Nagini mazonense: armless fossils of small animal reveal how snakes may have lost their limbs

Scientists have unearthed two 300-million-year-old fossils of a small animal that adapted to losing its forelimbs, shedding light on how vertebrates evolved a “snake-like body plan “.

Modern reptiles like snakes and earthworms have achieved various types of body plans through the reduction of limbs and extreme elongation of their bodies, researchers including Arjan Mann of the Smithsonian National Museum of Natural History have said. United States.

Such body plans helped some of these early animals adapt to different methods of movement in different ecologies, developing degrees of swimming or arboreal lifestyles.

Dr Mann and his team found two fossils of the ancient animal from Francis Creek Shale in Illinois, US, according to the study.

The rock formations here are well known for preserving the remains of ancient animals in great detail.

The new species, nicknamed Nagini mazonense and described Sunday in the newspaper Nature ecology and evolutionexhibited extreme elongation of the body and corresponding reduction of the limbs.

Nagini may have grown to around 10 cm long (4 inches), with a snake-like body and no forelimbs, the scientists said.

“Our new study presents a description of a new fossil species of highly elongated serpentine recumbirostran known as Nagini mazonense from the famous Upper Carboniferous (309-307 Ma)-old Mazon Creek Lagerstätte in Illinois, USA, Dr. Mann wrote in an article linked to the study on Tuesday.

Recumbirostran is a group of member vertebrates that lived during the Carboniferous Period and the next 47 million years in the Permian Era.

Nagini belongs to a specific subgroup of highly elongated recumbirostrans called molgophids, some of which had around 100 vertebrae, Dr Mann said.

While previously unearthed molgophids showed signs of limb reduction, Nagini completely lacked the presence of a forelimb and a pectoral girdle – the bony structure that supports the attachment of the forelimbs.

The fossil, however, retained a well-developed hind limb with four toes on each foot.

They said the species may also have a round snout and a long body with around 85 vertebrae and ribs based on soft tissue imprints left in the fossil record.

Although it’s unclear exactly how limbs are lost in reptiles, the new study suggests Nagini followed the “forelimb first” mode of limb loss found in snakes.

In this mode, the researchers said expression of the Tbx5 gene – known to play a key role in tissue and organ formation during embryonic development in several species – was altered, leading to “complete failure of the ‘establishment of a forelimb field during development’.

“The nail in the coffin here is really the absence of both a forelimb and, more importantly, the entire pectoral apparatus which is controlled in part by the same genes,” wrote Dr. Mann.

This forelimb-first reduction was consistent with the pattern seen in modern snakes and contrasts with the hindlimb-first reduction process found in many other four-limbed vertebrate groups, the researchers pointed out.

“The discovery of an ancient snake-like fossil that lacks forelimbs but retains hindlimbs is a fantastic find, as it reveals the existence of transitional forms before the complete loss of limbs during evolution,” said Rolf Zeller of the University of Basel in Switzerland. not an author of the study, says New scientist.

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