A catfish with barbels from the Silurian

Finally
a catfish from the Silurian with preserved barbels (Figs. 1, 2).

Ironically
catfish are members of the order Siluriformes (from ‘silurus’ Latin = large river fish). Previous oldest member of this clade: Late Cretaceous, 100mya.  Sir Roderick Murchison (1792–1871), a wealthy Scottish aristocrat, named the Silurian Period after an ancient Welsh Celtic tribe, the Silures. Appears to be a coincidence. The slow genesis of plants and arthropods on land occurred in the Silurian, along with a rise in oxygen levels, a rise in temperature and a rise in sea levels after the massive glaciation of the Ordovician.

Figure 1. Originally considered another Silurian Thelodus, this specimen nests with catfish in the LRT.

Figure 1. Originally considered another Silurian Thelodus, this specimen nests with catfish in the LRT. Here’s where DGS tracing helps pick out the details from a ‘fish silhouette’ fossil.

Not sure what the museum number is on this one.
In the large reptile tree (LRT, 1602 taxa; subset Fig. A) this taxon is labeled ‘unnamed Sil. catfish‘ (in the purple clade). In the LRT the new taxon is not as primitive as the armored catfish, Hoplosternum. Worthy of note, basal catfish in the LRT are air breathers employing the intestine or modified gill arches, not their air bladder, which they need to swim upright. Clarias is the famous walking catfish (Figs. 3–5) able to traverse land in search of other ponds. The spiny pectoral fins (Fig. 4) keep it upright and act as ground undulates as it wriggles from pond to pond.

Figure A. Subset of the LRT focusing on basal vertebrates (fish).

Figure A. Subset of the LRT focusing on basal vertebrates (fish). The base of the LRT will change by the next time you see it with the addition of several jawless fish. 

The identity of this specimen
might have been overlooked because it appears like a silhouette, offering little detail. Digital Graphic Segregation (DGS) enables details to be colored, identified and later scored in the LRT.

Figure 3. Silurian catfish face

Figure 2. Silurian catfish face. Note the left barbel is aligned with a crack.

Extant velvet catfish,
members of the clade Diplomystidae, are considered primitive.

Figure 6. Clarias head with barbels in vivo.

Figure 3. Clarias head with barbels in vivo.

Clarias batrachus (Linneaus 1758, up to 50 cm in length) is the extant walking catfish. The skull bones are nearly identical to those in the placoderm, Entelognathus. The spiny pectoral fins keep the walking catfish upright as it wriggles from pond to pond. No scales or bones appear on the surface. The teeth are short bristles on pads. The maxilla is absent.

FIgure 1. Clarias, the walking catfish is a living placoderm with skull bones colorized as homologs of those in Entelognathus (Fig. 2). Here the mandible shifts forward and the opercular shifts backwards relative to Entelongnathus in the Silurian.

Figure 4. Clarias, the walking catfish skull bones identified. Note the ossified spines at the leading edge of the pectoral fin. 

Figure 3. Clarias batrachus, the walking catfish, in vivo. The pelvic fin is tiny. The single dorsal fin is elongate. The anal fin is also elongate. The skull is flat and provided with sensory barbels.

Figure 5. Clarias batrachus, the walking catfish, in vivo. The pelvic fin is tiny. The single dorsal fin is elongate. The anal fin is also elongate. The skull is flat and provided with sensory barbels.

Generally recognized fossil catfish
include Qarmoutus hitanensis from the same Eocene North African beds as the early whale, Basilosaurus. Reported by NatGeo.com (citation below): Even though the fossil is relatively old in the way we ordinarily think of ages in millions of years, it is still essentially anatomically modern and directly comparable to living catfishes,” says John Lundberg of Drexel University’s Academy of Natural Sciences. “It’s one of the best preserved and oldest of its family.”

Afterthought about fish with spines in their fins
Spiny sharks (Acanthodii), like Brachyacanthus (Fig. 6), also briefly appeared in the Silurian and Devonian. Since the walking catfish uses its spiny fins to ‘walk’ on land, I wonder if spiny sharks, especially those with longer, thinner pectoral and pelvic spines, did the same, perhaps on the sea floor, not on land?

Figure 1. Surprising homologies in Pteronisculus and Brachyacanthus indicate a close relationship, despite the spiny fins.

Figure 6. Brachyacanthus has short, thick spiny fins, distinct from the long spines found in the walking catfish.

That might explain
why those extra spines appeared between the pectoral and pelvic fins, as extra hooks in the substrate?


References

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

https://www.nationalgeographic.com/news/2017/03/ancient-egypt-catfish-fossil-palaeontology-science/

https://pubs.geoscienceworld.org/gsa/geology/article-abstract/5/4/196/195354/Fossil-catfish-and-the-depositional-environment-of?redirectedFrom=fulltext

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