animal > Ancient beasts times subclass
  Second subclass of ancient animal (pantotheria)
  The first real beast return-oriented sub-subclass among the currently includes two items: the tooth mesh (symmetrodonta) and the real ancient beast head (eupantotheria). Their sharp teeth arranged in a triangle three molars, upper and lower molars triangle vertices inside and outside the location of the opposite. Molar teeth of mammals of a simple triangle, and the real ancient beasts, after the molars in the development of a triangle with the seat, which is a big step forward. Usually that is the true purpose of ancient beast Cretaceous and Cenozoic marsupials and placental direct ancestor, the vast majority of known species produced in the Late Jurassic, only amphitherium (double beast) a is produced in the Middle Jurassic world. An example is to amphitherium features real purpose of the ancient beast.
  amphitherium blaiville (double beast) just under the jaw fossil material. Mandible slender, corner burst education (similar to that with the higher mammals). Number of teeth: four incisors, one canine, four front teeth animal, up to seven molars or 8. Asymmetrical lower molar with a three-point triangular seat and a seat with such crown surface structure can be compared with the post all kinds of mammals, but different from the original animal subclass. Thus presumably, the ancient beast is really true subclass of animal ancestors. amphitherium fossils found in Britain, the era of the late Middle Jurassic.
  With regard to the Tooth mammals (symmetrodont) arranged in three sharp molars relatively symmetrical triangle, the main point at the apex of the triangle, with no seat, can be seen on the teeth of ancient animals may be true purpose beast ancestors, then the Late Jurassic extinction .
Translated by Google