Quantifying tooth variation within a single population ofAlbertosaurus sarcophagus(Theropoda: Tyrannosauridae) and implications for identifying isolated teeth of tyrannosauridsThis article is one of a series of papers published in this Special Issue on the themeAlbertosaurus.

Abstract

Documenting variation in theropod dinosaurs is usually hindered by the lack of a large sample size and specimens representing several ontogenetic stages. Here, variation within 140 disassociated and seven in situ tyrannosaur teeth from the Upper Cretaceous (lower Maastrichtian) monodominant Albertosaurus sarcophagus (Theropoda: Tyrannosauridae) bonebed is documented. This sample represents the largest data set of teeth from one population of A. sarcophagus containing both adult and juvenile specimens. Tooth variation was assessed using multivariate analyses (principal component, discriminant, and canonical variate analyses). Heterodonty in the teeth of A. sarcophagus contributes to the large amount of variation in the data set. Premaxillary teeth are significantly different from maxillary and dentary teeth, but there is no quantifiable difference between a priori identified maxillary and dentary teeth. Juvenile and adult teeth of A. sarcophagus show apparent quantitative differences that are size dependent on closer investigation, suggesting a cautious approach when interpreting multivariate analyses to identify novel tooth morphologies. Multivariate analyses on teeth of A. sarcophagus and published tooth data from other North American tyrannosaurid species reveals species-level clusters with little separation. The degree of separation among tooth clusters may reveal a phylogenetic signal in tyrannosaurid teeth.

Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds

“…1 and 2). Additionally, although size is often used as a proxy for degree of skeletal maturity in many studies (20,24,(34)(35)(36)(37)(38)(39)(40)(41), size correlates poorly with morphological maturity, as quantified by maturity score in OSA, even though OSA may reconstruct missing data as present and thus raise the maturity score higher than a strict scoring of the individual would give (Figs. 1 and 2).…”

Theropod teeth from the Middle-Upper Jurassic Shishugou Formation of northwest Xinjiang, China

“…As noted by Smith (2005), Smith et al (2005), Brusatte et al (2007), Buckley et al (2010), and Han et al (2011), morphology and size of denticles, length of the carinae, and crown ornamentations (i.e., interdenticular sulci, longitudinal ridges, flutes, etc. ), are pivotal features to identify isolated teeth and should be explored further in many theropod taxa.…”

“…Contrary to Smith et al (2005), crown angle values (CA) sensu Smith et al (2005) were not used in the morphometric analyses as this angle can be affected by the extent of the enamel layer both mesially and distally (Buckley et al 2010) and only weakly reflects apical displacement (CH personal observations). Additionally, CA values obtained by Smith (2005) and Smith et al (2005) differ from those calculated in this study using the same formula (i.e., the law of cosines on CBL, CH, and AL), and Smith (2005) and Smith et al (2005) likely used Basal cross-section of crown in C showing CBW (crown-base width), DDT (dentine thickness distally), DLAT (dentine thickness labially), DLIT (dentine thickness lingually), and DMT (dentine thickness mesially), in basal view.…”

“…), are pivotal features to identify isolated teeth and should be explored further in many theropod taxa. Likewise, discriminant analysis based on dental measurements appeared to be a promising technique (yet to be used with caution, see Buckley et al 2010) that facilitates the taxonomic identification of isolated teeth.…”

On the earliest record of Cretaceous tyrannosauroids in western North America: implications for an Early Cretaceous Laurasian interchange event

“…Thus far, ontogenetic dimorphism of premaxillary tooth serrations is proposed for Tyrannosaurus and Daspletosaurus (Currie 2003;Carr and Williamson 2004;Li et al 2009). Although unserrated premaxillary teeth are also known from Campanian strata that yield more basal tyrannosaurids such as Albertosaurus (including Gorgosaurus; Currie 1987), a recent study of Albertosaurus sarcophagus teeth finds serrations in both juvenile and adult premaxillary teeth (Buckley et al 2010). The same is noted by Currie (2003) for Gorgosaurus (Albertosaurus) libratus.…”