An early Cambrian chileate brachiopod from South Australia and its phylogenetic significance

The first record of a chileate (Rhynchonelliformea, Chileata, Chileida) brachiopod, Chile? sp. in South Australia is described based on a well preserved, phosphatised ventral valve from the early Cambrian (lower-mid Botoman; Pararaia tatei trilobite Zone) Parara Limestone exposed in Horse Gully, Yorke Peninsula. The ventral valve of Chile? sp. is the only known record of a phosphatised chileate and provides the first critical insight into the ontogeny of the poorly understood Cambrian Chileata. The early ontogeny of Chile? sp. closely parallels that of the aberrant early Cambrian paterinate-like phosphatic-shelled Salanygolina from Mongolia. In both Salanygolina and Chile? sp., the anterior margin of the well defined ventral larval shell is indented by an unrestricted notch that, through later ontogeny, develops into a foramen, directly anterior to the umbo. In subsequent ontogenetic development, this subtriangular foramen is enlarged by resorption and covered posteriorly by the colleplax - a triangular plate - in the umbonal foramen. The ontogeny of Chile? sp. further supports the notion that the umbonal foramens and colleplax of Chileata and Salanygolina are homologous and they belong in the stem of the Rhynchonelliformea.