Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology
(A)— Bivariate plot of PC-I and PC-II, with both axes drawn to the same scale. All loadings for PC-I are similar and positive, indicating that PC-I represents body size (small primates are at left and larger primates are at right; the coefficient of determination (R2) for PC-I and body weight is greater than 0.8). Loadings for PC-II contrast thorax length and foot length, with climbers having a longer thorax and shorter foot, and leapers having a longer foot and shorter thorax. (B)— Bivariate plot of PC-III and PC-II, with both axes drawn to the same scale. Interpretation of PC-II is the same as in A, but here the scale is expanded. Loadings for PC-III contrast lumbus length and scapula length, with climbers having a longer lumbus and shorter scapula, and leapers having a longer scapula and shorter lumbus. Darwinius can be projected into this PCA in two ways: as the juvenile it is (filled red circle) or the adult it is projected to become (open red circle; projection computed by augmenting each body segment by the amount it is expected to grow to reach adulthood, using growth curves of . Position of Notharctus is shown for comparison, based on measurements in . Family abbreviations: Lemuroidea– Che, Cheirogaleiidae; Dau, Daubentoniidae; Ind., Indriidae; Lep, Lepilemuridae. Lorisoidea– Gal., Galagidae; Lor., Lorisidae. Tarsioidea– Tar., Tarsiidae. Ceboidea– Cal., Callitrichidae; Ceb., Ceboidea. Note that Darwinius falls in the middle of both plots, near Callitrichidae in size, and overlapping Lemuridae and Cebidae in trunk and limb proportions. Darwinius is interpreted as an arboreal quadruped specialized neither for slow climbing nor for leaping.