Fish evolution: Semionotus to Lepisosteus

Convergent with the stickleback/seahorse clade
these taxa shift the jaw joint anterior to the orbit, evolve a longer rostrum and have an armored body.

Putting sister taxa together graphically
shows how evolution turned a shorts-snouted Late Triassic armored fish into a long-nosed extant gar, reflecting their nesting in the large reptile tree (LRT, 1595+ taxa, Fig. 3).

Mea culpa
Earlier I nested the gar, Lepisosteus) with the stickleback, Gasterosteus. In order to do that I gave different identities to the skull bones than shown here (Fig. 2). At the time there were no other taxa with the jaw joint anterior to the orbit. Swordfish nested nearby and their juveniles have long, toothy jaws. So it all made sense. Now I see that Semionotus has the same arrangement. Both are traditional holosteans. Other traditional holosteans, Pseudoscaphirhynchus, the sturgeon, and Amia, the bowfin continue to nest outside the rest of the Holostei (Fig. 2). Adding taxa (not characters) solves all such problems.

Semionotus bergeri (Agassiz 1843; Late Triassic) also has thick scales and small fins. Here the maxilla is even smaller.

Lepidosteus osseus (also Lepisosteus Lacepéde 1803) is the extant longnose gar. The rostrum is elongated. The mandible is anterior to the orbit, as in the stickleback, Gasterosteus. Ganoid scales cover the body.

This is a new cladogram of fossil fish
representing a new hypothesis of interrelationships.

References
Agassiz L 1843. Poissons Fossil 833.
de Lacepéde BG 1803. Histoire naturelle des poissons. Tome Cinquieme. 5(1-21):1-803 + index.

wiki/Lepidosteus
wiki/Semionotus