If pop culture is your only window into extinct animals, then you do not remotely understand how much we know.
We know the entire lifecycle of a tyrannosaurus. We know from the sheer amount of remains we have, from every stange.
We know roughly how they sounded (as the person above me said).
We know they had remarkable vision.
We know they had the second. strongest sense of smell in history.
We know from their bones that they grew to a certain size and stayed there until about 14 or so, then absolutely ballooned up to their adult size in about three or four years.
We know they likely lived in family groups, because we have bones with certainly fatal injuries for a solitary animal (broken legs and such) that are completely healed.
We know exactly how other dinosaurs look, down to colors and patterns, because bones are not the only information that is preserved.
The Sinosauropteryx is one such dinosaur. Because pigmentation molecules were preserved in the feather impressions, we know it's colors, and it's tail rings (which one would argue would be it's "iconic feature."
(Art credit Julio Lacerda)
Microraptor is another! We know from feather impressions that it had four wings. We know from pigmentation that it was an iredecent black, like a raven.
This is not limited to dinosaurs, or feathers. We've found pigmentation in scales and skin. We've completely reconstructed two extinct penguins, colors and all. We've figured out the colors of some non-avian and non-feathered dinosaurs. We can identify evidence of feathers existing on animals without feather impressions.
We have feathered dinosaurs preserved in amber.
We can defer likely behavioral patterns through adaptations we see in bones, and from the environments they were found in. We can see how certain movements evolved through musculature attachments (yes, how muscles attached is often preserved). We know avian flight likely evolved by "accident" by the way early raptorforms moved their arms to strike at their prey.
We also understand behavior in extant animals and can easily speculate likely behaviors in extinct animals. (A predator running for it's life is not going to exhibit hunting behaviors)
We learn and understand way more from "rocks" than paleontologists are given credit for. And if you watch a movie like Jurassic World, which has no interest in portraying anything with any sort of accuracy, and your take away is "We can't possibly know anything about these animals," then you don't understand science.
As for shrinkwrapped reconstructions, we understand how muscles attach, and how fat works. Artists who lean into shrinkwrapping are are not generally concerned with scientific accuracy, or biology. They're only concerned with Awesombro.
If true paleoartists tried to reconstruct a hippo, while they naturally would not get every bit correct, it would certainly look like a real animal, and not that alien monster that tumblr is so fond of using as "proof" that paleontologists don't know anything (an art piece that itself was extreme and satirical, and a condemnation of the particular subset of paleoartists I mentioned earlier)
Every time paleoblr tries to show you how extinct animals actually looked, all we get is a chorus of "thanks i hate it" and "stop ruining dinosaurs!"
