When talking about species driven to extinction in historic times we automatically think of the Dodo, Carolina Parakeet, Tasmanian tiger, Caribbean monk seal among others. We might as well think of the Steller’s sea cow, Hydrodamalis gigas (picture below of one of the specimens at the NMNH).
H. gigas was a sirenian (sea cows: manatees & dugongs) that lived in the northern Pacific until about 240 years ago. This was one of the largest sea cows that have lived, only surpassed by Hydrodamalis cuestae from the Late Pliocene of California, which is estimated to have reaches up to 9.03 meters (~30 feet!) whereas one of the H. gigas measured by Steller (the first person to describe live specimens) was about 7.51 meters (~25 feet) (Domning, 1978).
The picture below is of a mounted skeleton of H. gigas at the Museum National d’Histoire Naturelle in Paris. It is most likely specimen A.14516, which is the only mounted skeleton at the MNHNP (Mattioli & Domning, 2006). It is a nice mount, but there is something wrong with it……
Look at the hand/flipper, its huge, and very dugong or manatee like (see the more detailed picture below). You see, G. W. Steller was one of the few persons to give an account of H. gigas from observing live (or recently killed) specimens (and hence the name Steller’s sea cow). His description of the hand is significant because the morphology is unlike that of any other known sirenian (Steller, 1899). According to Steller’s description, the forelimb of H. gigas had no fingers, in fact he describes the ends of the limb as having a posteriorly oriented hook-like structure made up of, most likely, stratified squamous keratinized epithelium (thickened hardened skin). The habitat of H. gigas were shallow waters where feeding would have exposed them to higher wave action, therefore the loss of fingers as well as having a hardened pad or surface would have provided more traction when using the forelimbs as propulsion or stabilization in these shallower waters. Domning (1978) concluded from the osteology and inferred myology that additional forelimb adaptations are also present in H. gigas. These adaptations such as reduction of some muscles and modifications to the elbow joint, made the limb better suited for movement in a more parasagittal direction (Domning, 1978).
To sum it all up, Hydrodamalis gigas had no fingers, it also had other forelimb adaptations that permitted it to “walk” in shallow marine substrates when feeding. The Paris mount is nice, but wrong, in that it has huge flippers instead of fingerless stumps.
You can see the second part of this saga here!!
Domning, D. P. 1978. Sirenian evolution in the North Pacific Ocean. University of California Publications in Geological Sciences 118:1-176.
Mattioli, S. & D. P. Domning. 2006. An annotated list of extant skeletal material of Steller’s sea cow Hydrodamalis gigas (Sirenia: Dugongidae) from the Commander Islands. Aquatic Mammals 32:273-288.Steller, G. W. 1899. The beasts of the sea. (Translated by W. and J. E. Miller); pp. 179-218 in D. S. Jordan (ed.), The fur seals and fur-seal islands of the North Pacific Ocean. Part 3, Article 8. Government Printing Office, Washington, DC.