Morphospace occupation of temnospondyl growth series: a geometric morphometric approach

<p>A morphometric analysis based on 16 landmarks (specific geometric points) identified on the skull roof of differentgrowth stages of various temnospondyls revealed patterns of shape change during ontogeny. Data from 50 individualsfrom 12 taxa, encompassing euskelians (dissorophoids, eryopids and zatracheids) and stereospondylomorphs wereplotted in a morphospace diagram defined by two principal-component axes (PC 1 and PC 2) of a principal-componentanalysis of the shape variables. The morphospace occupation reflects phylogenetic relationships of the main clades oftemnospondyls. All stereospondylomorphs investigated here have similar ontogenetic trajectories with long intervals onPC 1. Eryopids and zatracheids have shortened their trajectories on PC 1 and are separated in morphospace relative tothe stereospondylomorphs and dissorophoids. Outgroup comparison with Cochleosaurus bohemicus (Fric, 1876) suggeststhat a long ontogenetic trajectory with gradual development represents the plesiomorphic condition for temnospondyls.More derived stereospondylomorphs (among the taxa considered here, but excluding groups such as derivedrhytidosteids and brachyopoids) increased the length of their trajectories on PC 1 and show a peramorphic pattern,resulting in the long and slender skull of piscivorous predators. Dissorophoids exhibit truncated ontogenetic trajectoriesand occupy the morphospace region of larval stereospondylomorphs, thus attaining a paedomorphic appearanceprobably by hypomorphosis. Amphibamid and branchiosaurid dissorophoids have clearly distinguishable larval andpostlarval developments, indicating that these forms had evolved a lissamphibian-like type of metamorphosis.</p>