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Fig. 12 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 12. Comparison of orthal bite force (BF) distribution across lower tooth-row at closed gape (CG) and open gape (OG). A. Didelphis marsupialis Linnaeus, 1758, a generalized mammal showing relatively low orthal BF magnitudes at both CG and OG. B. Ursus arctos Linnaeus, 1758, which shows very little ability to preserve high orthal BF at high gape among the therians sampled, but has very high orthal BF at CG. C. Crocuta crocuta (Erxleben, 1777), a taxon capable of preserving a large amount of orthal BF at high gape, and showing similar orthal BF values at CG and OG. Color bar at right is scaled to units of the combined (across-taxa) sample standard deviation in estimated orthal bite force values (generated using all muscle categories, see text). Therefore, colors within the postcanine toothrow correspond to matching, size-scaled, orthal BF magnitudes across all sampled taxa (and in Peligrotherium tropicalis as seen in Fig. 6A).

Fig. 8. 2D in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 8. 2D histograms showing distribution of estimated force magnitudes for Group 1 (G1) and Group 2 (G2) muscle recruitment scenarios (on ordinate), as a function of mesiodistal location (MDL; on abscissa). A. Canis familiaris. B. Crocuta crocuta. C. Diceros bicornis. D. Didephis marsupialis. E. Equus quagga. F. Erinaceus europaeus. G. Procyon lotor. H. Puma concolor. I. Sus scrofa. J. Tayassu pecari. K. Tupaia sp. L. Ursus arctos. Abbreviations: BF, bite force; JF-W/B, working-/balancing-side joint force.

Fig. 7 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 7. Violin boxplots showing distribution of Group 1 minus Group 2 values (on left) and closed gape minus open gape values (on right) for N = 12 representative extant therians. A. Canis familiaris (domestic dog). B. Crocuta crocuta (spotted hyaena). C. Diceros bicornis (black rhino). D. Didephis marsupialis (opossum). E. Equus quagga (quagga). F. Erinaceus europaeus (European hedgehog). G. Procyon lotor (racoon). H. Puma concolor (mountain lion). I. Sus scrofa (domestic pig). J. Tayassu pecari (white-lipped peccary). K. Tupaia sp. (treeshrew). L. Ursus arctos (brown bear). Abbreviations: T, total bite force; O, orthal bite force. Vertical axes represent magnitude values in au.

Fig. 6 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 6. Results of closed gape minus open gape analysis of orthal bite force (BF) for Peligrotherium tropicalis Bonaparte, Van Valen, and Kramarz, 1993. A. Lower left working-side hemimandible of P. tropicalis shown in closed gape (CG) and open gape (OG) position, postcanine crown surfaces are colorized by relative orthal BF (warmer colors represent higher relative orthal BF, and correspond among the taxa seen in Fig. 12). B. Violin boxplot showing distribution of total CG minus OG BF and its orthal component marginal over all locations in the woking-side postcanine toothrow. C. 2D histogram plot showing distribution of estimated bifulcral force magnitudes for CG and OG, as a function of mesiodistal location (MDL). JF-W/B, working-/balancing-side joint force.

Fig. 9. 2D in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 9. 2D histograms showing distribution of estimated force magnitudes for closed gape (CG) and open gape (OG) mandible positions (on ordinate), as a function of mesiodistal location (MDL; on abscissa). A. Canis familiaris. B. Crocuta crocuta. C. Diceros bicornis. D. Didephis marsupialis. E. Equus quagga. F. Erinaceus europaeus. G. Procyon lotor. H. Puma concolor. I. Sus scrofa. J. Tayassu pecari. K. Tupaia sp. L. Ursus arctos. Abbreviations: BF, bite force; JF-W/B, working-/balancing-side joint force.

Fig. 11 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 11. Comparison of orthal Group 1 (G1) vs. orthal Group 2 (G2) bite force (BF) across the lower postcanine tooth-row. Warmer colors correspond to higher G1 muscle advantage, and cooler colors correspond to higher G2 advantage. A. Canis familiaris Linnaeus, 1758. B. Sus scrofa Linnaeus, 1758. C. Equus quagga Boddaert, 1785. Note that Sus scrofa matches Peligrotherium tropicalis most closely, in having greater G1 advantage disto-buccally and greater G2 advantage mesio-lingually. Color scale is based on range of G1 minus G2 orthal BF magnitudes scaled by the value of single sample (within-taxon) standard deviation in this value.

