Giant Middle Jurassic (Bathonian) cf. Laevaptychus sp. of the Aztlán section, Hidalgo State, central Mexico

Abstract

Here we present aptychi and one perisphinctid ammonite from a 2.23 km-thick sedimentary section along the Aztlán Creek, Hidalgo state (East Central Mexico). The sedimentary sequence is predominantly build-up by basinal carbonates and is assigned to the Tepexic/Cahuasas (partim) formations, which are of Bathonian to Callovian in age and were deposited in the proto-Atlantic Basin at the western Tethys realm, Caribbean sub province. These strata yielded fourteen poorly preserved aptychi, of which two could be identified. One of them is the largest aptychi ever formally reported for the Jurassic and is identified as cf. Laevaptyhcus sp. This specimen reaches 182 mm in the harmonic margin. The finding represents the first report of Middle Jurassic aptychi from Mexico. The perisphinctid ammonoid is assigned to the genus Procerites sp. and is Bathonian in age.