2018 Spring LC Magazine

Soon after the fossil discovery, I wanted to identify the habitats and environments in which these animals lived in the Late Devonian Period. To better understand the paleoenvironments of the fossil sites, I enlisted the help of my friend, Bucknell University sedimentary geologist Jeff Trop. We determined that the geology of these Late Devonian-aged rocks exposed along U.S. Route 15 depict a diverse and rich ecosystem, with plants on the stream banks, and diverse fish inhabiting the stream channels, wetlands and lakes on the floodplains. Among the many fossils the students and I have collected, one stands out as extremely rare: a femur bone about two inches long and a half-inch in diameter that belonged to an early tetrapod — the first vertebrates to evolve limbs from fins — which allowed them to crawl onto land. This femur is among the oldest tetrapod bones ever found. It is now in the collections of the Academy of Natural Sciences of Drexel University in Philadelphia, where Ted Daeschler is the curator of vertebrate paleontology. Ted, also a collaborator of mine, was the first to discover early tetrapod remains in Late Devonian-aged rocks in Pennsylvania in 1993. Ted made these and other important paleontological discoveries at the Red Hill site near Hyner in Clinton County. These early tetrapods evolved into the first amphibians, which led to reptiles, dinosaurs, birds and mammals. Our newly discovered fossil is from one of the very first tetrapods. The significance of the discovery is heightened by the fact that the tetrapod bone was found among hundreds of other fossils, including extinct groups of fishes, freshwater clams and plants, offering clues about the ecosystem that the amphibian-like creature once inhabited. A very diverse assemblage of animals and plants in stream channels and the floodplain are preserved in the rocks along U.S. Route 15. From these we can reconstruct the ecosystem at the time when the fin-to-limb transition in vertebrates was occurring. These plants and animals inhabited an ecosystem vastly different from Central Pennsylvania today. During the late Devonian Period, traveling north to south, the path now tracked by U.S. Route 15 would have run through an ocean to the shoreline, then across wetlands, streams and rivers. The banks of those streams would have been stabilized by trees and other plants, allowing the streams to carve deeper channels. This greater depth, • M O R E A B O U T M Y R E S E A R C H • Students are excited to see areas where we are making important discoveries.” in turn, allowed different species of fish to inhabit these streams. Additionally, the vegetated banks provided important habitat elements including shade and humidity for early-evolving tetrapods. We can look at the transition in habitats from the shoreline to upland, now fully terrestrial, and see changes in fossil plants and animals indicative of these changing habitats. Having these important sites close to campus allows me to take students to sites where evidence of a significant transition in vertebrate evolution was occurring in the Late Devonian era. Students get to touch and see evidence of fossil animals and plants that were alive during this important period of time, and they are excited to see areas where we are making important discoveries, thinking they may find the next important discovery. Jeff Trop, Ted Daeschler and I have presented our findings at several scientific meetings, including the Geological Society of America and the Society of Vertebrate Paleontology. My research into the paleoecology of the fin-to-limb transition in vertebrates is ongoing, and I hope to locate more fossil sites that preserve the animals and ecological conditions associated with this important event. 15 www.lycoming.edu

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