Megacephalosaurus eulerti was a one of the last of the pliosaurs – a group of short-necked big-headed plesiosaurs – living during the Late Cretaceous (~93 million years ago) in what is now the Midwestern United States, a region that at that time was covered by the Western Interior Seaway.
Although known only from fossil skulls and a few neck bones, based on the proportions of related pliosaurs it probably reached around 9m long (~30′) with its 1.75m (~5’9″) head alone making up 20-25% of that measurement.
Its elongated jaws were lined with pointed conical teeth, and pits in the bones of its snout may have housed a complex sensory system, possibly giving it the ability to detect the movements or even bioelectric fields of nearby prey.
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