Mosasauroid phylogeny under multiple phylogenetic methods provides new insights on the evolution of aquatic adaptations in the group

Abstract

Mosasauroids were a successful lineage of squamate reptiles (lizards and snakes) that radiated during the Late Cretaceous (95–66 million years ago). They can be considered one of the few lineages in the evolutionary history of tetrapods to have acquired a fully aquatic lifestyle, similarly to whales, ichthyosaurs and plesiosaurs. Despite a long history of research on this group, their phylogenetic relationships have only been tested so far using traditional (unweighted) maximum parsimony. However, hypotheses of mosasauroid relationships and the recently proposed multiple origins of aquatically adapted pelvic and pedal features in this group can be more thoroughly tested by methods that take into account variation in branch lengths and evolutionary rates. In this study, we present the first mosasauroid phylogenetic analysis performed under different analytical methods, including maximum likelihood, Bayesian inference, and implied weighting maximum parsimony. The results indicate a lack of congruence in the topological position of halisaurines and Dallasaurus. Additionally, the genus Prognathodon is paraphyletic under all hypotheses. Interestingly, a number of traditional mosasauroid clades become weakly supported, or unresolved, under Bayesian analyses. The reduced resolutions in some consensus trees create ambiguities concerning the evolution of fully aquatic pelvic/pedal conditions under many analyses. However, when enough resolution was obtained, reversals of the pelvic/pedal conditions were favoured by parsimony and likelihood ancestral state reconstructions instead of independent origins of aquatic features in mosasauroids. It is concluded that most of the observed discrepancies among the results can be associated with different analytical procedures, but also due to limited postcranial data on halisaurines, yaguarasaurines and Dallasaurus.

Estimating the evolutionary rates in mosasauroids and plesiosaurs: discussion of niche occupation in Late Cretaceous seas

“…Each of the 3 replicate runs involved 10 million steps with sampling every 1,000 generations, with a burnin of 4 million steps. This protocol is similar to the one followed by Simões et al (2017) but used an additional independent run for each analysis (i.e., three instead of two) and set a more conservative burnin (40% instead of 25%). We used Tracer 1.5 (Rambaut & Drummond, 2009) to determine whether the runs reached stationary phase, and to assess convergence of the independent runs.…”

“…The mosasauroid matrix was acquired from Simões et al (2017), which is a recent version of the dataset first introduced in Bell's (1993) PhD thesis and published by Bell (1997). The recent version of Simões et al (2017) was further modified with respect to some taxon names (as in Madzia & Cau, 2017). In sum, the dataset consists of 44 operational taxonomic units (OTUs) analyzed using 125 characters (see Supplemental Information II for BEAST file, Supplemental Information III for NEXUS file, and Supplemental Information IV for character list).…”

An Enigmatic Miniaturized and Attenuate Whole Lizard from the Mid-Cretaceous Amber of Myanmar

“…Early and Late Cretaceous squamate faunas frequently contain forms with morphological adaptations to an aquatic envir o n m e n t , p r o b a b l y r e l a t e d t o t h e development of shallow seas (associated with a rise of the sea level) and to high sea-surface temperatures (Rage, 2013) and the favorable conditions for fossilization that these conditions provide. These include ''aigialosaurs,'' ''dolichosaurs,'' and closely related forms, all considered nonmosasaurid pythonomorphs (Caldwell, 2000;Rage and N´eraudeau, 2004;Sim˜oes et al, 2017). Although these forms resemble Barlochersaurus in having elongated bodies and attenuated limbs, they are readily distinguishable on the basis of their evident adaptations to an aquatic lifestyle (including pachyostosis, paddlelike limb, and very long necks, among others).…”

“…Nonetheless, even if Barlochersaurus was a terrestrial lizard, it cannot be ruled out that it might belong to a group sister to aquatic pythonomorphs. Besides this aquatic radiation, which would ultimately give rise to the large mosasaurs, many of the main extant groups of terrestrial anguimorphs were already known in the Late Cretaceous (Sim˜oes et al, 2017).…”

A New Hypothesis of the Phylogenetic Relationships of the Tylosaurinae (Squamata: Mosasauroidea)

“…There have been attempts to examine the position of Mosasauridae within Squamata (Rieppel, 1980;Carroll and deBraga, 1992;deBraga and Carroll, 1993;Caldwell et al, 1995;Caldwell, 1996Caldwell, , 1999Conrad, 2009;Gauthier et al, 2012;Reeder et al, 2015), and the relationships of the lineages within Mosasauridae (Bell, 1993(Bell, , 1997Caldwell, 1996;Polcyn and Bell, 2005;Caldwell and Palci, 2007;Leblanc et al, 2012;Palci et al, 2013;Jiménez-Huidobro et al, 2018). However, none of these studies have been focused on tylosaurine mosasaurs, and none have included a revision of all tylosaurine species and thus all valid terminal taxa.…”