A time-calibrated phylogeny of the attine fungus-growing ants with age estimates for the origins of the five known ant agricultural systems. Agricultural systems, indicated by colored rectangles, are defined by phylogenetically distinct groups of associated fungal cultivars and were reconstructed under likelihood and parsimony methods with identical results. Tree topology is the maximum-likelihood reconstruction, identical with regard to attine phylogeny to the Bayesian codon-model result. Numbers on branches indicate support values from four analyses: parsimony bootstraps, ML bootstraps, Bayesian nucleotide-model posterior probabilities, and Bayesian codon-model posterior probabilities (“−,” < 50; “*,” 100). The three solid circles represent node assignments for Dominican amber fossil calibrations, and the open circle marks the root of the dating-analysis tree. Bars below the time scale summarize four separate relaxed-molecular-clock analyses dating the origin of the five agricultural systems. Black bars represent the most recent node containing all members of the system (“crown-group”) and red bars additionally include the branch leading to that node (“stem-group”). For each system, pairs of red and black bars from top to bottom correspond to (i) Bayesian uncorrelated lognormal, root age prior to 73.5 ± 4.5 mya; (ii) penalized likelihood, root age 81 mya; (iii) penalized likelihood, root age 73.5 mya; (iv) penalized likelihood, root age 66 mya. The tree shown here is the result of dating analysis (iii). Ant head photos (top to bottom): Mycocepurus tardus, Myrmicocrypta infuscata, Apterostigma collare, Mycetophylax emeryi, Cyphomyrmex rimosus, Cyphomyrmex longiscapus, Trachymyrmex opulentus, Trachymyrmex cornetzi, Acromyrmex octospinosus, Atta laevigata. Fungus gardens: (A) Lower attine agriculture. (B) Coral fungus agriculture. (C) Yeast agriculture. (D) Higher leaf-cutter agriculture. Country abbreviations: ARG, Argentina; AUS, Australia; BRAZ, Brazil; CR, Costa Rica; MAD, Madagascar; CR, Costa Rica; JAP, Japan; PAN, Panama; GUAT, Guatemala; GUY, Guayana; TRI, Trinidad; MEX, Mexico. Photo credits are given in Acknowledgments.