Dinosaur-era fossil provides insight into snake evolution

Snakes first appeared during the age of dinosaurs, but the fragmentary nature of many early fossils has made it difficult for scientists to understand their evolution. Now, a remarkably preserved fossil discovered in southeastern Brazil is providing new clues about the history of these ancient reptiles.
The fossil belongs to Tametara mirim, a snake that lived between 75 and 85 million years ago during the Cretaceous Period. Measuring about 42 centimetres long, it inhabited a lush ecosystem alongside enormous long-necked plant-eating dinosaurs, crocodiles and birds.
Although the fossil does not preserve the entire animal, part of the skull was exceptionally well preserved, allowing researchers to reconstruct the snake’s brain anatomy. The brain shape and skull bone structure revealed that Tametara had adapted to a burrowing, or fossorial, lifestyle, similar to some modern species such as coral snakes.

Snakes evolved from lizard ancestors and are believed to have first appeared around 170 million years ago during the Jurassic Period. However, well-preserved fossils from this era are extremely rare, with only a small number discovered from the later Cretaceous Period.
“Snakes represent one of the most extreme body plans among all vertebrates, animals with a backbone”, said Tiago Simões, an evolutionary biology professor at Princeton University and lead author of the study published in Nature. “Understanding the origin of this peculiar and highly diverse group remains one of the biggest mysteries in vertebrate evolution”.
The fossil, discovered in Presidente Prudente in Brazil’s São Paulo state, preserves about 60 per cent of the skull and 70 per cent of the vertebral column. Researchers said Tametara is among only a few exceptionally preserved Cretaceous snakes, offering rare information about the early evolution of the snake nervous system.
The discovery suggests that early snake evolution was far more complex than previously believed. Rather than following a single path, ancient snakes developed different adaptations that allowed them to survive in a variety of environments, including underground, on land and in marine habitats.

“We predict the ancestral condition for all snakes was not one strongly adapted to a single habitat. Rather, it was a transitional one, lying between fossorial and ground-dwelling environments”, Simões said.
Scientists believe Tametara likely fed on insects, although there is no direct evidence of its diet. Since the fossil did not preserve teeth, researchers could not determine whether it was venomous. While modern snakes have no limbs, fossils show that some early snakes retained hind legs. Although the hip area of Tametara was not preserved, researchers believe it likely had strong back limbs similar to related Cretaceous species.
The researchers also reconstructed the brain anatomy of another ancient snake, Dinilysia patagonica, which grew to around two metres long. The comparison revealed significant diversity in brain structure among early snakes, suggesting they had developed different sensory abilities early in their evolutionary history.
Compared with many modern snakes, Tametara had smaller cerebral hemispheres, linked to cognition and a smaller optic tectum, associated with vision. Scientists said these differences likely reflected its underground lifestyle, where strong eyesight was less essential.
The discovery provides a rare glimpse into the evolution of early snakes, showing that their transformation into the diverse species known today was a long and complex journey shaped by different environments and survival strategies. — Reuters