The Ossification Sequence of Aneides lugubris, with Comments on Heterochrony

Abstract

Post-hatching ontogeny is described for the skeleton of a large, direct-developing, terrestrial plethodontid salamander, A. lugubris. This species appears to have the most prolonged ontogeny of the plethodontids. Until the end of the 2nd year of life, osteological ontogeny is similar to that of other species, but beyond that point major changes occur. Ossification of the long bones continues throughout life and is never completed. Elements such as the pelvic plate ossify continuously, but never completely. Mesopodial elements remain cartilaginous throughout life. The most dramatic changes relate to the feeding system. The anterior part of the skull becomes grotesquely enlarged in the largest specimens with extensive coossification. Maxillary and dentary teeth decrease in number but increase in size and complexity. Features identified as supportive adaptations appear during ontogeny, more so in the feeding than in the locomotory mechanism. Data are interpreted in the framework of recent studies of heterochrony.