Size meaning...? Mass? Height? Wingspan? Length? Laden or unladen? Also, many of these aren't one animal but orders, genus or groups of species with a lot of variety (e.g. how large is A Bear*?). Assuming you mean the largest example from each measuring snout-to-tailend, here's my probably out-of-date understanding.
Apatosaurus (22m)
Ichthyosaur (huge variety anywhere from 2-20m, most common species probably 4m - take your pick!)
Tyrannosaurus (12m)
Hadrosaur (largest is 15m, but most species around 10m - so I'm putting it here)
Stegosaurus (9.5m - but much lighter than the biggest triceratops)
Triceratops (9m)
Gallimimus (8m)
Pterodactyl (assuming we're using the common name that includes pterosaurs, 6m length and up 12m wingspan)
Ankylosaurus (6m)
Velociraptor (2m - but Utahraptor up to 7m)
*Prof Bear included.
