The oldest parareptile and the early diversification of reptiles

Abstract

Amniotes, tetrapods that evolved the cleidoic egg and thus independence from aquatic larval stages, appeared ca 314 Ma during the Coal Age. The rapid diversification of amniotes and other tetrapods over the course of the Late Carboniferous period was recently attributed to the fragmentation of coalswamp rainforests ca 307 Ma. However, the amniote fossil record during the Carboniferous is relatively sparse, with ca 33% of the diversity represented by single specimens for each species. We describe here a new species of reptilian amniote that was collected from uppermost Carboniferous rocks of Prince Edward Island, Canada. Erpetonyx arsenaultorum gen. et sp. nov. is a new parareptile distinguished by 29 presacral vertebrae and autapomorphies of the carpus. Phylogenetic analyses of parareptiles reveal E. arsenaultorum as the closest relative of bolosaurids. Stratigraphic calibration of our results indicates that parareptiles began their evolutionary radiation before the close of the Carboniferous Period, and that the diversity of end-Carboniferous reptiles is 80% greater than suggested by previous work. Latest Carboniferous reptiles were still half as diverse as synapsid amniotes, a disparity that may be attributable to preservational biases, to collecting biases, to the origin of herbivory in tetrapods or any combination of these factors.

Commentary: A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes

“…Furthermore, since the Laurin and Reisz (1995) matrix was published there have been more than 20 new parareptiles described from across the clade, such as M. mckinzieorum (Tsuji et al, 2010), Emeroleter levis (Tsuji et al, 2012), Delorhynchus cifelli , Abyssomedon williamsi (MacDougall and , and the earliest parareptile Erpetonyx arsenaultorum (Modesto et al, 2015). The absence of any new parareptile taxa, aside from A. pteroticus and O. kitchingorum, is problematic, as the authors have ignored the vast majority of parareptile research that has occurred in the last two decades.…”

“…Later studies recovered mesosaurs in varying places within Amniota, with one study recovering mesosaurs as the basal-most lineage of a clade to which the name Sauropsida was attached (Laurin and Reisz, 1995). Numerous others recover it as the sister to all other parareptile clades (Tsuji et al, 2012;Modesto et al, 2015;MacDougall et al, 2016MacDougall et al, , 2017 replicating the results of Gauthier et al (1988), and one study recovers the clade being nested within Parareptilia as the sister taxon of bolosaurids (Bever et al, 2015). 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.…”

New occurrences of tetrapod ichnotaxa from the Permian Orobic Basin (Northern Italy) and critical discussion of the age of the ichnoassociation

“…These tracks radiate by the late Cisuralian (Artinskian–Kungurian), probably reflecting a radiation of the Reptilia (Modesto et al . , ). Hyloidichnus only occurs in Artinskian to Lopingian strata (Gand & Durand ; Hminna et al .…”

“…; Modesto et al . , ). The diversification and dispersal of Reptilia tracks in the late Cisuralian (Artinskian – early Kungurian) has been discussed in several studies (Haubold & Lucas , ; Gand & Durand ; Lucas et al .…”

A case study of developmental palaeontology in <i>Stereosternum tumidum</i> (Mesosauridae, Parareptilia)

“…Hypothesized viviparity in Mesosaurus is another potential indicator of a fully aquatic lifestyle (Piñeiro et al, 2012a). Most recent studies suggest mesosaurs group basally within parareptiles; a small amniote clade that originated in the Late Carboniferous (Tsuji and Müller, 2009;Modesto et al, 2015; though see contradictory hypothesis of Laurin and Piñeiro, 2017). Evolutionary novelties in this clade include impedence-matching hearing in nycteroleterids (Müller and Tsuji, 2007), caudal regeneration in mesosaurs (Delfino and Sánchez-Villagra, 2010), derived feeding mechanisms and bipedality in bolosaurids (Reisz et al, 2007;Berman et al, 2000), and secondarily aquatic lifestyles as well as (ovo)viviparity in mesosaurids (Modesto, 2006;Piñeiro et al, 2012a), all of which occurred in parareptiles as early as the Early Permian.…”