Vertebrates “lost” the bones of the skull when they landed

(ORDO NEWS) — After analyzing the composition of the bones in the skulls of fossils and modern fish, as well as the oldest terrestrial and modern vertebrates, scientists came to the conclusion that one anatomical feature inherent in our common ancestor forever limited the evolution of the skulls of land animals.

Vertebrates “creeped out” on land quite late, about 380 million years ago, when the first forests were already growing on the earth and numerous invertebrates lived. In the future, these primitive “fish with legs” gave rise to all modern and fossil terrestrial vertebrates, from amphibians to dinosaurs and humans.

However, the transition from the water to the land stage of our evolution did not pass without a trace: after analyzing the skull bones of more than 100 species of modern and fossil animals, scientists found that the “fish with legs” skulls differed significantly from the skulls of their fish ancestors, and not only in the number of bones , but also by the complexity of their connections.

The skulls of terrestrial vertebrates have fewer bones than fish, but simply counting them misses some important details, according to the authors of the study.

To avoid this, they used network analysis , in which an individual bone is not only assigned a number, but also recorded where in the skull it is located and which other bones it connects to.

As a result, after analyzing the bones of the skulls of the first tetrapods, their ancestors and descendants, scientists found that the structure of the skull in terrestrial vertebrates is more complicated: since there are fewer bones, each must connect to more of its neighbors.

Modern frogs and salamanders had the most complex skulls of any animal studied, and the oldest tetrapods, such as the Tiktaalik , had more “fused” skulls than fish that lived at the same time.

Vertebrates lost the bones of the skull when they landed
The skull of a giant salamander is one of the most complex skulls of our time

The decrease in the number of bones occurred at the same time as the emergence of vertebrates on land, and in the future this significantly limited the evolution of their skulls: fewer bones – fewer options for their shapes and sizes.

While the skulls of fish of different evolutionary lines can differ radically, in terrestrial vertebrates they are all organized “according to a single plan” – a distant legacy of our common ancestors who left the water for life on earth.

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