Actinistian gular plates from the Cretaceous of Mexico and the problems assigning gular plates taxonomically

Abstract

Two gular plates of an indeterminate actinistian are described from the Cretaceous of Muhi quarry, Hidalgo state, in central Mexico. Their narrow shape belongs to the few actinistian gular plates with a high length / width ratio (above 4) in contrast to most known actinistian gular plates with a length / width ratio below 4. The gulars of Muhi quarry are assigned, with caution, to the actinistian family Mawsoniidae on the basis of the length / width ratio (around 4.5) of the gular, which can be found in three other genera of the family. There are not enough characteristics in actinistian gular plates alone to erect a new genus or species. Noteworthy is the large size of the Muhi gulars that corresponds to a body length of about 1.6 m – the length of Latimeria today. The gulars are preserved in association with a basibranchial tooth plate and a few neural spines. This is the third actinistian record from the Cretaceous of Mexico.