Data from: Cope’s rule and the adaptive landscape of dinosaur body size evolution

The largest known dinosaurs weighed at least 20 million times as much as
the smallest, indicating exceptional phenotypic divergence. Previous
studies have focused on extreme giant sizes, tests of Cope's rule,
and miniaturization on the line leading to birds. We use non-uniform
macroevolutionary models based on Ornstein–Uhlenbeck and trend processes
to unify these observations, asking: what patterns of evolutionary rates,
directionality and constraint explain the diversification of dinosaur body
mass? We find that dinosaur evolution is constrained by attraction to
discrete body size optima that undergo rare, but abrupt, evolutionary
shifts. This model explains both the rarity of multi-lineage directional
trends, and the occurrence of abrupt directional excursions during the
origins of groups such as tiny pygostylian birds and giant sauropods. Most
expansion of trait space results from rare, constraint-breaking
innovations in just a small number of lineages. These lineages shifted
rapidly into novel regions of trait space, occasionally to small sizes,
but most often to large or giant sizes. As with Cenozoic mammals,
intermediate body sizes were typically attained only transiently by
lineages on a trajectory from small to large size. This demonstrates that
bimodality in the macroevolutionary adaptive landscape for land
vertebrates has existed for more than 200 million years.