To Be or Not to Be ... an Acanthodian

Groenlandaspis disjectus

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Found in the Upper Devonian (~365 million years ago) of Scotland, Cosmacanthus malcolmsoni caused a bit of confusion when it was unearthed in the mid-1800's. It had a peculiar spine that seemed to place it with the members of Class Acanthodia, which all sported a spine structure on their dorsum and venter that had membranous connections to the body mass. However, upon further comparison, the difference between C. malcolmsoni and acanthodians widened, and it was placed in Class Placodermi. Newman (2004) reviewed this taxonomic revision and found it to be better, seeing as it is similar spinal plates to, and was nearby, the known placoderm Groenlandaspis disjectus.

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Newman, M.J. (2004). “A Systematic Review of the Placoderm Genus Cosmacanthus and a Description of Acanthodian Remains from the Upper Devonian of Scotland.” Paleontology, Vol. 48 (5), 1111-1116.