The first land animals had fewer skull bones than fish

Scientists from Bristol UniversitiesPompeu Fabra University in Barcelona and University College London have discovered that tetrapods have more complex connections between their skull bones than fish by examining the skulls of fossil animals from the transition from the aquatic to terrestrial environment. These modifications in cranial anatomy have hampered the evolution of tetrapod skulls rather than encouraging the diversity of life on Earth.

Tetrapods evolved from fish and were the oldest land animals with their limbs and toes, and ancestors of everything from amphibians to humans.

To better understand how skulls changed as tetrapods evolved, scientists have determined the anatomy of the skull bones in more than 100 extant and extinct creatures.

Lead author James Rawson from the School of Geosciences in Bristol said: “The skulls of tetrapods generally have fewer cranial bones than their fish ancestors, but just calculating the number of bones is missing some important data. We used a technique called network analysis, where the arrangement of the skull bones – to which the bones are connected – is recorded as well as the number of bones.”

Author Dr. Borja Estiv-Altava, who is an expert in this technique, said: Traditionally, anatomy research has mostly been descriptive or qualitative. Network analysis provides a sound mathematical framework for estimating anatomical relationships between bones: a type of data that is often overlooked in most studies of morphological evolution.”

Scientists note, “Tetrapods that have fewer skull bones than fish have made the organization of their skulls more complex.”

Mr Rawson added: “It may seem strange, but having fewer bones means that each of these bones has to connect to a greater number of its neighbors, 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 first tetrapods became more coherent into a single unit, while their fish ancestors had skulls made up of several distinct sections.

By looking at a variety of skull bone anatomy over time, scientists have also discovered that the origin of tetrapods coincides with a decline in a variety of skull bone arrangements.

Professor Emily Rayfield, senior author of the study, said: “We were surprised that these changes in the skull seemed to limit the evolution of tetrapods, rather than promoting radiation into new habitats on Earth. We think that neck evolution, extinction or suffocation in skull growth may be responsible.”

Mr. Rawson is over: We also observe a similar decrease in the skeletal variation of the limb bones in early tetrapods, but the decline in limbs occurred 10 million years ago. Various factors were influencing the development of the skull and limbs in early tetrapods, and we have a lot to learn about this crucial time in our evolutionary history. “

Journal reference:

  1. James Rawson, Dr. Borja Esteve-Altava, Dr. Laura Burrow, Dr. Hugo Dutell, and Professor Emily Rayfield. Early development of tetrapods in the skull is characterized by increased complexity, limitations, and compensation for the development of limb-fins. science progress. two: two: 10.1126 / sciadv.adc8875