Ncert Exercises & Solutions

Q.19 What were the characteristics of life forms that had been fossilised?

The organisms with hard parts are likely ot be fosssilsed, than those who don not have such parts. The harder the material, better it would be presereved soft parts fossils occur rarely, e.g., birds and pterosaurs have very light bones, hollowed out and specialised for flight.

So, they have sparser tossile record as compared to mammals, whose bones are partially mineralised during life.