Well, Samurott is definitely the odd one out, because it's based on an entirely different animal than Oshawott and Dewott. It's a sea lion rather than an otter. The Bulbapedia page about its origin is actually really interesting:Honestly, Dewott is kind of the bad link because it isn't like croconaw weird, but it really is just not fitting with the rest of the line. Oshawatt is cute and a klutz, Saumoratt is a big strong samauri, but dewott as a mid-stage tries to be a incredibly feirce guy that isn't really good looking, he just ooks off in his designs.
Origin
While its pre-evolutions are based on otters, Samurott is rather based on a sea lion and an armored samurai.[1][2] While it was decided that Oshawott would be based on an otter, the designers had issues in creating a fully evolved form which was more interesting than just a bigger otter standing on two legs. At that point Yusuke Ohmura went to see real-life otters at an exhibit, but his attention was rather caught by the strength displayed by a nearby sea lion, and thus decided that the fully evolved form would rather be based on the latter animal.[2] Furthermore, to represent the variety in the human population of Unova, it was decided that the evolution families of the starter Pokémon would be based on the West, China and Japan. In the case of the Oshawott family, it had to represent Japan, and thus was based on Japanese samurai.[2] Samurott's inspiration also comes from the lifespan of a samurai, from a child (Oshawott) to a military commander (Samurott).
Samurott's tail may be based on a Japanese war fan. The "helmet" over its head appears to be based on the rare-spined murex shell. The markings on its chest make it reminiscent of a giant otter. Its ability to withdraw, attack with, and return its blade may be a reference to iaido, a Japanese martial art that uses similar swordplay in combat.
While its pre-evolutions are based on otters, Samurott is rather based on a sea lion and an armored samurai.[1][2] While it was decided that Oshawott would be based on an otter, the designers had issues in creating a fully evolved form which was more interesting than just a bigger otter standing on two legs. At that point Yusuke Ohmura went to see real-life otters at an exhibit, but his attention was rather caught by the strength displayed by a nearby sea lion, and thus decided that the fully evolved form would rather be based on the latter animal.[2] Furthermore, to represent the variety in the human population of Unova, it was decided that the evolution families of the starter Pokémon would be based on the West, China and Japan. In the case of the Oshawott family, it had to represent Japan, and thus was based on Japanese samurai.[2] Samurott's inspiration also comes from the lifespan of a samurai, from a child (Oshawott) to a military commander (Samurott).
Samurott's tail may be based on a Japanese war fan. The "helmet" over its head appears to be based on the rare-spined murex shell. The markings on its chest make it reminiscent of a giant otter. Its ability to withdraw, attack with, and return its blade may be a reference to iaido, a Japanese martial art that uses similar swordplay in combat.