New ways in the extinction of ancient jawless fishes

Pteraspis, poisson sans mâchoire du Dévonien

More than 500 million years (Ma), The oldest known vertebrates Resembling small, jawless larvae that filter nutrient particles from water. In time, they resembled our present-day fishes, but that took about 100 Ma The first jaw vertebrae appear. The latter (gnathostomes) have flourished to this day. In contrast, jawless vertebrates (agnathans), except for lampreys, disappeared after a phase of decline by about 370 Ma. This extinction was explained by competition with gnathostomes, which succeeded thanks to their morphological innovations. But how this rivalry between these two groups would have unfolded remains unclear today. In this context, Bradley R. from the University of Illinois at Urbana-Champaign. Scott and Phillip S.L. Andersen published a study on September 16, 2022 in the journal Paleobiology They try to use statistical analysis to determine whether competition was the determining factor in the disappearance of most of the Agnathans.

Morphology is a valuable clue that provides information about past lifestyles

Competition is a biological relationship that the study authors define as “Use of the same resources (food or habitat) by more than one taxon (group of organisms that share common characteristics, author note) Same place, same time”. But unlike today, direct observation of biological interactions in fossils is usually impossible. So it is important to focus on the only thing that fossil organisms give us to see with the naked eye: their morphology. In fact, some traits have uses, functions in living things. For example fins allow you to swim, but still go further. The shape of the fins, or the overall shape of the body, are highly variable traits according to the ecology of an organism. They combine to meet a need in the living environment, allowing researchers to draw typical examples. from this,”Fish living in open environments have a hydrodynamic body, large antero-dorsal fins (…). Also benthic vertebrates (living on the sea floor, editor’s note) have large pelvic fins […] or laterally compressed body, especially in rocky environments or with vegetation“, explain the authors of the study.

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There may be competition between certain groups…

These different anatomical characteristics were pooled for different major groups of agnathans and gnathostomes to carry out a statistical analysis.

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