The Top 5 Mistakes People Make About Prehistoric Animals

People often considered dinosaurs as slow lizards, but actually, they are more like flightless birds.

First, birds come from dinosaurs, specially the maniraptoran dinosaurs, like Troodon and Dromaeosaurus.
Second, there are high possibilities that dinosaurs were warm-blooded.

Third, footprints indicate most dinosaurs could run really fast.

This is impossible, as the most early ancestor of humans lived in the Pliocene, almost 60 Ma after the last non-avian(all dinosaurs, excluding birds and scansoriopterygidae) dinosaurs died.

Huge: Velociraptor was 2 meters long, it could reach absurde heights, so big, up to a person's knee!!
Flesh tearing: Argentinosaurus was a huge... sauropod! It ate plants. But heres a way to solve both problems with one dinosaur: Gasparinisaura, the dinosaur (no, not that unknown woman) in the picture (yeah, I know its blurry, blame my camera). It was a very small patagonian herbivore.

The sauropods could not pump blood to the brain if they were underwater. Probably they could wade, but not swim. They could go to water only if it was chest-deep, beyond that, they would probably die, lacking blood.

They are completely different things. The dinosaurs belong in the superorder Dinosauria and the pterosaurs on the order Pterosauria (both kinda obvious, right?), they are both archosaurs, they just belong in the same class. plesiosaurs, nothosaurs and pliosaurs are all sauropterygians, they aren't even archosaurs, but lepidosauromorphs instead. The three are Saurians, but that means almost nothing, because being a Saurian, you could be a lizard, a tuatara, a snake, a bird, a crocodile, a dinosaur, an amphisbaenid, a rauisuchian, a placodont, well basically, you could be any reptile, except for anapsids, icthyosaurs and some extinct lizards.