Ophthalmothule was a medium-sized plesiosaur, measuring 5–5.5 metres (16–18 ft) long. It was noted to have unusually large eye sockets, which suggests a paleobiological specialization, such as deep water and/or nocturnal hunting. Along with Abyssosaurus, it is one of the youngest cryptoclidids known from boreal regions. The holotype is known from skeletal material that includes a complete cranium and a partial mandible, a complete and articulated cervical vertebrae, a set of pectoral and anterior to middle dorsal series, and the pectoral girdle and anterior humeri.[1]
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