A new, exceptionally preserved juvenile specimen of Eusaurosphargis dalsassoi (Diapsida) and implications for Mesozoic marine diapsid phylogeny

Abstract

Recently it was suggested that the phylogenetic clustering of Mesozoic marine reptile lineages, such as thalattosaurs, the very successful fish-shaped ichthyosaurs and sauropterygians (including plesiosaurs), among others, in a so-called ‘superclade’ is an artefact linked to convergent evolution of morphological characters associated with a shared marine lifestyle. Accordingly, partial ‘un-scoring’ of the problematic phylogenetic characters was proposed. Here we report a new, exceptionally preserved and mostly articulated juvenile skeleton of the diapsid reptile, Eusaurosphargis dalsassoi, a species previously recovered within the marine reptile ‘superclade’, for which we now provide a revised diagnosis. Using micro-computed tomography, we show that besides having a deep skull with a short and broad rostrum, the most outstanding feature of the new specimen is extensive, complex body armour, mostly preserved in situ, along its vertebrae, ribs, and forelimbs, as well as a row of flat, keeled ventrolateral osteoderms associated with the gastralia. As a whole, the anatomical features support an essentially terrestrial lifestyle of the animal. A review of the proposed partial character ‘un-scoring’ using three published data matrices indicate that this approach is flawed and should be avoided, and that within the marine reptile ‘superclade’ E. dalsassoi potentially is the sister taxon of Sauropterygia.

A tiny new Middle Triassic stem-lepidosauromorph from Germany: implications for the early evolution of lepidosauromorphs and the Vellberg fauna

“…Palaeagama 12,13 -whereas crown lepidosauromorphs are first recognized in the Middle Triassic, represented by the oldest known squamate 2 and rhynchocephalians 14,15 . However, the Triassic record of lepidosauromorphs is, in general, still extremely poor when compared to other lineages of diapsid reptiles [4][5][6][7] . Currently, only a few Triassic localities provide diagnostic lepidosauromorph taxa, including: the Czatkowice quarry in Poland (Early Triassic); the Vellberg locality in Germany (Middle Triassic); the Dont Formation in the Italian dolomites (Middle Triassic); the Lossiemouth Sandstone Formation in Northeast Scotland (Middle-Late Triassic); the Santa Maria Formation (Linha Bernardino locality) and Caturrita Formation (Linha São Luiz locality), in Southern Brazil (Late Triassic); and the Tytherington and Cromhall quarries in South West Britain (Late Triassic) 14,[16][17][18][19][20][21] .…”

“…Despite the most recent divergence time estimates based on molecular and morphological data indicating the origin of most diapsid lineages during the Permian 1,2 , several lineages of diapsids are recognized in the fossil record for the first time only in the Middle Triassic, such as squamates, rhynchocephalians, tanystropheids, and drepanosaurs [2][3][4] . Other lineages that first appeared in the fossil record in the Early Triassic or Late Permian considerably increase in abundance and taxonomic representation during the Middle Triassic, such as ichthyosauromorphs, sauropterygians, and turtles [5][6][7] . Additionally, there is a generally poor vertebrate fossil record for the Early Triassic, partially owing to the relatively long period of recovery from the Permian-Triassic mass extinction 8,9 .…”

Sensory Evolution and Ecology of Early Turtles Revealed by Digital Endocranial Reconstructions

“…Unique morphological characters, including the anapsid cranial configuration, which lacks temporal fenestrations, and the presence of a bony shell formed by a dorsal carapace and a ventral plastron have long obfuscated the phylogenetic affinities of turtles (Rieppel, 2007;Lyson et al, 2010). While most molecular studies have recovered turtles nested within diapsid reptiles and often as a sister-group to Archosauria (birds and crocodiles) (Hedges and Poling, 1999;Wang et al, 2013;Field et al, 2014), most studies based on comparative anatomy have placed turtles outside of Diapsida (Gauthier et al, 1988;Lee, 1997;Werneburg and Sánchez-Villagra, 2009;Neenan et al, 2013;Scheyer et al, 2017) or alternatively inside Lepidosauromorpha (deBraga and Rieppel, 1997;Rieppel and Reisz, 1999;Li et al, 2008;Liu et al, 2011). The scant fossil record of stem-turtles (i.e., non-Testudines Testudinata) has further obscured the evolutionary origin of this group.…”

Hindfins ofIchthyosaurus: effects of large sample size on ‘distinct’ morphological characters

“…Both studies hypothesized the origin of Ichthyopterygia before the divergence of archosauromorphs (which includes crocodiles) and lepidosauromorphs (which includes lizards). More recently, Scheyer et al (2017, fig. 12) proposed a phylogeny in which archosauromorphs, lepidosauromorphs and Ichthyopterygia diverged at the same time.…”