Palaeontological Significance of Stem- and Crown Groups
Placing fossils in their right order in a stem group allows the order of these acquisitions to be established, and thus the ecological and functional setting of the evolution of the major features of the group in question. Stem groups thus offer a route to integrate unique palaeontological data into questions of the evolution of living organisms. Furthermore, they show that fossils that were considered to lie in their own separate group because they did not show all the diagnostic features of a living clade, can nevertheless be related to it by lying in its stem group. Such fossils have been of particular importance in considering the origins of the tetrapods, mammals, and animals.
The application of the stem group concept also radically reformed the interpretation of the organisms of the Burgess shale. Their classification in stem groups to extant phyla, rather than in phyla of their own, made the Cambrian explosion much easier to understand without invoking unusual evolutionary mechanisms.
Read more about this topic: Crown Group
Famous quotes containing the words significance, crown and/or groups:
“To grasp the full significance of life is the actor’s duty, to interpret it is his problem, and to express it his dedication.”
—Marlon Brando (b. 1924)
“There might you have beheld one joy crown another, so and in such manner that it seemed sorrow wept to take leave of them, for their joy waded in tears.”
—William Shakespeare (1564–1616)
“Only the groups which exclude us have magic.”
—Mason Cooley (b. 1927)