A living fossil is not Russell Johnson (the professor from Gilligan’s Island) or dear Zsa Zsa Gabor (God bless you for holding on!).
I’ll chop it down to say that a living fossil is an organism that more closely resembles a fossil than anything living. For instance, the Atlantic horseshoe crab resembles the fossil record of trilobites more so than anything living. You can also think of living fossils as animals that have gone unchanged after millions of years therefore resembling the fossil record of their ancestors very closely. For instance, alligators and crocodiles haven’t evolved much in the past 230 million years. Horseshoe crabs have gone unchanged in the past 450 million years.
Most recently, a team led by Smithsonian scientists discovered a new living fossil, a primitive eel (Protoanguilla palau), from 10 specimens gathered from a cave in Palau. Palau is an island located in the Pacific 500 miles east of the Philippines and 2,000 miles south of Tokyo. What the scientists noticed was unique to this species (setting it apart from the 800 species of living eels) was the presence of a second upper jaw bone, fewer than the standard 90 vertebrae, and a full set of bony toothed gill rakers. Also, according to the press release from the Smithsonian, “The team’s analyses of total mitochondrial DNA indicate that P. palau represents an ancient, independent lineage with an evolutionary history comparable to that of the entire order of living and fossil eel species.”