Browsing by Author "Anderson, Jason"

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    A redescription of Brouffia orientalis Carroll & Baird, 1972 from the Upper Carboniferous of the Czech Republic and the status and affinities of protorothyridid amniotes
    (2024-09-11) Klembara, Jozef; Ruta, Marcello; Anderson, Jason; Mayer, Taran; Hain, Miroslav; Valaška, Daniel
    Abstract The Upper Carboniferous protorothyridid amniote Brouffia orientalis from Czech Republic is redescribed. Photogrammetric scanning of the holotype and only known specimen yields considerable new information on the skull and postcranium of this tetrapod and allows us to amend previous morphological descriptions to a substantial degree. A virtual 3D model built from photogrammetry scan data is used as the basis for a new reconstruction of the skull in dorsal, lateral, and ventral aspects and the lower jaw in lateral aspect. We expand and refine the diagnosis of Brouffia and compare it with other protorothyridids. We discuss the affinities of this taxon by coding it in a recently published data matrix of early amniotes, which we subject to maximum parsimony and Bayesian fossilized birth–death analyses. Brouffia emerges as the sister taxon to Coelostegus in all analyses, but the position of these two taxa within amniotes varies. In a parsimony analysis with unweighted characters, the (Brouffia + Coelostegus) clade forms the sister group to Synapsida. In various experiments of character reweighting, that clade is placed crownward of Captorhinidae on the stem-group of Reptilia, but anticrownward of remaining protorothyridids. The latter constitute either a paraphyletic array relative to Diapsida or their monophyletic sister group. The Bayesian analysis retrieves (Brouffia + Coelostegus) as the most basal plesion on the stem-group of Reptilia.
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    An Analysis of Enthesis-Bone Microstructure: Implications for Paleontological Soft Tissue Reconstructions.
    (2021-08) Whitebone, Stephanie Amber; Anderson, Jason; Theodor, Jessica; Matyas, John
    In the absence of direct preservation, evaluating a fossil organism’s soft tissue anatomy can be a daunting task. Studies that aim to evaluate fossil soft tissues must often rely on clear soft tissue bony correlates, such as bony eminences or concavities in the bone surface. These eminences and concavities are formed at the site of soft tissue attachment to bone, called entheses. However, even in large-bodied, adult organisms, a considerable proportion of soft tissues do not leave these clear indicators. Therefore, the evaluation of bony eminences/concavities is coupled with the use of an extant phylogenetic bracket. However, some fossil taxa are so phylogenetically removed from their extant bracketing taxa that anatomical comparisons are dubious at best. I have shown that scanning electron microscopy and histological staining make it possible to identify areas of soft tissue attachment on the bone surface in the absence of macroscopically visible eminences or concavities. There is also a differentiation between tissue types (muscle, tendon, articular cartilage, and aponeurosis) with collagen fibres incorporated into the bone tissue. At areas of articular cartilages, the surface is relatively smooth but with small, organized hummocky structures. Areas of fleshy muscle attachment are generally planar but with occasional round projections where the collagen fibres have been incorporated into bone tissue. Tendon entheses are areas where long string-like collagen fibres have been incorporated into bone tissue, usually within concave impressions on the bone surface. These areas are generally more organized than other entheses. Lastly, aponeurotic entheses are large areas of thick, high-density, disorganized collagen fibres. All four categories of bone surface microstructure have been observed through broad taxonomic sampling using extant organisms, and the same morphologies are also seen in three-dimensional preserved fossil specimens. These four bone surface microstructures are successfully categorized using image classification programming with novel convolutional neural network architecture. Using polarimetry, I quantify the differences between bone surface microstructures by measuring the orientation of collagen fibres and the homogeneity of collagen fibre density throughout the enthesis bone’s thickness.
