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.
References:
- Foffa, Davide, et al. “Complex rostral neurovascular system in a giant pliosaur.” Naturwissenschaften 101 (2014): 453-456. https://doi.org/10.1007/s00114-014-1173-3
- Madzia, Daniel, Sven Sachs, and Johan Lindgren. “Morphological and phylogenetic aspects of the dentition of Megacephalosaurus eulerti, a pliosaurid from the Turonian of Kansas, USA, with remarks on the cranial anatomy of the taxon.” Geological Magazine 156.7 (2019): 1201-1216. https://doi.org/10.1017/S0016756818000523
- Schumacher, Bruce A., Kenneth Carpenter, and Michael J. Everhart. “A new cretaceous pliosaurid (reptilia, plesiosauria) from the carlile shale (middle turonian) of russell county, kansas.” Journal of Vertebrate Paleontology 33.3 (2013): 613-628. https://doi.org/10.1080/02724634.2013.722576
- Wikipedia contributors. “Megacephalosaurus” Wikipedia, 30 Mar. 2025, https://en.wikipedia.org/wiki/Megacephalosaurus