"A Phylogenomic Analysis of Turtles"

For the past few decades, the placement of Testudines relative to other reptiles on the phylogenetic tree has been a heavily debated topic among scientists, herpetologists in particular. However, due to much research, some of the doubt has been removed. We now believe turtles are amniotes who are more closely related to crocodiles and birds rather than squamates and tuatara. Although we have gained a lot of insight, studies have not focused on the genomic links within the order itself.
In this study, the researchers assess the relationships among turtles. Researchers collected DNA from 32 turtles, in which each family is represented, and 6 out-group organisms, ranging from a mammal to a squamate. Researchers sequenced and assembled the DNA using a relatively new technique called ultra-conserved elements. They then used statistical models, in which each program assembled the same phylogeny.

Scientists extracted DNA from each organism and generated sequences for each. However, this study used a relatively new technique called ultra-conserved elements. This phylogeny happened to be the same as the currently accepted tree, meaning the phylogenetic names correlated with the genus, species, etc.

In rooting the phylogenetic tree, the scientists interestingly created, or defined, a new phylogenetic group. Archelosauria is a clade that includes the both archosaurs and chelonians, meaning this group includes turtles, crocodiles, dinosaurs, and birds. This is one of the largest, if not the largest, vertebrate groups to ever receive a scientific name.

Thus study also showed that molecular phylogenies are more credible than morphological topology. Using ultra-conserved elements, scientists are able to better reconstruct recent divergences. Assessing the organisms’ DNA will always be a better method to construct a phylogeny than assessing its morphology. There are numerous cases of convergent evolution that could cause confusion in constructing a phylogeny via morphology. The article gives the example of Trionychians. Morphology-based phylogeny constructions place them in Crytopdira, which is clearly not the case.

Therefore, all future studies should use genomic or molecular methods to create the most believable phylogeny.

Nicholas G. Crawford, James F. Parham, Anna B. Sellas, Brant C. Faircloth, Travis C. Glenn, Theodore J. Papenfuss, James B. Henderson, Madison H. Hansen, W. Brian Simison, A phylogenomic analysis of turtles, Molecular Phylogenetics and Evolution, Volume 83, February 2015, Pages 250-257, ISSN 1055-7903, http://dx.doi.org/10.1016/j.ympev.2014.10.021.