Browsing by Author "Anderson, Jason S."

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    The anatomy of the dermatocranium and mandible of Cacops aspidephorus Williston, 1910 (Temnospondyli: Dissorophidae), from the Lower Permian of Texas
    (Taylor and Francis, 2020-01) Anderson, Jason S.; Scott, Diane; Reisz, Robert R.
    For the first time, the cranial suture pattern for the type species of Cacops, C. aspidephorus, is described in detail. A majority of sutures, including the lower jaw, the skull roof, and the palate, are now known in detail, although details are still lacking for the posterior skull table. Notable new information about C. aspidephorus includes the presence of a lateral exposure of the palatine (LEP), a lateral exposure of the ectopterygoid (LEE) that fuses with the jugal with growth, and a subtympanic flange composed mostly of the supratemporal. Cacops aspidephorus is very similar to C. morrisi, but differences, including a fully closed otic notch in C. aspidephorus, are sufficient to maintain both as distinct species. Uniquely, C. aspidephorus shows palatal dentition of the same size as the marginal dentition, but it remains to be seen whether this is a widespread feature or ontogenetically transient. These new data will finally permit the inclusion of this iconic taxon, described over 100 years ago, into larger-scale phylogenies of dissorophoid and temnospondyl relationships.
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    Biological Lineages in Philosophical Focus
    (2020-08) Alves Neto, Celso Antônio; Ereshefsky, Marc; Haber, Matthew; Reydon, Thomas A.C.; Delehanty, Megan; Waters, C. Kenneth; Anderson, Jason S.
    Lineages are genealogical sequences of genes, cells, organisms, or other biological entities. They populate the natural world and are discussed in various fields in biology. However, they barely receive philosophical scrutiny. In this dissertation, I explore philosophical issues regarding the nature of lineages, as well as their conceptualization and representation in science. First, I offer a historical overview of lineages in biology. I describe how biologists characterize lineages in evolutionary biology, developmental biology, paleontology, and other areas. This overview reveals the importance of lineages to theorization, experimentation, modeling, and other scientific practices. These diverse practices motivate the philosophical issues discussed in the following chapters. Second, I address the question of what is a lineage. Biologists and philosophers define them as genealogical sequences of biological entities (De Queiroz, 1999; Hull, 1980; Mishler, 2010). This broad definition reveals a belief that many of those scholars share: lineage is a single unified category in science or, in other words, a single type of entity in biology. I argue against this position and, instead, defend pluralism: the existence of a plurality of lineage types in biology. Third, I analyze the very concept of lineage. This concept is imprecise, and this imprecision may be harmful to scientific communication and reasoning. Similar concerns apply to the concepts of molecular gene and evolutionary novelty (Brigandt & Love, 2012; Kitcher, 1992; Waters, 2014). I compare the concept of lineage with these concepts. While all of them play beneficial roles in scientific integration, I argue that the concept of lineage facilitates a distinctive type of integration among scientists. Finally, I discuss how biologists represent lineages and why these representations matter to science. Biologists typically represent lineages in a simplistic, idealized way. Most philosophers consider these representations important to science only insofar as they result in improved theories and representations of nature (Potochnik, 2017; Velasco, 2012; Weisberg, 2013; Wimsatt, 2007). I argue that this view is limited. Representing lineages also results in collaboration among scientists and other social, non-representational activities that are central to science.
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    An Earliest Carboniferous Actinopterygian Fauna from the Horton Bluff Formation of Nova Scotia
    (2020-01) Wilson, Conrad Daniel Mackenzie; Anderson, Jason S.; Theodor, Jessica M.; Cote, Susanne; Jamniczky, Heather A.; Anderson, Jason S.
