Re: Has earth's gravitational pull been constant over millions of years?

Earth's gravity hasn't changed much since life arose on it. The only thing that would make its gravity change would be if its mass increased a fair bit, and there's no evidence that that has happened. Although meteors keep running into our planet, they don't add enough to its enormous mass to make a difference.

Pretty much every biological group has a heyday in which they get really large. If you look at the distant ancestors of squids and octopi, you'll see that they were huge. Of course, any group that spends its life in water doesn't have to deal with gravity much, and so they can grow to great size, but the same goes with the terrestrial ancestors of insects, ferns, and lots of other groups. Mammals have had their growth spurt, after the dinosaurs died out. The reasons for this aren't known.

We still don't know very much about dinosaurs. Our ideas about their physiology and behaviour have changed quite a lot in the past decade or so. Their bones do seem to have been strong enough to support them.