RESEARCH

My passions

Origins of vertebrate diversity and disparity
Radiation of reptiles

Reptiles are one of the most successful groups of terrestrial vertebrates, but its evolutionary origin remains poorly understood, particularly in the Triassic and older. However, little is known about the tempo and mode of the early evolution of the group. To study their macroevolutionary patterns, I have focused on the radiation of the larger reptiles, the archosaurs. During the later part of the Triassic, archosaurs diversified into many unique groups including “rauisuchians,” aetosaurs, phytosaurs, crocodylomorphs, poposauroids, pterosaurs, dinosaur relatives, and dinosaurs. A similar radiation of living dinosaurs, birds, occurs in a similar manner. Studying both diversifications in concert has led to a number of new insights. Much of these new insights are gained through the discovery of new specimens during fieldwork

Building of body plans

Extant vertebrates possess body plans that have been constructed over tens to hundreds of millions of years and the patterns of trait acquisition can only be studied in the fossil record. However, the fossil record also provides the 'failed experiments' that also enrich our understanding of long extinct body plans and the edges of morphological disparity. I have studied how the dinosaur body plan comes to fruition by studying their closest relatives (dozens of new fossils found throughout the world), the origin of the archosaur body plan (far more complicated than I ever imagined), the origin of the crown group bird body plan. 

Invasive reptiles

I am currently studying the morphological and, hopefully, the molecular evolution of invasive reptiles in Florida. Over 50 breeding species of reptiles occupy the southern portion of Florida and some of these are rapidly expanding their range. This research includes quantifying morphology, examining shifts in gene frequencies, and exploring ecological changes. To further understand ontogeny in extinct vertebrates, I have also turned to understanding the ontogeny of these extant reptiles such as lizards, crocodylians, and snakes to better understand growth dynamic of extinct reptiles.

Role and interaction of ontogeny and phylogeny
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Early dinosaur evolution

Dinosaurs were one of the most successful group of terrestrial vertebrates to evolve in the Triassic. Much of what we understand about dinosaur origins comes from South American forms; however, new dinosaur fossils from the Late Triassic of North American is also very important to understanding the early evolutionary history of the group. Also, to better understand early dinosaurs, I have searched the world for their closest relatives. These new fossils have created great insights but also lots of confusion. Some of this confusion is the result of the emerging pattern of highly complex early dinosaur growth: growth of these animals appears to be unlike any living vertebrate today. 

Minaturizarion

A deep and critical understanding of the growth dynamics of reptiles at both minute (~5 cm body length) and gigantic (~40 m length) sizes is critical to defining the boundaries of vertebrates. How they achieve these sizes is not clear. This research includes understanding mechanical constraints during growth, comparisons of growth trajectories in an evolutionary context, and the role of material (e.g., bone) at small sizes. I am currently studying the smallest of all reptiles, chameleons and geckos.

Diversity dynamics
Extinction recovery

I am an instrumental member of an international team that has been studying and continues to carefully examine the impact of the end-Permian mass extinction on diversity. After the worst extinction in Earth’s history at the end of the Permian, the world’s ecosystems completely reorganized, but little is known about the rate of terrestrial recovery and the pattern of ‘recolonization’. One of the best places to study this transition is in eastern and central Africa (Tanzania and Zambia), an area only briefly explored. I am also starting the examine the end Triassic to the Early Jurassic extinction. However, we know little about the before (in the Late Triassic), so that is where I have began.

Formation of the living vertebrate communities (NSF CAREER funded)

Understanding resilience of a community – the capacity of a system to maintain functioning, structure, and feedbacks in the face of disturbance – has been a major goal of biologists, ecologists, and conservationists given increasing species extinctions, climate change, and human disturbance. Studies focused on resilience have occurred on short times scales and measurable variables (e.g., species and functional diversity) that are correlated with resilience have been identified. However, it is not clear how resilience is established and maintained over long timescales in the face of gradual changes (i.e., climate) or through major short-term catastrophes (e.g., impacts). Furthermore, the relationship between resilience, macroevolution, and the origin of ‘living’ communities has not been established. I am currently developing an innovative program that will integrate macroevolution and community resilience of vertebrates over long timescales (millions of years). The primary goal is to measure variables correlated with resilience in vertebrate assemblages from the Late Triassic into the Early Jurassic in the best terrestrial vertebrate record from this time – the American Southwest, with collection within Petrified Forest National Park.

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Preservation of Earth history information
Museums and proper field collections

Earth history data is protected by natural history museum across the world. Yet, public understanding, including governments, largely do not understand this relationship. Museums provide a wealth of information and are clear gateways to public engagement. It is my responsibility to: 1) preserve Earth history by responsibly collecting fossils and properly curating them; 2) maintain the the use of existing collections by studying them and properly managing their use and protection; and 3) provide those gateways for public engagement. My outreach program has accomplished and will continue to accomplish these goals.

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