. Chordate morphology. Morphology (Animals); Chordata. GEMUNDINA BOTHRIOLEPIS Figure 2-14. Restorotions of some fossil plocoderms. Pteraspis, Drepanaspis, and Birkema (Figure 2-13). Tremataspis differed from Cephalaspis in lacking the horn-like develop- ments of the head margin and in lacking fins. These genera agreed in having the head and trunk largely encased in armor. The tail was covered by scales or plates. The naso- hypophyseal duct opened on the top of the head just Ln front of the eyes, which lay near the midline. Behind the eyes were a dorsal "field" covered by small plates
. Chordate morphology. Morphology (Animals); Chordata. GEMUNDINA BOTHRIOLEPIS Figure 2-14. Restorotions of some fossil plocoderms. Pteraspis, Drepanaspis, and Birkema (Figure 2-13). Tremataspis differed from Cephalaspis in lacking the horn-like develop- ments of the head margin and in lacking fins. These genera agreed in having the head and trunk largely encased in armor. The tail was covered by scales or plates. The naso- hypophyseal duct opened on the top of the head just Ln front of the eyes, which lay near the midline. Behind the eyes were a dorsal "field" covered by small plates and the openings of the endolymphatic pores. Drepanaspis and Pteraspis (Figure 2-13) differed in having the nasohypophyseal opening at the margin of the mouth or inside the mouth. Drepanaspis was a very flattened form apparently of bottom living habit. Birkema (Figure 2-13) is an example of the anaspid. It was a laterally compressed fish of small size. It is thought that it foraged along the bottom by more or less standing on its head. This would account for the hypocercal type of tail seen in this group and in Pteraspis. Among the fossil gnathostomes, jawed fishes, the arthro- dires are well known, and of these Coccosteus and Dunkelo- steus are the best known. Dunkelosteus was large, its head and trunk were covered with bony armor, and the head artic- ulated with the trunk (Figure 2-14). It had paired fins and a long, tapered, isocercal tail. Bothriolepis (Figure 2-14) is a peculiar looking placoderm related to the arthrodire. Its ventrally located mouth sug- gests that it was a bottom feeder. Other arthrodires were of many shapes and forms. Geinundina (Figure 2-14) was a very flattened, shark-like form, covered with small bony plates. The shark array had many fossil representatives ranging from the Devonian Ciadoselache or the carboniferous Pleura- canthus (Figure 2-15). The former had a cover of fine scales, and the latter was probably naked. The acanthodians (Figure 2-15)
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