Trilobite Phylogeny Tree!

Date: 1/23/2018

BIOL212  |  Majors Animal Biology  |  Winter 2018

Systematics Lab

By : Hannah Fairchild, Tien Van, Zoe Du, Ayodhaya Kitsondhi

1. A Picture of our tree.

Figure 1: A picture of phylogeny tree for the Trilobite .

Figure 2: An image of our matrix table. It was used to determine phylogeny tree for the Trilobite.

-On our tree, figure 1, number 3 is the outgroup .#3 was an obvious outgroup to us because its physical
appearance and features were so different from the other trilobites, and barely resemble any
common ancestry when just looking at features. Moreover, as shown in figure 2 trilobite #3 didn’t  
have any characteristics that other trilobites in the tree have like eyes, square glabella, pleuron , lobe,
and spines.

2.  According to our tree (figure 1) and figure 2,  one ancestral characteristic was having a square glabella. It is the only trait that existed in trilobites #5 and #18 which it were the ancestral trilobites according to our tree. One derived characteristic would be having a circular glabella like the case of trilobite #4.

3.  According to your tree, is the rear ‘spine’ of species 6 homologous or

analogous (homoplastic) to that of species 14?  Explain.

    According to our phylogeny tree of Trilobite, the rear spine of species 6 is homoplasy to that of species 14 because they are not closely related to each other but they do share a common ancestor, which is species 19 (Figure 1.) Although both species 14 and 6 does share similar traits, species 14 may have gone through independent evolution (convergent) due to adaptation to the environment and their lifestyles in that population. Both species sharing a common ancestor does not influence their convergent traits but rather the environment they were in and having to adapt to that specific surroundings.

4.  Are there any traits that were lost but then evolved again independently?

    As our tree and data shown above, we can’t see very obvious traits that were once lost but then evolved again independently. According to the tree, we separated the Trilobites into two major groups -- one with the obvious spikes, which gradually degenerated eventually; the other one we named it the “Square Glabella” group since their glabella developed into the square shape which is noticeably different from the “Spike” group. Both of the groups transmit from complex structures to simpler structures; however, we did notice that pleuron was not present in ancestor but developed in later descendant, and then it came back again at the end (according to our Figure two where 0 means no such trait can be observed, and 0.5-1 means this trait was shown slightly or strongly).

5.  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?

One important difference between our tree and the one from From group of Tiger, Joss, Travis would be the way they set up their phylogeny tree. They used the traits/characteristics that they have chosen to make the matrix with then used it as “common ancestor” to all the provided species. On the other hand, with our tree we used chosen traits to determine how closely related each of these species are, then we looked at which given species would be descendend from another species. Upon reflection, there are flaws on both our tree and the other groups, but our tree might be a little bit better because we believe that some of these species are descending from another species given.