Heterochrony in the Late Devonian arthrodiran fishes Compagopiscis and Incisoscutum

WA Museum Records and Supplements | Updated 9 years ago

Abstract - The ontogenetic trajectories of dermal plates of the arthrodiran placoderrns Compagopiscis croucheri and lncisoscutum ritchiei from the Late Devonian Gogo Formation, Canning Basin, Western Australia were compared to assess the impact of heterochrony. Most characters showed peramorphosis. Allometric predisplacement occurred in: the biting division of the inferognathal; the anterior ventrolateral; and the median dorsal plate's breadth. Allometric hypermorphosis was seen in the increases of the prepineal length of the skull roof and the median dorsal plate length. Peramorphic traits contributed to a trend of skull elongation. Fewer paedomorphic features were found. Allometric postdisplacement that resulted in paedomorphosis occurred in the postmesial breadth and the orbital diameter of the skull roof. It is suggested that lengthwise growth occurs earlier in ontogeny than breadthways growth, and that dissociated heterochrony was an important mechanism in the evolution of these arthrodires.