I wish you'd asked yesterday! One of my early guesses was "water" - when I think I'm looking for an animal or plant I try to narrow down the habitat.
That led me to try "sea", then marine" and "oceanic".
I think I'll also have tried "first", as that's one of my common guesses. After that, all I can say is that guess 22 was "coelocanth", which peppered the board with orange. "Plesiosaur" was the next 10 letter word I could think of that would fit.