Taxonomic review of Berriasian and Valanginian ammonites from Zacatecas State (north-central Mexico) studied by Burckhardt in 1906

Abstract

A review of sixteen ammonoid specimens of the Berriasian and Valanginian age from Zacatecas, as recorded by Burckhardt in 1906, is presented as part of a larger-scale study of Valanginian ammonoid faunas from Mexico. The present update includes also museographic information and new images of Burckhardt's ammonites, as well as nine 3D models for better display of specimens. Six taxa have been identified to the species and two to generic level. In comparison to the original identifications of Burckhardt, four taxa have been transferred at the generic and four at the specific levels. Using stratigraphic range data from the literature, we assign the present ammonoid specimens to the uppermost upper Berriasian to lower Valanginian interval. The following biozones have been recognized: Tirnovella alpillensis, ‘Thurmanniceras’ pertransiens and Neocomites neocomiensiformis; with two subzones: ‘Thurmanniceras’ otopeta and Neocomites premolicus. Furthermore, a paleobiogeographic analysis of the taxa revised here indicates a clear affinity with contemporaneous ammonoid assemblages from the Mediterranean region.