Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greate... more Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greater taxonomic diversity among larger (>50 kg) theropod taxa than communities of the Campano-Maastrichtian, particularly to those of eastern/central Asia and Laramidia. The large carnivore guilds in Asiamerican assemblages are monopolized by tyrannosaurids, with adult medium-sized (50–500 kg) predators rare or absent. In contrast, various clades of theropods are found to occupy these body sizes in earlier faunas, including early tyrannosauroids. Assemblages with “missing middle-sized” predators are not found to have correspondingly sparser diversity of potential prey species recorded in these same faunas. The “missing middle-sized” niches in the theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile and subadults of tyrannosaurid species, functionally distinct from their adult ecomorphologies. It is speculated that if tyrannosaurids assimilated the ni...
SynopsisTyrannosaurid dinosaurs had large preserved leg muscle attachments and low rotational ine... more SynopsisTyrannosaurid dinosaurs had large preserved leg muscle attachments and low rotational inertia relative to their body mass, indicating that they could turn more quickly than other large theropods.MethodsTo compare turning capability in theropods, we regressed agility estimates against body mass, incorporating superellipse-based modeled mass, centers of mass, and rotational inertia (mass moment of inertia). Muscle force relative to body mass is a direct correlate of agility in humans, and torque gives potential angular acceleration. Agility scores therefore include rotational inertia values divided by proxies for (1) muscle force (ilium area and estimates of m. caudofemoralis longus cross-section), and (2) musculoskeletal torque. Phylogenetic ANCOVA (phylANCOVA) allow assessment of differences in agility between tyrannosaurids and non-tyrannosaurid theropods (accounting for both ontogeny and phylogeny). We applied conditional error probabilitiesa(p) to stringently test the nul...
Tyrannosaurid dinosaurs were ecologically unique vertebrates as the sole clade of large terrestri... more Tyrannosaurid dinosaurs were ecologically unique vertebrates as the sole clade of large terrestrial carnivores (adults >400 kg) in their continent-spanning habitats. Expanded ligaments between metatarsals, inferred by gross morphology of attachment correlates, have been hypothesized to have strengthened their specialized arctometatarsus. We tested the hypothesis of ligament presence with scanning electron microscopy and histological thin sections of putative attachment sites in a third metatarsal of the tyrannosaurid Gorgosaurus libratus, compared with a thin section from the unspecialized metatarsals of the early theropod Coelophysis bauri. In the Gorgosaurus metatarsal, Sharpey´s fibers and rough, pitted surface textures consistent with ligament coalescence occur at expansive distal regions and localized rugosities are ideally located for resisting torsional loading on the foot. Sparser Sharpey’s fibers occur at expected locations in other arctometatarsus-bearing coelurosaurs. ...
Jr. is a dinosaur paleontologist in the Department of Geology at the University of Maryland, Coll... more Jr. is a dinosaur paleontologist in the Department of Geology at the University of Maryland, College Park. He received his Ph. D. in geology and geophysics at Yale University. His primary research interests are the evolution and adaptations of theropod dinosaurs, especially the Tyrannosauridae (tyrant dinosaurs); the ecomorphology of predation; and the effect of plate tectonics on Mesozoic terrestrial vertebrate distributions. He is Director of the College Park Scholars Earth, Life & Time program, a two-year honors program for ...
Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greate... more Well-sampled dinosaur communities from the Jurassic through the early Late Cretaceous show greater taxonomic diversity among larger (>50 kg) theropod taxa than communities of the Campano-Maastrichtian, particularly to those of eastern/central Asia and Laramidia. The large carnivore guilds in Asiamerican assemblages are monopolized by tyrannosaurids, with adult medium-sized (50–500 kg) predators rare or absent. In contrast, various clades of theropods are found to occupy these body sizes in earlier faunas, including early tyrannosauroids. Assemblages with “missing middle-sized” predators are not found to have correspondingly sparser diversity of potential prey species recorded in these same faunas. The “missing middle-sized” niches in the theropod guilds of Late Cretaceous Laramidia and Asia may have been assimilated by juvenile and subadults of tyrannosaurid species, functionally distinct from their adult ecomorphologies. It is speculated that if tyrannosaurids assimilated the ni...
SynopsisTyrannosaurid dinosaurs had large preserved leg muscle attachments and low rotational ine... more SynopsisTyrannosaurid dinosaurs had large preserved leg muscle attachments and low rotational inertia relative to their body mass, indicating that they could turn more quickly than other large theropods.MethodsTo compare turning capability in theropods, we regressed agility estimates against body mass, incorporating superellipse-based modeled mass, centers of mass, and rotational inertia (mass moment of inertia). Muscle force relative to body mass is a direct correlate of agility in humans, and torque gives potential angular acceleration. Agility scores therefore include rotational inertia values divided by proxies for (1) muscle force (ilium area and estimates of m. caudofemoralis longus cross-section), and (2) musculoskeletal torque. Phylogenetic ANCOVA (phylANCOVA) allow assessment of differences in agility between tyrannosaurids and non-tyrannosaurid theropods (accounting for both ontogeny and phylogeny). We applied conditional error probabilitiesa(p) to stringently test the nul...
Tyrannosaurid dinosaurs were ecologically unique vertebrates as the sole clade of large terrestri... more Tyrannosaurid dinosaurs were ecologically unique vertebrates as the sole clade of large terrestrial carnivores (adults >400 kg) in their continent-spanning habitats. Expanded ligaments between metatarsals, inferred by gross morphology of attachment correlates, have been hypothesized to have strengthened their specialized arctometatarsus. We tested the hypothesis of ligament presence with scanning electron microscopy and histological thin sections of putative attachment sites in a third metatarsal of the tyrannosaurid Gorgosaurus libratus, compared with a thin section from the unspecialized metatarsals of the early theropod Coelophysis bauri. In the Gorgosaurus metatarsal, Sharpey´s fibers and rough, pitted surface textures consistent with ligament coalescence occur at expansive distal regions and localized rugosities are ideally located for resisting torsional loading on the foot. Sparser Sharpey’s fibers occur at expected locations in other arctometatarsus-bearing coelurosaurs. ...
Jr. is a dinosaur paleontologist in the Department of Geology at the University of Maryland, Coll... more Jr. is a dinosaur paleontologist in the Department of Geology at the University of Maryland, College Park. He received his Ph. D. in geology and geophysics at Yale University. His primary research interests are the evolution and adaptations of theropod dinosaurs, especially the Tyrannosauridae (tyrant dinosaurs); the ecomorphology of predation; and the effect of plate tectonics on Mesozoic terrestrial vertebrate distributions. He is Director of the College Park Scholars Earth, Life & Time program, a two-year honors program for ...
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