Olson (1983) questioned the hypothesis that the order Piciformes is monophyletic and suggested instead that each piciform suborder is allied with a nonpiciform group. His attempt to discredit the synapomorphies joining the Galbulae and Pici is refuted by corrections of his interpretations of previous work. The Piciformes share a complex derived hindlimb morphology involving zygodactyly, a tripartite flexor hallucis longus, and Type VI flexor tendons. Olson's argument for polyphyly combines inadequate data with the inappropriate technique of equating general overall similarity with affinity. His hypothesis is therefore rejected. Problems concerning fossil taxa are also discussed. Based on current information, we believe that a monophyletic origin of the Piciformes remains the hypothesis of choice.
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Raikow et al. (1983) studied this question.
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