It doesn't leave time stamps with those paths and landmarks.
True. Sometimes we get lucky and we can do some C-14 or something. Once in a great while we get "really" lucky and find a few strands of DNA. Mostly though, by the time we find the bones the kids have trampled on them and the winos have peed on them and time has taken its course. The computers help. Before computers, reconstructing a skeleton took half a lifetime. Now it's only a year or two.
In any case, evolution is definitely not a linear process. There were at least 5 gigantic extinction events, and several times when the Earth's temperature climbed to 140 degrees. Most of the animals we see today (dogs, cats) are only about 50 million years old. There was an extinction event just before that, called Cretaceous, at about 65 million years. And, the interesting thing about that is what it did to the Hox genes.
The Hox genes give body parts their shape, and their position. We know a lot about them from frogs, which are about 250 million years or so. Which would be around the time of the previous extinction event, the Triassic, when the earth was pretty warm. The interesting thing about the Hox genes is they're all together in the genome, they're all right next to each other. So we "believe" they probably evolved all at once.
If we deliberately tweak the Hox gene that codes for the head region of a frog, we can make it grow arms where it's eyes are supposed to be. They're full arms, with webbed fingers and everything. So this one single gene is directing a bunch of other genes, it's a "commander" that tells the others where and when to express themselves.
And it "makes sense", that the regular head to toe pattern of Hox genes didn't arise instantly, there must have been variations of it. But any frog with no eyes and arms instead, would have a huge disadvantage and would probably have been eaten by dinosaurs or some such thing. Which might explain why we don't find any such fossils.
The thing is, the engineering is a lot more interesting than the history. There's a ton of research right now on "homeotic transformations" where one body part looks like another. It works for internal organs too, not just limbs. Like, Hox-3.3 mice have an extra pair of ribs in the lumbar area, Hox-4 mice have ribs on their 7th cervical vertebrae and so on. Here's an example of a double homeotic transformation:
Hox A11 is one of the expanded set of vertebrate homeo box (Hox) genes with similarities to the Drosophila homeotic gene, Abdominal-B (Abd-B). These Abd-B-type Hox genes have been shown to be expressed in the most caudal regions of the developing vertebrate embryo and in overlapping domains...
pubmed.ncbi.nlm.nih.gov
This is all "genetic engineering", not necessarily evolution. But it shows us how new body plans might have developed, from mutations in a single gene. Which is something we didn't know until recently. It seems that every extinction event led to the subsequent appearance of a bunch of new species, and we really have no idea how or why at this point. But at least we know which parts of the genome were new and related to the visible genetic differences.
lmao 
