Data from: A phylogenomic rodent tree reveals the repeated evolution of masseter architectures

Understanding the number of times a trait has evolved is a necessary
foundation for comprehending its potential relationships with selective
regimes, developmental constraints, and evolutionary diversification.
Rodents make up over 40% extant of mammalian species and their ecological
and evolutionary success has been partially attributed to the increase in
biting efficiency that resulted from a forward shift of one or two
portions of the masseter muscle from the zygomatic arch onto the rostrum.
This forward shift has occurred in three discrete ways, but the number of
times it has occurred has never been explicitly quantified. We estimated
an ultrametric phylogeny, the first to include all rodent families, using
thousands of ultraconserved elements. We examined support for evolutionary
relationships among the five rodent suborders and then incorporated
relevant fossils, fit models of character evolution, and used stochastic
character mapping to determine that a portion of the masseter muscle has
moved forward onto the rostrum at least seven times (with one reversal)
during the ca. 70 MY history of rodents. Combined, the repeated evolution
of this key innovation, its increasing prevalence through time, and the
species diversity of clades with this character underscores the adaptive
value of improved biting efficiency and the relative ease with which some
advantageous traits arise.