The first global-scale phylogenetic network biogeography analysis of late Paleozoic and early Mesozoic terrestrial vertebrates and the influence of mass extinctions on animal distribution

BUTTON, DAVID J.; BUTLER, R. J.; LLOYD, GRAEME T.; EZCURRA, M. D.

Congreso; SVP anual meeting 2016; 2016

The Triassic was a pivotal time in the evolution of life, recording the biotic recoveryfrom the end Permian mass extinction. However, the presence of Pangaea complicatesour understanding of biogeographic processes during this interval. Although this wouldmean few physical barriers to dispersal, faunal provinciality may have been driven bylatitudinal and seasonal climate variation. The overlap between contemporaneous faunascan be quantified as the biogeographic connectedness (BC), the density of links in ataxon-locality network. Recent work has identified a reduction in BC in the MiddleTriassic relative to the late Permian in southern Gondwana. This has been used to arguefor the breakup of a cosmopolitan Early Triassic ?disaster fauna?, a result of the endPermian mass extinction, at this time. However, it is unknown if this local signal isrepresentative of global trends and BC during the Early and Late Triassic has yet to bequantified. In addition, calculation of BC to-date has not included phylogeneticinformation, instead treating taxa as independent entities. This likely underestimates thelinks between localities and renders results sensitive to taxonomic lumping or splittingand temporal differences between sampled localities.We address these problems by employing a novel method incorporatingphylogenetic information into the calculation of BC by weighting links between taxaaccording the phylogenetic distance between them. Bias due to increasing distance fromthe root through time is avoided by truncating the maximum length of branches prior tothe start of each time bin by a constant, k. This method is applied to a time-calibratedsupertree and global occurrence data of 1085 terrestrial amniote species, pooled into ninedistinct biogeographic regions. The phylogenetic BC of this network was calculated foreight time bins from the late Permian through to the end of the Early Jurassic. Results aresensitive to variation of k, but consistent patterns emerge. Global BC values remain highfrom the late Permian through to the end of the Ladinian, but decrease strongly in theLate Triassic and continue to decline in the Early Jurassic. These results demonstrate thata mainly cosmopolitan fauna was maintained until the end of the Middle Triassic, longerthan suggested by previous studies. This discrepancy may be due to differences betweenlocal and global patterns. In contrast, high provinciality occurs across the Triassic?Jurassic boundary indicating that biogeographic responses to mass extinctions are notuniform in terrestrial faunas.