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. 2014 Jun 11;9(2):e98605.
doi: 10.1371/journal.pone.0098605. eCollection 2014.

The functional and palaeoecological implications of tooth morphology and wear for the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada

Jordan C Mallon  1 , Jason S Anderson  2
Affiliations

The functional and palaeoecological implications of tooth morphology and wear for the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada

Jordan C Mallon et al. PLoS One. .

Abstract

Megaherbivorous dinosaurs were exceptionally diverse on the Late Cretaceous island continent of Laramidia, and a growing body of evidence suggests that this diversity was facilitated by dietary niche partitioning. We test this hypothesis using the fossil megaherbivore assemblage from the Dinosaur Park Formation (upper Campanian) of Alberta as a model. Comparative tooth morphology and wear, including the first use of quantitative dental microwear analysis in the context of Cretaceous palaeosynecology, are used to infer the mechanical properties of the foods these dinosaurs consumed. The phylliform teeth of ankylosaurs were poorly adapted for habitually processing high-fibre plant matter. Nevertheless, ankylosaur diets were likely more varied than traditionally assumed: the relatively large, bladed teeth of nodosaurids would have been better adapted to processing a tougher, more fibrous diet than the smaller, cusp-like teeth of ankylosaurids. Ankylosaur microwear is characterized by a preponderance of pits and scratches, akin to modern mixed feeders, but offers no support for interspecific dietary differences. The shearing tooth batteries of ceratopsids are much better adapted to high-fibre herbivory, attested by their scratch-dominated microwear signature. There is tentative microwear evidence to suggest differences in the feeding habits of centrosaurines and chasmosaurines, but statistical support is not significant. The tooth batteries of hadrosaurids were capable of both shearing and crushing functions, suggestive of a broad dietary range. Their microwear signal overlaps broadly with that of ankylosaurs, and suggests possible dietary differences between hadrosaurines and lambeosaurines. Tooth wear evidence further indicates that all forms considered here exhibited some degree of masticatory propaliny. Our findings reveal that tooth morphology and wear exhibit different, but complimentary, dietary signals that combine to support the hypothesis of dietary niche partitioning. The inferred mechanical and dietary patterns appear constant over the 1.5 Myr timespan of the Dinosaur Park Formation megaherbivore chronofauna, despite continual species turnover.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Overview of ankylosaur teeth.
A, unworn ankylosaurid tooth (TMP 1992.036.1178) in lingual view; B, unworn nodosaurid tooth (TMP 2000.012.0024) in lingual view; C, partial left maxillary tooth row of Panoplosaurus mirus (ROM 1215) in lingual view, exemplifying the distal shift in both tooth size and wear facet orientation (tooth positions numbered); D, isolated ankylosaurid teeth exhibiting various states of wear (facets shown with dashed outline). Clockwise from top left: TMP 1997.016.0106, TMP 1991.036.0734; TMP 1997.012.0042, TMP 1989.050.0026; E, isolated nodosaurid teeth exhibiting various states of wear (facets shown with dashed outline). Clockwise from top left: TMP 2000.012.0027, TMP 1997.012.0005 (this tooth exhibits paired, mesiodistally arranged wear facets indicative of interlocking tooth occlusion), TMP 1994.094.0014, TMP 1992.036.0101; F, microwear from an isolated ankylosaurid tooth (TMP 1991.050.0014) exhibiting many mesiodistally oriented scratches; G, pitted and scratched LM 12 microwear of the nodosaurid P. mirus (ROM 1215).
Figure 2
Figure 2. Rose diagrams depicting the orientation of microwear scratches along the tooth row of Euoplocephalus tutus (AMNH 5405).
Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 3
Figure 3. Rose diagrams depicting the orientation of microwear scratches in isolated teeth of Euoplocephalus tutus and other unidentified ankylosaurids.
Note the dominance of mesiodistally oriented scratches, particularly on the unidentified teeth. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 4
Figure 4. Rose diagrams depicting the orientation of microwear scratches along the tooth row of Panoplosaurus mirus (ROM 1215).
