Sphenacanthus, meaning “wedge spine”, was a genus of primitive proto-shark measuring 3 feet long which lived from the late Devonian Period to the end of the Permian Period 360-252 million years ago.
Sphenacanthus was named in 1837 by the Swiss ichthyologist Louis Agassiz; he also named the proto-shark Ctenacanthus that same year. Possibly because they were so similar, it was proposed in 1884 that Ctenacanthus and Sphenacanthus were the same creature, and since Ctenacanthus was named first, that genus had priority. This idea stuck around until 1902 when the various species formerly ascribed to Sphenacanthus were transferred to yet another genus called Cheiracanthus, which wasn’t a shark at all or even a close relative but was a type of cartilaginous fish called an acanthodian. This idea persisted until the early 1980s when the genus Sphenacanthus was resurrected as a valid genus.
Far more interesting than this creature’s taxonomic shuffling (which, let’s be honest, is only of interest to biologists) is that Sphenacanthus is believed to have lived in freshwater. Sphenacanthus became the namesake member of the family Sphenacanthidae which in turn belongs to the order Xenacanthiformes, which includes noteworthy genera like Xenacanthus and Orthacanthus.
Thirteen species have been ascribed to the genus Sphenacanthus. The drawing below depicts Sphenacanthus costellatus, whose fossils have been found in Eskdale, Dumfriesshire, Scotland within the Glencartholm Volcanic Beds, which dates to the early part of the Visean Stage of the early Carboniferous Period 345-340 million years ago.
Sphenacanthus costellatus. © Jason R. Abdale (October 19, 2026).
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Categories: Paleontology, Uncategorized
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