Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that tw... more Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that two spinosaurid dinosaurs (Spinosaurus aegyptiacus, Baryonyx walkeri) were diving “subaqueous foragers,” whereas a third spinosaurid (Suchomimus tenerensis) and other sampled nonavian dinosaurs were non-diving terrestrial feeders entering water only as waders. We outline shortcomings in this analysis that involve bone compactness sampling and measurement, lifestyle categorization, the inclusion and exclusion of taxa in the dataset, and flawed statistical methods and inferences. These many shortcomings undermine the evidence used to conclude that two spinosaurid taxa were avid divers. Bone compactness indices remain a valuable tool for interpretation of lifestyle in extinct species when based on sound dataset composition, robust statistical analysis, and consilience with evidence from functional, biomechanical, or paleoenvironmental considerations.
Powered flight evolved three times independently among tetrapods (Pterosauria, Aves, Chiroptera),... more Powered flight evolved three times independently among tetrapods (Pterosauria, Aves, Chiroptera), each transition involving a distinctive retooling of forelimbs into wings in response to similar aerodynamic functional constraints. In this dissertation I examine three aspects of the avian flight apparatus —wing shape, sternum shape, and humeral pneumaticity (internal air space)–– using a range of comparative techniques that may be extended in future research to the other two clades of powered fliers. Although avian wing shape has long been correlated with general aerodynamic demands (flight function, speed, lift, etc.), that correlation more recently has been shown to be less significant when considering the range of distinctive avian flight styles and migratory habits. Instead, phylogenetic proximity has left an imprint with closely related birds showing similar wing shapes. To rigorously test the association of wing shape with ecology and flight behavior, and to test the strength of association of wing morphology with other behavioral and ecological variables, I chose a functionally and ecologically diverse assemblage of birds known as waterbirds. In this group I found that wing shape is highly convergent and correlated strongly with foraging behavior, but not with habitat, flight style or migration pattern. The sternum, anchor to the major flight muscles, varies markedly in shape like the wing but has not been as intensively studied. I found that sternum shape, like wing shape, is highly convergent and retains phylogenetic signal but also is significantly correlated with flight style. The sternum may thus be more strongly linked than the wing to some biomechanical flight variables. Humeral pneumaticity has been shown to be correlated with body mass, particular flight styles, and some behaviors and ecological habitats, such as diving. Previous studies, however, were based only on the presence/absence of pneumatic foramina rather than the actual volume of internal air space. Using CT scans of a sample of avian hu [...]
Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by waterbird/landb... more Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by waterbird/landbird designation. Mouse over data points for identification and waterbird/landbird designation. Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum phylomorphospace showing PC1-3. Mouse over data point... more Interactive three-dimensional avian sternum phylomorphospace showing PC1-3. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by clade. Mou... more Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by clade. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by flight sty... more Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by flight style. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by clade. Mouse ov... more Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by clade. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that tw... more Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that two spinosaurid dinosaurs (Spinosaurus aegyptiacus,Baryonyx walkeri) were diving “subaqueous foragers,” whereas a third spinosaurid (Suchomimus tenerensis) and other sampled nonavian dinosaurs were non-diving terrestrial feeders entering water only as waders. We outline shortcomings in this analysis that involve bone compactness sampling and measurement, lifestyle categorization, the inclusion and exclusion of taxa in the dataset, and flawed statistical methods and inferences. These many shortcomings undermine the evidence used to conclude that two spinosaurid taxa were avid divers. Bone compactness indices remain a valuable tool for interpretation of lifestyle in extinct species when based on sound dataset composition, robust statistical analysis, and consilience with evidence from functional, biomechanical, or paleoenvironmental considerations.
A predominantly fish-eating diet was envisioned for the sail-backed theropod dinosaurSpinosaurus ... more A predominantly fish-eating diet was envisioned for the sail-backed theropod dinosaurSpinosaurus aegyptiacuswhen its elongate jaws with subconical teeth were unearthed a century ago in Egypt. Recent discovery of the high-spined tail of that skeleton, however, led to a bolder conjecture thatS. aegyptiacuswas the first fully aquatic dinosaur. The ‘aquatic hypothesis’ posits thatS. aegyptiacuswas a slow quadruped on land but a capable pursuit predator in coastal waters, powered by an expanded tail. We test these functional claims with skeletal and flesh models ofS. aegyptiacus. We assembled a CT-based skeletal reconstruction based on the fossils, to which we added internal air and muscle to create a posable flesh model. That model shows that on landS. aegyptiacuswas bipedal and in deep water was an unstable, slow-surface swimmer (<1 m/s) too buoyant to dive. Living reptiles with similar spine-supported sails over trunk and tail are used for display rather than aquatic propulsion, an...
