Author : Holly Anne Schreiber
Publisher :
ISBN 13 : 9781124908403
Total Pages : pages
Book Rating : 4.9/5 (84 download)
Book Synopsis Investigating the Phylogenetic Relationships and Morphological Variability of the Crura and External Shell of Extant Rhynchonellida (Brachiopoda) by : Holly Anne Schreiber
Download or read book Investigating the Phylogenetic Relationships and Morphological Variability of the Crura and External Shell of Extant Rhynchonellida (Brachiopoda) written by Holly Anne Schreiber and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Rhynchonellida (Brachiopoda), the earliest and most basal order of the extant rhynchonelliform brachiopod orders, originated in the Ordovician. Rhynchonellides represent a significant step in the evolution of rhynchonelliform shell morphology since rhynchonellides are the first of the extant brachiopods with true calcareous lophophore support structures, the crura. Rhynchonellida has a long and well-documented fossil record. However, despite their abundance and longevity, this evolutionarily important order remains vastly understudied. Since over ninety percent of rhynchonellide genera are extinct, it is essential to understand morphological and evolutionary patterns in extant rhynchonellides in order to understand these patterns in extinct members of the order. Variability of the internal and external shell features of brachiopods can result in inaccuracies in species delineation, diversity studies, functional analyses, and phylogenetic analyses. Furthermore, since brachiopods are sessile, filter-feeding animals, they rely on water flow through their mantle cavity for feeding and respiration. Variability in crura and overall shell morphology may greatly affect this water flow, thus the ability of the organism to feed and respire. The main goal of my dissertation research is to evaluate the morphological variability of extant Rhynchonellida in an evolutionary context, specifically of the crura and the external shell morphology, and investigate the phylogenetic relationships of the genera within this order. First, I analyze the phylogenetic relationships among the nineteen extant rhynchonellide genera using fifty-five morphological characters in order to investigate the relationships among the extant suprafamilial groups and examine the evolution of select rhynchonellide characters. Results indicate that two of the four extant rhynchonellide superfamilies are monophyletic, results that conflict with current molecular phylogenetic hypotheses. Evaluation of the evolution of select rhynchonellide characters indicates that the raduliform crural configuration is the most basal crural morph, and more derived Recent rhynchonellides are characterized by small size, greatly reduced shell ornamentation, and a rectimarginate commissure. This research also suggests that characters currently used to unite genera in rhynchonellide superfamilies need revision.Second, I quantify and test the morphological disparity among six crural morphs present in Recent adult Rhynchonellida using three-dimensional geometric morphometric techniques with the objective of delineating unambiguous crural guidelines for use in rhynchonellide classification and phylogenetic analyses, and I identify the primary shape parameters that vary among the different crural configurations. This research confirms that five of the six crural morphs found in Recent rhynchonellides are significantly different from one another. The canaliform crural morph consistently groups with the raduliform morph. The shape parameters that, when modified, account for all crural shapes found in Recent rhynchonellides are crura length, crura width, crura height, crura curvature, and the angle of divergence between the crura. Third, I describe patterns of morphological variation in overall shell morphology within and between the extant rhynchonellide species, Hemithiris psittacea and Notosaria nigricans, using elliptical Fourier analysis. My objective is to characterize the variability present in extant rhynchonellides in order to establish guidelines for use in the rhynchonellide classification and that can be applied to the fossil record. Analyses indicate that H. psittacea and N. nigricans each occupy a similar volume of morphospace, exhibiting comparable morphological variability. Results were then compared to the fossil rhynchonellide Notosaria antipoda. Results of multivariate statistical analyses reveal considerable overlap among populations of each species, while there is clear separation between species in all shell parameters. Analyses indicate that H. psittacea, N. nigricans, and N. antipoda each occupy a similar volume of morphospace, exhibiting comparable amounts of morphological variability.
