Steller’s Sea Cow

The Steller’s sea cow was a large marine mammal from a group of animals called sea cows. Unfortunately, due to human factors, such as predation, it was driven to extinction in the 18th century. The last Steller’s sea cow was believed to be wiped out around 1768. It lived from the Late Pleistocene to the Late Holocene.

The Hydrodamalis gigas were native to the islands in the Bering Sea and around shallow waters in the Bering Sea region. Due to its environment, it was able to grow to an immense size. They were given their name by the man who discovered them in 1741, German Zoologist Georg Wilhelm Steller.

Let’s take a look at this remarkable creature.

Appearance

The Stellar’s sea cow had a unique appearance similar to the existing members of the Sirenians, such as manatees and dugongs. They were far larger than modern-day sea cows, as they could reach lengths of up to 9 meters or 30 feet. In comparison, a manatee can only get to a third of that size at 9-10 feet.

It is estimated that the animal weighed anywhere between 8-10 tons, which gave it the title of one of the largest mammals, other than whales, to grace the Holocene epoch. Their heads were relatively small compared to their body size, with a blunt snout and downturned mouth adapted for grazing on kelp.

Unlike other sea cows, it couldn’t completely submerge itself below the water.

Another key feature of the Sirenians is their dental layout. They don’t possess any teeth. Instead, they used a pair of horny plates, named ceratodontes, which were located on the creature’s palate and mandible. They possessed two short, paddle-like forelimbs (flippers) that aided in maneuvering and stability. They lacked hind limbs.

They had a forked tail fluke, similar to whales, providing propulsion for their large bodies. Their skin was exceptionally thick, rough, and bark-like in texture, offering protection from the harsh cold-water environment. Steller describes individuals losing enough weight during the winter months to cause their ribs and vertebrae to be visible under the skin.

and mashing motions of the front of the mouth were emphasized at the expense of more traditional chewing movements in Hydrodamalis

Their bones were dense to help counteract the problems they faced with buoyancy. They even had a transparent third eyelid (a nictitating membrane) to help protect their eyes from damage underwater.

Their thick skin and likely a layer of thick blubber provided insulation in the frigid waters of their habitat. They likely had a slow metabolism, allowing them to conserve energy in their food-limited environment.

Habitat

Although the information detailing the complete natural history of the Steller’s sea cow is low due to its quick extinction after discovery, they were believed to be native to the Bering Sea region. This region in the North Pacific Ocean sits between North America and Russia. More specifically, they inhabited the shallow waters around the Commander Islands and the Aleutian Islands.

Fossil evidence indicates that the past distribution of the genus Hydrodamalis was much wider, including the coasts of Japan and North America. Herds were frequently found near the mouths of streams or rivers.

Diet

The Steller’s sea cow, like its relatives, was a herbivore and targeted sea grass, algae, kelp, and seaweed. Out of these food sources, kelp made up the bulk of their diet, as the availability of seagrass could not sustain a thriving population that required a significant quantity of food per day.

It is said that during hard times and periods of kelp forest decline, the steller’s sea cow would fast and adapt to the availability of kelp in their ecosystem.

Reproduction

Similarly to manatees, the Steller’s sea cow was a very social animal and would operate in family units. These groups would help one another and support injured members.

They were monogamous creatures, meaning that they would mate with one partner only and raise the young together. The female sea cow was only capable of having one child at one time due to her single set of mammary glands, and it would take around one year from conception to birth.

Threats

Studies using hunting records and life-history data from dugongs indicate that unsustainable overhunting was the primary driver of Steller’s sea cow extinction.

Hunters would kill them for their abundance of blubber. With an already small population, around 2000 individuals, upon their discovery, they did not stand a chance of population growth.

In terms of other animal predators, due to its incredible size, it is only killer whales or orcas and sharks that could take down the Steller’s sea cow. However, due to its positive buoyancy, it would have been hard for orcas to drag them below the water’s surface. It is also believed that the nature of the kelp forests prevented large sharks from hunting them.

More Amazing Facts about Steller’s Sea Cow

1. They were required to lift their head every 4-5 minutes so that they could consume a large quantity of plant matter.
2. Juveniles were kept toward the middle of the herd, and Steller describes herd members attempting to come to the aid of captured individuals.
3. Some researchers speculate that sightings of Steller’s sea cows, with their large size and unusual appearance, may have contributed to the rise of mermaid or sea monster legends among sailors and coastal communities.
4. They were very social animals.

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