of life on land, these modifications to cranium anatomy really restricted the evolution of tetrapod skulls.

Tetrapods advanced from fish and have been the earliest land animals with limbs and digits; the ancestors of the whole lot from amphibians to people.

The analysis, revealed this week in Science Advances, quantified the organisation of cranium bones in over 100 dwelling and fossil animals to higher perceive how skulls modified as tetrapods advanced.

Lead creator James Rawson of Bristol’s School of Earth Sciences mentioned: “Tetrapod skulls generally have fewer skull bones than their fish ancestors, but simply counting the number of bones misses some important data. We used a technique called network analysis, where the arrangement of skull bones – which bones connect to which – is recorded in addition to bone number.”

Author Dr Borja Esteve-Altava, an knowledgeable on this approach, mentioned: “Traditionally, anatomy research has been mostly descriptive or qualitative. Network analysis provides a sound mathematical framework to quantify anatomical relations among bones: a kind of data often overlooked in most studies on morphological evolution.”

The authors discovered that tetrapods having fewer cranium bones than fish made the organisation of their skulls extra complicated.

Mr Rawson added: “It might seem strange, but having fewer bones means each of those bones must connect with more of its neighbours, resulting in a more complex arrangement. Modern frogs and salamanders had the most complex skulls of all the animals we studied.” The skulls of the earliest tetrapods additionally turned extra consolidated right into a single unit, whereas their fish ancestors had skulls fabricated from a number of distinct sections.

By trying on the number of cranium bone preparations over time, the authors additionally found that the origin of tetrapods coincides with a drop within the number of cranium bone preparations. Professor Emily Rayfield, senior creator of the examine, mentioned: “We were surprised to find these changes to the skull seemed to limit tetrapod evolution, rather than promoting radiation to new habitats on land. We think that the evolution of a neck, extinction events or a bottleneck in skull development may be responsible.” 

Mr Rawson concluded: “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. It seems that different factors were affecting skull and limb evolution in early tetrapods, and we have so much more to learn about this crucial time in our own evolutionary history.”


‘Early tetrapod cranial evolution is characterised by increased complexity, constraint and an offset from fin-limb evolution’ by James Rawson, Dr Borja Esteve-Altava, Dr Laura Porro, Dr Hugo Dutel and Professor Emily Rayfield in Science Advances.

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