Scientists find out how snakes lost their limbs

(ORDO NEWS) — Two fossils of almost limbless animals found in the Francis Creek Shale deposits in northern Illinois, USA, have shown that less than 100 million years after vertebrates first had limbs, some of them in the process of evolution preferred to lose them again.

This happened for the first time at least 308 million years ago – it was then that the first snake-like creatures appeared on Earth. An article about this authored by American and Canadian biologists was published in the journal Nature Ecology & Evolution.

The new genus and species of predecessors of snakes was named Nagini mazonense, it belongs to a group of extinct reptiles called Molgofids.

The newly found Molgophid have completely reduced forelimbs and pectoral girdle, which represents the earliest case of limb loss in this taxon. Finds of such transitional forms are always of great value.

These animals could grow up to 10 cm in length, had a snake-like body without forelimbs, they also lacked the bony structures supporting the attachment of the forelimbs to the body, but still had a pair of small but fully formed hind legs with four toes on each foot.

Along with nearly complete skeletons estimated at 308 million years old, soft tissue impressions have also been found showing that N. mazonense had a rounded snout and an elongated, long body with about 85 vertebrae and ribs.

And in the area where one would expect the presence of the forelimbs, no signs of the presence of soft tissues were found – the animals crawled without using the forelimbs.

The ancestors of modern snakes also originally lost their upper limbs and chest girdle about 170 million years ago, but N. mazonense and other Molgophyda are not direct ancestors of today’s snakes – this is just a “failed natural experiment”, a lateral broken branch of earth evolution.

Aside from snakes and some lizards, the only modern vertebrates without legs are amphibians, including salamanders and caecilians, which look like large earthworms and are found in the tropics of Africa, Asia and America.

Molgophids related to the current find were found in approximately the same rocks in 2019, but in that case, the animals, called Infernovenator steenae, still had all four limbs.


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