Extended Data Fig. 3: Amino acid alignments highlighting substitutions (in purple) claimed to be Pleuronectoidei-specific by LEA¹.

By adding sequences from Psettodes and other non-flatfish carangarians into the alignments, we show that three out of the four Pleuronectoidei-specific substitutions discussed by the authors are in fact shared with Psettodoidei or other non-flatfish carangarian species. These include two missense substitutions in the musculature development-related gene sgca, which the authors suggest is related to the formation of the flat phenotype. Both substitutions are shared with Polydactylus sextarius, a symmetrical carangarian species, and, therefore, may not necessarily explain the evolution of the flatfish thin musculature. The hoxd12a substitution is shared between Pleuronectoidei and Psettodoidei. This gene is involved in the development of the flatfish dorsal fin, an important locomotion adaptation that improves their maneuverability in the benthic environment, and that may provide additional evidence for the single origin of the asymmetric body plan.