Fig. 10 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 10. Connectivity graphs summarizing the results of pairwise randomization tests performed on the per-vertex values of orthal bite force (BF) differences. Lines connect taxa that are not found to be significantly different, and gray-scale value of individual nodes are proportional to the value of the parameter tested (e.g., dark tones are lower in value, and higher values are closer to white). A. Graph summarizing pairwise significance tests of mean Group 1 (G1) minus Group 2 (G2) orthal BF. B. Graph summarizing pairwise significance tests of F-value (variance ratio) of G1 minus G2 orthal BF. C. Graph summarizing pairwise significance tests of mean closed gape minus open gape orthal BF. D. Graph summarizing pairwise significance tests of F-value (variance ratio) of closed gape minus open gape orthal BF.

Fig. 3 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 3. Comparison of 2D side-view and fully 3D definitions of parameters for the bifulcral model of mandibular leverage, shown using Didelphis marsupialis Linnaeus, 1758 as an example. A. Left side-view of mandible in closed gape position, showing the locations of the working-side condylar fulcrum green) and bite point fulcrum (blue). The example temporalis force vector (red) drives rotation about both of these fulcra, and produces output force vectors that are tangential to circles centered on their respective fulcra (dashed arcs). B. Oblique lingual view showing important points and lever arms corresponding to the working-side medial pterygoid force (MP-W; shown as a red arrow) using a fully three-dimensional model of bifulcral mandibular leverage. The very medially directed line-of-action for the medial pterygoid demonstrates the large differences in orientation between the condylar plane (CP; shown with a green transparent plane), bite plane (BP; shown with a blue transparent plane), and a parasagittal (side-view) plane. The three-dimensional bifulcral model calculates bite forces and joint forces by projecting load points into their respective planes, as distances perpendicular to these projections do not affect leverage calculations. Definition of numbered points: 1, mesial postcanine point (PM); 2, distal postcanine point (PD); 3, centroid of insertion area for working-side medial pterygoid (MP-W); 4, centroid of origin surface for MP-W on skull; 5, location of working-side joint (WJ); 6, projection of WJ into BP; 7, projection of an example bite vertex on the third lower molar into the CP. Abbreviations: BF, bite force; ILBP-W, in-lever of the bite plane on the working-side; ILCP-W, in-lever of the condylar plane on the working-side; JF-W, joint force on the working-side; MP-W, medial pterygoid working-side; OLBP-W, out-lever of the bite plane on the working-side; OLCP-W, out-lever of the condylar plane on the working-side. Not to scale.

Fig. 1 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 1. Reconstruction of cranial eidonomy and osteology of the meridiolestidan mammal Peligrotherium tropicalis Bonaparte, Van Valen, and Kramarz, 1993, Punta Peligro, Argentina, Early Paleocene. A. Illustrated life reconstruction (courtesy of Amy Bishop). B. Digitized skull and mandible reconstructions produced by Paéz-Arango (2008).

Fig. 2 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 2. Reconstructed skull and hemimandibles of meridiolestidan mammal Peligrotherium tropicalis Bonaparte, Van Valen, and Kramarz, 1993(digitized from models produced by Paéz-Arango 2008). A. Skull and mandibles articulated into closed gape position and showing the attachments of several major muscle groups. B. Right-inferior oblique view of lower left hemimandible and skull in open gape position. Here the left side of the skull is assumed to be the working-side (WS), and the right side the balancing-side (BS); see Tables 1 and 2. Colored tubes are the lines-of-action of their respective muscle category; matching colored surfaces represent corresponding estimated origin and insertion areas; and black spheres show the locations of corresponding origin or insertion centroids. Abbreviations: DM-W, deep masseter working-side; MP-W/B, medial pterygoid working-side/ balancing-side; PT-W, posterior temporalis muscle category working-side; SM-W, superficial masseter working-side.

Fig. 5 in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 5. Results of Group 1 (G1) minus Group 2 (G2) analysis of orthal bite force (BF) for Peligrotherium tropicalis Bonaparte, Van Valen, and Kramarz, 1993. A. Lower left working-side hemimandible of P. tropicalis with postcanine crowns colorized by relative G1 vs. G2 advantage (yellow shows areas where G1 produces higher orthal BF, while bluer colors correspond to higher G2 BF values; white areas are where G1 and G2 forces are sub-equal). B. Violin boxplot showing distribution of total GP1 minus GP2 BF and its orthal component marginal over all locations in the postcanine tooth-row (TR). C. 2D histogram plot showing distribution of estimated bifulcral force magnitudes for G1 and G2 muscle recruitment regimes, as a function of mesiodistal location (MDL). JF-W/B, working-/balancing-side joint force.

