[1] The type and referred specimens of Plesiosuchus were discovered by John Clavell Mansel-Pleydell in the 1860s alongside the remains of several other large-bodied marine reptiles along the coast of Dorset.

Hulke suggested that "this head and the lower jaw both belonged to one individual" as both the same dimensions and were discovered in close proximity in a reef exposed at low water in Kimmeridge Bay.

Some material was destroyed due to pyrite decay while the isolated bone fragment referred to as the "upper maxilla" has never been figured and cannot be located.

Young et al. (2012) resurrected the genus name Plesiosuchus as their phylogenetic analysis found a paraphyletic Dakosaurus and suggested more basal position for P. manselii within Geosaurini than previously thought.

NHMUK PV OR40103a includes the right mandibular ramus, some isolated teeth, a humerus, and numerous ribs and vertebrae that are partially or completely imbedded in matrix.

Although it is uncertain whether the holotype (and referred specimens) belong to adults or subadults as none of the vertebrae are well enough preserved to determine the nature of the neurocentral sutures, its total body length is estimated to be 5.42 m (17.8 ft).

The specimen NHMUK PV OR40103b, a short series of cervicodorsal vertebrae preserved in matrix, is also a thalattosuchian due to its possession of several apomorphies of the group.

However, Owen never provided evidence for this referral and there were no overlapping elements between NHMUK PV R1089 and the holotype of P. trochanterius (thought to be an isolated femur but is actually a humerus that was collected from the early Tithonian of Shotover Hill, Oxfordshire, England).

Additionally, NHMUK PV R1089 exhibits extreme reduction in dentition (13 dentary alveoli compared to 19–25 in Machimosaurus) that is otherwise observed in geosaurine metriorhynchids.

[1] Fossil teeth of a similar form were found also in the Czech Republic and formally published in 2021 (in a stratum dating to hauterivian, some 130 milliony years ago).

In palatal view, the palatine width narrows anteriorly from the suborbital fenestrae to the midline, in a distinct elongate triangular shape.

In dorsal view, the lateral margins of the prefrontals have an inflexion point directed posteriorly at an angle of approximately 70 degrees from the anteroposterior axis of the skull.

Young et al. (2012) resurrected the genus name Plesiosuchus as their phylogenetic analysis found a paraphyletic Dakosaurus and suggested more basal position for P. manselii within Geosaurini than previously thought.

Purranisaurus potens was removed as it is currently under re-description and "Metriorhynchus" brachyrhynchus was recoded due to the uncertainty of whether the Suchodus durobrivensis is a junior synonym of the former or its closest known relative.

The same problem exist in the identification of two recently discovered, but fragmentary, geosaurine skulls from the Kimmeridgian of Mexico that were initially referred to an unnamed species of Dakosaurus by Cau & Fanti (2011), Young et al. (2011) and others.