The depiction.
The Grotte Cosquer Animal is a paleolithic cave painting believed by some to be a prehistoric rendering of a sea serpent.
Description[]
The image was found in Grotte Cosquer, Cap Morgiou, near Marseille, France. This underwater cave was discovered in 1985 by Henri Cosquer, who also found the artwork six years later. The entrance, 120 feet below water level, would have been above water during the Ice Age.
A fur seal
The charcoal drawings of animals in the cave were confidently dated by Jean Courtin and Jacques Collina- Girard in 1994 as 18,000–19,000 years old. Most of the images are of land animals, especially horses, but fully 11 percent depict marine life, including auks, fishes, seals, and jellyfish.
A penguin
However, one stands out among the rest, as it depicts a creature with a fat, stout, bulky body, a small head on a relatively long neck, with two front flippers and two rear flippers. It is commonly accepted by archaeologists to be a penguin, as the climate would have been suited for them at the time, however, it is a somewhat inaccurate drawing of a penguin, if it is one.
A sea lion
It might also be a depiction of a fur seal or sea lion, but it may also be an unknown species of animal, such as a sea serpent or other type of creature one would call a "sea monster" - for example, a living plesiosaurus - hence it is classified as a cryptid.
One could also make the assumption that it is a depiction of an extinct species of giant penguins, like the Palaeeudyptinae.