Phylogenetic Patterns Of Enamel Microstructure In Dinosaur Teeth

Author : Sunny Hai-Ching Hwang
Publisher :
ISBN 13 : 9781109874495
Total Pages : 274 pages
Book Rating : 4.8/5 (744 download)

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Download or read book Phylogenetic Patterns of Enamel Microstructure in Dinosaur Teeth written by Sunny Hai-Ching Hwang and published by . This book was released on 2007 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fossil reptile teeth have been examined in thin section using microscopy since the mid-1800s, but little was known of their enamel microstructure until the advent of scanning electron microscopy (SEM). Reptile enamel remains tremendously understudied in comparison to mammalian enamel, because its aprismatic structure renders it difficult to characterize. The handful of SEM studies on dinosaur tooth enamel microstructure have all sampled far too few taxa and too small a variety of taxa to understand the true distribution of enamel types across Dinosauria. This study aims to correct that lack by examining the enamel microstructure of as many different dinosaur taxa as possible, both within less inclusive Glades ("families") to see interspecific variation, and throughout Dinosauria to see interfamilial variation. This study also explicitly and primarily looks at dinosaur enamel in a phylogenetic context, which previous studies of dinosaur enamel have not. Enamel characters of 54 saurischian and ornithischian taxa were first mapped on independently generated reference phylogenies to determine their evolutionary trends. Phylogenetic constraints play a larger role in shaping enamel microstructure in reptiles than previously thought. Within many monophyletic dinosaur clades, the combination of enamel types and enamel features within a tooth---the schmelzmuster---is the same in all the taxa due to their common ancestry, and their schmelzmusters are diagnostic of their respective clades. However, the enamel complexity of a taxon does not necessarily coincide with the position of the taxon on a phylogenetic tree; more derived taxa do not necessarily have more derived enamel and more primitive taxa do not necessarily have more primitive enamel. Therefore, there is no overall trend in enamel evolution within Dinosauria. Because so many schmelzmusters are unique to specific dinosaur clades, the identifications of several indeterminate teeth were refined using their enamel microstructure. Finally, features observed in dinosaur enamel microstructure were parsed into phylogenetic characters. These enamel characters were analyzed separately as well as added to datasets of skeletal characters for theropod and ornithischian dinosaurs. Tests for phylogenetic signal in enamel type were also performed. Phylogenetic analysis of enamel characters and tests for phylogenetic signal in enamel type confirm the pattern observed via character mapping, namely that there are enamel characters that diagnose different clades within Dinosauria, but that there is not an overall trend in enamel evolution within Dinosauria. Enamel characters alone are not enough to recover the traditional groups obtained via skeletal character analysis, but they can improve resolution within strict consensus trees when added to a skeletal character matrix.