17, 2000 -- A newly described legged fossil snake that
languished in a museum drawer in Israel since the 1970s may
uproot the snake family tree. The fossil suggests that the slithering
reptiles evolved from secretive, burrowing lizards and not fearsome,
crocodile-like mosasaurs that ruled the seas while dinosaurs
ruled the land.
The snake, described in this week’s issue of the journal
Science, casts doubt on an earlier suggestion that another
legged snake from the same marine deposits near Jerusalem
represents a link between modern snakes and the Cretaceous
marine reptiles known as mosasaurs.
are both such well-developed snakes that their ancestors had
to be fairly advanced terrestrial snakes, not marine reptiles,"
says paleontologist Olivier Rieppel of the Field Museum of Natural
History in Chicago, Ill., one of the scientists who studied
the newfound snake.
The newest specimen provides the latest evidence in a debate
over the origin of snakes that began in the 1860s when famed
paleontologist Edward Drinker Cope suggested that snakes had
inherited detachable jaws from the gaping, flexible jaws of
mosasaurs. Two researchers further argued in 1997 that an
Israeli fossil snake called Pachyrhachis problematicus
was an ancestor of all snakes and that its rudimentary legs
were remnants of the flippers mosasaurs used to speed through
water after prey.
But Israeli paleontologist G. Haas, who had originally described
Pachyrhachis in 1979, died before revealing a second and more
complete legged snake that lay unnoticed in a museum drawer
until Michael Polcyn of Southern Methodist University spotted
it a few years ago. Polcyn, Rieppel and three other researchers
describe that second specimen in this week’s Science as Haasiophis
They conclude that both it and Pachyrhachis resemble modern,
advanced snakes such as pythons and boas and are not more
primitive, ancestral snakes that belong at the root of the
snake family tree. Their conclusion undermines any evolutionary
connection between snakes and mosasaurs, leaving the alternative
possibility that snakes descended from burrowing lizards that
lost their legs. They surmise the two fossil snakes later
regrew tiny legs, which were too small to be of much practical
Modern pythons have a rudimentary hind limb, usually little
more than a claw of cartilage tipped with bone that they use
during mating and occasional fighting, and it is possible
that Haasiophis' leg served a similar purpose, Rieppel said.
Analysis of the "spectacular" new specimen "really tells
us that snakes were much more likely to have a terrestrial
origin," says Harry Greene of Cornell University. "We know
there are instances in the fossil record of terrestrial creatures
taking to the sea -- whales, for instance, are descended from
land animals -- but not the other way around."