Why a turtle is (still) not a lepidosaur

BMC Biology publishes today a research article (from Chiari et al) on the placement of turtles in the evolutionary tree, which supports their position as a sister group to the birds and crocodiles (collectively called the archosaurs). This isn’t the first time that a similar placement has been supported, as Blair Hedges discusses in an accompanying commentary. So why is it interesting?

Partly, it’s because there has been some recent dispute over the correct placement, particularly from a paper claiming microRNA analysis actually places turtles closest to other reptiles – snakes, lizards and the like, collectively termed lepidosaurs – a placement that agrees with more traditional taxonomic placements based on morphology. A reaffirmation of the grouping with archosaurs is therefore important.

And partly, it’s because of the strength of the analysis: the amount of sequence data used is large (the analysis is based on 248 separate genes), and the authors are careful to avoid analytical artefacts by analysing the influence of third codon positions – which can cause trouble through mutational saturation – and of the underlying heterogeneity between different gene trees. Much has been written recently about problems of reproducibility in science, and phylogeneticists should take some pride in a culture that in some ways represents the ideal: the continual updating and/or reinforcement of previous results with new data and new analytical techniques is encouraged, and a strong study is usually welcomed regardless of whether it conflicts with or simply corroborates existing conclusions.

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