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    Applications of strontium concentrations and isotopes preserved in vertebrate enamel and enamel-like tissues to paleoecology studies of Silurian conodonts from Gotland, Sweden, and Cretaceous Dinosaurs and Plesiosaurs from Alberta, Canada
    (2021-07-06) Terrill, David; Henderson, Charles; Anderson, Jason; Henderson, Charles; Anderson, Jason; Therrien, Francois; Wieser, Michael; Katzenberg, Anne; Fricke, Henry
    Paleoecology is faced with the challenge of determining the behaviour of extinct animals without direct observation. Geochemical approaches offer one of the most promising avenues to study paleoecology problems such as potential migratory patterns. While original biochemical signals are often obscured in fossilized tissues as a result of diagenesis, tooth enamel is an exception due to its very high mineral content and low porosity. Though there are many potential biological signals preserved in fossil enamel, this thesis focused on the trace element strontium. By analyzing strontium isotope ratios preserved in the enamel of terrestrial dinosaurs, possible migratory behaviours were examined in both hadrosaurs and ceratopsians found at Dinosaur Provincial Park in the Late Cretaceous Dinosaur Park Formation of Alberta, Canada. The movements of a hadrosaur individual were determined to extend beyond the Dinosaur Provincial Park area to a location just under 100 km to the east of the park. In contrast, a herd of ceratopsians preserved in a bonebed were shown to have travelled as far as 200 km from either the north or west. Strontium isotope ratios were also examined in the enamel of plesiosaurs and enamel-like tissues of conodonts to determine if either group inhabited freshwater habitats. Plesiosaur teeth collected from fluvial deposits of the Dinosaur Park Formation were found to largely preserve a terrestrial signal, suggesting some plesiosaurs may have primarily inhabited freshwater environments. Conodont elements from Silurian marginal marine deposits in Gotland, Sweden were also examined with a focus on potential differences through ontogeny. The results confirmed the conodont taxa Ozarkodina confluens lived exclusively in marine settings and did not spawn or spend time in coastal freshwater environments. Finally, Sr/Ca and Ba/Ca ratios were analyzed in an entire conodont community from the Silurian of Gotland, Sweden. Results revealed convincing evidence for trophic partitioning between co-occurring conodont taxa. Compositional variations were observed between the two main tissues found in conodont crowns, white matter and lamellar tissue. These tissues occur in different proportions in different taxa, and these proportions need to be kept in mind when interpreting their geochemical data.
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    Comparison of Paleodietary Reconstructions Using Pre- and Post-Glacial Mammut and Mammuthus
    (2017) Cammidge, Tasha Sabrina; Theodor, Jessica; Kooyman, Brian; Dutchak, Alexander; Anderson, Jason
    Mesowear, microwear and dental calculus analyses are utilized to complete dietary reconstructions on Mammut and Mammuthus, and are compared to modern Loxodonta africana. These analyses demonstrate that left and right, upper and lower, and imperfect molars may be utilized indiscriminately. Loxodonta africana are grazers or mixed-feeders. Mammut were primarily browsers, but may have changed their diets meal-by-meal or seasonally to graze or mixed-feed. Mesowear analysis of Mammuthus indicates a grazing diet, but microwear analysis indicates a mixed-feeding diet. Dental calculus analysis shows all three species were mixed-feeding. Mesowear and microwear show no differences in pre- and post-glacial diet for fossil proboscideans, but dental calculus showed large differences. In pre-glacial dental calculus there was a larger proportion of tiny grass starch granules, whereas post-glacially there is a larger proportion of large grass starch granules with lamellae. This result is consistent with a shift in Mammut and Mammuthus diet during the end-Pleistocene.
