Data from: Evolutionary tempo, supertaxa and living fossils

A relationship between the rate of molecular change and diversification
has long been discussed, on both theoretical and empirical grounds.
However, the effect on our understanding of evolutionary patterns is yet
to be fully explored. Here we develop a new model, the Covariant
Evolutionary Tempo (CET) model, with the aim of integrating patterns of
diversification and molecular evolution within a framework of a
continuously changing ‘tempo’ variable that acts as a master control for
molecular, morphological and diversification rates. Importantly, tempo
itself is treated as being variable at a rate proportional to its own
value. This model predicts that diversity is dominated by a small number
of extremely large clades at any historical epoch including the present;
that these large clades are expected to be characterised by explosive
early radiations accompanied by elevated rates of molecular evolution; and
that extant organisms are likely to have evolved from species with
unusually fast evolutionary rates. Under such a model, the amount of
molecular change along a particular lineage is essentially independent of
its height, which weakens the molecular clock hypothesis. Finally, our
model explains the existence of ‘living fossil’ sister groups to large
clades that are species poor and exhibit slow rates of morphological and
molecular change. Our results demonstrate that the observed historical
patterns of evolution can be modelled without invoking special
evolutionary mechanisms or innovations that are unique to specific times
or taxa, even when they are highly non-uniform.