Brachydeiridae is a family of small to moderately large-sized arthrodire placoderms from the Late Devonian of Europe, restricted primarily to the Kellwasserkalk Fauna of Bad Wildungen and Adorf.

[2] The superficial anatomy of brachydeirids is extremely diverse, and each genus has been previously placed in their own monogeneric families.

The half a dozen species of Brachydeirus are comparable (on a superficial level) in form and size to trout or small mackerels.

Oxyosteus is easily distinguished by a high, extremely compressed body and a long, thin rostrum.

As mentioned earlier, Synauchenia is unique in the entire order for having the trunk and head shields fused together into an immovable unit.