Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs

Abstract

Heterodontosaurids comprise an important early radiation of small-bodied herbivores that persisted for approximately 100 My from Late Triassic to Early Cretaceous time. Review of available fossils unequivocally establishes Echinodon as a very small-bodied, late-surviving northern heterodontosaurid similar to the other northern genera Fruitadens and Tianyulong. Tianyulong from northern China has unusual skeletal proportions, including a relatively large skull, short forelimb, and long manual digit II. The southern African heterodontosaurid genus Lycorhinus is established as valid, and a new taxon from the same formation is named Pegomastax africanus gen. n., sp. n. Tooth replacement and tooth-to-tooth wear is more common than previously thought among heterodontosaurids, and in Heterodontosaurus the angle of tooth-to-tooth shear is shown to increase markedly during maturation. Long-axis rotation of the lower jaw during occlusion is identified here as the most likely functional mechanism underlying marked tooth wear in mature specimens of Heterodontosaurus. Extensive tooth wear and other evidence suggests that all heterodontosaurids were predominantly or exclusively herbivores. Basal genera such as Echinodon, Fruitadens and Tianyulong with primitive, subtriangular crowns currently are known only from northern landmasses. All other genera except the enigmatic Pisanosaurus have deeper crown proportions and currently are known only from southern landmasses.

A new hypothesis of dinosaur relationships and early dinosaur evolution

“…The saurischian part of the dinosaur clade has been more unstable than the ornithischian clade, with numerous hypotheses having been proposed for the arrangement of taxa within it, with the main issue of contention being the phylogenetic position of herrerasaurids and Eoraptor (Nesbitt et al 2009b;Nesbitt 2011;Novas et al 2011;Sereno et al 2012). Padian et al (1999) erected Eusaurischia to contain all but the basal most members of Saurischia, however, Nesbitt (2011) found this clade to be synonymous with Saurischia, with Eoraptor, Herrerasaurus and Staurikosaurus being recovered as theropods.…”

Digital reconstruction of the mandible of an adultLesothosaurus diagnosticuswith insight into the tooth replacement process and diet

“…In particular, it is noted that the degree of dental wear is significantly different between the two, with Lesothosaurus specimens often displaying limited but consistent wear that is typified by missing tips (Thulborn, 1971; Weishampel, 1984; Williams, 2010). Heterodontosaurids, conversely, have heterodont dentition which shows strong wear that changes not only in its degree but also in the angulation along the dental battery (Norman et al, 2011; Sereno, 2012). In association with the more complex dental specialisation, complex jaw movements have been proposed for heterodontosaurids due to the tooth wear and sutural relationships of the bones in the lower jaw, the latter being specifically applied to Heterodontosaurus tucki (Crompton & Attridge, 1986; Porro et al, 2011; Norman et al, 2011; Sereno, 2012).…”

“…Heterodontosaurids, conversely, have heterodont dentition which shows strong wear that changes not only in its degree but also in the angulation along the dental battery (Norman et al, 2011; Sereno, 2012). In association with the more complex dental specialisation, complex jaw movements have been proposed for heterodontosaurids due to the tooth wear and sutural relationships of the bones in the lower jaw, the latter being specifically applied to Heterodontosaurus tucki (Crompton & Attridge, 1986; Porro et al, 2011; Norman et al, 2011; Sereno, 2012). Likewise, a cheek recess is also more pronounced in heterodontosaurids in comparison to Lesothosaurus although not all heterodontosaurids show this conditions equally, i.e., Abrictosaurus (Norman et al, 2011).…”

“…Norman et al (2011) note that the low number of alveolar foramina on the medial surface of the maxilla, specifically in the well-studied genera Heterodontosaurus and Fruitadens , supports slow, sporadic tooth replacement rates. Different genera of heterodontosaurids show variability in the characteristics of jaw action, tooth replacement rate, and wear (Butler, Porro & Norman, 2008; Norman et al, 2011; Porro et al, 2011; Sereno, 2012), and this is likely a function of their stratigraphic placement in the Elliot Formation in addition to suggested niche partitioning (Porro et al, 2011). …”

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.…”