Are you thinking of this "little" guy?
http://www.fireflybooks.com/books/0921820879A.html
And in the National Geographic program Extraterrestrial, they had a
huge whale-like species with wings living on a moon of a Saturn-like
exoplanet which had a very thick yet still Eath-like atmosphere.
http://channel.nationalgeographic.com/channel/extraterrestrial/
