Growth of larval axolotls and tiger salamanders. Data points are snout vent length (SVL) measured for individuals at the time of brain tissue collection. Lines were estimated by fitting a general linear model (R2= 0.957) to SVL data from both species. All terms of the model were significant (p < 0.05; see methods). Axolotl larvae = black circles, tiger salamander larvae = gray triangles. The blue bar shows the time period where anatomical changes consistent with metamorphosis were observed in tiger salamander larvae (A.t.t.).