Abstract
The biogeographical history of pterosaurs has received very little treatment. Here, we present the first quantitative analysis of pterosaurian biogeography based on an event-based parsimony method (Treefitter). This approach was applied to a phylogenetic tree comprising the relationships of 108 in-group pterosaurian taxa, spanning the full range of this clade's stratigraphical and geographical extent. The results indicate that there is no support for the impact of vicariance or coherent dispersal on pterosaurian distributions. However, this group does display greatly elevated levels of sympatry. Although sampling biases and taxonomic problems might have artificially elevated the occurrence of sympatry, we argue that our results probably reflect a genuine biogeographical signal. We propose a novel model to explain pterosaurian distributions: pterosaurs underwent a series of ‘sweep-stakes’ dispersal events (across oceanic barriers in most cases), resulting in the founding of sympatric clusters of taxa. Examination of the spatiotemporal distributions of pterosaurian occurrences indicates that their fossil record is extremely patchy. Thus, while there is likely to be genuine information on pterosaurian diversity and biogeographical patterns in the current data-set, caution is required in its interpretation.
Highlights
After their origin in the Middle or Late Triassic, pterosaurs acquired a virtually global distribution and their remains are known from every continent, including Antarctica (Barrett et al 2008; see Fossilworks and The Paleobiology Database)
5 Discussion 5.1 Interpretation of results The statistically significant Standard costs’ (SCs) results for the ‘all taxa’ and most time slices (Table 2) are interesting because they suggest that there is some non-random signal in the pterosaurian data. This signal pertains to elevated levels of sympatry rather than area relationships formed in response to palaeogeographical events
Our analyses suggest that there is no convincing statistical support for area relationships among pterosaurs or for the dominance of particular types of biogeographical processes such as vicariance or dispersal
Summary
After their origin in the Middle or Late Triassic, pterosaurs acquired a virtually global distribution and their remains are known from every continent, including Antarctica (Barrett et al 2008; see Fossilworks and The Paleobiology Database). We briefly review the small number of previous studies that have proposed hypotheses to account for aspects of the spatiotemporal distributions of pterosaurs We test these and other hypotheses by applying a cladistic biogeographical analysis using Treefitter 1.2b (Ronquist 1998; Sanmartin and Ronquist 2004), to a recent phylogeny for pterosaurs (Andres et al 2014) termed here the ‘reference phylogeny’ (Figures 1 and 2), in order to determine whether there is any statistical support for particular distribution patterns. Such analyses enable an assessment of the relative importance of processes such as vicariance, dispersal, extinction and sympatric speciation in pterosaurian evolution. We end with a brief discussion of the quality of the pterosaurian fossil record and future requirements and prospects for further work on the biogeographical history of this clade
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