Abstract

Three family-level cladistic analyses of temnospondyl
amphibians are used to evaluate the impact of
taxonomic rank, tree topology, and sample size on diversity
profiles, origination and extinction rates, and faunal turnover.
Temnospondyls are used as a case study for investigating
replacement of families across the Permo-Triassic
boundary and modality of recovery in the aftermath of the
end-Permian mass extinction. Both observed and inferred
(i.e. tree topology-dependent) values of family diversity have
a negligible effect on the shape of the diversity curve. However,
inferred values produce both a flattening of the curve
throughout the Cisuralian and a less pronounced increase in
family diversity from Tatarian through to Induan than do
observed values. Diversity curves based upon counts of genera
and species display a clearer distinction between peaks
and troughs. We use rarefaction techniques (specifically, rarefaction
of the number of genera and species within families)
to evaluate the effect of sampling size on the curve of estimated
family-level diversity during five time bins (Carboniferous;
Cisuralian; Guadalupian–Lopingian; Early Triassic;
Middle Triassic–Cretaceous). After applying rarefaction, we
note that Cisuralian and Early Triassic diversity values are
closer to one another than they are when the observed number
of families is used; both values are also slightly higher
than the Carboniferous estimated diversity. The Guadalupian–
Lopingian value is lower than raw data indicate, reflecting
in part the depauperate land vertebrate diversity from
the late Cisuralian to the middle Guadalupian (Olson’s gap).
The time-calibrated origination and extinction rate trajectories
plot out close to one another and show a peak in the
Induan, regardless of the tree used to construct them. Origination
and extinction trajectories are disjunct in at least
some Palaeozoic intervals, and background extinctions exert
a significant role in shaping temnospondyl diversity in the
lowermost Triassic. Finally, species-, genus-, and family trajectories
consistently reveal a rapid increase in temnospondyl
diversity from latest Permian to earliest Triassic as well as a
decline near the end of the Cisuralian. However, during the
rest of the Cisuralian family diversity increases slightly and
there is no evidence for a steady decline, contrary to previous
reports.