Simplify the following text for a Grade 15 native English-speaking person.
Original: Cuvier was a major figure in natural sciences research in the early 19th century , and was instrumental in establishing the fields of comparative anatomy and paleontology through his work in comparing living animals with fossils .
Simplified: He was a very important figure in scientific circles in Paris during the early 19th century and helped establish the fields of comparative anatomy and paleontology by comparing living animals with fossils .