Towards the end of the Devonian Period, between 385 and 360 million years ago, there were dramatic evolutionary changes to plants and animals living in freshwater habitats. This time interval witnessed the origin of limbed vertebrates (tetrapods), the diversification of fishes closely related to early tetrapods, and the elaboration of plant communities on land. PIs ongoing work in the Canadian Arctic (Ellesmere Island, Nunavut Territory) and Pennsylvania provide new evidence for understanding these monumentally important events. For example, a newly discovered site on Ellesmere Island includes numerous articulated fish that are one of the closest known relatives of limbed animals. In addition, 12 years of field study in the Catskill Formation in Pennsylvania has yielded abundant Late Devonian fossils notable for their taxonomic diversity and the quality of preservation of the vertebrates, plants, and arthropods. The biological diversity, environmental settings, and age of these North American systems serve as the basis for PIs proposed studies on the evolution of the earliest tetrapods and their lobe-finned fish precursors, and the development of the Late Devonian habitats that were a crucible for the evolutionary innovations in the Late Devonian. With substantial collections already in hand and great potential for additional field discoveries, the goals for this project include: 1) additional fieldwork to discover new material of key taxa at the cusp of the fish-tetrapod transition, 2) exploration of promising areas that may produce the earliest tetrapod fossils, 3) fossil preparation including molding and casting of important specimens for worldwide distribution, 4) description and evolutionary analysis of early limbed animals and their fish relatives, 5) functional analyses of skeletal structures in elpistostegid fishes that will provide an understanding of the biological significance of changes at the fish-tetrapod transition, and 6) assessing the geographic and environmental conditions associated with the origin of tetrapods. This work will have a broad impact through outreach in educational and informal science learning venues, and via internet, print and broadcast media.
