Redlichiida; Redlichiodea; Yunannocephalidae: Yunnanocephalus yunnanensis

Geological Time: Early Cambrian, (~525 million years ago)

Fossil Site: Chengjiang Biota, Quiongzhusi Section, Yu’anshan Member, Heilinpu Formation Mafang, Anning, Yunnan Province, China

Description: This trilobite is a member of the Order Redlichiida (some researchers place it in the Ptychopariida), Family Yunannocephalidae from the Early Cambrian Heilinpu Formation deposits near Yuxi, in Chengjiang Couty, Yunnan Province, China, known as Yunnanocephalus yunnanensis. The species is one found in several locations within Yunnan Province, the souce of the name of the genus and species. The diversity of soft-tissue fossils from the Cjengjiang Biota 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 Redlichioids of this type are considered to be the sister-group comprising all of the “higher” (non-Olenelloid) trilobites by Richard Fortey. Yunnanocephalus is thought to have lived on or close to the seafloor. This is a well-preserved 3-D member of the Chengjiang Biota that made up a glimpse of the Cambrian Explosion some 5-10 million years before the Burgess Shale fauna came into being.