Pedal distal phalanges of the Eocene adapoids Europolemur and Darwinius compared to phalanges of Notharctus and other primates
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Pedal distal phalanges of the Eocene adapoids Europolemur and Darwinius from Messel and Notharctus from Wyoming have been compared morphologically and metrically to representatives of all six superfamilies of extant primates. A detailed system of morphological types is established that differentiates pedal distal phalanges. Four major groups and 12 types can be recognised in primates. Primates additionally show a primary interruption of homogeneity (PIH) between the hallux and other pedal rays, as well as two distinct secondary interruptions of homogeneity (SIH) within more lateral pedal rays. Using morphology, PIH and SIH, we have developed a formula for pedal distal phalanges. Differences among Adapoidea are unexpectedly large. Notharctus shows less differentiation in the pedal phalanges than does Europolemur. Our analyses show that both species of Europolemur had a differentiated grooming claw. Preservation of the second distal phalanx in Darwinius is not sufficient for a detailed classification. Despite similarities of the grooming claws of Europolemur to those of some lemurs and lorises, we hesitate to classify adapoids with Lemuroidea and Lorisoidea as there are significant differences and a possibility of parallelism.