Research ArticleEVOLUTIONARY BIOLOGY

Wear biomechanics in the slicing dentition of the giant horned dinosaur Triceratops

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Science Advances  05 Jun 2015:
Vol. 1, no. 5, e1500055
DOI: 10.1126/sciadv.1500055

Figures

  • Fig. 1 T. horridus skeleton and dentitions.

    (A) Triceratops skeleton. (B) Transverse view of a dentary (lower jaw) tooth family in this dinosaur whose functional teeth wore to vertical slicing faces. The stippling depicted on the bifid roots is the cementum-like tissue described by Hatcher and colleagues (46). Image from (46) used with permission. (C) Naturally worn slicing teeth in the lower jaw of MOR 129734 showing the wear-induced bowing out of the central regions of the occlusal faces of the teeth (arrow) to form fuller-like implements.

  • Fig. 2 Triceratops tooth crown histology.

    (A) Occlusal plane section of AMNH FARB 32189 viewed with dissecting microscopy showing the entire complement of osseous tissue constituents. Wear tracks from the reciprocating tribological testing are shown. HMD, hard mantle dentine. (B) Enamel shell viewed with polarized microscopy with a λ wave plate filter. (C) Coronal cementum (CC) adjacent to the hard mantle dentine viewed with polarized microscopy with a λ wave plate. The dark granules represent cementocyte lacunae. The outermost layer lacks such structures and is composed of acellular cementum. (D) Orthodentine viewed with polarized microscopy with a λ wave plate showing dozens of daily formed incremental lines of von Ebner (28) (dark and light repeated bands spanning from upper left to lower right). (E) Vasodentine viewed with dissecting microscopy showing reticulated vascular canals (white structures) that once housed blood vessels.

  • Fig. 3 Microtribology wear measurements.

    (A) Microtribometer used to slide a diamond-tipped probe across polished cross-sections of the fossilized teeth and to evaluate tissue wear rates. (B) Topographic profiles of wear scars created in various tissues by the sliding diamond probe. (C) Hardness of tissues versus wear rate for each ceratopsian dental tissue (n ≥ 25 per tissue). (D) Average Triceratops dental tissue wear rates. Error bars ± 1 σ.

  • Fig. 4 Tooth wear simulation.

    (A) Initial dental tissue distribution used in the Matlab wear model. (B to G) Model result considering (B) all tissues [note: the rendering mimics the naturally worn occlusal faces of Triceratops teeth including recovery of a basin caused by the relatively fast-wearing vasodentine (see Fig. 1C)], (C) a dentition without cementum showing negligible topographical difference from the all tissue rendering, (D) a tooth composed of just primitive amniote orthodentine and enamel typical of reptiles showing a lack of a fuller basin, (E) a dentition without vasodentine showing an absence of recession in the middle of the tooth, (F) a dentition without mantle dentine showing a slightly shallower plateau developed near the tip of the tooth, and (G) a dentition without enamel resulting in a blunter cutting edge and overall more rounded occlusal face.

  • Fig. 5 Dental tissue evolution in Ceratopsia.

    (A) Phylogenetic hypothesis for Ceratopsia (50, 56, 57) with character mapping of degrees of dental occlusion and osseous tissues. NO, non-occluding dentition; IO, incipient occlusion; DO, dental occlusion; E, enamel; O, orthodentine; RC, root cementum; CC, coronal cementum; HMD, hard mantle dentine; V, vasodentine. (B) Mantle dentine in Leptoceratops (dark tissues denoted by arrows; UAMES 34151). (C) Coronal cementum in Leptoceratops (AMNH FARB 32188). (D) Vasodentine (tissue with voids) in Protoceratops (AMNH FARB 6251).

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