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    Contributions of Modularity and Integration to Phenotypic Variation and Complexity in the C. eos-neogaeus Hybridization Complex
    (2023-07) Duclos, Kevin Karl; Jamniczky, Heather; Theodor, Jessica; Yeaman, Sam; Mee, Jonathan; Anderson, Jason; Evans, Kory
    Evolutionary developmental biology links the key ideas of evolution, such as the study of evolvability, into the study of developmental properties and mechanisms. Biological complexity is recognized as key component of evolvability and the emergence of novel traits. However, the study of complexity and how it factors into evolvability has been mired in inconsistent definitions and the lack of a clear framework including the fact that phenotype is an end result of developmental processes. Complex phenotypes are the result of interactions between intrinsic factors, such as developmental processes and constraints, and extrinsic factors, including selective pressures and environmental stimuli. As such, complexity is tightly regulated and structured through ontogeny. In this thesis, I address the links between complexity, evolvability and the emergence of novelty using the C. eos-neogaeus hybridization complex as a study system. I first explore how the conceptual and methodological frameworks of modularity and integration allow explicit studies of the links between complexity and evolvability. I subsequently contextualize complexity in the framework of epigenetics sensu Waddington and identify hybridization, and hybrid organisms as pertinent models for the study of biological complexity. Using geometric morphometrics, I assess phenotypic integration and modularity in the cranial and postcranial skeleton of the C. eos-neogaeus hybridization complex. I show that hybridization results in varying patterns of modularity and phenotypic integration between parental species and hybrid lineages of the C. eos-neogaeus complex. I show that shared pairwise phenotypic integration between traits result in different effects on the directionality of shape variation across lineages. The modification of the directionality of shape variation, promotes phenotypic transgression and phenotypic novelty in hybrids. Finally, I explored topological variation and integration in the pectoral girdle across hybrid lineages and parental species of the C eos-neogaeus complex. I identify conserved patterns of modularity in the pectoral girdle within the C. eos-neogaeus complex despite lineage-specific variation in structure and the shape of individual bones within the pectoral girdle. While the factors promoting increases and decreases in complexity through evolution require further attention, my thesis illustrates how modularity and integration are crucial in organizing and maintaining complexity within and between species.
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    Evolutionary palaeoecology of the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada
    (2012-07-30) Mallon, Jordan; Anderson, Jason
    During the Late Cretaceous, megaherbivorous dinosaurs flourished in the Western Interior of North America (Laramidia). At any one time, there were typically two ankylosaurs (one ankylosaurid plus one nodosaurid), two ceratopsids (one centrosaurine plus one chasmosaurine), and two hadrosaurids (one hadrosaurine plus one lambeosaurine) living in sympatry. This diversity exceeds that of living megaherbivorous mammal communities, and is only rarely observed in the mammalian fossil record. Opinions differ about how this diversity was achieved. Some have argued that megaherbivorous dinosaurs thrived because of their low metabolic rates, or because of high primary productivity during the Late Cretaceous, implying that food resources were not limiting. A similar outcome might have been achieved if predation pressure from theropods was sufficiently high to depress megaherbivore population densities, leading to reduced demand on plant resources. Others have argued that dietary niche partitioning played an important role in the coexistence of these animals, with each species consuming a different plant resource than the next, thereby minimizing interspecific competition. This dissertation uses the megaherbivorous dinosaur assemblage from the upper Campanian Dinosaur Park Formation (DPF) of Alberta, Canada, as a model to test the dietary niche partitioning hypothesis by examining several aspects of ecomorphology known to relate to the procurement and mastication of food. These include feeding height, skull and beak morphology, jaw mechanics, and tooth morphology and wear. Evidence is sought for taxonomic separation in ecomorphospace, particularly between coexisting species, which is known to reflect niche relationships with some fidelity. Although sympatric taxa are better discriminated by some features than others, consideration of the total evidence supports the dietary niche partitioning hypothesis, as even the most closely related, sympatric taxa can be statistically distinguished according to their ecomorphology. Whether these dietary niche relationships arose as a result of long-term competition, or whether they evolved allopatrically is not clear. However, the fact that consubfamilial species coexistence was uncommon—and when it did occur, was either short-lived or involved only rare species—implies that the structure of the megaherbivorous dinosaur assemblage from the DPF was at least partly influenced by competitive interactions.
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    Foraminiferal Biostratigraphy in Proximity to the Albian/Cenomanian Boundary using Six Global Deep Sea Drilling Project Sites
    (2016) Sawyer, Melissa Slavka; Georgescu, Marius Dan; Henderson, Charles; Beauchamp, Benoit; Anderson, Jason; Theodor, Jessica
    The Cretaceous stages are poorly defined and inconsistencies in the named species of the lowermost Cenomanian biozone and rarity of other named species led to doubt over the current biozonation scheme and its validity. This study tests the previous biozonation definitions through a review of planktic foraminifera from six global Deep Sea Drilling Project sites. This study validates the use of T. globotruncanoides as the named species for the lowermost Cenomanian biozone despite the location of the referenced type specimen not being from the type locality. Several changes were applied to the biozonation of the late Albian; however, the named species Pseudothalmanninella ticinensis was not observed and a new biozone, Clavihedbergella subcretacea was assigned. Trends observed in the lower P. appenninica Biozone lead to the recognition of a new biozone, P. buxtorfi. These findings support the Cenomanian stage definition and help to define the Albian stage.
