system
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human
How do Palaeontologists build image of an organism from fossils? How accurate is their method?

I was recently saw a rabbit skeleton and could only imagine a monstrous creature but not a cute bunny. It got me thinking if dinosaurs were actually that intimidating.
gpt
Not a paleontologist but Comparative anatomy gives a lot of insight into fossils - e.g. Proportionally long legs (specifically lower legs) correspond to animals adapted for speed or sprinting. Robust bones are indicative of heavy set animals with lots of muscle of fat. Unusually dense bones can be indicative of aquatic animals.
  
 The texture of the bones themselves can reveal even more information - deeper scarring on muscle attachment sites means beefier muscles in that area; rugosities and landmarks on the bones can reveal places where keratin sheathes would anchor to or where blood vessels flow. Quill knobs are seen where feathers anchor on some dinosaurs.
 
Some fossils are preserved well enough to preserve scales, skin and feathers. A handful of fossils even preserve melanosomes which determines colour. Evolution also leaves lots of remnants of a species' ancestry behind - for example: pliosaur, crocodile and spinosaur teeth are extremely similar but theropod (the group of Dinosaurs spinosaurus belongs to) teeth are flat with serrated edges, so even though spinosaurus teeth are evolved convergently to other fish-eating animals, they have subtle remnants of traits only seen on theropod teeth, in this case being slightly less circular and having faint ridges where the serrated edge used to be. Teeth themselves are hugely informative of diet and environment too to the point that microscopic wear marks can tell you how a herbivore moves its mouth! In mammals, the patterns in teeth is even more unique (compare the pattern on an elephant molar to a cow to a human).
 
All these things offer different pieces of the puzzle. Phylogenetic bracketing takes all these clues, adaptions and identifying features and models the most likely relationships, this can then reveal where along the chain certain traits pop up (for example, feather-like filaments have been found across a range of distantly related dinosaur and even pterosaurs, indicating that all dinosaurs probably evolved from an animal with some level of proto-feathers). All of this can also be compared with chemical isotope analyses of fossils and the formations they are found in, to build up an even better picture.