Instructions: In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.
Input: A crown group is a group of living species and their ancestors back to the most recent common ancestor .
Output:
In phylogenetics , the crown group or crown assemblage of a collection of species consists of the living representatives of the collection together with their ancestors back to their most recent common ancestor as well as all of that ancestor 's descendants .