LAB 5 Trilobites Tree: How Did The Trilobites Evolve? Group Name: Dena ALMousawi - Amelia Giordano -Tu Tran - Hazel Arman

The tree should include species names or the numbers (on the fossil cards) at the tips and labeled synapomorphies along the branches.

1. Post a Picture of your tree.

  Figure 1. Trilobite morphologic phylogenetic tree. The phylogenetic tree was built based on the phenotypes of trilobite species, and includes the outgroup demonstrated as #3.

2. On your tree, which species is the outgroup? Why did you choose this species?  Explain.

The outgroup is Perconopsis interstricta, and is represented as #3. The Perconopsis interstricta has only two rings on its body and no eyes which makes it different from the rest of the considered trilobites.

3. According to your tree, what is one basal or ancestral characteristic? One derived characteristic?

On basal characteristic that we observed is the spine/eyes/axial rings and one derived characteristic is the pleuron/pygidial spine/.

4. According to your tree, is the rear ‘spine’ of species 6 homologous or analogous (homoplastic) to that of species 14? Explain.

What we determined is that the rear “spine” of the species 6 and 14 are homologous. The [6] and [14] have a close common ancestor so the considered trait cannot be an analogous- which is due to a random change.

5. Are there any traits that were lost but then evolved again independently? If so, what are they and where do they occur?

The pleural spine. As we make the phylogenetic tree, the trait of pleural spine has on the [6] species. However, this trait disappears until coming again on the [7] and behind it.

6. Describe one important difference between your tree and a tree estimated by a different lab group (identify which group’s tree you used). Upon reflection, which tree seems better?  Why?

The tree that we compared was from Octavia’s group. One important difference that we see between our tree and the tree of the other group is that Octavia’s group placed two species on one tip at the same time while we had one species on each tip. For the most part, our tree and the tree from Octavia’s group seemed similar however we prefer the organization of our tree because we separated the species each on its own tip, whereas they grouped some together.