Data from: Slow and fast evolutionary rates in the history of lepidosaurs

Biodiversity today is uneven, with equally ancient sister groups
containing few or many species. It has often been assumed that high
biodiversity indicates fast evolution, and yet in a classic work in 1944
George Simpson suggested that fast evolution might generate instability
and extinction, and that slow evolution led to high biodiversity. Here we
show that evolutionary rates can vary substantially through the history of
a clade and find evidence for Simpson’s claim. In a comparative
phylogenetic study deploying Bayesian methods, we find that Squamata,
comprising today over 10,000 species of lizards and snakes, showed slow
rates of evolution in the first two-thirds of their history, whereas their
sister clade, Rhynchocephalia, comprising just one living species, showed
high rates of evolution in the past. Slow and steady won the race for the
Mesozoic squamates, and the high-rate boom and bust existence of
rhynchocephalians at that time leaves them with a single survivor. We need
to explore other cases where fast evolution can lead to short-term high
diversification, but in the end long-term low biodiversity.