    This thesis examines four earliest Carboniferous (Tournaisian) actinopterygian specimens from the Horton Bluff Formation of Nova Scotia. I used traditional and μCT descriptive techniques in order to better understand actinopterygian evolution and the transition between Devonian and Carboniferous vertebrate faunas. NSM 017.GF.017.001 was investigated using microscopy and latex peel techniques and represents the oldest occurrence of a deep-bodied actinopterygian. NSM 017.GF.017.007 and NSM 017.GF.017.004 were investigated using microscopy and μCT. Neither specimen can be assigned to genus or species, however, each can be compared to a broader group. NSM 017.GF.017.007 is most similar to Devonian taxa, whereas NSM 017.GF.017.004 is most similar to actinopterygians deeply nested in a broad post-Devonian radiation. NSM 017.GF.017.005 was examined using μCT and was incorporated into a phylogenetic analysis. In this specimen, the plesiomorphic anatomy of the dermal shoulder girdle, pectoral fin, and opercular-gular series are contrasted with the derived anatomy of the hyoid arch. In the phylogenetic analysis, it is recovered as a late-diverging member of a grade of otherwise Devonian actinopterygians. The presence of NSM 017.GF.017.001 and NSM 017.GF.017.004 suggests that derived actinopterygians faunas were established by the Tournaisian; whereas the presence of NSM 017.GF.017.007 and NSM 017.GF.017.005 suggests that Hangenberg extinction survivorship was inclusive of early-diverging actinopterygians. NSM 017.GF.017.001 and NSM 017.GF.017.005 also evince actinopterygian body plan exploration, perhaps related to resource acquisition, in the Tournaisian and revise previous models of post-Hangenberg actinopterygian differentiation. More broadly, the disparity of this fauna weakens interpretations of a homogeneous earliest Tournaisian caused by mass extinction and suggest that faunal turnover was more gradual than expected, at least in Actinopterygii.
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    Metamorphosis and the Coronoid Dentition in the Axolotl Salamander, Ambystoma mexicanum
    (2022-01-19) Pardo, Jason D.; Anderson, Jason S.; Matyas, John R., Cobb, John A.; Hanken, James; Jamniczky, Heather; Rose, Christopher S.
    Amphibian metamorphosis consists of rapid and substantial changes across the entire body, largely associated with shifts in respiratory function and water balance. This coincides with a decrease in regenerative potential, including continuous tooth replacement in the coronoid bone of the lower jaw. In continuous tooth replacement, new teeth are initiated in a specialized epithelial lamina medial to the functional tooth row, which is supplied by stem cell populations residing in its distal tip. However, the current state of research makes it difficult to adapt this model organism to address these questions and limits our understanding of metamorphosis. In Chapter 2, I characterize anatomical and histological changes across experimentally induced metamorphosis in the axolotl. I use this to develop the temporal, anatomical, and histological framework in which to approach subsequent studies in this thesis. In Chapter 3, I investigate the signaling basis for changes in the dentition across metamorphosis. Using RNAseq, I characterize differential expression of tooth replacement related transcripts across metamorphosis, identifying candidate genes which are distinct from candidate pathways identified in other tooth replacement systems. In Chapter 4, I show that some of these candidate genes are differentially expressed across metamorphosis in multiple tissues, notably in the lung and gill, suggesting that metamorphosis itself may be a hormone-mediated pleiotropy. I then use phylogenetic comparative methods to show that this coincides with elevated rate of coronoid tooth loss in a part of the tetrapod tree where it is thought tetrapods shifted from gill-dominated to lung-dominated respiration. In Chapter 5, I explore the impact of a histone deacetylase inhibitor, which accelerates thyroid-induced metamorphosis of the tail but slows metamorphosis in the skull, suggesting that different pathways may be active in the tailfin compared to the head. In Chapter 6, I integrate these data into a survey of the literature on salamander metamorphosis.The research presented in this thesis provides a framework for future work on salamander metamorphosis using the axolotl as a model organism. I also present several novel hypotheses which I believe have the potential to drive future work on both amphibian metamorphosis and the origin of tetrapod terrestrialization.
