Fig. 6

Comparison of the chondrification sequence between different groups. The chondrocranial characters on the X-axis are ordered chronologically for Neornithes. The Y-axis shows the relative timing of chondrification in which “0” represents the appearance of the first cartilage in the chondrocranium and “1” the appearance of the last one. Some chondrification events have not been described for certain species, resulting in gaps in the sequences shown. a Struthio as representative of the Palaeognathae compared to the Neognathae, b comparison between Galloanserae and Neoaves, and c the ancestral chondrification sequence (Sauropsida, consensus line of all reptiles in this study (Table 2) compared to Neornithes