Data from: Phylogenetic evidence for a shift in the mode of mammalian body size evolution at the Cretaceous-Paleogene boundary

NOTE: Please also see Slater (2014) published in Methods in Ecology and
Evolution at http://dx.doi.org/10.1111/2041-210X.12201 1. Phylogenetic
comparative methods provide a powerful way of addressing classic questions
about tempo and mode of phenotypic evolution in the fossil record, such as
whether mammals increased in body size diversity after the
Cretaceous-Paleogene (K-Pg) extinction. 2. Most often, these kinds of
questions are addressed in the context of variation in evolutionary rates.
Shifts in the mode of phenotypic evolution provides an alternative and, in
some cases, more realistic explanation for patterns of trait diversity in
the fossil record but these kinds of processes are rarely tested for. 3.
In this study, I use a time-calibrated phylogeny of living and fossil
Mammaliaformes as a framework to test novel models of body size evolution
derived from paleontological theory. Specifically, I ask whether the K-Pg
extinction resulted in a change in rates of body size evolution or release
from a constrained adaptive zone. 4. I found that a model comprising an
Ornstein-Uhlenbeck process until the K-Pg event and a Brownian motion
process from the Cenozoic onwards was the best supported model for these
data. Surprisingly, results indicate a lower absolute rate of body size
evolution during the Cenozoic than during the Mesozoic. This is explained
by release from a stationary OU process that constrained realized
disparity. Despite a lower absolute rate, body size disparity has in fact
been increasing since the K-Pg event 5. The use of time-calibrated
phylogenies of living and extinct taxa and realistic, process-based models
provides unparalleled power in testing evolutionary hypotheses. However,
researchers should take care to ensure that the models they use are
appropriate to the question being tested, and that the parameters
estimated are intepreted in the context of the best-fitting model.