The World at the Time of Messel

Flat nails and scutiform distal phalanges characterize the hands and feet of primates. However, these display a variety of forms and combinations: Lemuroidea and Lorisoidea have a distinct pedal grooming claw; Daubentonia has additional claws; Tarsius has two pedal grooming claws; Callithrichidae have claws on fingers and most toes. The adapoid primates Darwinius and Europolemur from Messel have been interpreted both to have and to lack a grooming claw (Koenigswald, 1979; Franzen, 1994; Franzen et al., 2009). A single two-state character, “presence or absence of claws or grooming claws,” was used to represent claws in the cladistic analyses of Seiffert et al. (2009), Williams et al. (2010), and Gingerich et al. (2010). However, the distal phalanges in primates are quite diverse, and the claws or claw-like structures of primates may not be adequately represented by a single two-state character. In a detailed survey we provisionally distinguished 11 morphological types of distal phalanges in primates. Some are shown in Figs. 1–11. In the course of this survey, we realized that it is not sufficient to simply note the presence or absence of particular types of distal phalanges, their occurrence on specific fingers or toes having great significance as well. Many primate taxa have distal phalanges of different forms on different digits of the hands and feet. Thus in addition to characterizing the form of individual phalanges, the position and combination with other types of phalanges has to be recognized. Positions and combinations are especially important when isolated distal phalanges of fossils are discussed (Godinot 1992; Bloch et al., 2010) because their positions and combinations are unknowable. Very few skeletons of fossil primates are known that allow an unquestionable assignment of distal phalanges to specific fingers or toes. Messel in Germany is one of the few localities where such assignments are possible because the fossils are preserved in oil shale as partial or complete articulated skeletons.