Autapomorphies of Probolodus heterostomus:

1. Mamilliform teeth outside mouth (120): (0> 1) present. Paralleled in nodes 218 and 277.

2. Number of rows of premaxillary teeth (122): (1> 0) one. Paralleled in node 195 and in Aulixidens eugeniae, Carlana eigenmanni, Carnegiella strigata, Grundulus cochae, Odontostoechus lethostigmus, Paracheirodon axelrodi, and Piabucus melanostomus .

3. Number of teeth in inner premaxillary row (129): (1> 0) four or fewer. Paralleled in node 198 and in Markiana nigripinnis .

4. Posterior extent of ventral process of quadrate (151): (0> 1) falling short of posterior margin of symplectic. Paralleled in the Hyphessobrycon luetkenii clade and Iguanodectinae, in nodes 284, 289, and 298, and in Astyanax mexicanus, A. cf. rutilus, Aulixidens eugeniae, Cyphocharax spilotus, Diapoma speculiferum, Hemiodus cf. thayeria, Metynnis maculatus, Micralestes stormsi, Moenkhausia sanctaefilomenae, Nematocharax venustus, Psellogrammus kennedyi, and Pseudocorynopoma doriae . Some trees: Paralleled in node 302.

5. Posterior margin of cleithrum (234): (0> 1) with concavity ventral to first postcleithrum. Reversal of synapomorphy 4 of node 204. Paralleled in nodes 196 and 289 and in Roeboexodon geryi .

6. Position of ventral end of posttemporal (253): (0> 1) posterior to lateral margin of epioccipital. Paralleled in nodes 211 and 228 and in Bryconamericus scleroparius, Hoplias cf. malabaricus, Markiana nigripinnis, and Prochilodus lineatus .

7. Dorsal-fin bony hooks in adult males of species bearing hooks on fins (311): (0> 1) present. Paralleled in nodes 248 and 268 and in Astyanax cf. asuncionensis, A. lineatus, Bario steindachneri, Bryconamericus rubropictus, Hyphessobrycon luetkenii, H. socolofi, and Nematocharax venustus .

8. Caudal-fin bony hooks in adult males of species bearing hooks on fins (312): (0> 1) present. Paralleled in node 268 and in Acrobrycon tarijae, Astyanax cf. asuncionensis, A. lineatus, Bario steindachneri, Hyphessobrycon luetkenii, and H. socolofi .