Scientists have yet to identify the strange prehistoric-like “mutant”, which has similarities to a dolphin but is twice as large as a human being.
Found on the shoreline of Sakhalin Island, which is closer to the United States than it is to Moscow.
The extraordinary pictures show a bloodied carcass ripped apart with its bones showing.
They also show what appears to be thick long hair hanging off the creature’s remains, a characteristic that has puzzled marine biologists.
Nikolay Kim, deputy head of the Forecasting Department at the Sakhalin Research Institute of Fisheries and Oceanography, said he believed it to be a species of “big dolphin”.
“According to a characteristic of the skin, it is a rare species,” he said.
“I doubt that it lived in our waters. Most likely, the animal was brought by a warm current.
“We often get tropical and subtropical species here and when they cool down they stay here and then die.
“I can confidently say that this is some kind of a dolphin.
“However, it has fur. It’s unusual. Dolphins do not have any fur.”
Pictures of the carcass have caused a sensation on Russian social media, with many local people speculating about what the animal is.
One said: “It looks like some mutant sea monster with a beak.”
Some claim it resembles a Ganges River dolphin, which are normally found in the fresh water regions of India, Pakistan, Nepal and Bangladesh.
One online comment beside a photograph jokes: “Probably, our summer is so cold that even the Indian Dolphins getting into local waters, are covered with fur.”
With a small triangular hump instead of a dorsal fin, a brown colour and the tendency to swim on their sides, Ganges dolphins are different from other typical species of dolphins.
However, crucially, they have no fur and only grow to about 2.4 metres in length – much smaller than the carcass washed up on the Russian coastline.
There are about 40 different species of dolphin in the world with the largest being the Orca, which grows to up to 31ft long (10m) and is more commonly known as the Killer Whale.
According to the famous marine park Sea World, dolphins are born with short hair but shed it shortly after birth.