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Out of Their Shell, Are Turtles More Like Birds or Lizards?

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The turtle’s family tree has always been a bit of a mystery. “Turtles have a lot of unique morphological characters,” explains Nick Crawford, a post-graduate biology researcher at Boston University. “Basically, having a shell makes the rest of you look really different from your closest relatives.”

Scientists looking at the turtle’s muscles and bones tend to think that they belong next to snakes and lizards. But scientists doing molecular analysis have placed their bets with turtles and birds. A recent paper in the journal Biology Letters hopes to put the issue to rest.

By comparing 1,145 so-called “ultraconserved elements”—basically parts of DNA that have remained consistent for the longest—from a variety of species including snake, chicken, human, and, of course, turtles, Crawford found “overwhelming support for the hypothesis that turtles evolved from a common ancestor of birds and crocodilians.”

The results directly contradict a paper published in the same journal last year offering microRNA evidence that turtles are closer to lizards.

So who’s got the strongest claim to the slow movers?

“MicroRNAs are hard to study in an evolutionary context unless you have a complete genome from each species you're studying,” explains Crawford, and turtles still haven’t been given the full genomic once-over. Is it enough for a family tree smackdown? Crawford thinks so. He’s already taken his technique and moved on to birds.