Palaeobranchiostoma

Palaeobranchiostoma hamatotergum is an extinct chordate from the Early Permian-aged Whitehill Formation in South Africa. It is known from a single, 11 mm long specimen found in black shale. The body shows the presence of a notochord-like structrure running along the length of the body, along with gill slits, along with several unpaired fins, including a tail (caudal) fin with rays that is round and small, a pronounced pelvic fin and a humped dorsal fin covered in spikes. In its original description it was considered to be a cephalochordate (also known as a lancelet), though some other authors have considered its placement in the group as not definitive, due to a number of aspects of its anatomy like the fins being strongly divergent from living lancelets.