Face plates on the sea robin and flying gurnard

Updated April 14, 2020
with new illustrations of the skulls.

Updated again April 24, 2021
with newer illustrations of the skulls and a new nesting for Dactylopterus (Fig. 2) with the basal ray fin fish, Calamopterus (Fig. 3).

Both the sea robin,
Prionotus (Fig. 1), and the flying gurnard, Dactylopterus (Fig. 2), have bizarre skull morphologies.Only one is a member of the clade of scorpionfish (Scorpaenidae).

The question today is:
“Which bone(s) create those face plates?” That question becomes all the more important because outgroup taxa have no cheek bones whatsoever. So these taxa and their relatives have no post orbital, no jugal, no squamosal, and no lacrimal despite the ‘so1–4’ labels put on them by Gregory 1938 in his famous book of fish skulls and the many dozens of diagrams he provided therein (Figs. 1, 2).

Figure 2. Prionotus, the sea robin, has more of a barracuda-like face. Uniquely, medial spines from the pectoral fin evolve to act like fingers for walking on the sea floor.

Figure 1. The sea-robin, Prionotus, has a more extensive circumorbital ring/face-mask

By default,
I’ve labeled those face plates with tetrapod homologies.

According to Wikipedia:
“As the name suggests, scorpionfish have a type of “sting” in the form of sharp spines coated with venomous mucus. The family is a large one, with hundreds of members. Like many perciform fishes, scorpionfish are suction feeders that capture prey by rapidly projecting a suction field generated by expansion of the fish’s buccal cavity.

Like the true gurnards (sea robins), to which they may be related, they possess a swim bladder with two lobes and a “drumming muscle” that can beat against the swim bladder to produce sounds. They have heavy, protective scales and the undersides of their huge pectoral fins are brightly coloured, perhaps to startle predators.”

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

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

Wikipedia continues:
“Morphological traits uniting the flying gurnards (Dactylopteridae) and the Syngnathiformes have long been noted. Most authors placed them with  the Scorpaeniformes, but DNA sequence data quite consistently support the view that the latter are paraphyletic with the Gasterosteiformes(sticklebacks + sea horses) sensu lato. Flying gurnards are particularly close to the Aulostomidae (trumpetfish) and Fistulariidae (cornetfish), and would have to be included with these.”

Figure 6. Skull of Calamopleurus updated with new colors.

Figure 3. Skull of Calamopleurus updated with new colors.

In the large reptile tree (LRT, 1645+ taxa then, 1838+ now) the sea robin and flying gurnard are not related to cornetfish and sea horses, but former is related to lionfish. The latter is related to basal ray fin fish.

Dactylopterus volitans (Linneaus 1758; 50 cm) 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 (above). Note the remnant of the heterocerval tail (above), a primitive trait. Like its sister, the skull has a wide and slightly concave box shape. The mouth is horizontal. The nares are vertical on the anterior corners of the skull. Distinct from its sister, the teeth are tiny to absent.

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.

Problems like this are frustrating,
then rewarding as new insights suddenly make sense of things. More such phylogenetic insights in various teleosts are re-identifying other facial bones and rearranging the tree topology. Still not finished with this yet, but there is progress every day. Having no one but Gregory 1938 as a guide, I’m learning as I go. Thank you for your patience here.


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.

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