What is the difference between the STEM group and the koruna group?

The

STEM/Crown Group terminology was invented to classify the relationship of live and extinct organisms Willi Hennig, German taxonomy, father Cladistics, in the late 1940s. It was part of his "theory of phylogenetic systematics" that revolutionized the way biologists and paleontologists look at life.

The conditions are defined as follows. The group of the crown includes all the living species of the group and all the extinct offspring back to the common ancestor of all living species. The STEM Group includes all species that are not part of the koruna group. According to the definition, each member of the STEM group must be extinct. If they were not disappeared, they would be defined as part of the koruna group.

The STEM Group animals, such as animals represented by numerous early tetrapod, mammals and creeping fossils that have been dug, provide us with important information about evolution and how the animals have tried different strategies to adapt to their environment. Groups of tribeThey are non -deserted paraphyletic, which means they can be more complicated than containing only a certain species and all its offspring. The STEM Group may contain several early offshoots of the group, of which only one has evolved into the crown group.

STEM groups are quite common in paleontology. One example would be mammals of the STEM group or synapers-although mammals are also technically synapers, because they come from them-they were called "mammals similar to reptiles" until they were realized, but the STEM mammals were not at all. The earliest synappers were called "naked lizards" because they would resemble lizards, but without scales. As the synappers continued to evolve, they have gained more mammalism. Sometimes synappers are called "basal mammals" or "mammals of the STEM group".

Fish have several groups of tribal groups, including acanthodiánus, or barbed sharks and placoderma or armored fish. AcanthodIans, despite their name, are considered to be closely related to ancestors of bony fish, while placoderms, closely associated with ancestors of modern sharks, included the first vertebral supernder, Both groups lived during the paleozoic era, about 300-400 million years ago.