Top Highlights

• The history of animals has the shape of a tree. A single “root” gives rise to a series of branchings as we follow the process forward in time. One species splits into two, and each of those species splits again (if it does not die out first). If a species splits, and both sides survive and split repeatedly, the result may be the evolution of two or...
• Here is a diagram of this part of the tree of life. Lots of groups are omitted from the picture, both outside and inside the branches shown. The moment we’re talking about is labeled “the fork.” On each path downstream of the fork, more branchings occurred. One side eventually sees fish appear, then dinosaurs and mammals. This is our side. On the o...