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Ancestor of snakes, lizards likely gave birth to live young
Date:
December 17,
2013
Source:
George Washington University
Summary:
The ancestor of snakes and lizards likely gave birth
to live young, rather than laid eggs, and over time species have switched back
and forth in their preferred reproductive mode, according to new research.
.........................
The ancestor of snakes and lizards likely gave birth to live
young, rather than laid eggs, and over time species have switched back and
forth in their preferred reproductive mode, according to research published in
print in Ecology Letters Dec. 17.
"This is
a very unusual and controversial finding, and a major overturn of an accepted
school of thought," said Alex Pyron, Robert F. Griggs Assistant Professor
of Biology in the Columbian College of Arts and Sciences at the George
Washington University. "Before, researchers long assumed that the ancestor
of snakes and lizards laid eggs, and that if a species switched to live birth,
it never reverted back. We found this wasn't the case."
The findings
push researchers' understanding of the evolution of live birth a lot further
back in time to 175 million years ago, showing that live birth has a much more
ancient past as a strategy than previously believed. The findings are backed by
several recent plesiosaur and mosasaur fossil discoveries and the fossil record
of a few lizards from the Cretaceous Period, which had embryos in the mother
and had live birth.
Dr. Pyron
analyzed an evolutionary tree containing all groups of squamates -- the group
that comprises lizards and snakes -- which he and a team of researchers published
in the journal BMC Evolutionary Biology earlier this year. The tree, which uses
DNA sequencing technology to group thousands of lizards and snakes, includes
all families and subfamilies and most genus and species groups.
In total,
about 115 groups of lizards and snakes, or about 2,000 species, have live
birth. The other 8,000 species lay eggs -- at least right now.
Dr. Pyron is
working next to analyze all tetrapods -- a group composed of animals with four
legs, such as amphibians, reptiles, birds, mammals and turtles -- to see if
there are any new surprises about the evolution of their reproductive modes. He
also wants to test the genetics at work behind the evolutionary switching of
reproductive mode.
Story
Source:
The above
story is based on materials provided by George Washington University. Note: Materials may be edited
for content and length.
Journal
Reference:
- R. Alexander Pyron, Frank T. Burbrink. Early origin of viviparity and multiple reversions to oviparity in squamate reptiles. Ecology Letters, 2013; DOI: 10.1111/ele.12168
