Fig. 4 in The Mad2 Spindle Checkpoint Protein Undergoes Similar Major Conformational Changes upon Binding to Either Mad1 or Cdc20

Fig. 4. Putative homologies of molar features among toothed monotremes, occlusal views; mesial is to the left in all the drawings. A. Monotrematum, the geologically oldest upper molar known for monotremes (left upper molar shown). Outline restoration for M2 (A1); the same in stipple drawing (A2). B. Steropodon, the geologically oldest lower molars known for monotremes (left lower molars shown). Diagrammatic drawing (B1); the same in stippled drawing (B2). C. Obdurodon dicksoni. Left upper molars (C1); left lower ultimate premolar and first molar (C2). D. Hypothetical occlusal relationship of the upper and lower molars for basal monotremes; hypothetical models of upper molar (reversed crown view of right M2 of Monotrematum) and lower molars (crown view of Steropodon). Hypothetical contacting relations between the upper and the lower structures at the beginning of occlusion (D1); contacting relations near the mid−point of occlusion (analogous to the centric occlusion in the boreosphenidan mammals with the "pestle−to−mortar" occlusion (D2); contacting relations near of the end of the occlusal cycle (D3). The matching of the upper and the lower molar models is based on the similarity in the lowers between Steropodon and Obdurodon dicksoni and the similarity in the uppers of Monotrematum and O. dicksoni. E. Three stages (E1–E3) showing the sequence of upper−to−lower occlusion, in correspondence with D1–D3, as the lower molars moved across the transversely wider upper molar. Arrows denote direction of movement of the lower molars. Relative positions of the overlapping upper and lower molars of E1, E2, and E3 correspond to the contact points of the upper and lower structures labelled in D1–D3. See text for explanation. All original drawings, based on: A, photos of Pascual et al. (1992a, b) reversed; B, a cast of the holotype, reversed; C, SEM photos of Archer et al. (1993), with premolar reversed from the right side to be consistent with the left m1; D and E originals.