Intelligence and senses
Steller wrote *)Bering Island by Golder, P. 232:
"signs of a wonderful intelligence I could not observe"
Little is known about the brainpower of sirenians. Their brain is smoother than most mammals', and they have the lowest brain-to-body ratio of any mammal. This suggests that seacows may not be the smartest mammals in the sea. Recently, however, this assumption is changing. Manatees have the ability to recognize and remember the topography of their habitat. They can be trained to some extent. This presumably also applies to dugong and Steller's cow.*)R.L. Reep and T. J. O'Shea
Also the altruistic behaviour of the seacows, which effectively came to help their harpooned comrades, may be considered as an indication of intelligence.
Main sensory organs of seacows seem to be the whiskers, in particular those in the face. These seem to be connected to clusters of nerves in the brain called "Rindenkerne"*)R.L. Reep and T. J. O'Shea.
Presumably the hearing and vision capabilities were not very well developed, and also not much needed, as their heads were under water most of the time.
Steller wrote*)de Bestiis, by Miller, Page 45: "as to voice, the animal is dumb and utters no sound". It is probable, however, that they had a simple repertoire of sounds (like living sirenians), which had played a role during mating and between mother and calf.