Cambrian (Stage 4 to Wuliuan) brachiopods from Sonora, Mexico

Abstract

AbstractThe Cambrian successions at the Chihuarruita Hill outcrop, Sonora, Mexico, have yielded two successive linguliform brachiopod assemblages that are transitional between Cambrian Stage 4 and the newly recognized global Wuliuan Stage. The lowermost assemblage includesDictyoninasp.,Paterinasp.,Eothelesp.,Hadrotreta rara? (Cooper), andLinnarssonia arellanoi? (Cooper), coming from the upper part of the Buelna Formation. The younger, recently named El Gavilán Formation contains a more diverse linguliform brachiopod assemblage, includingAcrothele concavaCooper,Batenevotreta?mexicanan. sp.,Dictyonina minutipunctaCooper,Eothelesp.,Eoobolussp.,Hadrotreta rara? (Cooper),Linnarssonia arellanoi? (Cooper),Micromitrasp.,Paterinasp., andPrototretasp. The El Gavilán Formation contains a diverse trilobite fauna suggesting Delamaran age in terms of the Laurentian regional stratigraphical scheme. The base of the global Wuliuan Stage and Miaolingian Series is defined by the first occurrence ofOryctocephalus indicus; in the absence of the index species, the base should be provisionally placed at the base of the El Gavilán Formation. The Wuliuan age of the brachiopod assemblage recovered from the El Gavilán Formation is supported by the occurrence ofAcrothelein the Cambrian biostratigraphical succession of Himalaya, where the genus makes its first appearance in theKaotaia prachinaZone. In addition, the co-occurrences ofAcrotheleandEothelecan be taken as an indication of the Wuliuan age of the fauna. A new biogeographic analysis confirms that theEotheleFauna first appeared at the end of Cambrian Stage 4, as a result of increased faunal migration within the southern tropical latitudes directed from Australasian Gondwana to Laurentia.UUID:http://zoobank.org/6598f51f-cb07-4df3-bd1f-025a13e64edf