One little shield-bearing aquarium catfish converges with Devonian placoderms

Earlier we learned (with taxon inclusion)
that catfish nest with placoderms, rather than other ray-fin fish, when give the opportunity to do so. This is a novel hypothesis still awaiting confirmation from future studies that are equally inclusive.

Today the angel catfish,
Synodontis angelicas (Cuvier 1816, originally Silurius clarias, Linneaus 1758; Figs. 1,2; 9-18cm in length), has an overdeveloped skull, posteriorly wrapping around its dorsal and pectoral fins. In this way it recalls, by convergence, the pectoral shields of giant Devonian arthrodire placoderms like Dunkleosteus and Coccosteus (Fig. 3), but with that weak, ventral, sucker mouth, more closely mimics another placoderm, Dicksonosteus (Fig. 4).

Rather than using the same bones
that traditional placoderms use to cover their torsos, Synodontis extends the skull and pectoral bones it already has in similar protective, stiffening patterns.

Synodontis is a weird catfish.
Some species swim upside down. The first ray of the dorsal fin and the pectoral fins have a hardened first ray which is serrated. The lips are modified into a sucker mouth, convergent with sturgeons + ratfish and some bottom-dwelling Devonian placoderms (Fig. 4).

Hopefully seeing catfish in this new light
will open up all sorts of interest and study on this previously overlooked relationship.

Bottom-dwelling taxa from many clades
give rise to swift, vicious, open water predators. But it’s the flat, bottom-dwelling taxa that ultimately give rise to basal Tetrapoda, like Tinirau, Tiktaalik and Panderichthys.

Something to think about
next time you see an upside-down catfish in an aquarium. “That’s a living placoderm!”

Synodontis clarias (originally Silurus clarias, Linnaeus 1758; 9-18cm length) is the extant angel catfish or squeaker, a type of mochokid catfish. The skull bones extend past the dorsal fin in this fish that sometimes swims upside-down. The sucker mouth is weak and ventrally oriented, convergent with bottom-dwelling placoderms, like Bothriolepis.

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.

https://en.wikipedia.org/wiki/Synodontis_angelicus