This taxon was difficult to nest.
The text below represents my third try.
(It’s okay to make mistakes. Keep trying. Not trying gets you nowhere.)
Anomalops katoptron (Kner 1868; 35cm; Figs. 1, 2) is the extant splitfin flashlightfish nesting basal to jacks in in the large reptile tree (LRT, 1911+ taxa), like the two Seriola taxa (Fig. 7). Anomalops currently arises from a plesiomorphic Palaeocene taxon close to Massamorichthys (Fig. 5).
Anomalops has a light-emitting organ
filled with luminious symbiothic bacteria beneath the large eyeball. This organ blinks 90x a minute by flipping down (Fig. 2). It uses those twin ‘headlights’ to detects zooplankton prey in the light-less depths.
Note the tall ascending process
of the premaxilla (Fig. 3), the tiny nasal and lack of a parietal, the fusion of the frontal and postparietal, among several other synapomorphies. The teeth are extremely tiny.
Where does the light organ evolve from?
It sits in the large orbit along with the eyeball. A related and recently added taxon, the pineconefish (Monocentris, Fig. 4) has something similar, but not as distinct. A more plesiomorphic Monocentris relative, Massamorichthys (Fig. 5), is known from Palaeocene fossils. I’ll add taxa to make this transition more gradual as I find them.
Johnson GD and Rosenblatt RH 1988. Mechanisms of light organ occlusion in flashlight fishes, family Anomalopidae (Teleostei: Beryciformes), and the evolution of the group. Zool J Linnean Soc. 1988;94: 65–96.
Kner R 1868. Über einige Fische aus dem Museum Sitz.. B. Akad. Wiss. Wien, Math.-Naturw. Kl., 58 (1), 26