DESCRIBING THE LOWER JAW OF THE STEM TETRAPOD TIKTAALIK ROSEAE (LATE DEVONIAN: FRASNIAN) THROUGH COMPUTED TOMOGRAPHY DATA

Describing the morphology of stem tetrapods is essential to understanding the evolutionary transition between finned and limbed animals. In particular, the lower jaw can be useful to reconstruct musculature and potential feeding behavior. This element is well studied in certain taxa of significance to the fin-to-limb transition such as the finned Eusthenopteron foordi and the limbed Acanthostega gunneri, but has received almost no attention in important transitional forms such as Tiktaalik roseae. In this project, we describe the lower jaw of T. roseae through computed tomography data and map out the individual bones within it for the first time, using the left jaw of a large individual recovered from fluvial deposits of the Upper Devonian (Frasnian age) Fram Formation of Ellesmere Island, Nunavut in 2004. Both primitive features, such as the nature of the coronoid fossae, and derived characters, such as extensive “scarf”-jointed sutural morphology, can be observed in this specimen. These characters appear to support a specialization for feeding in a shallow water setting proposed in other recent studies of stem tetrapods. Finally, we constructed a three-dimensional digital model of the jaw to compare to those of similar organisms, in order to track anatomical change through the evolutionary history of this lineage.