Data from: Early Cenozoic increases in mammal diversity cannot be explained solely by expansion into larger body sizes

A prominent hypothesis in the diversification of placental mammals after
the Cretaceous/Paleogene (K/Pg) boundary suggests that the extinction of
non-avian dinosaurs resulted in the ecological release of mammals, which
were previously constrained to small body sizes and limited species
richness. This “dinosaur incumbency hypothesis” may therefore explain
increases in mammalian diversity via expansion into larger body sizes,
that were previously occupied by dinosaurs, but does not directly predict
increases in other body size classes. To evaluate this, we estimate
sampling-standardised diversity patterns of terrestrial North American
fossil mammals within body size classes, through the Cretaceous and
Paleogene. We find strong evidence for post-extinction diversity increases
in all size classes. Increases in the diversity of small-bodied species
(less than 100 g, the common body size class of Cretaceous mammals, and
much smaller than the smallest non-avialan dinosaurs [~400 g]) were
similar to those of larger species. We propose that small-bodied mammals
had access to greater energetic resources or were able to partition
resources more finely after the K/Pg mass extinction. This likely resulted
from a combination of widespread niche clearing due to the K/Pg mass
extinctions, alongside a suite of biotic and abiotic changes that occurred
during the Late Cretaceous and across the K/Pg boundary, such as shifting
floral composition, and novel key innovations among eutherian mammals.