My Research
The large carnivorous animals of the Mesozoic era are some of the most enigmatic magafauna that have ever existed. Theropod dinosaurs existed for hundreds of millions of years in varying population structures, in highly differing ecosystems, and on every continent across the globe. They lend themselves fantastically to so-called "sexy-science", yet there is a surprising lack of research into their ecology. My current research is primarily concerned with the community structure and behavior of megatheropods. My research utilizes dental microwear analysis to distinguish ontogenetic niche shift in large theropod dinosaurs, identifies patterns in communities through geologic time in relation to predator body size and growth rate, and examines optimal foraging and dietary niche in predatory dinosaurs.
Ontogeny And Community Structure
Dental Microwear
Despite dominating biodiversity in the Mesozoic, dinosaurs were not speciose. Oviparity constrained even gigantic dinosaurs to less than 15 kg at birth; growth through multiple morphologies led to the consumption of different resources at each stage. Such disparity between neonates and adults could have influenced the structure and diversity of dinosaur communities. Here, we quantified this effect for 43 communities across 136 million years and seven continents. We found that megatheropods (more than 1000 kg) such as tyrannosaurs had specific effects on dinosaur community structure. Although herbivores spanned the body size range, communities with megatheropods lacked carnivores weighing 100 to 1000 kg. We demonstrate that juvenile megatheropods likely filled the mesocarnivore niche, resulting in reduced overall taxonomic diversity. The consistency of this pattern suggests that ontogenetic niche shift was an important factor in generating dinosaur community structure and diversity.
The feeding ecology of giant oviparous organisms is often complex, and contributes significantly to the form and function of communities. Given the immense separation of body size between juvenile and adult tyrannosaurs it is likely they consumed different prey, and influenced their communities in distinct ways. Dental microwear texture analysis has been effective in characterizing generalized diet in both extant and extinct reptiles and mammals. Here we examine the dental microwear of four tyrannosaur genera at three age classes, using both scale-sensitive fractal analysis and 2d textural analysis. Our interpretations are guided by dietary components identified in modern carnivorous mammals and reptiles. We find significant differences in dental wear through ontogeny within all genera, and among multiple age classes between genera, indicating ontogenetic and taxonomic dietary separation. Specifically, our results indicate adult and juvenile tyrannosaurs consumed brittle foods with relatively little bone interaction, possibly indicative of consuming thick integument and flesh mostly whole. Conversely, sub-adult tyrannosaurs, particularly Tyrannosaurus consumed more malleable foods, with high instance of durophagy, potentially through the utilization of defleshed carcasses as a dietary supplement. Finally, we find significant differences in dental wear between multiple age classes of co-occurring tyrannosaurs, a possible avenue of competition avoidance within these genera.
Flightlessness
Competition in non-avian dinosaur communities was likely complicated due to the utilization of ontogenetic niche shifts by megatheropods, which may have assimilated the niches of mesocarnivores. However, a few 100-1000kg giant paravians were successful enough to co-occur with megatheropods despite body-size overlap with juveniles. What physiological traits enabled giant paravians to compete with megatheropods, the role of ancestral flight-adaptations and whether paravians exhibit the effects of such competition are unknown. Here we examine the locomotor capabilities of volant and non-volant paravians and non-paravian theropods across body size to determine top speed and efficiency. We assess prey availability and competitive overlap based on body size and running speed in four dinosaur assemblages containing giant paravians. Finally, we re-examine the phylogenetic placement of the enigmatic giant paravian Dakotaraptor steini to contextualize its competitive capacity. We identify two distinct non-volant paravian cursorial styles; giant paravians were limited in their top speeds, but were highly efficient runners, while small non-volant paravians were fast, but inefficient. We further find volant paravians among the least well adapted to cursorial locomotion. Volant paravians likely a traded cursoriality for the ability to vertically partition feeding niches, and small paravians likely avoided competition with larger carnivores by relying on ambush and short-distance pursuit. Giant paravians may have competed directly with megatheropods, and relied on highly efficient running to utilize large hunting ranges. Our recovery of Dakotaraptor in or near the Unenlagiidae further supports the hypothesis of long range persistence hunting, and likely facilitated its coexistence with the niche-assimilating megatheropod Tyrannosaurus rex.
Collaborations
Endocast Morphology
Quantum Computing
Tyrannosaurus rex and other tyrannosaurid dinosaurs were apex predators during the latest Cretaceous, which combined giant size and advanced neurosensory systems. Computed tomography (CT) data have shown that tyrannosaurids had a trademark system of a large brain, large olfactory bulbs, elongate cochlear ducts, and expansive endocranial sinuses surrounding the brain and sense organs. Older, smaller tyrannosauroid relatives of tyrannosaurids developed some, but not all, of these features, raising the hypothesis that tyrannosaurid-style brains evolved before the enlarged tyrannosaurid-style sinuses, which might have developed only with large body size. This has been difficult to test, however, because little is known about the brains and sinuses of the first large-bodied tyrannosauroids, which evolved prior to Tyrannosauridae. We here present the first CT data for one of these species, Bistahieversor sealeyi from New Mexico. Bistahieversor had a nearly identical brain and sinus system as tyrannosaurids like Tyrannosaurus, including a large brain, large olfactory bulbs, reduced cerebral hemispheres, and optic lobes, a small tab-like flocculus, long and straight cochlear ducts, and voluminous sinuses that include a supraocciptal recess, subcondyar sinus, and an anterior tympanic recess that exits the braincase via a prootic fossa. When characters are plotted onto tyrannosauroid phylogeny, there is a two-stage sequence in which features of the tyrannosaurid-style brain evolved first (in smaller, nontyrannosaurid species like Timurlengia), followed by features of the tyrannosaurid-style sinuses (in the first large-bodied nontyrannosaurid tyrannosauroids like Bistahieversor). This suggests that the signature tyrannosaurid sinus system evolved in concert with large size, whereas the brain did not. -From McKeown, et al., 2020
Vacuum gap λ/2 microwave resonators are demonstrated as a route toward higher integration in superconducting qubit circuits. The resonators are fabricated from pieces on two silicon chips bonded together with an In-Sb bond. Measurements of the devices yield resonant frequencies in good agreement with simulations. Creating low loss circuits in this geometry is also discussed. -From Lewis, Henry & Schroeder, 2017