Thalassomedon fossil map
Where fossils of Thalassomedon have been found, shown on the Earth as it looked about 100 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 100 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 | 100.5–93.9 million years ago (Cenomanian) |
| Periods | Cretaceous |
| Family | Elasmosauridae |
| Named by | Welles 1943 |
| Fossil records | 2 occurrences at 2 locations (PBDB) |
| Found in | United States |
| Rock formations | Graneros Shale, Belle Fourche |
About Thalassomedon
Thalassomedon (from Greek, thalassa, "sea" and Greek, medon, "lord" or "ruler", meaning "sea lord") is a genus of plesiosaur, named by Welles in 1943.
Text in “About” is quoted from the Wikipedia article Thalassomedon (revision 1348846340), 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: Q2467257.
