In the longer version of the show, some authorities like Neil Shubin and Peter Ward were giving short comments on what will survive, what the Earth will look like in the future, etc. I wonder if those scientists are involved in writing the script.
I agree, most future creatures in the show were quite hard to believe. And the writers seem to prefer cephalopods too much, and underestimating vertebrates. Of all major vertbrate groups, only fish remain at the end? What happened to tough crocodiles, versatile snakes (nowhere in the series), and fecund small mammals?