New discovery places turtles next to lizards on family tree

Jul 20, 2011

(PhysOrg.com) -- Where do turtles belong on the evolutionary tree? For decades, the mystery has proven as tough to crack as the creatures' shells. With their body armor and retractable heads, turtles are such unique creatures that scientists have found it difficult to classify the strange animals in terms of their origins and closest relatives.

"We know turtles evolved from a along with birds, and snakes about 300 ago, but who modern-day turtles are most closely related to is one of the biggest and most controversial questions in the field of systematics," said Tyler Lyson, a Yale University graduate student who studies the between different .

Some researchers have analyzed turtles' genes and found they are most closely related to the group of animals that includes and birds. Others, comparing turtles' physical features to those of other reptiles, have placed them next to lizards or outside of the larger subclass of animals that includes lizards, crocodiles and birds altogether.

Now Lyson and his colleagues have used a novel approach involving microRNAs that strongly suggests turtles belong next to lizards.

Co-author Kevin Peterson, a paleobiologist at Dartmouth College, developed a technique to use microRNAs — small molecules that control gene activity and can switch certain genes on and off — to study evolutionary relationships. After discovering hundreds of microRNAs in the Carolina anole lizard, Peterson and co-authors then compared these to the microRNAs of a western painted turtle and an American alligator. The team found that four of the lizard's microRNAs were also present in the turtle, but were absent in birds, crocodiles and all other animals.

"Different microRNAs develop fairly rapidly in different animal species over time, but once developed, they then remain virtually unchanged," Peterson said. "They provide a kind of molecular map that allows us to trace a species' evolution."

The discovery, detailed online in Biology Letters, contradicts past studies that placed turtles next to crocodiles and birds rather than lizards. According to Lyson, those past findings were ambiguous and limited in scope, looking at just a few dozen genes, while the new technique analyzed all of the thousands of microRNAs found in turtles, lizards, and crocodiles.

"Our data unambiguously places turtles next to lizards," Lyson said. "But the data itself isn't infallible. We still need more data from these species in order to say definitely that and lizards are evolutionary cousins."

Next, the team plans to use its microRNA analysis on other animals to help determine their origins and relationships as well, and is developing a web-based platform to share the software with other researchers around the world.

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More information: Lyson, T. R. et al. Biology Letters doi:10.1098/rsbl.2011.0477 (2011).

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User comments : 5

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DavidMcC
not rated yet Jul 20, 2011
They certainly resemble a lizard with a shell!
kevinrtrs
1 / 5 (4) Jul 20, 2011
We know turtles evolved from a common ancestor along with birds, lizards and snakes about 300 million years ago

Just how DO they know this? Were they there all the time, watching these things evolve from a common ancestor? One needs to take such statements with a big grain of salt and a lot of gall. This is simply speculation of the highest order. But then the whole evolutionary theory is a big speculation anyway. Because these things have to do with origins - things that happened in the past - we cannot be certain that they did indeed happen as speculated. We can only take these things by faith.
Where are the missing links for instance that shows a lovely trail from the common ancestor to these current modern creatures? Yes, that's a cliche already but it still is a vexation of the first order - there are no undisputed missing links - even after millions of fossils [of completely fully formed creatures] have been found.
jsa09
5 / 5 (2) Jul 20, 2011
Hey Kev - one thing about finding links along every single evolutionary branch. It requires well preserved fossils. More than that, The fossils have to be somewhere where people have already looked. Maybe the fossils are preserved that will provide all the links you think we need, but if they do still exist, then it means no one has yet looked in the correct place.

But it is not safe to assume that we will be able to find fossils of every stage of evolutionary development there are just not that many fossils.
Donutz
not rated yet Jul 20, 2011

Just how DO they know this?


There are actually good, reasonable answers to this question. And if you had the slightest interest in actually learning something about the subject that you're always pretending authority on, you'd know that. Fercrissakes kev, get an education on the subject before you spout off. You know so little about it that you don't even realize how little you know. Or how moronic you sound.
Peteri
not rated yet Jul 20, 2011
Kevinrts is actually an agent of the Devil.