The significance of enamel thickness in the teeth of Alligator mississippiensis and its diversity among crocodyliforms

Abstract

Enamel is the hardest tissue in the vertebrate body. Although variation in enamel microstructure is often linked with diet, the gross proportions of the tissues that compose vertebrate teeth remain relatively unexplored in reptiles. To investigate the patterns of enamel thickness in crocodyliforms, we used micro‐computed tomography scanning to evaluate enamel thickness in teeth of Alligator mississippiensis from rostral, intermediate and caudal locations in the tooth row from an ontogenetic range of animals. We also evaluated enamel thickness in the derived teeth of several extinct crocodyliforms with disparate craniodental morphologies. Our data show that enamel thickness scales isometrically with skull length. We also show that enamel is relatively thicker in caudal teeth than teeth in more rostral positions, concordant with the higher bite forces they experience during feeding. We compared our data with existing enamel thickness data reported from dinosaurs and mammalian taxa to find that archosaurs have markedly thinner enamel than most mammals. These findings serve as a basis for future investigations into the diversity and function of the proportions of dental tissues.

Modeling tooth enamel in FEA comparisons of skulls: Comparing common simplifications with biologically realistic models

“…The resampling magnitude was 7/5x for the Varanus model. The percentage of enamel in extant animals is often computed based on a volumetric approach, where the relative enamel thickness is the 3D average enamel thickness divided by the cube root of the volume of dentine ( Olejniczak et al., 2008 ; Sellers et al., 2019 ). Here we used planar measurements of enamel as a proxy for enamel thickness, since the planar measurement approach enabled us to resample to the required resolution right away.…”

“…However, to our knowledge, no sensitivity study has compared realistic amounts of enamel with models in which the tooth is modeled as all bone or all enamel in reptiles, Tseng et al 2011 conducted a sensitivity study testing the effects of changing the number of material properties in the mandibles of wolves. In most extant taxa, relative enamel thickness (average enamel thickness divided by the cube root of the volume of dentine) is between 2 and 40 percent of the tooth ( Sellers et al., 2019 ). Enamel thickness is dependent on the interplay of various factors including enamel microstructure, overall tooth shape, diet, ontogeny, composition, and presence of surface topology and position within the dentigerous elements ( Sander 1999 ).…”

“…Enamel thickness is dependent on the interplay of various factors including enamel microstructure, overall tooth shape, diet, ontogeny, composition, and presence of surface topology and position within the dentigerous elements ( Sander 1999 ). Primates have especially high relative enamel thickness, whereas reptiles generally have lower relative enamel thickness ( Sellers et al., 2019 ). Even the thickest enamel layers of highly derived durophagous marine taxa (e.g., ichthyosaurians, mosasaurs, and placodonts) comprise only about 10% of the diameter of the tooth ( Sander, 1999 ).…”

Sampling impacts the assessment of tooth growth and replacement rates in archosaurs: implications for paleontological studies

“…Our raw measurement of CAH and tooth height include both enamel and dentin thickness. The enamel layer in extant crocodylians is thin (Enax et al, 2013) and scales nearly isometrically (Schmiegelow, Sellers & Holliday, 2016;Sellers, Schmiegelow & Holliday, 2019), with minor changes related to tooth shape (intrafamilial heterodonty) (Osborn, 1975;Kieser et al, 1993;Gignac, 2010;D'Amore et al, 2019) as opposed to size. To calculate CAH as a measure of dentin only, we subtracted the average enamel thickness value, and used this corrected CAH value in our calculations.…”

Crocodile Tooth Histology from a Pliocene Deposit in Chinchilla, Queensland

“…Extant crocodylian teeth are thecodont, cone-shaped and unicuspid (Dauphin & Williams, 2008). They vary in shape and sharpness from the anterior to pos terior in both the upper and lower jaws (Sellers et al, 2019). Tooth size and shape may also differ with sex and age.…”