Temporal niche separation in Arthrodires from the Gogo Formation, Western Australia

Niche partitioning allows competing species to use the environment to facilitate their coexistence and is common in modern (Feer & Pincebourde, 2005; Helfman, 1986) and ancient (Motani, Rothschild, & Wahl Jr, 1999; Schmitz & Motani, 2011) ecological communities. The three-dimensionally preserved fish fauna of the Gogo Formation provide an ideal opportunity to determine if niche differentiation was present in the Canning Reef environments. Temporal niche separation allows species to operate in the same environment but at different times and may account for the biodiversity found amongst the Gogo fishes. Orbit size has been shown to be highly correlated with eye size which in turn is highly correlated to temporal period of activity (Schmitz & Wainwright, 2011). Thus by measuring the orbit size of vertebrates it is possible to infer their temporal niche and identify temporal niche separation between otherwise similar species whose behaviour is unable to be observed directly. Qualitative assessments of the orbits of fossil fish from the Gogo formation have been suggestive of species-specific differences in eye size. Quantitative measurements of orbits and head length of five Gogo Arthrodire genera and two Dipnoan genera this have confirmed assessment. Eye size is species-specific. Ontogenetic growth series for Compagopiscis and Griphognathus show allometric growth indicating that there are no ontogenetic changes associated with eye size for these genera.