Unusual Choia Chengjiang Biota Sponge Fossil

Description: This is an as unusual member of the Desmospongia, the most diverse of modern-day sponges. Greater than 90% of the extant 5,000 known species of sponges are desmosponges. Such a representation in the fossil record is not maintained where less than half the known genera are of this type, a consequence of the fact that the skeletons do not fossilize readily. Desmosponges skeletons are composed of sponging fibers and/or siliceous spicules. Sponges are known from the late Precambrian, with few localities contributing to the fossil record over time. The Chengjiang Biota is one such fossil lagerstatte. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

The specimen is a member of the type genus of the Family Choiidae, and has an unusual hat-like shape. It is thought to have lain on the bottom convex side up as seen in the restoration. While this species is only known from the Chengjiang Biota, another member of the genus is known from the somewhat younger Burgess Shale. Somewhat more of the specimen may still be trapped under the matrix. While this species is only known from the Chengjiang Biota, another member of the genus is known from the somewhat younger Burgess Shale (see my other offerings for an example of Choia carteri).

Also see: Chengjiang Biota Fauna List Chengjiang Fossils