By special request from Caitlin, who asked that I write about otters, dinosaurs, and aliens, but the dinosaurs and aliens cannot eat the otters.
I've had a handful of otter experiences. One of my favorites was at the Australia Zoo, which was Steve Irwin's zoo. They were doing an "otter show", and the keeper was wearing some nice thick Wellies. The otters were a small Asian species called the small-clawed otter. The little monsters were doing their best to chew through the boots, and the keeper was talking about how vicious these cute, adorable animals really were. She told us that a "certain animal expert" at the park was overly dismissive of the wee darlings, boasting about his animal handling prowess. So he picked one up and promptly had his thumb bitten down to the bone. He sheepishly admitted his error as he was sent off to the emergency room for stitches. Of course, we all knew who that person was, and she dropped plenty of hints along the way to be sure.
I also had a customer at an aquarium store come in to tell me that her koi pond had been raided and wiped out by river otters. She had spent a great deal of money on koi, and all of them were otter snacks by the end of the summer. She decided all future pond residents would be feeder goldfish after that!
In 2004, an otter species that existed in the time of the dinosaurs was discovered in some Chinese fossil beds. They're calling it a "beaver-tailed otter", and it was about the size of a housecat. It appears to have eaten aquatic animals and insects. It was found with the fossils of other mammal species, one of whom seems to have fed upon dinosaurs and was about the size of an opossum!
As far as otters and aliens go, I recently read a study about the Eurasian otter adapting its food habits based on alien species being introduced to rivers in Italy. The smallmouth bass, a US native, was introduced to Italian rivers, but it was about 13 years before there was evidence of significant predation of these fish by the otters. At first they thought the otters had a learning curve with catching the fish, but it turned out that the bass needed to be present in large enough numbers for the otters' opportunistic feeding habits to affect them. Otters need a LOT of food, as they have high metabolisms, so they'll eat whatever gives them the maximum food for the minimum effort. As the alien bass started nudging out native species, they became so plentiful that the otters were pretty much stuck eating a lot of bass.