Complex sentence: The sons worked as assistants for their father, but later ascended to renowned paleo in 1908, Sternberg planned an expedition to the Lance Creek area in eastern Wyoming, where the family had not worked before.
Split into simpler sentences: The sons worked as assistants for their father, but later ascended to renowned paleontologists. Early in 1908, Sternberg planned an expedition to the Lance Creek area in eastern Wyoming, where the family had not worked before.