An integrated, holistic analysis of the avian jaw apparatus within the system of avian cranial kinesis shows a complex series of movements of the two jaws, rather than just a simple opening and closing of both jaws. Because of the complex arrangement of the jaw muscles, birds have achieved different adaptive configurations of these muscles for various movement combinations. Specialization of the several jaw muscles are correlated, nevertheless, with independent movements of each jaw, such as the evolution of the M. ethmomandibularis in parrots for independent raising of the lower jaw and the M. pterygoideus retractor in several avian groups for independent lowering of the upper jaw.
The mammalian order Lagomorpha (hares, rabbits, pikas) comprises two families (Ochotonidae and Leporidae; McKenna and Bell 1998; Nowak 1999), and Recent members have a nearly world−wide distribution (Hoffman 1993; Nowak 1999). Detailed examination of the pedal morphology of extant and fossil lagomorphs revealed a unique channel (the “calcaneal canal”) running diagonally through the lagomorph calcaneus. The ancientness, ubiquity, and appearance of the calcaneal canal in all, including the earliest recognized lagomorph calcanea, and its absence from the pedes of other mammalian taxa, may indicate a long evolutionary separation of lagomorphs from other, previously suggested lagomorph relatives.
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