We are able to learn all of the following from fossils except

how living things change over time
bone structure of an organism
the type of hair animals had
the type of teeth an animal had

You can't learn the type of hair creatures had in fossils as hair is very hard to fossilize because what makes things fossilize is after it gets old enough a layer of hard rock will eventually turn into a fossilized object. anything can fossilize as long as it is physically strong enough to withstand 1,000 years of age.

Pro insulin undergoes extensive posttranslational modification along the production pathway .