Calibrated diversity, tree topology and the mother of mass extinctions: the lesson of temnospondyls

<p>Three family-level cladistic analyses of temnospondylamphibians are used to evaluate the impact oftaxonomic rank, tree topology, and sample size on diversityprofiles, origination and extinction rates, and faunal turnover.Temnospondyls are used as a case study for investigatingreplacement of families across the Permo-Triassicboundary and modality of recovery in the aftermath of theend-Permian mass extinction. Both observed and inferred(i.e. tree topology-dependent) values of family diversity havea negligible effect on the shape of the diversity curve. However,inferred values produce both a flattening of the curvethroughout the Cisuralian and a less pronounced increase infamily diversity from Tatarian through to Induan than doobserved values. Diversity curves based upon counts of generaand species display a clearer distinction between peaksand troughs. We use rarefaction techniques (specifically, rarefactionof the number of genera and species within families)to evaluate the effect of sampling size on the curve of estimatedfamily-level diversity during five time bins (Carboniferous;Cisuralian; Guadalupian–Lopingian; Early Triassic;Middle Triassic–Cretaceous). After applying rarefaction, wenote that Cisuralian and Early Triassic diversity values arecloser to one another than they are when the observed numberof families is used; both values are also slightly higherthan the Carboniferous estimated diversity. The Guadalupian–Lopingian value is lower than raw data indicate, reflectingin part the depauperate land vertebrate diversity fromthe late Cisuralian to the middle Guadalupian (Olson’s gap).The time-calibrated origination and extinction rate trajectoriesplot out close to one another and show a peak in theInduan, regardless of the tree used to construct them. Originationand extinction trajectories are disjunct in at leastsome Palaeozoic intervals, and background extinctions exerta significant role in shaping temnospondyl diversity in thelowermost Triassic. Finally, species-, genus-, and family trajectoriesconsistently reveal a rapid increase in temnospondyldiversity from latest Permian to earliest Triassic as well as adecline near the end of the Cisuralian. However, during therest of the Cisuralian family diversity increases slightly andthere is no evidence for a steady decline, contrary to previousreports.</p>