Article ID Journal Published Year Pages File Type
6349170 Palaeogeography, Palaeoclimatology, Palaeoecology 2016 9 Pages PDF
Abstract

•Cretaceous•Ammonoid biology•Biomats•Anoxic sea floor•Northeastern Mexico

Here we present evidence for a semi-sessile early juvenile stage of ammonites. Our hypothesis is based on fossil evidence in early diagenetic limestone concretions discovered in platy limestone deposits of Cenomanian age in the northern state of Coahuila, Mexico. In these locations densely packed post-embryonic shell assemblages were attached to fossilized algal or bacterial mats and preserved in sediments deposited under permanently anoxic bottom conditions. Tiny ammonites, as well as gastropods and byssate pectinid bivalves are abundant and restricted to these mats. They do not occur elsewhere in the sediment. The ammonite hatchlings were apparently unable to escape from mats sinking to the hostile sea floor and must thus have been semi-sessile, similar to the associated gastropods and bivalves.

Related Topics
Physical Sciences and Engineering Earth and Planetary Sciences Earth-Surface Processes
Authors
, , ,