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    Geometric morphometric analysis of the breast-shoulder apparatus of Greater Antillean anole ecomorphs
    (2016-01-27) Tinius, Alexander; Russell, Anthony; Theodor, Jessica; Glor, Richard; Anderson, Jason; Ereshefsky, Marc; Jamniczky, Heather; Syme, Douglas
    Anoline lizards of the Greater Antillean islands have repeatedly followed parallel paths of morphological adaptation, resulting in ecologically and morphologically similar ecomorph communities (ecomorphs) on each island. Locomotor performance has been shown to be a key factor related to differential microhabitat occupancy of anoles, but to date studies on possible differences in the form and configuration of the postcranial skeleton and musculature (deep anatomy) that relate to ecomorphological differentiation are scant. Here I employ the breast-shoulder apparatus (BSA; the skeleton, musculature, and connective tissue that comprise the pectoral region of tetrapods) to examine the morphological variability of the pectoral region of island anoles. I employ microcomputed tomography to image the skeletal elements of the BSA, and three-dimensional geometric morphometric analysis to compare the shapes of the skeletal features of twenty-six anole species representing four distinctive ecomorphs (trunk-ground, trunk-crown, crown-giant, twig). My material is sourced from three Greater Antillean islands (Jamaica, Puerto Rico, and Hispaniola). Despite several limitations of the techniques employed, I show that a comprehensive understanding of the interactions between ecological preferences and morphological adaptations can only be gained from an investigation of the complex integration of form, function, and ecological role. The geometry of the shoulder girdle in situ, and that of its components, differs between anole species. These morphological differences show a hierarchy of influences: they are primarily driven by ecomorph designation, but are also influenced by patterns of phylogenetic relationship, which contrasts with the findings from linear measurements and counts used to characterise ecomorphs. The three arboreal ecomorphs are characterised by a differential shape of the presternum, which is likely associated with changes in the musculature of these anoles, and made possible through the insensible transition between the pre- and mesosternum, facilitating migration of the rib attachment sites. This has potentially facilitated adaptive radiation in anoles. My investigations further show that linear external measurements cannot be employed to predict patterns of variation in the skeletal elements of the BSA. Varying environmental factors on the three islands examined allowed for the occurrence of similar, but not identical, skeletal patterns of ecological-morphological adaptation in geographically distinct areas.
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    Neck Mobility of the Plesiosaur Nichollsaura borealis
    (2017) Nagesan, Ramon; Anderson, Jason; Bertram, John; Henderson, Donald; Theodor, Jessica; Jamniczky, Heather
    For 135 million years during the Mesozoic the elongate-necked plesiosaurs lived in the oceans around the globe. Using 3D modeling, comparative anatomy, and soft tissue reconstruction I estimated the neck mobility of the plesiosaur, Nichollssaura borealis. I produced a series of 3D models of the cervical vertebral column from computed tomography scans of N. borealis. To quantify the range of motion, the intervertebral mobility was measured along the cervical vertebral column by manipulating the 3D models in the dorso-ventral and medio-lateral planes. The neck moves most in the lateral plane up to a maximum mean intervertebral mobility of 13.51˚ (+/-1.113˚). Extant phylogenetic bracketting was used to reconstruct and map the hypothetical musculature onto the preserved morphology of N. borealis. The hypothesized soft tissues show that musculature used for medio-lateral movements may have dominated in N. borealis. Studying N. borealis’s neck mobility allows us to understand plesiosaur prey captures abilities, hydrodynamics.
