The question can be broken into two parts 1) does size matter, and 2) if size matters then what was different about the Earth during the Mesozoic era that allowed the dinosaurs to grow so large?
In 1638, Galileo answered the first part of the question in his book Dialogues Concerning Two New Sciences. Contrary to Gulliver's Travels and countless Science Fiction movies showing animals the wrong size, Galileo made it very clear that size matters.
Galileo explained how size matters in his book Dialogues Concerning Two New Science a title similar to his book Dialogues Concerning Two Chief World Systems where he argued the evidence supporting the heliocentric model of the solar system. Thus he considered these two ideas to be of relatively equal importance.
While Galileo was successful in convincing the Church and the conservative science community that the world is not flat, the conservative science community has yet to embrace Galileo's Square-Cube Law even though it is clearly correct and fundamental to understanding every major science discipline.
Numerous elementary science educators would like to teach Galileo's Square-Cube Law, yet they do not like being embarrassed by their students asking them to explain the incongruity between Galileo's Square-Cube Law and the large dinosaurs and flying pterosaurs. Thus the problem of how dinosaurs grew so large is a scientific paradox that has been holding back science for literally hundreds of years.
Scientists have identified four specific problem areas regarding the large terrestrial Mesozoic animals: 1) insignificant bone strength, 2) insignificant muscle strength, 3) unacceptably high blood pressure existing in the tallest dinosaurs such as the Brachiosaurus, and 4) grossly insignificant power for cold-blooded reptiles to fly.
Yes, dinosaurs were vertebrates as they had an internal skeleton and a backbone to support their large bodies.
Not all dinosaurs had large feet. Some dinosaurs were small and didn't have big feet.
One clade of dinosaurs, the theropods, were carnivorous. Many of them were large and ate other dinosaurs. Today, birds are the only surviving group of dinosaurs. Some birds of prey eat other birds, so dinosaurs still eat other dinosaurs today.
Some dinosaurs, such as Allosaurus, were large meat eaters. Apatosaurus was large, so it had a lot of meat, and bringing down an animal that large would be a feast for carnivorous dinosaurs. Young Allosaurus, on the other hand, weren't huge but they were relatively vulnerable and thus made easy meals for carnivorous dinosaurs.
Ceratosaurus was a large meat eater, so it ate large herbivorous dinosaurs. They may have hunted dinosaurs such as Dryosaurus, Camptosaurus, Drinker, Othneila, and even Stegosaurus. They would have scavenged on dead sauropods, as well.
The smallest carnivorous dinosaurs, such as Compsagnathus, are insects and small vertebrates. Large carnivorous dinosaurs usually ate large and small herbivorous dinosaurs. Some, however, ate fish, including Spinosaurus and Baryonyx.
Stereotypically so, just as the Tyrannosaurus Rex is to dinosaurs. Not the largest but...not really the most anything.
tyrannosaurus Rex
The dinosaurs were killed by a very, very large rock called a woodwind.
Many people actually believe that A large flood killed all of the dinosaurs, A large earthquake caused the crater that engulfed the dinosaurs, or A large volcanic eruption resulted in global climate change., but no. it was actually that of A large asteroid strike resulted in a massive explosion that altered plant life. It created an explosion so big that it basicly wipes out the entire species of dinosours!
The closes living relatives to all dinosaurs large and small are birds.
There were no ocean dwelling dinosaurs. Large marine reptiles that are often thought of as dinosaurs include plesiosaurs, pliosaurs, mosasaurs, and icthyosaurs.