Abstract
Mosasauroid squamates represented the apex predators within the Late Cretaceous marine and occasionally also freshwater ecosystems. Proper understanding of the origin of their ecological adaptations or paleobiogeographic dispersals requires adequate knowledge of their phylogeny. The studies assessing the position of mosasauroids on the squamate evolutionary tree and their origins have long given conflicting results. The phylogenetic relationships within Mosasauroidea, however, have experienced only little changes throughout the last decades. Considering the substantial improvements in the development of phylogenetic methodology that have undergone in recent years, resulting, among others, in numerous alterations in the phylogenetic hypotheses of other fossil amniotes, we test the robustness in our understanding of mosasauroid beginnings and their evolutionary history. We re-examined a data set that results from modifications assembled in the course of the last 20 years and performed multiple parsimony analyses and Bayesian tip-dating analysis. Following the inferred topologies and the ‘weak spots’ in the phylogeny of mosasauroids, we revise the nomenclature of the ‘traditionally’ recognized mosasauroid clades, to acknowledge the overall weakness among branches and the alternative topologies suggested previously, and discuss several factors that might have an impact on the differing phylogenetic hypotheses and their statistical support.
Highlights
Mosasauroidea was a species-rich clade of squamates adapted to an aquatic lifestyle, with evolutionary history being recorded exclusively in the Upper Cretaceous strata (e.g., Russell, 1967; Bell, 1997; Polcyn et al, 2014)
High values of Decay Index (DI) were further calculated for the clade of advanced plioplatecarpines formed by Latoplatecarpus willistoni, Platecarpus tympaniticus, and Plioplatecarpus spp. (DI = 7 and 8, respectively), the clade of P. tympaniticus and Plioplatecarpus spp. (DI = 7 and 5), and the two species of the mosasaurine Globidens (DI = 8 and 5)
Considering that (1) the ‘dolichosaurs’ are traditionally regarded as non-mosasauroids, and (2) ‘aigialosaurs’ and mosasaurids are frequently inferred more closely related to each other than either is to the ‘dolichosaurs’, we propose a new definition that seems to adhere to the traditional use of Mosasauroidea (i.e., ‘aigialosaurs’ plus mosasaurids, but not ‘dolichosaurs’) and reflects the uncertainties surrounding the phylogenetic placements of near-mosasaurids and early mosasaurids as inferred, among others, in the present study
Summary
Mosasauroidea was a species-rich clade of squamates adapted to an aquatic lifestyle, with evolutionary history being recorded exclusively in the Upper Cretaceous strata (e.g., Russell, 1967; Bell, 1997; Polcyn et al, 2014). During their history, mosasauroids distributed globally and evolved different ecological strategies (Polcyn et al, 2014; Bardet et al, 2015). Recent analyses integrating morphological and molecular data show a good support for close relationships of Mosasauria and Serpentes within Toxicofera (Reeder et al, 2015)
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