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, 8 (7), e69235

Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs

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Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs

Michael D D'Emic et al. PLoS One.

Abstract

Background: Tooth replacement rate can be calculated in extinct animals by counting incremental lines of deposition in tooth dentin. Calculating this rate in several taxa allows for the study of the evolution of tooth replacement rate. Sauropod dinosaurs, the largest terrestrial animals that ever evolved, exhibited a diversity of tooth sizes and shapes, but little is known about their tooth replacement rates.

Methodology/principal findings: We present tooth replacement rate, formation time, crown volume, total dentition volume, and enamel thickness for two coexisting but distantly related and morphologically disparate sauropod dinosaurs Camarasaurus and Diplodocus. Individual tooth formation time was determined by counting daily incremental lines in dentin. Tooth replacement rate is calculated as the difference between the number of days recorded in successive replacement teeth. Each tooth family in Camarasaurus has a maximum of three replacement teeth, whereas each Diplodocus tooth family has up to five. Tooth formation times are about 1.7 times longer in Camarasaurus than in Diplodocus (315 vs. 185 days). Average tooth replacement rate in Camarasaurus is about one tooth every 62 days versus about one tooth every 35 days in Diplodocus. Despite slower tooth replacement rates in Camarasaurus, the volumetric rate of Camarasaurus tooth replacement is 10 times faster than in Diplodocus because of its substantially greater tooth volumes. A novel method to estimate replacement rate was developed and applied to several other sauropodomorphs that we were not able to thin section.

Conclusions/significance: Differences in tooth replacement rate among sauropodomorphs likely reflect disparate feeding strategies and/or food choices, which would have facilitated the coexistence of these gigantic herbivores in one ecosystem. Early neosauropods are characterized by high tooth replacement rates (despite their large tooth size), and derived titanosaurs and diplodocoids independently evolved the highest known tooth replacement rates among archosaurs.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Dental histology of the sauropod dinosaurs Camarasaurus and Diplodocus.
Thin sections of Camarasaurus (A, C) and Diplodocus (B, D) premaxillary teeth showing incremental lines of von Ebner (white arrowheads) in dentin. Teeth are oriented with their long axis horizontal and the occlusal surface directed to the right. A shows the tip of tooth 3iii of Camarasaurus, and B shows the tip of tooth 4iv of Diplodocus. C and D are enlarged images of one ‘limb’ of tooth 3ii and 4iii, respectively. Abbreviations: edj, enamel-dentin junction; en, enamel; pc, pulp cavity. [planned for page width].
Figure 2
Figure 2. Tooth replacement in the sauropod dinosaurs Camarasaurus and Diplodocus.
Reconstructed skulls (A, D) and premaxillary teeth (B, C) of Camarasaurus (A, B) and Diplodocus (C, D). B and C include CT-generated sagittal and transverse sections of premaxillary alveoli and photographs of thin sections of Camarasaurus (UMNH 5527) and Diplodocus (YMP 4677). Premaxillae show replacement teeth in each of the four alveoli adjacent to the symphysis labelled by their position along the tooth row (1–4) and their position in the replacement sequence at each tooth position (i–v). Sagittal sections in B and C were taken at premaxillary tooth position 4 in Camarasaurus and premaxillary tooth position 1 in Diplodocus. The symphysis faces the bottom of the page in transverse sections. Photographs of thin sections of Diplodocus and Camarasaurus teeth show enamel (en), the pulp cavity (pc), daily-deposited incremental lines of von Ebner (arrowheads mark every other line) in the dentin (den), and the crown-root junction (crj). The 20 mm scale bar is for the premaxilla and tooth images in (B); 10 mm scale bar is for premaxilla and tooth images in (C). Skull reconstructions are from , [planned for page width].
Figure 3
Figure 3. Cladogram of sauropodomorphs showing the optimization of key features related to elevated tooth replacement rates.
The light gray field indicates taxa that have at least three replacement teeth at each tooth position; dark gray field encapsulates taxa that have narrow tooth crowns. Silhouettes along the top of the cladogram show the number and size of replacement teeth in one tooth position. These include (from left to right): Patagosaurus (MPEF-PV 1670), Mamenchisaurus , Diplodocus (this study), Nigersaurus [Sereno, Wilson, Witmer, Whitlock, Maga, Ide and Rowe, unpublished data], Camarasaurus (this study), and the Río Negro titanosaur (MPCA-79) . Number of replacement teeth is unknown in Brachiosauridae, but the taxon is optimized to have had at least three. Cladogram based on with the addition of Tazoudasaurus and Bonitasaura . [planned for column width].

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Publication types

Grant support

Funding was provided by the Scott D. Turner Award (University of Michigan) to MDD. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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