In 1912, however, the Germab meteorologist Alfred Wegener examined the fit of the Atlantic coasts more carefully than had predecessors and grouped all the continents together into one great land mass, which he called Pangea.

특히 than 뒤에 왜 had가 붙엇는지 이해가 안되요
그리고 than had predecessors를 모라고 해석해야되나요?