The Upper Devonian fish Bothriolepis (Placodermi: Antiarchi) from near Canowindra, New South Wales, Australia
Abstract
The Upper Devonian fish fauna from near Canowindra, New South Wales, occurs on a single bedding plane, and represents the remains of one Devonian palaeocommunity. Over 3000 fish have been collected, predominantly the antiarchs Remigolepis walkeri Johanson, 1997a, and Bothriolepis yeungae n.sp. The nature of the preservation of the Canowindra fauna suggests these fish became isolated in an ephemeral pool of water that subsequently dried within a relatively short space of time. This event occurred in a non-reproductive period, which, along with predation in the temporary pool, accounts for the lower number of juvenile antiarchs preserved in the fauna. Thus, a mass mortality population profile can have fewer juveniles than might be expected. The hypothesis that a single species of Bothriolepis is present in the Canowindra fauna is based on the consistent presence of a trifid preorbital recess on the internal headshield and separation of a reduced anterior process of the submarginal plate from the posterior process by a wide, open notch. Principal Components Analysis (PCA) based on head and trunkshield plate measurement shows no separation of Bothriolepis individuals into distinct clusters and is consistent with this hypothesis. A wide range of plate shape variation can thus occur within a species of Bothriolepis, and caution should be used when separating species on this basis in the future.
