Megalneusaurus fossil map
Where fossils of Megalneusaurus have been found, shown on the Earth as it looked about 160 million years ago and on today’s map.
Dots are fossil collections recorded in the Paleobiology Database. The “then” view moves today’s fossil sites back to their positions 160 million years ago (the time slice nearest the median age of the fossils) using the Merdith et al. (2021) plate model; positions are approximate. Open on the timeline map →
| Group | Plesiosaurs & kin |
|---|---|
| Lived | 161.5–154.8 million years ago (Oxfordian) |
| Periods | Jurassic |
| Named by | Knight 1898 |
| Fossil records | 1 occurrences at 1 locations (PBDB) |
| Found in | United States |
| Rock formations | Sundance |
About Megalneusaurus
Megalneusaurus is a genus of large pliosaurid plesiosaur from the Late Jurassic of North America. It was provisionally described as a species of Cimoliosaurus by the geologist Wilbur Clinton Knight in 1895, before being given its own genus by the same author in 1898. The only known species is M. rex, known from several specimens mainly found in the Redwater Shale Member, within the Sundance Formation, Wyoming, United States. A specimen discovered in the Naknek Formation in southern Alaska was referred to the genus in 1994. The loss of most fossils has led some paleontologists to consider the genus as dubious, although its validity is maintained by many authors. The binominal name literally means "king of large swimming lizards", due to the size of the first specimen.
Estimated to be around 7–9 meters (23–30 ft) long, Megalneusaurus is one of the largest known North American pliosaurs. As its name suggests, the genus was considered the largest sauropterygian identified before the discovery of some Kronosaurus fossils in 1930. Like some other plesiosaurs, Megalneusaurus have four flippers, a short tail, and most likely an elongated head and short neck, suggesting that it is a thalassophonean-like pliosaurid. The rear flippers were larger than those at the front.
Text in “About” is quoted from the Wikipedia article Megalneusaurus (revision 1368824786), licensed under CC BY-SA 4.0; introduction excerpted verbatim, formatting removed. Ages, family, authority and fossil records: Paleobiology Database, accessed 23 October 2026. Ages are those of the rock layers the fossils were found in. Wikidata: Q1911639.
