The common ancestor was *using tools *beyond the ability of chimps. I’m not sure exactly when making tools in the sense of chipping flint developed.
A bit bigger than that, I think. But within that order of magnitude in kilos.
The common ancestor would have be H. erectus (or some other name, but similar species, depending on the classification scheme you use). H. erectus arose about 1.8MYA. And you forgot the Denisovans, also a descendant. H. erectus made the famous hand axes. The oldest worked stone tools are about 2.5MYA. Chimps use stone tools, but they don’t modify the stones.
Well, the book Science Made Stupid explains that:
What I’ve never understood is why most large marine reptilians also went extinct in the KT event. Shouldn’t the same conditions that protected turtles and crocodilians have saved them too?
It is a puzzlement.
They may simply have been unable to adapt to the changed conditions. Turtles and crocodilians are built for survival.
Of that, I think we can be certain! 
To go a little further, turtles and crocodilians can live on the land and in the water, and everything in between. They also have adapted to both salt water and fresh water. They both lay eggs while at least some of the large marine reptiles did not. It could have been only eggs that survived. The disruption of the ecosystem probably cut the food supply severely for large marine predators unless some of them had adapted to deep water hunting in the manner of sperm whales.
Yeah, I realized what that sounded like. I just meant failed to adapt as opposed to got wiped out instantly by the event.
Actually, ichthyosaurs and pliosaurid plesiosaurs were already long extinct by then, having disappeared about 25 million years earlier for unknown reasons.
The remaining plesiosaurs and mosasaurs were large, active predators that probably fed on live prey and would have been more susceptible to disruption of the food chain than crocodiles, which can survive as scavengers. In the case of the mosasaurs, ammonites, their principle prey, became extinct during the event. Many shell-building marine animals were affected by the event, possibly due to problems in building their shells because of disruption of mineral balance in the oceans. The ammonites may have taken the mosasaurs with them.
Chronos:
Coming back to those questions for a minute, there isn’t really an easy answer. The hominin* tree looks bushier and bushier all the time, and at any give time there were probably several species wandering around all of whom might have been interbreeding, too.
Traditionally, though, we have defined the genus Homo as “stone tool making”, so when we first found modified stone tool, the assumed too maker was called H. habiilis. They made simple choppers that were thought to be used to crack open bones to get at the marrow. Brain size was slightly bigger than chimp size, but still pretty close.
But H. habilis has been a controversial species ever since it was described and some anthropologists would lump them in with one of the Australopithecines. To complicate things, modified stone tools have been found recently that seem to be associated with Australopithecine bones (2-3MYA), so maybe they were a stone tool maker, too.
Whether making those stone tools was a “big jump” or not is debatable. *H. erectus *(and the other associated species) really did comprise a “big jump” though, as the level of sophistication of the hand axes far exceeds that of the choppers. Just how many Erectus-like species there were is debatable, and you see all sorts of names floating around identifying local variants. But, for simplicity’s sake, it’s sometime easier to just talk about Erectus-like species. Erectus was also the first species to leave Africa (although that is somewhat in dispute), and there’s a famous fossil site dating to about 1.7MYA in [the former Soviet Republic of] Georgia. Erectus is also credited with taming fire, which is a really big jump. Brain sizes for these guys were ~ 1/2 - 2/3 of ours, and they first appear about 1.8MYA in the fossil record. The funny thing is, though, as smart as these guys were, their tool kit didn’t change much at all for over a million years, so that makes one wonder just how “smart” they were.
*Hominin is the term more commonly used there days to denote Us + our ancestor back to the time our line split from the chimp line.
Did they need to do anything differently during that million years requiring different tools? We use different tools to work on a steam engine that a PC, but did their behavior change from cutting up dead things to eat?
Fascinating. Thanks.
I have no expertise in this area, but this convo about limited success of intelligence reminded me of this: xkcd: Land Mammals. It’s humor of course, but given the author I think we can safely assume it’s well-researched and fact-based.
It seems the main beneficiary of human intelligence is … cows. They certainly outweigh us by a large margin. And given their relatively short lives as we manage them, they also certainly outnumber us over our lifetimes as well despite their 5-10x larger individual weight.
Bottom line: So we’ve finally figured out what intelligence is actually good for: having cows!!
The ones that didn’t do anything differently aren’t around anymore. So I guess you could say the didn’t “need” to do anything different as long as they were OK with going extinct sooner than those who did do things differently (us, and those who became us).
What species did what things differently during those millions of years?
You asked if H. erectus “needed” to change. The answer can only be seen in hindsight. Those populations of Erectus that didn’t change are no longer with us. Certain of those populations that did change became us.
Still surprising that with all the competition, an intelligent species of dinosaurs didnt develop in all those millions of years. We already know many dinos lived in large family groups or packs and probably worked together for protection and/or hunting. So if a species has opposable thumbs, a language, and works as a group why dont they develop? Look at the intelligent behaviors of many insects such as bees and ants.
Corvids and Parrots, all dinosaurs, are some of the most intelligent animals on the planet.