WFS News:Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs

@WFS,World Fossil Society,Riffin T Sajeev,Russel T Sajeev

Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs

Citation: D’Emic MD, Whitlock JA, Smith KM, Fisher DC, Wilson JA (2013) Evolution of High Tooth Replacement Rates in Sauropod Dinosaurs. PLoS ONE 8(7): e69235. https://doi.org/10.1371/journal.pone.0069235

Editor: Alistair Robert Evans, Monash University, Australia

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

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].

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].

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 [47], Diplodocus (this study), Nigersaurus [Sereno, Wilson, Witmer, Whitlock, Maga, Ide and Rowe, unpublished data], Camarasaurus (this study), and the Río Negro titanosaur (MPCA-79) [48]. Number of replacement teeth is unknown in Brachiosauridae, but the taxon is optimized to have had at least three. Cladogram based on [30] with the addition of Tazoudasaurus [49] and Bonitasaura [50]. [planned for column width].

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 [47], Diplodocus (this study), Nigersaurus [Sereno, Wilson, Witmer, Whitlock, Maga, Ide and Rowe, unpublished data], Camarasaurus (this study), and the Río Negro titanosaur (MPCA-79) [48]. Number of replacement teeth is unknown in Brachiosauridae, but the taxon is optimized to have had at least three. Cladogram based on [30] with the addition of Tazoudasaurus [49] and Bonitasaura [50]. [planned for column width].

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.

@WFS,World Fossil Society,Riffin T Sajeev,Russel T Sajeev

You can leave a response, or trackback from your own site.

Leave a Reply