Fabbri et al.1 claim that the huge sail-backed dinosaur Spinosaurus aegyptiacus and the spinosaur... more Fabbri et al.1 claim that the huge sail-backed dinosaur Spinosaurus aegyptiacus and the spinosaurid Baryonyx were “subaqueous foragers,” diving underwater in pursuit of prey, based on their measure of bone “compactness.” Using thin-sections and computed tomographic (CT) scans of thigh bone (femur) and trunk rib from various living and extinct vertebrates, they claim to be able to distinguish taxa with “aquatic habits” from others. Their conclusions are undermined by selective bone sampling, inaccuracies concerning spinosaurid bone structure, faulty statistical inferences, and novel redefinition of the term “aquatic.”
Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by flight style. M... more Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by flight style. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Digital restoration of fossils based on computed tomographic (CT) imaging and other scanning tech... more Digital restoration of fossils based on computed tomographic (CT) imaging and other scanning technologies has become routine in paleontology. Digital restoration includes the retrodeformation and reconstruction of a fossil specimen. The former involves modification of the original 3D model to reverse post-mortem brittle and plastic deformation; and the latter involves the infilling of fractures, addition of missing pieces, and smoothing of the mesh surface. The restoration process often involves digital editing of the specimen in ways that are difficult to document and reproduce. To record all actions taken during the digital restoration of a fossil, we outline a workflow that generates both the restored bone and the sequence of steps involved in its retrodeformation and reconstruction. Our method can also generate an animation showing the transformation of the original digital model into its final form. We applied this method to a dorsal rib and frontal bone of a small-bodied Juras...
Synopsis Wing shape plays a critical role in flight function in birds and other powered fliers an... more Synopsis Wing shape plays a critical role in flight function in birds and other powered fliers and has been shown to be correlated with flight performance, migratory distance, and the biomechanics of generating lift during flight. Avian wing shape and flight mechanics have also been shown to be associated with general foraging behavior and habitat choice. We aim to determine if wing shape in waterbirds, a functionally and ecologically diverse assemblage united by their coastal and aquatic habitats, is correlated with various functional and ecological traits. We applied geometric morphometric approaches to the spread wings of a selection of waterbirds to search for evolutionary patterns between wing shape and foraging behavior, habitat, and migratory patterns. We found strong evidence of convergent evolution of high and low aspect ratio wing shapes in multiple clades. Foraging behavior also consistently exhibits strong evolutionary correlations with wing shape. Habitat, migration, an...
Proceedings of the National Academy of Sciences, 2020
Developmental novelties often underlie the evolutionary origins of key metazoan features. The anu... more Developmental novelties often underlie the evolutionary origins of key metazoan features. The anuran urostyle, which evolved nearly 200 MYA, is one such structure. It forms as the tail regresses during metamorphosis, when locomotion changes from an axial-driven mode in larvae to a limb-driven one in adult frogs. The urostyle comprises of a coccyx and a hypochord. The coccyx forms by fusion of caudal vertebrae and has evolved repeatedly across vertebrates. However, the contribution of an ossifying hypochord to the coccyx in anurans is unique among vertebrates and remains a developmental enigma. Here, we focus on the developmental changes that lead to the anuran urostyle, with an emphasis on understanding the ossifying hypochord. We find that the coccyx and hypochord have two different developmental histories: First, the development of the coccyx initiates before metamorphic climax whereas the ossifying hypochord undergoes rapid ossification and hypertrophy; second, thyroid hormone di...
Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that tw... more Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that two spinosaurid dinosaurs (Spinosaurus aegyptiacus, Baryonyx walkeri) were diving “subaqueous foragers,” whereas a third spinosaurid (Suchomimus tenerensis) and other sampled nonavian dinosaurs were non-diving terrestrial feeders entering water only as waders. We outline shortcomings in this analysis that involve bone compactness sampling and measurement, lifestyle categorization, the inclusion and exclusion of taxa in the dataset, and flawed statistical methods and inferences. These many shortcomings undermine the evidence used to conclude that two spinosaurid taxa were avid divers. Bone compactness indices remain a valuable tool for interpretation of lifestyle in extinct species when based on sound dataset composition, robust statistical analysis, and consilience with evidence from functional, biomechanical, or paleoenvironmental considerations.
Powered flight evolved three times independently among tetrapods (Pterosauria, Aves, Chiroptera),... more Powered flight evolved three times independently among tetrapods (Pterosauria, Aves, Chiroptera), each transition involving a distinctive retooling of forelimbs into wings in response to similar aerodynamic functional constraints. In this dissertation I examine three aspects of the avian flight apparatus —wing shape, sternum shape, and humeral pneumaticity (internal air space)–– using a range of comparative techniques that may be extended in future research to the other two clades of powered fliers. Although avian wing shape has long been correlated with general aerodynamic demands (flight function, speed, lift, etc.), that correlation more recently has been shown to be less significant when considering the range of distinctive avian flight styles and migratory habits. Instead, phylogenetic proximity has left an imprint with closely related birds showing similar wing shapes. To rigorously test the association of wing shape with ecology and flight behavior, and to test the strength of association of wing morphology with other behavioral and ecological variables, I chose a functionally and ecologically diverse assemblage of birds known as waterbirds. In this group I found that wing shape is highly convergent and correlated strongly with foraging behavior, but not with habitat, flight style or migration pattern. The sternum, anchor to the major flight muscles, varies markedly in shape like the wing but has not been as intensively studied. I found that sternum shape, like wing shape, is highly convergent and retains phylogenetic signal but also is significantly correlated with flight style. The sternum may thus be more strongly linked than the wing to some biomechanical flight variables. Humeral pneumaticity has been shown to be correlated with body mass, particular flight styles, and some behaviors and ecological habitats, such as diving. Previous studies, however, were based only on the presence/absence of pneumatic foramina rather than the actual volume of internal air space. Using CT scans of a sample of avian hu [...]
Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by waterbird/landb... more Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by waterbird/landbird designation. Mouse over data points for identification and waterbird/landbird designation. Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum phylomorphospace showing PC1-3. Mouse over data point... more Interactive three-dimensional avian sternum phylomorphospace showing PC1-3. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by clade. Mou... more Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by clade. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by flight sty... more Interactive three-dimensional avian sternum phylomorphospace showing PC1-3, colored by flight style. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by clade. Mouse ov... more Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by clade. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that tw... more Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that two spinosaurid dinosaurs (Spinosaurus aegyptiacus,Baryonyx walkeri) were diving “subaqueous foragers,” whereas a third spinosaurid (Suchomimus tenerensis) and other sampled nonavian dinosaurs were non-diving terrestrial feeders entering water only as waders. We outline shortcomings in this analysis that involve bone compactness sampling and measurement, lifestyle categorization, the inclusion and exclusion of taxa in the dataset, and flawed statistical methods and inferences. These many shortcomings undermine the evidence used to conclude that two spinosaurid taxa were avid divers. Bone compactness indices remain a valuable tool for interpretation of lifestyle in extinct species when based on sound dataset composition, robust statistical analysis, and consilience with evidence from functional, biomechanical, or paleoenvironmental considerations.
A predominantly fish-eating diet was envisioned for the sail-backed theropod dinosaurSpinosaurus ... more A predominantly fish-eating diet was envisioned for the sail-backed theropod dinosaurSpinosaurus aegyptiacuswhen its elongate jaws with subconical teeth were unearthed a century ago in Egypt. Recent discovery of the high-spined tail of that skeleton, however, led to a bolder conjecture thatS. aegyptiacuswas the first fully aquatic dinosaur. The ‘aquatic hypothesis’ posits thatS. aegyptiacuswas a slow quadruped on land but a capable pursuit predator in coastal waters, powered by an expanded tail. We test these functional claims with skeletal and flesh models ofS. aegyptiacus. We assembled a CT-based skeletal reconstruction based on the fossils, to which we added internal air and muscle to create a posable flesh model. That model shows that on landS. aegyptiacuswas bipedal and in deep water was an unstable, slow-surface swimmer (<1 m/s) too buoyant to dive. Living reptiles with similar spine-supported sails over trunk and tail are used for display rather than aquatic propulsion, an...
