Here's a post about "firsts" bias from Overcomming Bias. If we read a news story about oldest sculptures, when life first appeared on earth or whatever, it is almost always to explain that the date is earlier than we thought and how surprising this is. Part of the answer has to do with physical evidence, finding a younger fossil is unremarkable. But there is a difference between the oldest known fossil and the best estimate of when the animal first appeared; theories are not just collections of facts. This suggests the estimates are biased because if they weren't we should be changing our estimates in both directions.
I haven't done a massive survey or anything but I think the same bias is involved with animals. I can't remember reading an article explaining that animals are dumber than we previously thought. Descartes thought that animals had no sensation at all. For the last 300 years what we know about animals has only been moving in one direction, which suggests systematic bias.
Of course the opposite bias also exists; some animals really are very stupid but a few people are quite prepared to get hot under the collar about people being mean to them.