Sauroposeidon
The press release in 1999 immediately garnered international media attention, which led to many (inaccurate) news reports of "the largest dinosaur ever!". While "Sauroposeidon" likely represents the tallest known dinosaur taxon, it does not hold records for either the longest or most massive. "Patagotitan" or "Argentinosaurus" make better candidates for the title "World's Largest Dinosaur" (presuming to ignore, as is conventional, "Amphicoelias"), though incomplete fossil evidence makes exact rankings impossible.
Hector's ichthyosaur
Hector's ichthyosaur, or the New Zealand ichthyosaur, is an unidentified extinct genus of ichthyosaur discovered in 1874. Its remains have been lost, and it may be the largest animal ever to have existed. It was named by Richard Lydekker in honor of James Hector.