Colosteus scutellatus (Newberry 1856, Hook 1983; Westphalian, Late Carboniferous, 305 mya; 1m in length; AMNH 6916) was originally considered a fish (Pygopterus) and renamed by Cope 1869. Here Colosteus nests between Pholidogaster and Phlegethontia on a branch convergent with traditional tetrapods.

The skull was ovate, the vomers and dentaries had fangs, the fins had transformed to tiny four-fingered limbs. The lacrimal did not reach the external naris. The scales remained large and rhomboid-shaped. Pectoral girdle had not yet evolved an external scapula and coracoid.

Aytonerpeton microps (Clack et al. 2016; Early Carboniferous) is an earlier sister to Collosteus. Over the naris is a round bound identified by Clack et al. 2016 as a septomaxilla. In sister taxa that bone is the prefrontal, but in Aytonerpeton the dorsal process of the lacrimal divides the prefrontal in two. The posterior half of the prefrontal is gone, but would have filled the anterior semi-circle, judged to the anterior part of the a giant orbit by Clack et al. Small toes are present here, as in another colosteid, Pholidogaster.