Figure 2.

(a) Comparative diaphyseal femoral growth curves of D. austriacus, an amniote (L. viridis) and a urodele (D. monticola), of nearly the same size, and their implication in elaborating different scenarios of early tetrapod growth strategy according to the different phylogenetic hypotheses: (b) Ruta & Coates (2007), (c) Anderson (2007) and (d) Vallin & Laurin (2004). (a) Desmognathus, whose histological organization is typical (i.e. not derived) of other urodeles, is morphologically similar to Discosauriscus. The reconstruction of the curves is explained in the electronic supplementary material. Femora of three individuals of Discosauriscus illustrate each growth stage: larval (KO96, 5 years old), metamorphic (Z15697, 7 years old) and juvenile (KO153, 9 years old). The tightening of the last peripheral LAGs indicates that long bones of the largest specimens, aged up to 10 years, are no longer intensely growing in thickness, i.e. individuals are not far from sexual maturity. The growth-curve tendency of Discosauriscus is similar to that of Desmognathus and other urodeles: slow bone deposition and late acquisition of sexual maturity. (b–d) Light-grey bars indicate an endochondral ossification with cartilaginous epiphyses (Haines 1942; Sanchez et al. 2007) and dark-grey bars, secondary centres of epiphyseal ossification (Haines 1942). All character optimizations, with Dipnoi as an out-group, show the salamander-like ossification as a primitive trait compared to that of amniotes.