The pooled sample does not include the isolated tooth because it could not be placed confidently within the jaw. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 5
Figure 5. Rose diagrams depicting the orientation of microwear scratches in isolated teeth of Panoplosaurus mirus and other unidentified nodosaurids.
Most of these teeth are dominated by mesiodistally oriented scratches, as in ankylosaurids. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 6
Figure 6. Overview of ceratopsid teeth.
A, isolated right maxillary tooth (TMP 1993.036.0407) in lingual (left) and mesial (right) views; B, isolated left dentary tooth (TMP 2002.012.0054) in labial (left) and distal (right) views; C, isolated right dentary tooth (AMNH 21606) in occlusal view. Arrow denotes tooth apex. Dashed line indicates boundary between mantle dentine (external) and orthodentine (internal); D, left dentary tooth row of Centrosaurus apertus (ROM 767) in labial view, showing the first 20 teeth (numbered); E, RD 17 microwear of the centrosaurine Ce. apertus (ROM 767); F, LD 22 microwear of the chasmosaurine Chasmosaurus sp. (ROM 839).
Figure 7
Figure 7. Rose diagrams depicting the orientation of microwear scratches along the tooth row of Centrosaurus apertus (ROM 767).
Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 8
Figure 8. Rose diagrams depicting the orientation of microwear scratches in ceratopsids.
Most scratches are oriented dorsodistally-ventromesially; however, there appears to be a second common mode whereby the scratches are oriented mesiodistally. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 9
Figure 9. Overview of hadrosaurid teeth.
A, isolated dentary tooth (TMP 1966.031.0032) in unknown (mesial or distal) view (left), and labial view (right); B, left dentary tooth battery of the hadrosaurine Gryposaurus notabilis (ROM 873) in lingual view; C, right dentary tooth battery of the lambeosaurine Lambeosaurus lambei (CMN 351) in lingual view; D, transverse section of a hadrosaurid dentary tooth battery (TMP 1966.031.0032), illustrating the lingual worn zone (LWZ) and buccal worn zone (BWZ). Dashed lines denote tooth contacts; E, right dentary tooth battery of L. lambei (CMN 351) in labial view, showing the occlusal surface (tooth positions numbered); F, right dentary tooth 12(1) of Corythosaurus sp. (ROM 1947) in occlusal view. Large, black arrow denotes tooth apex. Dashed line indicates boundary between mantle dentine (external) and orthodentine (internal). Small, white arrows point to stepped orthodentine-coronal cementum interface, which can be used to infer the feeding movements of the mandible; G, RD 13(1) microwear of Prosaurolophus maximus (CMN 2870); H, LD 24(2) microwear of Corythosaurus sp. (ROM 868).
Figure 10
Figure 10. Comparison of microwear scratch orientation between the lingual worn zone (LWZ) and buccal worn zone (BWZ) of the dentary tooth battery.
Note that scratches in the BWZ are not more mesiodistally inclined than in the LWZ, as would be expected if teeth in the BWZ served a grinding function. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 11
Figure 11. Rose diagrams depicting the orientation of microwear scratches along the tooth row of Prosaurolophus maximus (CMN 2870).
Note that, at the position of the eleventh tooth family, the most prominent mode of scratches shifts from a dorsomesial-ventrodistal orientation mesially to a dorsodistal-ventromesial orientation distally. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 12
Figure 12. Rose diagrams depicting the orientation of pooled microwear scratches in hadrosaurids.
Scratches are typically oriented dorsodistally-ventromesially; however, a second common mode comprises mesiodistally oriented scratches. Where possible, scratch orientations have been standardized to correspond to teeth from the right dentary (0° =  mesial, 90° =  apical).
Figure 13
Figure 13. PCA biplots at coarse (suborder/family), medium (family/subfamily), and fine (genus) taxonomic scales.
Arrows depict microwear feature loadings. Note that the same broad taxa occupy the same areas of microwear space through time, despite species turnover. Abbreviations: MAZ, megaherbivore assemblage zone; P, average pit count; S, average scratch count; W, average feature width.
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