The splitfin flashlightfish, Anomalops, enters the LRT


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.)

Figure 1. The splitfin flashlightfish, Anomalops, showing off its suborbital light organ.

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.

Figure 2. The light organ folds quickly, 90x each minute. Related taxa don’t have anything likes this unique organ… so far. Adding taxa always solves problems like this.

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.

Figure 3. Skull of Anomalops in layers from Johnson and Rosenblatt 1988, colorized here.

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.

Figure 4. Monocentris is the extant pineconefish.
Figure 6. Maasamorichthys with colors added.
Figure 3. Seriola rivoliana is the high fin Amberjack is basal to gobies and tetraodontiformes.
Figure 7. Seriola rivoliana is the high fin Amberjack basal to gobies and tetraodontiformes.

References
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

wiki/Splitfin_flashlightfish
wiki/Beryciformes

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