The Devonian placoderm fish Bothriolepis canadensis revisited with three-dimensional digital imagery

Abstract

The external morphology of the Late Devonian placoderm fish Bothriolepis canadensis from the Escuminac Formation (Miguasha, Canada) is reanalyzed using cutting-edge technology in three-dimensional (3D) digital imagery such as 3D surface scanner and 3D modeling software. Nineteen well-preserved specimens of B. canadensis were used to reconstruct a 3D digital model of the dermal armor, whereas four specimens were used to reconstruct the fleshy posterior part of the body. Digital manipulation of the model allows us to investigate some biomechanical aspects and constraints of the morphology. Mobility of the cephalic armor, submarginal plates and pectoral fins has been previously hypothesized based on inaccurate reconstructions. In contrast to previous interpretations, there is no indication of mobility between the cephalic and thoracic armors. The submarginal plate is immobilized on the cephalic armor; a gill opening is located between the submarginal and anterior ventrolateral plates of the thoracic armor. The median dorsal ridge of the thoracic armor forms a hydrodynamic dorsal crest with its maximum height along the posterior median dorsal plate, which most likely has an important role in locomotion. The fully retracted and protracted (70°) position of the pectoral fins allows only for restricted movement excluding the possibility of stroking and using them as anchoring devises. Maximum of mobility is reached in a protracted angle of 16°, which allows a rotation of 32° around the brachial process and 15° in an up-and-down movement. The 3D model of B. canadensis brings out unexpected novelties on one of the supposedly best-known Devonian fish. © Society for Vertebrate Paleontology January 2014.