Constructing a Phylogenetic Tree for Selected Chordates
The diagrams above, show some of the common ways to draw phylogenetic trees. Diagrams A, B, C, and D each show the evolutionary history of the same animal group, but the orientations and layouts vary. The diagrams have a line at the base (or side) called the 'root' from which all other lines emerge, forming a 'tree' shape. The root depicts a common ancestor of all the organisms. From the root the lines branch, ending with organisms at the tips. Organisms that share more branches are more closely related.
Purpose: Each group will be given the name of a different animal in Phylum Chordata and some of its distinguishing characteristics. From these, the class will develop a comparative table of all the animals, and then use the information in the table to construct a phylogenetic tree.
Procedure: Your teacher wiII give you a piece of paper with the name of an animal on it. Use pages 905 - 909 in your text to identify which of the following characteristics your animal has. Check your results with the teacher, then fill in the corresponding column of the data table by putting an 'X' in the box if the animal has the characteristic.
Explanation of Characteristics: (These are in 'evolutionary order', in other words, characteristic #1 evolved before characteristic #2, and so on.)
Characteristic #1 / Dorsal Nerve Cord (running along the back or 'dorsal' body surface)Notochord (a flexible but supporting cartilage-like rod running along the dorsal surface)
Characteristic #2 / Paired Appendages (legs, arms, Wings, fins, flippers, antennae)
Characteristic # 3 / Vertebral Column (bony backbone replaces notochord)
Characteristic # 4 / Paired Legs
Characteristic #5 / Amnion (a membrane that holds the amniotic fluid surrounding the embryo; may or may not be inside an egg shell ).
Characteristic #6 / Mammary Glands (milk-secreting glands that nourish the young.
Characteristic #7 / Placenta (structure attached to inside of uterus of mother and joined to the embryo by the umbilical cord; provides nourishment and oxygen to the embryo).
Characteristic #8 / Canine teeth short (same length as other teeth)
Foramen Magnum Forward (spinal cord opening, located forward, under the skull
Construct a phylogenic Tree: Working in small groups, construct a phylogenetic tree to represent the evolutionary relationships between the selected chordates.