Article: Heterochrony in a fossil reptile: juveniles of the rhynchosaur Scaphonyx fischeri from the Late Triassic of Brazil
Michael J. Benton and Ruth Kirkpatrick
A juvenile (?one year post-hatching) specimen of Scaphonyx fischeri, an advanced rhynchosaur from the Late Triassic Santa Maria Formation (Carnian) of Brazil, is described. This is the youngest rhynchosaur ever reported, and it was probably 0.38 m long overall, compared to adult body lengths of 1.3-1.6 m. It is compared with an ontogenetic series of skulls of this species, ranging in length from 55 to 250 mm. An allometric analysis suggests that the posterior portion of the skull roof widens relatively more rapidly than overall size increase (positive allometry), while the length of the posterior region of the skull shows negative allometry. These relative shape changes during ontogeny are compared with ancestral rhynchosaurs whose ontogenies appeared to stop earlier than that of Scaphonyx. This peramorphic shift in ontogeny is tentatively identified as an example of hypermorphosis.