A long-standing hypothesis in adaptive radiation theory is that ecological opportunity constrains rates of phenotypic evolution, generating a burst of morphological disparity early in clade history. Empirical support for the early burst model is rare in comparative data, however. One possible reason for this lack of support is that most phylogenetic tests have focused on extant clades, neglecting information from fossil taxa. Here, I test for the expected signature of adaptive radiation using the outstanding 40-My fossil record of North American canids. Models implying time- and diversity-dependent rates of morphological evolution are strongly rejected for two ecologically important traits, body size and grinding area of the molar teeth. Instead, Ornstein–Uhlenbeck processes implying repeated, and sometimes rapid, attraction to distinct dietary adaptive peaks receive substantial support. Diversity-dependent rates of morphological evolution seem uncommon in clades, such as canids, that exhibit a pattern of replicated adaptive radiation. Instead, these clades might best be thought of as deterministic radiations in constrained Simpsonian subzones of a major adaptive zone. Support for adaptive peak models may be diagnostic of subzonal radiations. It remains to be seen whether early burst or ecological opportunity models can explain broader adaptive radiations, such as the evolution of higher taxa.
Maximum clade credibility tree from topology-only Bayesian analysis of canid morphological data
Maximum clade credibility tree from Bayesian tip-dating analysis of canid morphological data. Branch lengths are in units of millions of years
An R data object containing p and t files, as well as the tree with the highest Likelihood, from the Bayesian tip dating analysis of canid morphological data. Note that branch lengths for trees in the t files are not in units of millions of years; to obtain time scaled branch lengths, one needs to divide lengths by the corresponding clock rate from the p files
a csv file containing ecomorphological data for extant canids and select non-canid caniforms. Data used in discriminant analyses for classifying fossil canids to dietary regimes.
a .csv file containing mean ecomorphological trait values for fossil canids. used in discriminant function analyses and in subsequent macroevolutionary analyses
CSV file containing Ln(body mass), relative grinding areas and dietary classifications for fossil and extant North American canids used in macroevolutionary analyses
An R script used to perform discriminant analyses for classifying fossil canids to dietary regimes
discrete trait analyses
An R script for performing analyses of dietary evolution under Markov models. The script fits models and estimates rates to the best tree and a sample of 500 trees from the posterior distribution (see posteriorSample.csv)
continuous trait analyses
An R script for performing analyses of body size and relative grinding area evolution. The script fits models to a sample of trees drawn from the posterior distribtion (see posteriorSample.csv)
CSV file containing a single column - these are the trees sampled from the posterior distribution when accounting for phylogenetic uncertainty in macroevolutionary model fitting.
A nexus data file containing 123 characters coded for 133 living and fossil canids. The MrBayes block contains blocks to perform both topology-only and tip-dating analyses. Comments are provided showing which blocks to uncomment to perform specific analyses.