Abstract
The early amniote clade Mesosauridae has long been of interest to scientists, primarily due to the members of the clade being the oldest secondarily aquatic tetrapods and their role as a line of evidence for continental drift. In the landmark phylogenetic analysis of Parareptilia by Gauthier and colleagues in 1988, Mesosauridae was found to be the sister taxon of all included parareptiles. Over the last three decades several studies regarding the phylogenetic placement of mesosaurs have helped to reinforce their position as the most basal parareptile clade. The most recent study of Mesosauridae is by Laurin and Pineiro, who reassess the phylogenetic position of the clade within early amniotes. This new analysis recovered mesosaurs as being the sister clade to all other sauropsids, supporting the results of an earlier study by Laurin and Reisz in 1995. However, we feel that there are two main issues with this new study that need to be addressed. The first is the use of an outdated phylogenetic matrix and the fact that the authors patently ignore over two decades of parareptilian research when conducting their phylogenetic analysis, whereas the second involves the problems associated with lateral temporal fenestration and its extreme variability in reptiles. We discuss how these two issues could have influenced the results that were obtained from this study, and how, when they are taken into account, a different picture regarding the phylogenetic position of Mesosauridae is reconstructed to that of Laurin and Pineiro.
Highlights
The enigmatic amniote clade Mesosauridae has long been of interest to those that study Palaeozoic tetrapods, largely due to the fact that the group contains the oldest secondarily aquatic tetrapods
The 2017 paper “A Reassessment of the Taxonomic Position of Mesosaurs, and A Surprising Phylogeny of Early Amniotes” by Laurin and Piñeiro is the latest publication to tackle the issue of the phylogenetic position of Mesosauridae
A modified version of the data matrix from MacDougall et al (2017), which was itself based in part upon the Laurin and Reisz (1995) matrix, was used for the phylogenetic analyses presented in this study
Summary
The enigmatic amniote clade Mesosauridae has long been of interest to those that study Palaeozoic tetrapods, largely due to the fact that the group contains the oldest secondarily aquatic tetrapods. The 2017 paper “A Reassessment of the Taxonomic Position of Mesosaurs, and A Surprising Phylogeny of Early Amniotes” by Laurin and Piñeiro is the latest publication to tackle the issue of the phylogenetic position of Mesosauridae. The results of their phylogenetic analysis reaffirm the Laurin and Reisz (1995) placement of Mesosauridae at the very base of Sauropsida (sensu Laurin and Reisz, 1995, in which Sauropsida = Mesosauridae + Reptilia). Their phylogenetic analysis produced the unique tree topology of having the remaining Parareptilia nested within Eureptilia as the sister taxon of younginiforms
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