Thalassoleon fossil map
Where fossils of Thalassoleon have been found, shown on the Earth as it looked about 5 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 5 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 | Early mammals |
|---|---|
| Lived | 7.246–2.58 million years ago (Messinian to Piacenzian) |
| Periods | Neogene |
| Family | Otariidae |
| Named by | Repenning and Tedford 1977 |
| Fossil records | 20 occurrences at 9 locations (PBDB) |
| Found in | United States, Japan, Mexico |
| Rock formations | Capistrano, Purisima, Almejas, Drakes Bay, Senhata, Nakawatari |
About Thalassoleon
Thalassoleon ("sea lion", from Greek: thalassa, the sea; and leon, lion) is an extinct genus of large fur seal. Thalassoleon inhabited the Northern Pacific Ocean in latest Miocene and early Pliocene. Fossils of T. mexicanus are known from Baja California and southern California. T. macnallyae is known from central California, and T. inouei (which may be a synonym of T. macnallyae) is known from Japan. Thalassoleon could be the ancestor of the modern northern fur seal.
T. mexicanus was comparable in size to the largest modern fur seals, with an old-male skull length of 272 mm and an estimated minimal weight of 295–318 kg (650–700 lb). Holotype of T. macnallyae, UCMP 112809, is a male equal in size to T. mexicanus.
Text in “About” is quoted from the Wikipedia article Thalassoleon (revision 1345024860), 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: Q593613.
