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The taxonomy of Early Devonian placoderm material from the Lochkovian and Pragian of the Prague basin, previously attributed to the genera  Radotina  and  Holopetalichthys , is revised. The Pragian species  Radotina tesselata  Gross 1958 shares detailed similarities with the holotype of the Lochkovian  Radotina kosorensis  Gross 1950, which is also the holotype of the genus; the assignation of both species to  Radotina  is supported. However, the Lochkovian material previously attributed to  Radotina kosorensis  also contains two unrecognised taxa, distinguishable from  Radotina  at the generic level: these are here named  Tlamaspis  and  Sudaspis . The disputed genus  Holopetalichthys , synonymised with  Radotina  by some previous authors, is shown to be valid. Furthermore, whereas  Radotina ,  Tlamaspis  and  Sudaspis  can all be assigned to the group Acanthothoracii, on the basis of several features including possession of a projecting prenasal region of the endocranium,  Holopetalichthys  lacks such a region and is probably not an acanthothoracid. Skull roof patterns and other aspects of morphology vary greatly between these taxa.  Radotina  has a substantially tesselated skull roof, whereas the skull roofs of  Tlamaspis  and  Holopetalichthys  appear to lack tesserae altogether.  Tlamaspis  has an extremely elongated facial region and appears to lack a premedian plate.  Sudaspis  has a long prenasal region, but unlike  Tlamaspis  the postnasal face is not elongated. Past descriptions of the braincase of  'Radotina'  and the skull roofs of  'Radotina'  and  'Holopetalichthys'  incorporate data from more than one taxon, giving rise to spurious characterisations including an apparently extreme degree of skull roof variability. These descriptions should all be disregarded.

plos one

Unique diversity of acanthothoracid placoderms (basal jawed vertebrates) in the Early Devonian of the Prague Basin, Czech Republic: A new look at Radotina and Holopetalichthys