Life evolved in the ocean. Lungs came from gills, hands and feet from fins. The hard shelled egg was the great advance which allowed amphibians to leave the water behind for good. Although amphibians have only primitive lungs (and usually rely on skin diffusion), there have been massive ones eg the 9m long crocodile-like Prionosuchus!
Dinosaurs diverged from other reptiles eg crocodiles by virtue of a vertical leg and hip that could carry weight more efficiently, and therefore allow the animal to run faster.
Ichthyosaurs and Pleiosaurs went straight back into the water after evolving the adaptations to live on land! Only loosely related to the land dinosaurs. Still had to breathe air. Ichthyosaurs look like dolphins or sharks but were not related [convergent evolution – same solutions found by genetically different organisms]. Pleiosaurs swam by “flying” underwater with their paddles, like sea lions or turtles do now.
The expansion of species in Jurassic Period accompanies the splitting up of Pangaea into separate land masses with deep rift valleys and strings of islands appearing, allowing for diversification.
Warm or cold blooded? Big dinosaurs would have not been able to eat enough to survive if warm blooded. But perhaps so big that they retained heat for long periods – “homoeothermic”.
3 main groups of land dinosaurs – Theropods and Ornithopods and Sauropods. Theropods are hunters, long jaws, forward facing eyes, 2 or 3 fingers, probably bright colours. Sauropods are plant eaters, need bigger digestive systems so mostly 4 footed, long necks and tails. Ornithopods have 2 feet but 4 or 5 fingers, side facing eyes, beaked. Probably dull coloured. NOT the ancestors of birds!
There’s no such thing as a Brontosaurus! Turned out that it had already been described and given the name Apatosaurus. Not sure why it was still a popular kids’ dinosaur when I was growing up, nearly 100 years after they changed the name back. Diplodoccus looks similar but actually much lighter, although just as long, certainly the longest complete skeleton found. Brachiosaurus has a distinctive bump on top of the head. The issue of which was the largest dinosaur ever is controversial, because there are creatures described where the remains have now been lost, plus there are often only a couple of bones on which to estimate size by. Argentinosaurus and Paralititan were probably the heaviest dinosaurs ever, roughly 100 tonnes. Previous theories suggested these creatures were aquatic, and could reach high into trees, but anatomically it appears that it would have been difficult for them to extend their necks above 45 deg angle. There is also the issue of how blood managed to get pumped all the way from the heart to the (ridiculously tiny) brain – perhaps a second heart in the neck!?
The ornithopods were unarmoured, were mostly 2 footed and could efficiently chew, so they became v successful in the Cretaceous. Plant eaters with beaks.
The Spinosaurus is now accepted to have been a good 6m longer than T Rex. The function of the spectacular sail is unknown!
T-rex had ridiculously small arms, just 2 fingers, and too short to actually reach the mouth, but nonetheless they have significant areas for muscle attachment so must have served some purpose. Big debate still going on about whether a T-rex could actually run – there have never been any tracks found of a large predator running, and depending on the body weight, it might have needed thigh muscles making up half or more of total body mass! Would also have been at risk of breaking its legs. Certainly would have struggled to change direction. If it didn’t run, maximum speed was probably about 11mph, so possibly more of a scavenger.
Velociraptor had the spectacular 2nd toe claw, but, unusually for Jurassic Park, they are not accurately represented. They were smaller than humans, and covered in feathers! Presumably they derived from flying birds (they had hollow bones and a wish bone, just like modern birds), but the feathers may have had functions to do with brooding or running.