Reevaluation of the holotype of Plesiosaurus (Polyptychodon) mexicanus Wieland, 1910 from the ?Upper Jurassic of Mexico: a thalattosuchian, not a sauropterygian

the holotype of the first sauropterygian described from mexico, plesiosaurus mexicanus wieland, 1910, was recently rediscovered and is here described and discussed for the first time in almost a century. the holotype specimen belongs to an indeterminate metriorhynchine crocodyliform. doubts remain as to the stratigraphic origin of the specimen, whether upper jurassic or lower cretaceous. it adds a specimen to the recently recognised wealth of the mexican gulf in thalattosuchians.