Testing paleohistological assumptions using a large-scale study of Alligator mississippiensis with application to a fossil alligator from the southern Appalachians
Location
Culp Center Rm. 304
Start Date
4-25-2023 2:20 PM
End Date
4-25-2023 2:40 PM
Faculty Sponsor’s Department
Geosciences
Name of Project's Faculty Sponsor
Blaine Schubert
Competition Type
Competitive
Type
Oral Presentation
Project's Category
Histology
Abstract or Artist's Statement
Histological analysis of long bone thin sections has in recent decades been broadly applied to infer growth rates and ecology in extinct vertebrates, particularly within non-analogous clades. Meaningful interpretation of bone histology and extrapolation to an extinct organism’s life history requires a robust understanding of the factors influencing bone growth and histological presentation. Archosaurs are commonly the subject of osteohistological studies and, as such, much of our knowledge of their paleohistology is derived from the two extant lineages: avian dinosaurs and crocodilians. The American alligator (A. mississippiensis) is widely available for study in the United States and several osteohistological analyses have been published. These studies focused on intraskeletal variation, histovariability, and skeletochronology in one or a few specimens, and in one study a larger sample of pen-raised captive born specimens. However, no published studies test paleohistological assumptions using large-scale geographic and climatic variation in bone histology among extant wild crocodilians. To fill this gap in our knowledge of archosaurian osteohistology, we prepared a collection of humeral and femoral thin sections of 45 Alligator from North Carolina, Arkansas, Georgia, and South Carolina. Previously prepared thin sections from pen-raised Louisiana Alligator were also included. For this study we began by comparing growth rates inferred from counts and measurements of arrested growth (LAGs), which represent annual cycles, and femoral dimensions which correlate strongly to body length. Comparison of these data revealed that, on average, Alligator specimens subject to shorter growing seasons (i.e., those in cooler climates) tend to show more LAGs when compared to more southerly Alligator specimens of similar size. Bone tissue also varies between specimens, suggesting a variable tempo of bone growth in response to differing climatic and environmental regimes. Finally, histological thin sections of early Pliocene Alligator fossils from the Gray Fossil Site (GFS), Washington Co., Tennessee were prepared to explore the paleobiology of this biogeographically unique Appalachian alligator. Assessing variation in this fossil taxon’s closest living relative (A. mississippiensis) provides insight into the paleoecology and growth rates of the GFS Alligator, as well as the climate of the southern Appalachians during the past. Results suggest that the fossil species may have grown more slowly than extant relatives along the southeastern United States coastal plain, and that some parts of the skeleton reached asymptotic growth at a smaller size.
Testing paleohistological assumptions using a large-scale study of Alligator mississippiensis with application to a fossil alligator from the southern Appalachians
Culp Center Rm. 304
Histological analysis of long bone thin sections has in recent decades been broadly applied to infer growth rates and ecology in extinct vertebrates, particularly within non-analogous clades. Meaningful interpretation of bone histology and extrapolation to an extinct organism’s life history requires a robust understanding of the factors influencing bone growth and histological presentation. Archosaurs are commonly the subject of osteohistological studies and, as such, much of our knowledge of their paleohistology is derived from the two extant lineages: avian dinosaurs and crocodilians. The American alligator (A. mississippiensis) is widely available for study in the United States and several osteohistological analyses have been published. These studies focused on intraskeletal variation, histovariability, and skeletochronology in one or a few specimens, and in one study a larger sample of pen-raised captive born specimens. However, no published studies test paleohistological assumptions using large-scale geographic and climatic variation in bone histology among extant wild crocodilians. To fill this gap in our knowledge of archosaurian osteohistology, we prepared a collection of humeral and femoral thin sections of 45 Alligator from North Carolina, Arkansas, Georgia, and South Carolina. Previously prepared thin sections from pen-raised Louisiana Alligator were also included. For this study we began by comparing growth rates inferred from counts and measurements of arrested growth (LAGs), which represent annual cycles, and femoral dimensions which correlate strongly to body length. Comparison of these data revealed that, on average, Alligator specimens subject to shorter growing seasons (i.e., those in cooler climates) tend to show more LAGs when compared to more southerly Alligator specimens of similar size. Bone tissue also varies between specimens, suggesting a variable tempo of bone growth in response to differing climatic and environmental regimes. Finally, histological thin sections of early Pliocene Alligator fossils from the Gray Fossil Site (GFS), Washington Co., Tennessee were prepared to explore the paleobiology of this biogeographically unique Appalachian alligator. Assessing variation in this fossil taxon’s closest living relative (A. mississippiensis) provides insight into the paleoecology and growth rates of the GFS Alligator, as well as the climate of the southern Appalachians during the past. Results suggest that the fossil species may have grown more slowly than extant relatives along the southeastern United States coastal plain, and that some parts of the skeleton reached asymptotic growth at a smaller size.