Research

Broadly, my research focuses on growth and development and how these processes influence the evolution of vertebrates. Development is a universal feature of biology, and understanding the history of development is a major part of understanding the evolution of life.

To explore this biological process I investigate patterns of pre- and postnatal change during ontogeny in archosaurian reptiles. This group exploded in diversity and disparity in an evolutionary radiation following the largest mass extinction in earth history, and still contains major ecological players in modern ecosystems. Therefore, this group provides an excellent system to explore large-scale evolutionary patterns in deep time.

I use my interdisciplinary background to explore biological questions in a geological context:

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Histology of a silesaurid tibia (Griffin & Nesbitt 2016)

In what ways can the ontogeny of extinct organisms inform us of their biology?

Ontogenetic information, particularly osteohistology, is commonly used to form hypotheses about the paleobiology of extinct organisms, including metabolism, growth rate, ecology, and population structure. This area of research has generally focused on the transition from non-avian to avian dinosaurs and non-mammalian to mammalian synapsids. I am particularly interested in analysis of growth patterns in the transition to dinosaurs from more inclusive archosaurian clades (e.g., Ornithodira, Dinosauromorpha) following the Permian-Triassic mass extinction and through the end Triassic mass extinction.

How can the ontogenetic age/skeletal maturity of fossil vertebrates be determined?

Determining the ontogenetic status of a fossil individual is crucial to correct identification and proper systematic placement. Ontogenetically immature individuals may be misidentified as adults of different taxa, which can complicate phylogenetic reconstruction, paleodiversity estimates, and paleobiogeography. Understanding ontogenetic patterns (both histological and morphological), especially those that are phylogenetically conserved, is therefore crucial to determining relative skeletal maturity. Although size has usually been taken as a proxy for developmental maturity, skeletal maturity, body size, and ontogenetic age can be disjunctive, and I am interested in ways to account for this complication in determining the relative maturity of fossil vertebrates.

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Ontogenetic sequences showing high levels of intraspecific variation in the development of an early dinosaur (Griffin & Nesbitt 2016)

In what way does individual variation in developmental patterns impact ontogenetic and phylogenetic signal?

Intraspecific variation is the material on which natural selection acts and is therefore central to evolutionary theory. Sequence polymorphism—intraspecific variation in relative timing of developmental events—is well known in extant vertebrates but has been paid little attention in paleontology, in part because of the large sample sizes necessary to recognize this pattern in fossil taxa. The quantification of sequence polymorphism and the reconstruction of ontogenetic sequences in extinct vertebrates has enormous potential for understanding ontogenetic patterns that would have been otherwise obscured. Further, knowledge of which phylogenetic characters are ontogenetically variable, and their degree of variability, is crucial to accurately reconstruct the phylogeny of a clade and determine a clade’s plesiomorphic character states.

How do conserved developmental patterns influence evolution?

Comparative ontogenetic studies are necessary to determine the tempo and mode of the evolution of development, and ontogenetic series of fossil organisms allow this study to be undertaken in the context of geological time. To explore this question, I study how developmental strategies are conserved through the evolutionary history of archosaurs and how conserved developmental pathways influence the evolution of morphology.