(ORDO NEWS) — An important breakthrough in the evolution of vertebrates was the appearance of jaws, as well as the ability to bite and chew associated with them. In a new study, paleontologists have figured out the origin of this important part of the skeleton and the first stages of its development.
Nearly all modern vertebrates whether mammals, birds, reptiles, amphibians, cartilaginous or bony fish have a lower jaw, which is needed for biting and chewing. However, lampreys and other cyclostomes, the most primitive of modern vertebrates, lack jaws.
At first, no one had jaws – the most ancient vertebrates in this respect resembled primitive lampreys. Not too advanced these jawless makes and, say, the lack of myelinnecessary for the rapid conduction of an impulse in the nervous tissue.
At the same time, the first vertebrates had gills, thanks to which they could breathe underwater. Those, in turn, were equipped with bone supports – gill arches. It was these bones that at some point were able to change their function and become the basis for the first jaws.
“The jaws are an extremely important part of the body of gnathostomats, that is, jawed animals,” said William Deakin, a graduate student at the University of Bristol (UK) and one of the authors of the new study.
“They are not just widespread: almost everyone has jaws and are always used for the same purpose – to capture and process food. This cannot be said, for example, about the front or hind limbs and tail, which can have very different purposes.
Therefore, William considers jaws to be an extremely valuable object of evolutionary research. Indeed, this part of the skull of different vertebrates can be characterized using strictly defined and universal parameters and, therefore, can be compared objectively.
121 species of ancient vertebrates, describing 45 different jaw parameters for each of them. This is primarily about the so-called placoderms, or armored fish – namely, those that lived in the seas at the end of the Silurian and Devonian periods of the Paleozoic era.
Pretty soon the placoderms completely died out. It is worth noting that, despite the external similarity, these animals cannot be called relatives of “real” fish – our contemporaries.
Among the species considered is the famous Dunkleosteus ( Dunkleosteus ), whose impressive jaws could crush the strongest bones. And this despite the lack of teeth : they were replaced by the sharp edges of the bones.
The authors of the study applied complex mathematical models and data analysis to highlight the most important parameters of the jaw apparatus for evolution. They even created a large set of “hypothetical jaws” models and built a space of morphological features with which they quantitatively described and compared all this diversity.
Paleontologists concluded that the most ancient jaws were well adapted for rapid slamming and had high strength.
Therefore, their owners were predators. It is curious that the most successful designs were the most ancient. In the future, as more and more new systematic groups appeared, the jaw apparatus changed rapidly and sometimes lost its optimal structure.
In addition, the evolutionary divergence of vertebrates presented them with a choice: animals had to “prefer” either strong or fast-slamming jaws. Subsequently, this dilemma influenced the evolutionary development of many vertebrates.
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