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Wear facets and enamel spalling in tyrannosaurid dinosaurs

100%

Schubert B. W., Ungar P. S.

Acta Palaeontologica Polonica

2005

tom 50

nr 1

Numerous paleontologists have noted wear facets on tyrannosaurid lateral teeth over the past century. While several workers have proposed explanations for these features, there remains to this day no consensus concerning their etiology. Here we report on an examination of wear surfaces on these teeth from the Upper Cretaceous (mid−Campanian) Judith River Group of southern Alberta, Canada. This study reveals two distinct types of wear features on the labial and lingual sides of tyrannosaurid lateral teeth: irregular “spalled” surfaces and wear facets. The irregular spalled surfaces typically extend to the apex of the tooth, which evidently reflects flaking of enamel resulting from forces produced during contact between tooth and food. These surfaces are often rounded, presumably from antemortem wear following spalling. Wear striations on these surfaces are oriented heterogeneously. The wear facets, in contrast, occur on only one side of the tooth and are typically elliptical in outline and evince parallel wear striations. Similar patterns of parallel wear striations in extant mammals reflect tooth−tooth contact. We therefore propose that wear facets in tyrannosaurids were formed by repeated tooth−tooth contact between the lingual side of maxillary teeth and labial side of dentary teeth. It remains unclear whether this contact was serendipitous or adaptive, though it appears to be unusual for reptiles, as we have found no evidence for wear facets in extant varanids and crocodilians.

A dental microwear texture analysis of the Mio-Pliocene hyaenids from Langebaanweg, South Africa

81%

Stynder D. D., Ungar P. S., Scott J. R., Schubert B. W.

Acta Palaeontologica Polonica

2012

tom 57

nr 3

Hyaenids reached their peak diversity during the Mio−Pliocene, when an array of carnivorous species emerged alongside dwindling civet−like and mongoose−like insectivorous/omnivorous taxa. Significantly, bone−cracking morphological adaptations were poorly developed in these newly−emerged species. This, their general canid−like morphology, and the absence/rarity of canids in Eurasia and Africa at the time, has led researchers to hypothesise that these carnivorous Mio−Pliocene hyaenas were ecological vicars to modern canids. To shed further light on their diets and foraging strategies, we examine and compare the dental microwear textures of Hyaenictitherium namaquensis, Ikelohyaena abronia, Chasmaporthetes australis, and Hyaenictis hendeyi from the South African Mio−Pliocene site of Langebaanweg with those of the extant feliforms Crocuta crocuta, Acinonyx jubatus, and Panthera leo (caniforms are not included because homologous wear facets are not directly comparable between the suborders). Sample sizes for individual fossil species are small, which limits confidence in assessments of variation between the extinct taxa; however, these Mio−Pliocene hyaenas exhibit surface complexity and textural fill volume values that are considerably lower than those exhibited by the living hyaena, Crocuta crocuta. Dental microwear texture analysis thus supports interpretations of craniodental evidence suggesting low bone consumption in carnivorous Mio−Pliocene hyaenas.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Schubert B. W.

2 Ungar P. S.

1 Scott J. R.

1 Stynder D. D.

1 2012

1 2005

Wyniki wyszukiwania

Wear facets and enamel spalling in tyrannosaurid dinosaurs

A dental microwear texture analysis of the Mio-Pliocene hyaenids from Langebaanweg, South Africa