The Functional and Palaeoecological Implications of Tooth Morphology and Wear for the Megaherbivorous Dinosaurs from the Dinosaur Park Formation (Upper Campanian) of Alberta, Canada

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.

Unusual cranial and postcranial anatomy in the archetypal ankylosaur Ankylosaurus magniventris

“…This is approximately equivalent to that predicted for a large elephant subsisting on dry vegetation (Laws 1970). Of course, these nutritional requirements could have been attained more efficiently through the added consumption of energy-rich fruiting bodies, for which the miniscule, cusp-like teeth (Mallon and Anderson 2014b), and comparably selective beak shape of Ankylosaurus (particularly in relation to Euoplocephalus; Ősi et al 2017) were apparently well adapted. Small and nutritious invertebrates may also have supplemented the diet on occasion (see below).…”

“…Lyson and Longrich (2011) found it made up <0.05% of associated dinosaur specimens from the Hell Creek, Lance, and equivalent formations, Wilson (2008) found it was less than 0.05% of isolated specimens from microvertebrate localities, and Horner et al (2011) did not recover any specimens from the middle or upper third of the Hell Creek Formation and found it was 5% of the fauna in the lower third. Ankylosaurus may have been ecologically rare, or it may have been an infrequent visitor to the coastal plain depositional environments where it was more likely to fossilize (similar comments were made by Mallon and Anderson (2014b) concerning ankylosaurids from the older Dinosaur Park Formation). Carpenter (2004) suggested that the late Maastrichtian Edmontonia sp.…”

“…Ankylosaurs also did not possess an elevated centre of mass as elephants do to aid in systematic tree felling (Mallon et al 2013). Lastly, ankylosaurs were certainly not capable of chewing tough tree bark in the same way as elephants (Mallon and Anderson 2014b), and so were unlikely to practice bark stripping and the indirect destruction of trees via pathogenic infection. For these reasons, although remarkable herbivores, we do not think ankylosaurs had the same modifying influence on their respective ecosystems.…”

Ornithischia

“…For instance, the diverse rounded-to-spade-shaped, denticulate, and often precisely occluding dentition of ornithischian dinosaurs has greatly informed paleontologists and functional anatomists of their past feeding behavior. In accordance with their morphological diversity, macro-and microscopic dental wear patterns have provided direct evidence of true feeding motions of the lower jaw during feeding, including orthal (i.e., dorsoventral, or up-and-down, jaw motion), palinal motion (i.e., caudally oriented, or backward, jaw motion while teeth are occluded), and long-axis rotation of each side of the jaw at the predentary joint (Mallon and Anderson 2014;Nabavizadeh and Weishampel 2016). These feeding motions vary both between and among clades of Ornithischia, and each gives a paleoecological context of the animals' respective time periods (Nabavizadeh 2016).…”

Tooth wear and microwear of theropods from the Late Maastrichtian Marília Formation (Bauru Group), Minas Gerais State, Brazil

“…Some studies described striated surfaces on dinosaur teeth and suggested they are directly related to mastication (Weishampel 1984;Fiorillo 1991Fiorillo , 1995Fiorillo , 1997Fiorillo , 1998Weishampel & Norman 1989;Upchurch & Barrett 2000;Barrett 2001;Rybczynski & Vickaryous 2001;Sankey et al 2002;D'Amore 2009;Erickson et al 2012bErickson et al , 2015Sereno 2012;Mallon & Anderson 2014). Most of these studies analysed herbivorous ornithischians and sauropods, by comparing and contrasting the feeding habits of theropods, varanids, crocodyliforms and mammals.…”