The flying gurnard, Dactylopterus, moves to the base of the ray-fin fish

Traditionally the flying gurnard,
Dactylopterus (Fig. 1), nests with sea horses and pipefish, even though, with those giant pectoral fins and free ‘fingers’ it looks more like the sea robin, Prionotus. This was one of those difficult-to-understand taxa, until it suddenly made sense.

Figure 1. Dactylopterus skull with colors added to match tetrapod taxa.
Figure 1. Dactylopterus skull with colors added to match tetrapod taxa.

At last and finally,
toothless Dactylopterus nests with a very toothy basal ray fin fish, Calamopterus (Figs. 2-4).

Figure 6. Skull of Calamopleurus updated with new colors.
Figure 2. Skull of Calamopleurus updated with new colors.
Figure 3. Calamopleurus skull from a different view.
Figure 3. Calamopleurus skull from a different view.

Dactylopterus volitans
(Linneaus 1758; 50 cm; Fig. 1) is the extant flying gurnard, a bottom-feeder living in warm shallow seas. Typically Dactylopterus is allied with long-snouted pipefish and seahorses. Here it nests much earlier, with Calamopterus (Figs. 2-4). Note the remnant of the heterocercal tail (Fig. 5), a primitive trait. Like its tooth sister, Calamopterus, the skull of Dactylopterus has a wide and slightly concave box shape in cross section. The mouth is horizontal. The nares are vertical on the anterior corners of the skull created by robust prefrontals. Distinct from its sister, the teeth of Dactylopterus are tiny to absent.

Figure 4. Calamopleurus overall. The pectoral fin is not a wing yet, as in Dactylopterus, figure 1.

When startled
the butterfly-like pectoral fins spread wide as the undulating tail pushes the fish away from danger. The tabulars are quite large and extend like a dorsal shield. The pelvic fins are below the giant pectoral fins, convergent with more derived fish. The anterior pectoral fin spines are separate from the large fan and are more mobile, like sea robin (Prionotus) ‘fingers’, but webbed.

Figure 3. The heterocercal tail bones of Dactylopterus reflect their ancient ancestry. This was predicted, sought and found online yesterday.

Calamopleurus cylindricus
(Agassiz 1841, Early Cretaceous; 25cm) is a relative of Amia, the bowfin and basal to the cave and electric eels. Many fossil specimens are known of this genus.

Once you get these two taxa together,
the resemblance is obvious, both overall and in detail. Getting these two together took the addition of another similar fossil taxon, Sauropsis longimanus (Fig. 4), Solnhofen (Late Jurassic fish traditionally allied with Pachycormiformes. Yes, the species name does mean ‘long hand’, setting the stage for the flying gurnard of the modern era.

Figure 4. Sauropsis longimanus from the Late Jurassic also nests with Calamopleurus and Dactylopterus.
Figure 4. Sauropsis longimanus from the Late Jurassic also nests with Calamopleurus and Dactylopterus.

References
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Agassiz L 1833-43. Recherches sur les poissons fossiles. Imprimerie de Petitpierre et Prince, Neuchâtel.

wiki/Calamopleurus

wiki/Flying_gurnard

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