Fig 1.
The skull and dentition of the primitive deperetellid tapiroid Irenolophus qii gen. et sp. nov. (IVPP V 25831) from the late early Eocene of the Erlian Basin, Inner Mongolia, China.
(A) left lateral view of skull and mandible. (B) right lateral view of skull. (C) dorsal and (D) ventral views of the skull. (E) occlusal view of the mandible. (F-H) line drawing of the skull and mandible in lateral view (F), left P1-M3 in occlusal view (G), and right p2-m3 in occlusal view (H).
Fig 2.
Scatter plot of P4-M1 (A-B) and p3-m1 (C-E) proportions in Irenolophus and other deperetellids, with regression lines for width as the function of length in Teleolophus (see S1 Table).
Fig 3.
Carpals of the primitive deperetellid Irenolophus qii gen. et sp. nov. (IVPP V 25831).
A reconstruction of articulated left carpals (reversed) in anterior view in the center. (A to D) right scaphoid in proximal (A), lateral (B), distal (C), and medial (D) views. (E to I) right lunar in proximal (E), medial (F), lateral (G), distal (H), and anterior (I) views. (J to L) right trapezium in proximal (J), anterior (K), and posterior (L) views. (M to P) right magnum in proximal (M), medial (N), lateral (O), and distal (P) views. (Q to T) right unciform in anterior (Q), proximal (R), medial (S), and distal (T) views. Abbreviations: c, cuneiform; l, lunar; m, magnum; r, radius; s, scaphoid; td, trapezoid; tm, trapezium; u, unciform; III, IV, V, third, fourth, and fifth metacarpals.
Table 1.
Measurements of skull and mandible of Irenolophus qii (mm).
Table 2.
Measurements of upper teeth of Irenolophus qii and I. primarius (mm).
Table 3.
Measurements of lower teeth of Irenolophus qii and I. primarius (mm).
Table 4.
Measurements of some carpals of Irenolophus qii (IVPP V 25831) (mm) Measurements correspond to the tables 14, 15, 17, and 42 of Qiu and Wang [15].
Fig 4.
Upper cheek teeth and lower jaw of deperetellid Irenolophus primarius from the Arshanto Formation at Huheboerhe of the Erlian Basin, Inner Mongolia, China.
(A) occlusal view of the left maxilla with P2-M1, and M2–3 fragments (AMNH FM 81851). (B-D) lower jaw with right c, left i3, c, and p1-m3 in occlusal (B), lingual (C), and buccal (D) views (AMNH FM 81799).
Fig 5.
Right mandible of deperetellid Irenolophus sp. (IVPP V 25832) from the Arshanto Formation at Nuhetingboerhe of the Erlian Basin, Inner Mongolia, China.
(A) occlusal, (B) lingual, and (C) buccal views of the right mandible.
Fig 6.
Enamel microstructure of the second lower molar of deperetellid Irenolophus sp. (IVPP V 25832).
(A) vertical Hunter-Schreger Bands (HSB) in anterior view of the protolophid. (B) vertical HSB in the cross sections with polarized light and ordinary light; arrows showing the ordinary light directions. (C) vertical HSB and transitional zones in cross section. (D) prism shape in cross section. (E) parazone, diazone, and transitional zones in the tangential section. (F) Schmelzmuster in the vertical section. Abbreviations: d, diazone; EDJ, enamel-dentine junction; IPM, interprismatic matrix; P, prism; p, parazone; S, seam; and t, transitional zone.
Fig 7.
The gradational changes of premolars in tapiroid lineages with different patterns of the premolar molarization.
(A) The hypothesized phylogenetic relationships of Tapiroidea [12] with deperetellids added, showing the premolars of tapiroids gradually molarized through different patterns over time. The premolars in Tapiridae modified from Schlaikjer [40] (Museum of Comparative Zoology, Harvard University). (B) The three patterns of premolar molarization in perissodactyls modified from Holbrook [38]. All premolar series are shown from the left side, and the last tooth is P4. Abbreviations: pac, paraconule; pr, protocone; epc, endoprotocrista; hy, hypocone; and mel, metaconule. Scale bar = 10 mm.