Acanthodian

Acanthodian : Spiny Shark

The Acanthodians are one of the earliest known jawed vertebrates. The oldest acanthodians found are from the Lower-Silurian. This group disappears from the known fossil record at the Permian-Triassic extinction event, long after they had already dwindled in diversity.

In my experience is the acanthodian Mesacanthus pusillus the third most common fossil that can be found in the Orcadian basin. The only drawback is that 95% of the found specimens are blobs of spines and scales which do not resemble a fish of any kind. So an intact specimen is not as abundant as one might think.

Diplacanthus crassisimus is a far less common fossil but if one is found they tend to be more complete that their smaller kin.

The Cheiracanthus murchisoni, the biggest of these sharks and also the most rare. This is also due to the fact it is not present in every Orcandian fishbed that I have come across. 

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