Abstract
Unlike most herbivores, sauropod dinosaurs evolved simple teeth that were replacedrapidly. Sauropod craniodental morphology is conserved relative to that of manyarchosaur clades, but tooth breadth and replacement rate vary substantially. Twoneosauropod clades, Titanosauria and Diplodocoidea, independently evolved bothnarrow-crowned teeth and high tooth replacement rates among a suite of other con-vergent features. Brachiosaurids also evolved somewhat narrower-crowned teeth, butthe two brachiosaurids whose tooth replacement rate has been examined to date havelow replacement rates. Poor and uneven sampling across Sauropoda limits our under-standing of the evolution of tooth replacement rate and related ecological inferences.To better understand the evolution of tooth replacement rate and tooth breadth, weintegrated histological and tomographic data to nearly double the number of exam-ined sauropod genera, focusing on improved sampling through the Cretaceous. Weprovide histological descriptions of the dentine and enamel of two Early Cretaceoustaxa, Abydosaurus and Moabosaurus. The former has unusually thin daily incrementsin its dentine, indicating prolonged tooth formation times. The dentine of the latteris typical of what is observed in most sauropods, but it has enigmatic banding in itsenamel. We performed ancestral state reconstruction on a time-calibrated phylogenyto show that the earliest macronarians and brachiosaurids retain the ancestral sau-ropod condition of relatively low tooth replacement rates (2–3 months to replace atooth in each alveolus), whereas diplodocoids evolved much higher rates (2–5 weeksto replace a tooth in each alveolus). Early diverging somphospondylans had a broadrange of tooth replacement rates. Broad-crowned teeth exhibit some correlation withlow tooth replacement rates, whereas narrow-crowned teeth display a more variablerelationship with replacement rate.