This lesson introduces phylogeny and explains how biologists organize animal diversity into evolutionary relationships. Understanding these relationships helps scientists interpret how animal groups share ancestors and how major features evolved.
Phylogeny is the branching history of evolutionary relationships among organisms. A phylogenetic tree is a scientific hypothesis about how species and groups are related through common ancestors. Its branches represent proposed patterns of divergence; the tree is not simply a ranking of organisms from “simple” to “advanced.”
All flashcards
What is phylogeny?
Phylogeny is the branching evolutionary history and pattern of relationships among organisms.
What does a phylogenetic tree show?
It presents a hypothesis about how organisms are related through evolution and common ancestors. Its branches can be revised when new evidence becomes available.
What are Eumetazoa?
Eumetazoa are animals with true, differentiated tissues. They include the major groups Radiata and Bilateria.
What distinguishes Ecdysozoa?
Ecdysozoa includes animals such as nematodes and arthropods that undergo ecdysis, the shedding of an outer cuticular layer.
What features give Lophotrochozoa its name?
Some members have a feeding structure called a lophophore, while others have a larval stage called a trochophore. The name refers to these features across the clade, not to a requirement that every member has both.
Quiz questions
What does a phylogenetic tree represent?Answer: A hypothesis about evolutionary relationships and common ancestry.
Which kinds of evidence can modern phylogenetic studies analyze?Answer: DNA, RNA, proteins, anatomy, and fossils.
How did molecular evidence revise the proposed relationship between arthropods and annelids?Answer: Arthropods were grouped with nematodes, while annelids were grouped with mollusks and other lophotrochozoans.
What placement did rRNA analyses support for brachiopods and bryozoans?Answer: Among protostomes, in the clade Lophotrochozoa.
What did a later reanalysis using more sophisticated methods support about animal relationships?Answer: That sponges diverged before the other major animal groups.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.