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Figure 7 The NTRK receptor and 14 major neurotrophic factors are displayed as coloured boxes. Their phylogenetic distribution and inferred evolutionary origin are mapped onto the tree (see Supplementary file 1–Supplementary Table 22 and Supplementary file 1–Supplementary Table 23). Gene births are indicated as coloured boxes above the respective branch of the tree (left). Inferred losses are shown as coloured crosses in the matrix. Bold labels to the left of a branch indicate branch ancestors: Ac = Actinopterygii, B = Bilateria, Ch = Chordata, Eu = Eumetazoa, Gn = Gnathostomata, M = Metazoa, Sa = Sarcopterygii. The neurotrophic factors of Cladistia, the sister group of Actinopteri, are inferred and distinguished by a question mark as the dataset lacks species from this lineage.