Ashley Morhardt | Washington University in St. Louis (original) (raw)
Please see more about my work here: http://ashleymorhardt.wix.com/homepage
Supervisors: Drs. Kari Allen and Amy Bauernfeind
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Museo Paleontológico Egidio Feruglio
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Papers by Ashley Morhardt
Journal of anatomy, Jan 11, 2016
Morphologists have historically had to rely on destructive procedures to visualize the three-dime... more Morphologists have historically had to rely on destructive procedures to visualize the three-dimensional (3-D) anatomy of animals. More recently, however, non-destructive techniques have come to the forefront. These include X-ray computed tomography (CT), which has been used most commonly to examine the mineralized, hard-tissue anatomy of living and fossil metazoans. One relatively new and potentially transformative aspect of current CT-based research is the use of chemical agents to render visible, and differentiate between, soft-tissue structures in X-ray images. Specifically, iodine has emerged as one of the most widely used of these contrast agents among animal morphologists due to its ease of handling, cost effectiveness, and differential affinities for major types of soft tissues. The rapid adoption of iodine-based contrast agents has resulted in a proliferation of distinct specimen preparations and scanning parameter choices, as well as an increasing variety of imaging hardwa...
Were the teeth of dinosaurs exposed or covered to some degree by extra-oral structures? Previous ... more Were the teeth of dinosaurs exposed or covered to some degree by extra-oral structures? Previous studies have examined jaw and cranial muscles and nerves in extant sauropsids and applied these findings to dinosaurs. Few have examined the anterior regions of the sauropsid jaw, and those that have present conflicting results. This study tested the hypothesis that there is a significant, quantitative correlation between the number of extra-oral foramina on the cranialforward bones and overlying soft tissues among extant sauropsids. Utilizing an Extant Phylogenetic Bracket (EPB) approach, I further hypothesized that similar foramina trends between extant sauropsids and dinosaurs would be most parsimoniously consistent with the presence or absence of lipor cheek-like outer coverings in dinosaurs. Soft tissue dissection, foramina counts, and linear measurements of three the premaxilla, maxilla, dentary were conducted for extant sauropsid specimens (turtles, lizards, snakes, crocodilians, birds), certain mammalian taxa, and Saurischian and Ornithischian dinosaurs. Dinosaur taxa were compared to the extant sauropsid sample to constrain inferences regarding the presence of extra-oral tissues. Data analyses show that the number of extra-oral foramina is statistically correlated with the presence or absence of extra-oral tissues. When compared to the rest of the sample, dinosaurs included in this study fall within the range of organisms that have extra-oral coverings. The results of this study support the hypothesis that foramina density is correlated to some degree with extra-oral structures.
Journal of anatomy, Jan 11, 2016
Morphologists have historically had to rely on destructive procedures to visualize the three-dime... more Morphologists have historically had to rely on destructive procedures to visualize the three-dimensional (3-D) anatomy of animals. More recently, however, non-destructive techniques have come to the forefront. These include X-ray computed tomography (CT), which has been used most commonly to examine the mineralized, hard-tissue anatomy of living and fossil metazoans. One relatively new and potentially transformative aspect of current CT-based research is the use of chemical agents to render visible, and differentiate between, soft-tissue structures in X-ray images. Specifically, iodine has emerged as one of the most widely used of these contrast agents among animal morphologists due to its ease of handling, cost effectiveness, and differential affinities for major types of soft tissues. The rapid adoption of iodine-based contrast agents has resulted in a proliferation of distinct specimen preparations and scanning parameter choices, as well as an increasing variety of imaging hardwa...
Were the teeth of dinosaurs exposed or covered to some degree by extra-oral structures? Previous ... more Were the teeth of dinosaurs exposed or covered to some degree by extra-oral structures? Previous studies have examined jaw and cranial muscles and nerves in extant sauropsids and applied these findings to dinosaurs. Few have examined the anterior regions of the sauropsid jaw, and those that have present conflicting results. This study tested the hypothesis that there is a significant, quantitative correlation between the number of extra-oral foramina on the cranialforward bones and overlying soft tissues among extant sauropsids. Utilizing an Extant Phylogenetic Bracket (EPB) approach, I further hypothesized that similar foramina trends between extant sauropsids and dinosaurs would be most parsimoniously consistent with the presence or absence of lipor cheek-like outer coverings in dinosaurs. Soft tissue dissection, foramina counts, and linear measurements of three the premaxilla, maxilla, dentary were conducted for extant sauropsid specimens (turtles, lizards, snakes, crocodilians, birds), certain mammalian taxa, and Saurischian and Ornithischian dinosaurs. Dinosaur taxa were compared to the extant sauropsid sample to constrain inferences regarding the presence of extra-oral tissues. Data analyses show that the number of extra-oral foramina is statistically correlated with the presence or absence of extra-oral tissues. When compared to the rest of the sample, dinosaurs included in this study fall within the range of organisms that have extra-oral coverings. The results of this study support the hypothesis that foramina density is correlated to some degree with extra-oral structures.