Answer
The answer is the 20th century. P.A. Lundgren was a Swedish paleontologist and geologist born in 1882 and died in 1964. His major contributions to the field of paleontology and geology took place during the 20th century, primarily in the mid-to-late part of the century. Lundgren conducted extensive research and made significant discoveries in paleontology and geology, leaving a lasting impact on those fields.