The Acanthothoraci is possibly a paraphyletic order made up of an ensemble of generalized placoderms.
The group containing the species 'Radotina' prima appears to be most closely related to the arthrodires, phyllolepids, petalichthyids and ptyctodontids based on the histological structure of their dermal tubercles.
Another group containing the genera Brindabellaspis, Romundina and Palaeacanthaspis shares several features with the antiarchs, including their cranio-thoracic joint.
The third group of acanthothothoracids, containing the genera Radotina, Kossoraspis and Kimaspis, share a partly tesselated skull-roof suggesting an affinity with the rhenanids.
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