I don’t have a single favorite, but every now and then a critter will become the subject of my latest ADHD hyperfixation. I remember thinking skunks were cool in 5th grade. They’re like badgers with chemical weapons. For the months leading up to getting my first guide dog I devoured stuff about dogs in general. I had always had pet dogs so it wasn’t a new subject, just a more intense interest.
For a while it was octopi, then parrots. For some time in 2015 or early 2016 it was possums, the US’s only marsupial.
Right now it’s monkeys. I used to think monkeys were gross and disturbing in an uncanny valley sort of way, so humanlike but not human at the same time. But I’ve taken a shine to orangutans. They’re quiet and introverted like me. Also new world monkeys like capuchins and woollies. Having a prehensile tail would be awesome.
I’ve been fascinated by pterosaurs lately. The book Pterosaurs by Mark P Witton is great.
Pterosaurs interest me because of their wing morphology. Instead of having the wing membrane between all the “fingers” like a bat, it’s attached to their equivalent of a pinky finger in such a way it can fold up enough that they could use all four limbs to navigate on land. They just have such an interesting body shape that no animal today really has.
They also got much bigger than birds. Like, to the point that I want to write a fantasy book where the premise is that dragons are like …the only pterosaur that survived extinction. Because it would be cool to have a dragon that’s directly not related to modern reptiles, birds, or mammals…but still is speculatively based on a flying animal that did once exist.