Last Saturday’s 50th Anniversary episode of Doctor Who contained a hell of a lot of references to the earlier shows. I caught a few, but Buzzfeed have collated 35 of them here.
Update: Wired also published their own list, which adds plenty more things to look out for.
In the third chapter, the Codex describes a diverse category of bipedal (or in a few cases quadrapedal) creatures. Since the main identifying factor of these creatures is that, whilst mostly alien, the all have humanoid legs and feet from the knees down, I have decided to classify these as “peda” (things with feet) in order to mirror the “flora” and “fauna” sections.
The chapter begins with the usual introductory pages, showing a variety of creatures per page, but then goes on to discuss other creatures in more detail, showing what appears to be an example of their native habitat, with images of the animal in isolation, along with a page and a half of text (in the alien script) describing them.
The animals described in the Codex range from minuscule single celled organisms, to insects, fish, reptiles, birds and mammals, however that is about all the similarity there is with what we know from our planet.
For example, one page details a diverse collection of tiny single celled organisms that apparently make up a beam of light, perhaps a kind living photos. Other tiny organisms appear to dwell in coils of green organic rope, or within some form of solid rainbow. The book carefully lays out the different creatures in neat rows and columns, exactly as you’d expect to see Earthly creatures classified.
On a larger scale, however, many of the other animals are most un-Earthly, such as a group of similar looking creatures that appear to have mechanical parts. For example, one has wheels, another some kind of drill in its tail, and the third appears to have what looks like the end part of a key attached.