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    Nesting and Egg Incubation in Dinosaurs: Morphological and Statistical Investigations into the Study of Eggs, Eggshells, and Nests
    (2016) Tanaka, Kohei; Zelenitsky, Darla Karen; Brinkman, Donald; Anderson, Jason; Therrien, François; Dutchak, Alexander; Theodor, Jessica
    Archosaurs (e.g., crocodylians, dinosaurs, and birds) are the most diverse and successful terrestrial vertebrates. An understanding of the nesting strategies in both extinct (e.g., non-avian dinosaurs) and extant archosaurs (i.e., crocodylians and birds) is crucial for advancement of our knowledge on the evolution and diversification of this group. However, nesting methods and behaviors of non-avian dinosaurs are still poorly understood due to the limitations of the fossil record. In this dissertation, certain features of eggs and nests in dinosaurs (e.g., clutch size, egg mass, substrates of nests, water vapor conductance of eggs, and eggshell porosity) are compared with those of their closest living relatives (i.e., birds and crocodylians) and aspects of dinosaur nesting (i.e., nest type, incubation behavior, incubation heat source, and incubation period) are inferred and reconstructed. Findings in this dissertation suggest that nests and nesting styles among non-avian dinosaurs were diverse, and that bird-like traits were acquired throughout their evolution. Analyses of eggs and eggshell porosity indicate that more basal dinosaurs (i.e., ornithischians, sauropodomorphs, Lourinhanosaurus) completely covered their eggs with nest materials during incubation, although more derived forms (e.g., oviraptorosaurs, troodontids) used open nests, like modern birds, in which the eggs were not fully buried. The lithologies of the clutches of basal dinosaurs reveal their nests were probably incubated with external heat sources (e.g., microbial respiration, solar radiation), like those of modern crocodylians and megapode birds. Distribution and lithologies of some ornithischian and some sauropodomorph clutches show that heat from microbial respiration, in particular, was used for incubation, whereas other sauropodomorphs may have used inorganic heat sources, such as solar radiation. More derived dinosaurs (i.e., maniraptorans) had eggshell porosities and clutch lithologies that indicate their nests were partially open, indicating that these taxa brooded their eggs. Regardless of the type of nest, heat source, or incubation behavior, incubation period of most non-avian dinosaurs examined was relatively short, more comparable to that of birds than crocodylians. Major dinosaur (and archosaur) clades show diversity in their nesting and incubation, and also reveal a transition to more bird-like nesting features through evolution.
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    Osseous skull development of Ambystoma macrodactylum krausei from post-hatching through metamorphosis
    (2014-02-21) Wilson, Sian Caroline; Anderson, Jason; Hallgrimsson, Benedikt
    Salamander developmental morphological data contribute to deciphering evolutionary relationships of modern/fossil amphibians. This study examines the osseous skull morphology of Ambystoma macrodactylum krausei, from post-hatching through metamorphosis using μCT and synchrotron scanning methods. Skull elements and overall skull shape were described through ontogeny (including one adult). Landmark-based principal components analyses examined shape trends across collection years, premetamorphosis (PM) and metamorphosis (M), and scanning methods. Covariance matrices were compared across collection years. Modularity hypotheses were tested. A. m. krausei forms a prefrontolacrimal. Procrustes-transformed coordinates were significantly different for both collection years and PM/M, but were not significantly different for scanning methods. All shape trends had a significant allometric component. Generally, covariance matrices were more similar during PM than during M across collection years. No support for modularity hypotheses was found; however, the strength of cranial integration was different in the lower jaw and cranium, and through PM/M.
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    Phylogenetic implications of the morphology and development of the braincase of caecilian amphibians (gymnophiona)
    (2011) Maddin, Hillary C.; Russell, Anthony P.; Anderson, Jason
    Caecilians, one of the three living groups that comprise Lissamphibia (frogs, salamanders, and caecilians ), are considered the least well understood for many aspects of their biology. The current study set out to develop a framework, within which aspects such as morphology and evolution could be explored, by attempting to resolve the poorly understood phylogeny of caecilians by examining the morphology of the braincase and stapes. The braincases and stapedes of twenty-seven species of caecilian were examined using micro-computed tomography and histologically-prepared specimens. The braincases were first examined for their potential to yield phylogenetic information by deciphering variation in the antotic region. Deriving from assessments of homology based on transmitted structures, eight different patterns of antotic foramina are identified and the distribution of these patterns is congruent with hypotheses of relationships based on molecular data. It is demonstrated that heterochrony was likely a driver of morphological variation; however, causes of such modifications failed to be correlated with the patterns observed. Description of the entire braincase and stapes permitted the identification of thirty-two new morphological characters. These characters are shown to be sufficient for resolving genus-level relationships in the context of previously developed matrices, in a way that is congruent with hypotheses based on molecular data. A combined phylogenetic analysis of morphological and molecular data provides a test of congruence between morphological characters in a total evidence context, permitting ancestral character state reconstructions to be conducted and the plesiomorphic condition of the braincase and stapes of Gymnophiona to be inferred. The ability for the braincase to reveal phylogenetic information in the broader context of lissamphibian phylogeny was explored by considering the auditory apparatus. New observations, combined with those made previously, are used to infer the presence of the lissamphibian-type ear in caecilians, suggesting the secondary loss of the tympanic and opercularis hearing pathways in caecilians. The evolution of the lissamphibian-type ear is most parsimoniously explained under the rnonophyletic ternnospondyl hypothesis of lissamphibian phylogeny. The data presented here, and the new phylogenetic framework incorporating morphology, provide a means to further explore evolution in a group with diverse factors influencing the evolution of morphology.
