Extinct species to include in the main tree

[hyanwong]

At the moment we hand-code a few extinct species into the tree, in particular the elephant bird & moa, and the dodo & solitaire. @davidebbo and I thought that a sensible (approximate) line to draw would be if the species was of an age that it is likely to have had contact with humans (often this means humans were responsible for extinction).

This would mean including some extra things such as Glyptodon. We should probably make a list somewhere. There's an incomplete list at

https://en.wikipedia.org/wiki/Category:Species_made_extinct_by_human_activities

Although many of the items there are subspecies rather than full species, so we would need to do some pruning.

NB: see also #41 (comment)