THE LATERAL LINE SYSTEM OF A MIDDLE DEVONIAN TETRAPODOMORPH FROM RED HILL, NEVADA

Red Hill, Nevada has produced Middle Devonian (late Givetian) tetrapodomorph fossils, with specimens controversially assigned to Tinirau clackae and Bruehnopteron murphyi. We examined the cephalic lateral line canal morphology of these tetrapodomorph skulls (UCMP 117884, 118283, 118605, 190999) under the microscope and through X-ray Computed Tomography. Three-dimensional segmentation of the lateral line canals reveals that the canal pathways run similarly through the Red Hill tetrapodomorph specimens; however, the lateral line tubules (extensions of the sensory canal) show different morphologies. We identified two main patterns of variations: (1) UCMP 118283, the smallest of the four specimens (34 mm in the Length of Parieto-Ethmoidal Shield – LPE, from anterior end of premaxilla to posterior edge of the parietal along the midline), displays tubules that are truncated with little to no bifurcation; (2), UCMP 117884, 190999, and 118605, all of which are greater than 100 mm in LPE, display similar tubules but with extensions from the canal that show a greater degree of branching. We conclude that the variation of lateral lines systems are either a result of ontogeny or taxonomy. Examination of additional Red Hill fossil specimens are necessary in order to determine whether both taxa are valid species. Our study on the visualization of the lateral line systems will provide new insight regarding the taxonomic placement of early fossil tetrapodomorph. Furthermore, this serves as a first step to systematically compare the fossilized cephalic lateral line canals in the broad Tetrapodomorpha lineage and shed light on the sensory system evolution of vertebrates.