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'New start' for snake origin debate
A fossil uncovered in Argentina has revealed a two-legged creature that is the most primitive snake known, a discovery that promises to fire up the scientific debate about whether snakes evolved on land or in the sea.
The snake's anatomy and the location of the fossil show it lived on land, researchers said, adding evidence to the argument that this creature evolved on land.
Snakes are thought to have evolved from four-legged lizards, losing their limbs over time. But scientists have long debated whether those ancestral lizards were land-based or marine creatures.
The newly found snake lived in Patagonia. Its size is unkown, but it wasn't more than a metre long, said Hussam Zaher of the University of Sao Paulo in Brazil.
He and an Argentine colleague reported the find in last Thursday's issue of the journal Nature.
It's the first time that scientists have found a snake with a sacrum, a bony feature supporting the pelvis, Zaher said. That feature was lost as snakes evolved from lizards, he said, and since this is the only known snake that hasn't lost it, it must be the most primitive known.
The creature clearly lived on land, both because its anatomy suggests it lived in burrows, and because the deposits where the fossils were found came from a terrestrial environment, said Zaher.
So, if the earliest known snake lived on land, that suggests snakes evolved on land, he said.
There has been little new evidence in recent years in the land-versus-sea debate, and "we needed something new", said Zaher.
"We needed a new start. And this snake is definitely a new start for this debate."
He said that although the creature had two small rear legs, it crawled like a modern-day snake and probably used its legs only on occasion, though for what purpose is unclear.
The creature, named Najash Rionegrina, is "a fantastic animal", said Jack Conrad, a researcher at the American Museum of Natural History in New York and co-curator of an upcoming exhibition on lizards and snakes.
"It's really going to help put to rest some of the controversy that's been going on around snake evolution and origins," he said, adding that he had never taken sides in the land-versus-sea debate, "but this is starting to convince me."
Olivier Rieppel, a fossil-reptile expert at the Field Museum in Chicago, called the find important and said that Najash is clearly the most primitive known snake.
If snakes did evolve on land rather than in the sea, their fossil record might be less complete because early fossils would have been better preserved in a marine environment, he said.
That, in turn, suggests "we may not know all the lineages of early snake evolution", he said. Maybe several snake lineages lost the legs of their lizard ancestors independently, he added.
The creature's name comes from a Hebrew word for "snake" and the Rio Negro province of Argentina, where the discovery was made.
fossil
the remains, or a mark, of a prehistoric animal or plant that has been buried in rock for a very long time and that has become hard
revealed
when something is made known that was secret or unknown before
creature
a living thing such as an animal, a bird, a fish or an insect, but not a plant
primitive
at or connected with a very early stage of development
debate
an argument or discussion expressing different opinions about a question
evolve
to develop from early simple forms; to change over time
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anatomy
the structure or parts of a living thing
limbs
a leg or an arm of a person
ancestral
about the people in your family who lived a long time before you
marine
connected with the sea
burrows
a hole in the ground made by certain animals in which they live
terrestrial
living on the land or on the ground, rather than in water, in trees or in the air
modern-day
of the present time
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curator
a person whose job is to be in charge of the objects or works of art in a museaum or art gallery, etc.
controversy
public discussion and disagreement about something
origins
the time when or place where something first comes into existence
reptile
an animal, such as a snake or crocodile, that has rough skin, lays eggs, and whose body temperature changes with the temperature around it.
preserve
to keep something safe or in good condition
lineage
the children who come from one particular ancestor
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