Evolution of the Early Triassic Ammonoids from the Eastern Boreal Realm

摘要

The mode and trends of evolution in the Early Triassic ammonoids of the eastern Boreal Realm are discussed. The ammonoid assemblages discussed include phylogenetically related immigrant and endemic species. The species is considered to be the main unit of evolution. Fourteen lineages are reconstructed. In most lineages studied, the suture was the main focus of evolutionary activity (main cluster of evolution), whereas anaboly (superimposition) was the major evolutionary mode. Five types of recapitulation are recognized.