Fossils dating before 1741
The transition from Hydrodamalis cuestae to H. gigas occurred within two to four million years*)Domning 1978, P. 104
. The new species approximately ranged from the Kuriles via the Bering Sea to northern California. For a long period there were very few fossil finds, as the sea rose by more than 100 meters over the last 20.000 years and the coastal areas of those early periods are now well below sea level. Therefore there is also little archeological evidence of sea cow hunting by early humans.
During the last 5,000 years the rise of the sea level slowed down, and some more recent fossils have been found.
i. South of the Aleutian and Commander Islands
- An isolated rib bone belonging to the Steller's sea-cow, Hydrodamalis gigas (Zimmermann, 1780), is described from the Middle Pleistocene Mandano Formation of the Boso Peninsula, central Japan.
It represents the southernmost occurrence of the Steller's sea-cow in the world. The specimen also provides evidence that the Steller's sea-cow had distributed at least by the Middle Pleistocene in the adjacent sea around the Japanese Islands*)source: http://ci.nii.ac.jp/naid/110002703586/en.
- Monterey Bay (seafloor), age ± 18,900 years: skull fragment without rostrum, occiput and mandibles, also in the Smithsonian's National Museum of Natural History.
ii. On western Aleutians:
- Amchitka Island, age ± 127,000 years, now in the Smithsonian's National Museum of Natural History: left half and parts of right mandible, ribs C5-7, T1, half hemal arch, rib fragments, left scapula, parts of left and right humerus, both radius and ulna. From another individual: a rib, right scapula.
- Adak Island, skeletal elements, age ± 1,710 years*)Savinetzky, 1992, whereabouts unknown.
- Buldir Island, worked piece of rib, age ± 1,611 years*)Savinetzky, 1992, whereabouts unknown.
- Kiska Island, right rib from rear thorax, possibly from human middens, age ± 1,040 years, now in the Burke museum, Seattle.
- In the 19th century fossil bones, presumably of seacows, have been found on Semitkhi (Semichi), Attu und Agattu*)Stejneger (1883: 84).
Domning writes 2007 "it seems that a population of sea cows quite possibly survived [and were hunted] in the Near
Islands into the 18th century" (before the Russian arrival).
iii. On Bering Island:
1992 Savinietzky made a series of 25 radiocarbon dates of redeposited
sea cow bones found in the coastal deposits, dating between 2.400 and 400 years. Whereabouts of these specimen unknown.
Of the remaining available skeletal elements from Bering Island probably only the Helsinki-specimen and some bones in Washington (USNM218376) date from before 1741.
The Helsinki skeleton of a young male is probably also the only available specimen from a single individual. Hampus Furuhjelm, Governor of Russian Alaska, had collected it 1861 on v. Nordmann's*)Nordmann, Alexander von, Director of Zoologic Museum Helsinki
request. The museum in Helsinki communicated that the exact age has not yet been analysed.
A skeleton, which 1892 Prof. B. W. Everman bought from a "creole"*)Russian-Alëut half-breed
, lay under about 1 meter of sand about 3 kilometre inland, and probably was also a complete skeleton of one individual from the Pleistocene, which once had been thrown far inland by a large wave (Steller reported he had found far and high inland whole sea-cow skeletons, between driftwood and whale bone). Supposedly the specimen should have been donated to the Washington National Museum of Natural History, however, its whereabouts are unknown.