Changes in the tree canopy supported the earliest gliding lizards

There are only three known fossil specimens of the long-extinct gliding lizard with the name Coelurosauravus elivensis. Dating from the late Permian – 260 million to 252 million years ago – this unusual reptile inhabited the wetlands and forests of Madagascar when conditions were temperate, warm, and humid. The species is notable for its patagium – a membranous flap of skin stretching between the front and hind legs – which enabled it to glide; This makes it the oldest known gliding reptile in the world.

The three fossils were discovered between 1906 and 1907, and the species was described to science in 1926. Since then, however, scientists have debated exactly how the patagium was supported and used, and how this lizard moved in its environment. A team of researchers has now examined the three fossils in detail C. elfensis from Madagascar and a number of related specimens, all belonging to the same family of reptiles (Weigeltisaurida), to learn more about this unusual lizard.

Experts from the French National Museum of Natural History in Paris (Muséum national d’Histoire naturelle) and the Staatliches Museum für Naturkunde Karlsruhe in Germany further suggest that this remarkable lizard most likely evolved its ability to fly in response to changes in the forests of the time.

“Pensylvanian [late Carboniferous] Forests, although taxonomically and vertically heterogeneous, had fairly open canopy layers with spatially separated arboreal taxa, resulting in little canopy overlap. In contrast, Cisuralian [early Permian] Forests show evidence of denser communities suggesting more continuous canopy layers. Such a change in forest structure could explain why no pre-Weigeltisaurid gliders have been reported, although several arboreal or scansorial amniotes have been described from Pennsylvania and Cisural deposits,” said lead author of the study, Valentin Buffa, of the Center de Recherche en Paléontologie at French Natural history museum.

“These dragons were not forged in mythological fire, they simply had to travel from place to place. As it turned out, gliding was the most efficient mode of transport, and here, in this new study, we see how their morphology made that possible.”

The researchers were particularly interested in understanding how all the bits of the C. elfensis The skeleton fitted together, so they focused on the postcranial parts – the body, including the torso, limbs, and remarkable gliding apparatus, the patagium. Previous analyzes of the reptile had suggested that its patagium was supported by bones extending from its ribs, as do modern gliding lizards of the genus Draco found in Southeast Asia.

Since no complete specimen was found among the fossils, the researchers had to piece together the extant parts of the fossils to get a better picture of the lizard’s skeletal structure. Their thorough examination indicated that the patagium of C. elfensis was not supported by extensions from the ribs. Instead, it has been suggested that the approximately 29 pairs of long, rod-shaped bones supporting the gliding membrane originated either simply from the animal’s skin and trunk muscles, or from its gastralia.

Gastralia are skin bones found in the skin covering the stomach region of some reptiles, including crocodiles, tuatara, and dinosaurs. When these bones are in C. elfensis Had gastralia been modified, they would have been positioned more toward the lower lateral surface of the body and not toward the dorsal aspect, as seen in modern times Draco lizards. The researchers concluded that the rods of bone were flexible and that the rolling up and down of the flight membrane would likely have been controlled by the abdominal muscles.

The researchers combined these findings with others derived from the bone structure observed in the fossils, and arrived at a refined vision of how this agile creature moved through its tree-dwelling habitat.

“Sharp, curved claws and a compressed body shape support the idea C. elfensis has been perfectly adapted to move vertically up tree trunks. The similarity in length of the front and hind legs further indicates that it was an expert climber – their proportional length helped it stay close to the tree surface and prevented it from tipping and losing its balance. Its long, slender body and whip-like tail, also seen in contemporary arboreal reptiles, further supports this interpretation,” explained Valentin Buffa.

An analysis of the similarities and differences between C. elfensis and live gliding lizards from the genus Draco noticed, that The fossil species was probably less efficient at gliding than the modern one Draco species due to their larger body size. Its estimated wing loading of around 107.9 N/m² is 4.5 times higher than that of Draco Species that would likely result in a significant drop in altitude per glide and would correspond to a steep descent angle greater than 45 degrees.

“C. elfensis bears a striking resemblance to the contemporary genus Draco,” said Valentin Buffa. “While its habits were probably similar to those of its modern counterpart, we do see subtle differences.”

“As Draco lizards, Coelurosauravus was able to grab its patagium with its front claws, stabilizing and even adjusting it in flight, allowing for greater maneuverability. However, an extra joint in one finger may have enhanced this ability. This may have been a necessary compensation for the lower positioning of the Patagium, which likely made it more unstable.”

The research is published in the Journal of Vertebrate Paleontology.

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Through Alison Bosman, Earth.com Staff writer