Fig. 5

The heterochrony seen at the transcriptome level is not directly consistent with the number of patterned cusps. a Coordinates of the samples on PCA1 showing a systematic offset between upper (black) and lower (gray) samples, the latter being more “mature” than the former. b Heterochrony measured on bell-shaped genes: toy example showing how, as a proxy for heterochrony, we are using the simple time shift from upper to lower. c Distribution of this time shift, which is significantly positive, indicating that the upper molar germ is most often delayed in comparison with the lower germ. d Proportion of the upper–lower distance, which can be explained by a simple time-translation. The average is indicated by a red arrow. e Total number of patterned cusps at each developmental stage for upper (black) and lower (gray) molar of the RNA-seq time series. At each stage, embryos of the same litter and same weight as those chosen for the RNA-seq time series in panel (a) were used for in situ hybridizations with a Fgf4 probe marking the SEK