MicroRNAs support a turtle + lizard clade
Tyler R. Lyson1, Erik A. Sperling1,†, Alysha M. Heimberg2, Jacques A. Gauthier1, Benjamin L. King3 and Kevin J. Peterson2,*
1Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA
2Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA
3Mount Desert Island Biological Laboratory, Salisbury Cove, ME 04672, USA
Present address: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
*Author for correspondence (firstname.lastname@example.org).
Despite much interest in amniote systematics, the origin of turtles remains elusive. Traditional morphological phylogenetic analyses place turtles outside Diapsida—amniotes whose ancestor had two fenestrae in the temporal region of the skull (among the living forms the tuatara, lizards, birds and crocodilians)—and allied with some unfenestrate-skulled (anapsid) taxa. Nonetheless, some morphological analyses place turtles within Diapsida, allied with Lepidosauria (tuatara and lizards). Most molecular studies agree that turtles are diapsids, but rather than allying them with lepidosaurs, instead place turtles near or within Archosauria (crocodilians and birds). Thus, three basic phylogenetic positions for turtles with respect to extant Diapsida are currently debated: (i) sister to Diapsida, (ii) sister to Lepidosauria, or (iii) sister to, or within, Archosauria. Interestingly, although these three alternatives are consistent with a single unrooted four-taxon tree for extant reptiles, they differ with respect to the position of the root. Here, we apply a novel molecular dataset, the presence versus absence of specific microRNAs, to the problem of the phylogenetic position of turtles and the root of the reptilian tree, and find that this dataset unambiguously supports a turtle + lepidosaur group. We find that turtles and lizards share four unique miRNA gene families that are not found in any other organisms' genome or small RNA library, and no miRNAs are found in all diapsids but not turtles, or in turtles and archosaurs but not in lizards. The concordance between our result and some morphological analyses suggests that there have been numerous morphological convergences and reversals in reptile phylogeny, including the loss of temporal fenestrae.
turtle, microRNA, amniote
Received May 5, 2011.
Accepted June 27, 2011.
This journal is © 2011 The Royal Society