Machaeracanthus sp.

Machaeracanthus belongs to the class Acanthodii.

The acanthodia (Acanthodii, from the Greek άκανθα akantha, "thorn" and ειδής eides, "with the appearance of") are an extinct class of fish, whose species have characteristics common to both bony and cartilaginous fish. They were small fish, characterized by having at beginning of each fin a large bony spine (except in the caudal) despite having a cartilaginous skeleton, which is why in the past they were incorrectly called “spiny sharks”. It is the oldest known group of gnathostomes (vertebrates with articulated jaws). Its poor fossilization makes it difficult to deduce its relationship with other vertebrates.​

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