Original paper

Late Cretaceous fish cans: Fish preserved in ammonite body chambers from the middle Santonian of Coahuila State, northeastern Mexico

Nyborg, Torrey; Ifrim, Christina; Moreno-Bedmar, Josep A.; Múzquiz, Hector Porras; Giersch, Samuel; Vega, Francisco J.

Abstract

Seven partially disarticulated fishes preserved in body chambers of ammonites are described from limestone of middle Santonian (Late Cretaceous) age in northern Coahuila, northeastern Mexico. Three ammonites preserve one fish and one ammonite preserves three fish, all of them in the ammonite's body chamber. In each case, the head is oriented adapically and is close to the last septum of the phragmocone. Seafloor conditions are considered to be hostile; therefore, once the fish entered the ammonite shell, its shelter sunk into oxygen depleted water levels which caused the fish to suffocate and die. Fish are slightly disarticulated with some delicate skeletal elements showing a unidirectional scatter away from the rest of the skeleton towards the ammonite aperture, which can be entirely explained by normal disarticulation due to the early stages of connective tissue breakdown. Due to the nature of fish preservation, it is believed the fish entered the dead ammonite shell to feed or to seek shelter from a predator, whereas other hypotheses are found less likely. The ammonites represent different morphotypes, and each shell preserves a different fish morphotype. The scenarios developed describe thus more general patterns in Cretaceous seas.

Keywords

ammonitesfishesnortheastern mexicoupper cretaceous