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    Revisiting the Paleoenvironment and Mammal Fauna of the late Uintan Swift Current Creek Locality, Saskatchewan
    (2023-06) Ehrman, Benjamin A.; Theodor, Jessica; Theodor, Jessica; Anderson, Jason; Dutchak, Alex; Cote, Susanne
    The Swift Current Creek (SCC) locality was previously described as being similar to the “Rocky Mountains” fauna, an informal grouping of near-coeval assemblages in Utah and Wyoming, but otherwise having high faunal endemism (Storer 1984). Its paleoenvironment was described as a semi-arid, “tropical,” enclosed forest (Storer 1984). This interpretation of its environment contradicts the “Rocky Mountains” fauna comparison, as its Utah component (Myton Pocket- MP) is now interpreted to have been a savannah. This thesis sought to review SCC’s paleoenvironment and faunal endemism using a revised faunal list with palaeoecological methods not applied during previous studies of SCC. First, a rarefaction analysis was used to quantify the locality’s level of sampling, the likelihood of finding new mammal genera, and the diversity of specific taxonomic groups. A cenogram analysis was used to interpret SCC’s paleoenvironment based on body mass distribution (BMD) data. Similarity index calculations served to quantify SCC’s generic faunal similarity with near-coeval localities, including the Rocky Mountain’s MP and Badwater 6 (BW6; in Wyoming) localities. Faunal endemism was interpreted using a distance decay regression analysis, with Holocene localities serving as a baseline for comparative interpretation of differing patterns in faunal similarity. The rarefaction analysis results indicated that SCC is moderately sampled, and that continued sampling may result in the discovery of new mammal genera (especially rodents). The cenogram’s BMD is reflective of a humid, warm, enclosed forest. Some diversity signals from the rarefaction analysis support the interpretations of SCC’s environment, while others leave room for doubt. Descriptions of SCC being similar to the “Rocky Mountains” fauna were found to be inaccurate. The Swift Current Creek locality has high similarity value with BW6, but not with MP. The distance decay regression for SCC and its coeval localities did not express a significant decline in faunal similarity, and the rate of declining faunal similarity was much less drastic than in Holocene localities; demonstrating that SCC’s faunal endemism is not as high as past literature has indicated.
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    Salamander Braincase Morphology, and its Impact on Discombobulation
    (2016) Szostakiwskyj, Matthew; Anderson, Jason; Jamniczky, Heather; Theodor, Jessica
    Salamander phylogeny has been difficult to assess via morphology due to paedomorphosis, the retention of juvenile characters in the adult form, resulting in a large discrepancy between the topologies recovered by morphological and molecular datasets, prompting one author to comment that ontogeny “discombobulates” phylogeny. To investigate whether the addition of braincase morphology, an evolutionarily conserved module, to the current character set can resolve the incongruence between morphological and molecular datasets, I scanned 28 specimens of salamander, representing all 10 families, with micro-computed tomography; this represents the first time all 10 families have been visualized in 3D. I created a set of morphological characters describing the braincase, which I concatenated with the current datasets and performed both parsimony and Bayesian analyses. My results suggest that metamorphosis is strongly misleading morphological topologies, and demonstrate the importance of understanding how development impacts terminal morphology for character selection in future phylogenetic analyses.