Porifera and Chancelloriidae of the Cambrian of Sonora, Mexico: A review

Abstract

Archaeocyaths, articulated reticulosans, protospongiid sponge spicules, fragments of chancelloriid scleritomes and isolated sclerites are typical components of the lower-middle Cambrian Sonora biota of Mexico. This report briefly introduces the Cambrian sponges and chancelloriid fossils of the Sonoran platform described and illustrated to date. Early Cambrian (Series 2, stages 3 and 4) sponge spicules, Kiwetinokia sp. and extinct sponge-like archaeocyaths occur in the Puerto Blanco Formation, at the Cerro Clemente and Cerro Rajón in the Caborca region, northwest Sonora. Besides, a variety of chancelloriid sclerites belonging to Chancelloria, Allonia, and Archiasterella have been described in that region. Also, Chancelloria sclerites have been documented in the Arrojos Formation of the Caborca region. A fauna of hexactinellid sponges and chancelloriids was recorded from the middle Cambrian (Wuliuan Stage, Miaolingian Series) strata from the Arivechi section, in the eastern part, and San José de Gracia and El Sahural sections in the central Sonora. The middle Cambrian El Mogallón Formation in the Arivechi area yield assemblages of reticulosan thin-wall sponges, isolated protospongiid spicules and chancelloriid sclerite morphotypes. Fragments of articulated scleritomes of Chancelloria eros were reported for the first time for the Cambrian of Mexico, and sclerites of Allonia and Archiasterella in the Cerro El Sahuaral near San José de Gracia. Protospongiid spicules and isolated sclerites of chancelloriids were determined in the Cerro El Chihuarruita section at the San José de Gracia area. The mid-Cambrian Sonoran faunas have been compared with the Burgess Shale biota in Canada, and those of the Utah formations, in the USA localized around the Laurentia. Nevertheless, as the chancelloriid fauna is cosmopolitan, some of these genera are also present in other palaeocontinent including Siberia, China, and Australia. Sponges and chancelloriids are an important biotic component of the Sonoran communities. Their discovery constitutes a valuable tool for the reconstruction of the faunas, their paleoecology and paleoenvironments. These findings expand the paleogeographical distribution of these faunas during the Cambrian in the warm platform of Sonora.