When you know what once existed (or still exists), you have a point to start from when designing your own fantasy creature or alien lifeform.
In the days before computers I used to rely heavily on books to learn about various birds and animals. Magazines and journals like National Geographic, Science and Discover were also useful for information and photographs. I used to be able to count on nature programs on PBS and the Science Channel for additional inspiration, but now there's only the few shows like Nature and Earth (BBC).
The internet has provided quite a few new resources, ranging from formerly book-based guides like online encyclopedias and identification guides like The Cornell Lab of Ornithology All About Birds to general science websites like IFL Science. But usually all those are good if you already know what you are looking for. Sometimes you are instead looking for that flash of inspiration, that moment of serendipity when you see something new and can say, "Oh! I can use that! Well, maybe not that, but something like that...."
I have several friends on Facebook who share marvelous videos such as Marching Dinosaurs (which, at five minutes long might be too long to share at a young writers session, but I really want to!) and the latest scientific discovery or dinosaur dig. (I love #13 of the "Top Thirteen Fossil Stories of 2016".)
What are some resources you use, either for inspiration or to learn more?