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    A multimethod analysis to assess locomotor capabilities in stem tetrapods from Blue Beach (Tournaisian; Early Carboniferous), Nova Scotia
    (2020-01) Lennie, Kendra Ilana; Anderson, Jason S.; Theodor, Jessica M.; Jamniczky, Heather A.; Manske, Sarah Lynn
    In vertebrate evolution the fin-to-limb transition was an important precursor to the diversification and radiation of terrestrial animals into novel environments. This transition began in the Devonian and continued through the Carboniferous and involved physiological and biomechanical changes. I used a multi-method approach to assess external and internal limb bone features to evaluate Early Carboniferous (Tournaisian) limb bones from Blue Beach and associated them with aquatic to terrestrial lifestyles. Tournaisian tetrapod material was collected at Blue Beach located near Hantsport, Nova Scotia, but much of it has not been formally described because the disarticulated and isolated tetrapod elements made identification to the species level difficult. In this thesis I described new morphotypes attributable to the family level which are used in the following chapters. Once the external morphology of the Blue Beach bones was described I compared them with the femora of extant aquatic, amphibious, and terrestrial tetrapods to evaluate which locomotor behaviour the fossil femora most resembled. I additionally examined cross-sectional bone profiles of Blue Beach tetrapod femora to infer lifestyle. Midshaft analyses relied on a single two-dimensional image to represent a dynamically structured bone so I also used a novel method for assessing three-dimensional trabecular data to qualitatively and quantitatively infer lifestyle from the Blue Beach femora. From the various analyses of internal and external bone morphology it was clear that external bone features of modern and early fossil tetrapod femora are dissimilar, which lead to difficulties in drawing conclusions based off external qualitative data. Internal data, from two-dimensional midshaft and three-dimensional trabecular structures, produced quantitative results that lead to the same conclusion, that the Blue Beach femora are consistent with those of aquatic animals. This implies that the initial diversification of the tetrapod body plans present in the Early Carboniferous was not the result of terrestrialization but appears to have preceded it.
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    Osteology and Histology of Plesiosaurs (Reptilia: Sauropterygia) from Non-marine (Fluvial to Estuarine) and Marine Depositional Environments
    (2019-12-19) Campbell, James Alexander; Anderson, Jason S.; Theodor, Jessica M.; Henderson, Donald M.; Caldwell, Michael W.; O'Keefe, Frank Robin; Dutchak, Alex R.
    Plesiosaurs are a highly diverse group of secondarily-aquatic reptiles that lived from Late Triassic to Late Cretaceous time. Plesiosaurs are known primarily from marine deposits, but also occur sparingly in non-marine units. Here, I describe the osteology and histology of plesiosaurs from both non-marine (Dinosaur Park Formation, DPF) and marine (Bearpaw and Pierre Shale Formations; BF, PSF), Upper Cretaceous-aged deposits of western Canada. These sediments were deposited in the Western Interior Basin, which was inundated by a large marine corridor known as the Western Interior Seaway. Non-marine (fluvial to estuarine) sediments of the DPF have yielded a stratigraphically extensive collection of elasmosaurid plesiosaur specimens. These specimens are notable as they belong to individuals that are small-bodied relative to some elasmosaurid specimens from marine units. In this study, I test whether the small-bodiedness of DPF specimens is due to the presence of immature individuals or a small-bodied taxon. Analyses of select DPF elasmosaurid specimens indicate the presence of a small-bodied taxon. Furthermore, a well-preserved partial skeleton from this unit is recognized as the holotype of a new genus and species. The holotype and referred specimens span both estuarine and fluvial sediments and may indicate an example of niche-partitioning within the predominantly marine Plesiosauria. The small body size is also consistent with those of plesiosaurs from other non-marine units. I also describe select elasmosaurid and polycotylid specimens from the BF and PSF, respectively. One elasmosaurid belongs to a large-bodied taxon which may be closely-related to, or possibly conspecific with, the DPF taxon. Another elasmosaurid belongs to a small-bodied, likely new, taxon. The two polycotylids were originally considered to be a juvenile and adult of Dolichorhynchops bonneri, based on their similar morphologies and large discrepancy in size. However, both specimens are osteologically mature, possibly reflecting interspecific differences; alternatively, these body size differences may be due to sexual dimorphism. Finally, this dissertation constitutes one of the first histological studies on plesiosaurs from non-marine units and Canada. This study also contributes to our limited understanding of plesiosaur ontogeny.
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