Quick one today
as today’s two fish (Fig. 1) look dissimilar, yet, given all the present candidates in the large reptile tree (LRT, 1556 taxa) they nest together. Likely Mimipiscis gave rise to Amphicentrum, given the former’s Devonian presence relative to the latter’s Carboniferous appearance. Both are in the lineage of extant tuna.
If you think THAT’S untenable,
remember human, bat and bird ancestors all looked like salamanders (amphibian-like reptiles, like Silvanerpeton) were just starting to climb out on land at that time.
Mimipiscis bartrami (Choo 2011, formerly Mimia toombsi Gardiner and Bartram 1977; Late Devonian) is a paleoniscid sister, chronologically basal to Amphicentrum in the LRT. The nasal is enlarged, pushing the prefrontal to the back of the orbit and the postfrontal above it. The premaxilla rises to mid orbit.
Amphicentrum granulosus = Cheirodus granulosus (McCoy 1848, 1855; 20cm; Carboniferous) is a disc-shaped fish lacking pelvic fins, covered in large rectangular ganoid scales. Several skull bones are fused. The squamosal is tall. The preopercular and pelvic fins are missing. Teeth are absent from the upper jaws. Note the heterocercal tail.
Choo B 2012. “Revision of the actinopterygian genus Mimipiscis (=Mimia) from the Upper Devonian Gogo Formation of Western Australia and the interrelationships of the early Actinopterygii”. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 102: 77–104. doi:10.1017/s1755691011011029
Gardiner BG and Bartram AWH 1977. The homologies of ventral cranial fissures in ostheichthyans. Pp. 227-245, 8 figs. in: Andrews, S. M., Miles, R, S, & Walker, A. D. (eds.): Problems in Vertebrate Evolution, London.
McCoy F 1855. A synopsis of the classification of the British Palaeozoic rocks, with a systematic description of the British Palaeozoic fossils. Fasciculus 3, Mollusca and Palaeozoic fishes. British Palaeozoic Fossils, Part II. Palaeontology 407-666.