Fabbri et al.1 claim that the huge sail-backed dinosaur Spinosaurus aegyptiacus and the spinosaur... more Fabbri et al.1 claim that the huge sail-backed dinosaur Spinosaurus aegyptiacus and the spinosaurid Baryonyx were “subaqueous foragers,” diving underwater in pursuit of prey, based on their measure of bone “compactness.” Using thin-sections and computed tomographic (CT) scans of thigh bone (femur) and trunk rib from various living and extinct vertebrates, they claim to be able to distinguish taxa with “aquatic habits” from others. Their conclusions are undermined by selective bone sampling, inaccuracies concerning spinosaurid bone structure, faulty statistical inferences, and novel redefinition of the term “aquatic.”
Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by flight style. M... more Interactive three-dimensional avian sternum morphospace showing PC1-3, colored by flight style. Mouse over data points for identification and flight style categorization. Flight style following Viscor and Fuster (1987). Three-dimensional landmark data was collected from 128 avian sterna, standardized using a GPA, analyzed using a PCA, then plotted with the plotly R package. Supplemental figure for Chapter 3 of my dissertation.
Digital restoration of fossils based on computed tomographic (CT) imaging and other scanning tech... more Digital restoration of fossils based on computed tomographic (CT) imaging and other scanning technologies has become routine in paleontology. Digital restoration includes the retrodeformation and reconstruction of a fossil specimen. The former involves modification of the original 3D model to reverse post-mortem brittle and plastic deformation; and the latter involves the infilling of fractures, addition of missing pieces, and smoothing of the mesh surface. The restoration process often involves digital editing of the specimen in ways that are difficult to document and reproduce. To record all actions taken during the digital restoration of a fossil, we outline a workflow that generates both the restored bone and the sequence of steps involved in its retrodeformation and reconstruction. Our method can also generate an animation showing the transformation of the original digital model into its final form. We applied this method to a dorsal rib and frontal bone of a small-bodied Juras...
Synopsis Wing shape plays a critical role in flight function in birds and other powered fliers an... more Synopsis Wing shape plays a critical role in flight function in birds and other powered fliers and has been shown to be correlated with flight performance, migratory distance, and the biomechanics of generating lift during flight. Avian wing shape and flight mechanics have also been shown to be associated with general foraging behavior and habitat choice. We aim to determine if wing shape in waterbirds, a functionally and ecologically diverse assemblage united by their coastal and aquatic habitats, is correlated with various functional and ecological traits. We applied geometric morphometric approaches to the spread wings of a selection of waterbirds to search for evolutionary patterns between wing shape and foraging behavior, habitat, and migratory patterns. We found strong evidence of convergent evolution of high and low aspect ratio wing shapes in multiple clades. Foraging behavior also consistently exhibits strong evolutionary correlations with wing shape. Habitat, migration, an...
Proceedings of the National Academy of Sciences, 2020
Developmental novelties often underlie the evolutionary origins of key metazoan features. The anu... more Developmental novelties often underlie the evolutionary origins of key metazoan features. The anuran urostyle, which evolved nearly 200 MYA, is one such structure. It forms as the tail regresses during metamorphosis, when locomotion changes from an axial-driven mode in larvae to a limb-driven one in adult frogs. The urostyle comprises of a coccyx and a hypochord. The coccyx forms by fusion of caudal vertebrae and has evolved repeatedly across vertebrates. However, the contribution of an ossifying hypochord to the coccyx in anurans is unique among vertebrates and remains a developmental enigma. Here, we focus on the developmental changes that lead to the anuran urostyle, with an emphasis on understanding the ossifying hypochord. We find that the coccyx and hypochord have two different developmental histories: First, the development of the coccyx initiates before metamorphic climax whereas the ossifying hypochord undergoes rapid ossification and hypertrophy; second, thyroid hormone di...
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