Enigmatic Castericystis Carpoid Fossil

Description: The extinct carpoids are an informal grouping of Paleozoic fossils that closely resemble echinoderm, but lack radial symmetry. However, their classification remains controversial and they have been variously postulated to have been stem groups of other groups such as the basal deuterostomes or the craniates, tunicates, acraniates and chordates. Carpoids are known from the Middle Cambrian to Early Devonian.

Coming from Utah’s Marjum Formation, this fine carpoid fossil dates to the Middle Cambrian when these animals first appeared. The pictures speak to the strange body plan of this enigmatic creature. These small strange creatures had spiny tails, bulbous heads and were covered with spines. Having a body supported by calcitic plates, they resemble modern echinoderms such as starfish and their relatives. Some researchers believe that the common ancestor of echinoderms and vertebrates was a carpoid which is supported by the many shared features of echinoderms and vertebrate embryonic development.

Carpoids are distinct from all other animals, extant and extinct, because of their complete asymmetry, internally and externally. All the other examples I have had were the smaller Castericystis sprinklei from the Wheeler Formation. These are far more rare, with this representing the first I have had.