Dinosaurs! and Dinosaurs II - as ebooks available in multiple formats.
I consider Dinosaurs II one of the best dinosaur anthologies ever put together. While there are no real classics in it, every story manages to entertain. I haven't had the chance to read the first anthology, but skimming over its table of contents, I see several stories that are classics: "A Gun for Dinosaur" by L. Sprague de Camp, "Time's Arrow" by Arthur C. Clark, "The Last Thunder Horse West of the Mississippi" by Sharon N. Farber, and more.
Both books originally were released as part of a series of themed anthologies edited by Gardner Dozois and Jack Dann in the late '80s/early '90s. Each collection featured science fiction and fantasy stories concerning a particular animal or topic, so there were anthologies about cats, dogs, unicorns, dragons, hackers, future war, time travel, and so on. Apparently Baen has reissued the entire series as ebooks, so if dinosaurs aren't your thing, maybe mermaids are.
This is great news because previously the anthologies were only available if you stumbled upon them in a used book store or bought them online through eBay or Amazon. Hopefully other publishers will follow Baen's example and release digital copies of other works of paleofiction that have long been out of print.
Also of note: Baen recently republished science fiction author David Drake's Time Safari stories in the collection Dinosaurs & a Dirigible.