Abstract

A morphometric analysis based on 16 landmarks (specific geometric points) identified on the skull roof of different
growth stages of various temnospondyls revealed patterns of shape change during ontogeny. Data from 50 individuals
from 12 taxa, encompassing euskelians (dissorophoids, eryopids and zatracheids) and stereospondylomorphs were
plotted in a morphospace diagram defined by two principal-component axes (PC 1 and PC 2) of a principal-component
analysis of the shape variables. The morphospace occupation reflects phylogenetic relationships of the main clades of
temnospondyls. All stereospondylomorphs investigated here have similar ontogenetic trajectories with long intervals on
PC 1. Eryopids and zatracheids have shortened their trajectories on PC 1 and are separated in morphospace relative to
the stereospondylomorphs and dissorophoids. Outgroup comparison with Cochleosaurus bohemicus (Fric, 1876) suggests
that 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 derived
rhytidosteids 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 trajectories
and occupy the morphospace region of larval stereospondylomorphs, thus attaining a paedomorphic appearance
probably by hypomorphosis. Amphibamid and branchiosaurid dissorophoids have clearly distinguishable larval and
postlarval developments, indicating that these forms had evolved a lissamphibian-like type of metamorphosis.