Shifts in metabolic rates often accompany major evolutionary transitions in organismal function and ecology. Examples include the evolution of endothermy (warm-bloodedness) and elevated metabolism in archosaurs (birds and their close relatives, ~12,000 species) and mammals (~5,000 species). High metabolic rates are thought to be a key component of mammalian and archosaur species radiations, by allowing individuals to exploit a wider range of environmental and temporal niches (lifestyles). For their body size, extant birds have some of the highest growth rates and metabolisms of any vertebrates. High avian metabolic rates are also associated with highly canalized development, as seen in the relative lack of body size variation for individuals of a given age. The primary aim of this research is to understand how these extreme physiological and developmental specializations arose within the dinosaur ancestors of birds. This project will produce two major broader impacts. First, data and interpretations generated by this project will be incorporated into updates to an exhibit currently in development at the American Museum of Natural History (AMNH), ?Dinosaurs Among Us.? This exhibit is a multi-media showcase of the various lines of evidence supporting the hypothesis that birds evolved from non-avian dinosaurs. It uses fossil specimens, models, graphics, and interactives to reveal the latest findings about the dinosaurian origins of many typically avian traits. The PIs are actively involved in consulting on the scientific content of the exhibit, which, together with associated museum events and an extensive online presence, will reach a large portion of the 5 million annual visitors to AMNH and many others globally. Educational materials from the exhibit will reach a diverse group of students, many from underserved communities in New York City. Second, this project greatly enhances the infrastructure of the AMNH paleontology laboratory to conduct histological research on fossil tissues. Training in histological techniques will enable the PIs to further train AMNH staff and students, developing the human resources of the laboratory to support projects involving histological analysis for years to come.
Calculation of dinosaur growth rates (a proxy for metabolism) from their bone microstructure has demonstrated that the transition to modern avian endothermy did not occur in a single step. The earliest birds, for example, grew more rapidly than non-avian reptiles, but more slowly than their extant descendants. However, the origin of elevated metabolic rates among the earliest theropod dinosaur ancestors of birds remains unknown. This project seeks to fill this gap in knowledge, by using bone histology (examination of the microscopic organization of bone tissue) and gross morphology to measure growth rate and ontogenetic canalization for a phylogenetically basal theropod dinosaur, Coelophysis bauri. As it is one of the only extinct dinosaurs with a large sample size (hundreds of specimens) available from single populations, histological sectioning and growth curve construction for Coelophysis bauri will shed light on the metabolic condition of some of the earliest diverging theropod dinosaurs, and provide a framework within which the transition to rapid growth rates and developmental canalization among bird-line archosaurs may be assessed.