FIG. 4 in Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation

FIG. 4. — Homologies in upper molars of Mesungulatidae and Peligrotheriidae, and comparison with Periptychidae cheekteeth; A, left M3 of Mesungulatum houssayi Bonaparte & Soria, 1984; B, left M2-3 of Peligrotherium tropicalis Bonaparte, Van Halen & Kramartz, 1993; C, left P3-M3 of Periptychus rhabodon Cope, 1882. Abbreviations: ac, anterior cingulum; asc, anterior stylar cusp; ca, anterior crista; cp, posterior crista; hyo, hypocone; mo, metacone; pa, paracone; pc, posterior cingulum; psc, posterior stylar cusp; po, protocone; sty, stylocone. Scale bars: A, B, 5 mm; C, 10 mm.

FIG. 1 in Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation

FIG. 1. — Peligrotherium tropicalis Bonaparte, Van Valen & Kramartz, 1993, stereopairs in occlusal view; A, right dentary fragment with distal part of m1 alveolus, m2, and fragmentary alveolus of m3 (MLP 90-II-12-60); B, right isolated tooth, probably p4 (MLP 90-II-12-61); C, D, maxillar fragment; C, with right M1-M2; D, with left M1 fragment, M2-M4 and fragmentary alveolus of M5 (MLP 90-II-12-5). Scale bars: 5 mm.

FIG. 5 in Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation

FIG. 5. — Reconstruction of the occlusion of Peligrotherium tropicalis Bonaparte, Van Halen & Kramartz, 1993; A, right M1- M2 (MLP 90-II-12-58) and right dentary with m1 and m2-3 (UNPSJB PV 914), internal view; B, same specimens in occlusal view. Dotted line represents the lower p4, m1-2 and continuous line upper P4-M1. Abbreviation: pa, paracone. Scale bar: 5 mm.

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Fig. 4. Example 3D in Reconstructed masticatory biomechanics of Peligrotherium tropicalis, a non-therian mammal from the Paleocene of Argentina

Fig. 4. Example 3D renderings of the bifulcral mandibular leverage parameters used in this analysis. A. Example of bifulcral lever arms corresponding to the working-side superficial masseter (SM-W) shown in a semi-transparent hemimandible of Canis familiaris Linnaeus, 1758; the muscular resultant vector is shown as a red arrow, with corresponding bite force vectors (yellow arrows) and working-side joint force vectors (purple arrows) shown for three positions on the lower postcanine tooth row. As can be seen, the in-lever lengths around the bite point fulcra (used in the calculation of joint force) increase significantly mesially. In labial (A1) and oblique (A2) views. B. Example of the varying condylar planes (CP) and bite planes (BP) used in the 3D bifulcral analysis, shown in Diceros bicornis (Linnaeus, 1758) for a bite point on the lower first molar. The mandible is shown in semi-transparent gray, while the working- and balancing-side origin surfaces for the deep masseter muscles on the skull are shown bilaterally in solid pink; similarly, the isolated origin surfaces of the medial pterygoids are shown in solid green. The muscular lines of action (LOA) for these four muscles are also shown as solid tubes, while transparent triangles demonstrate the orientations of the CP and BP for the corresponding muscle. In superior (B1) and oblique (B2) views. Not to scale. Abbreviations: BS, balancing-side; BV, bite vertex; ILBP-W, in-lever of the bite plane on the working-side; SM-W, superficial masseter working-side; WS, working-side.

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FIG. 2 in Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation

FIG. 2. — Peligrotherium tropicalis Bonaparte, Van Valen & Kramartz, 1993 (MLP 90-II-12-58), maxillary fragment with right M1-M2, and left M1 fragment and M2-M4, occlusal view. Abbreviations: ca, anterior crista; cp, posterior crista; pa, paracone. Scale bar: 5 mm.

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FIG. 3 in Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation

FIG. 3. — Peligrotherium tropicalis Bonaparte, Van Valen & Kramartz, 1993 (MLP 90-II-12-58), roots of right M1-M2, anterointernal view. Scale bar: 5 mm.