[4] Picrocleidus beloclis is another plesiosaur originating in the middle Jurassic and found in the Oxford clay formation.

Starting from the base of the skull and moving posteriorly the cervical vertebrae elongate and the neural spines broaden.

[1] The pectoral girdle in Muraenosaurus is broader than in most plesiosaurs and helped to situate the animal as a member of Cryptoclididae.

Muraenosaurs and elasmosaurs share a plesiosauromorph body type typified by having a small head at the end of a long neck.

It was initially believed that this innovation leads to a largely flexible neck and a relatively short and sturdy body.

The defining features of Cryptocleidoidia include a low fin aspect ratio, a wide rounded interpterygoid vacuity, and extreme specialization of the cheek region.

[8] The interpterygoid vacuity is completely absent in elasmosaur species but well represented in cryptoclidids, including Muraenosaurus.

[7] Muraenosaurus was initially discovered in the Oxford Clay which represents an ancient sea that was both shallow, with an average depth less than 50 meters, and warm (20 °C).

The sea was abundant with nutrients and light filtered easily through the shallow water to create a highly productive ecosystem.

The sea floor was littered with bivalves, arthropods, gastropods and foraminifera while the pelagic zone was home to a wide variety of species from marine reptiles to teleosts.

Long necked plesiosaurs have been discovered with varying contents lithified within their stomachs which give some indication of what Muraenosaurus may have been eating.

[9][15] Initially, long necked plesiosaurs were thought to be strictly fish eaters due to their conical teeth, a shared trait with modern piscivores.

[9] It is also proposed that species like Muraenosaurus fed upon benthic fishes by floating above them and reaching its head down into the benthos.

[15] Plesiosauromorphs may also have employed a strategy called benthic grazing where they would harvest relatively immobile species such as cephalopods from the sea floor.

The shredding teeth of lamniform sharks indicates that perhaps they were scavengers or detrivores and that they only fed upon dead plesiosaurs.

Models have indicated that not only do stones reduce pivoting at depth but it is also possible they dampened the ossilations in a plesiosaur's neck, helping provide stability to counter underwater currents.