The Explorer Corps sourcebook also mentions the 'six-legged bear' and the 'demon horses' - two rather interesting tidbits. A bear in itself means nothing, but who would just randomly imagine a six-legged bear?
"Quick, time's short on the new sourcebook, ideas for extraterrestrial animals. Okay how about a 6 legged horse and a demon bear?"
"Dude, that's Sleipnir from Viking mythology and the Demon Bear from X-Men"
"Oh alright, damn you, a 6 legged BEAR and a demon HORSE, okay?!"
BTW they dropped the idea I guess for the ghost bear, but the logo still has 6 paws. And visions of varying plausibility are still a big part of BT to this day.