TRILOBITE! By Hannah Zaini, Tien Pham, Karley Quibilan, Auryana Ashoori
1. On your tree, which species is the outgroup? Why did you choose this species? Explain.
Among all the trilobites, we determined the species Peronopsis interstricta, species 3, to be our outgroup. We chose this species because the species anatomy does not contain the majority of the traits that link the other trilobites together. The Peronopsis interstricta also does not contain the basic trait of eyes to place itself in a group with the other species.
2. According to your tree, what is one basal or ancestral characteristic? One derived characteristic?
According to our tree, one basal or ancestral characteristic is the axial rings. We know this trait is ancestral because it is found in both the outgroup and the descendants. One derived characteristic is the presence of spots because they formed further down the tree and only for some descendants of the ancestor in addition is not found in the outgroup.
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 tree, the rear spine of species 6 and species 14 are analogous because they evolve independently of one another. The traits are not homologous because species 6 and 14 does not share a common ancestor that has a rear spine. The trait is therefore analogous, or a convergent trait, since it evolved independently.
4. Are there any traits that were lost but then evolved again independently? ________If so, what are they and where do they occur?
The trait of spots occurs in species 14 and 10 and appears again in species 19 independently of one another. Our tree indicates this trait is analogous to one another and evolved independently because these three species do not share a common ancestor with the trait of spots.
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?
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?
This tree is from Josselin’s group in class AA. In our tree, we had species 6 and 11 with a very recent common ancestor, while Josselin’s tree had species 6 and 11 with a further common ancestor. Their tree had species 6 with a very close ancestor with species 7 while our species 7 broke off earlier in the lineage. Overall, our trees are pretty similar. I would say Jos’s tree would be better because they do not have any polyphyletic groups, while we do have two. Our tree shows a convergent trait of spots and a rear spine while they did not have any convergent trait.
This matrix table shows what our group first made into a table before we started making our trilobite phylogeny tree based on what differences stood out the most; the trilobite basics on what they have (1) and what they don't have (0).
Trilobite #
|
Genal Spike
|
Spikey Pleuron
|
Spots
|
4
|
0
|
0
|
0
|
19
|
1
|
1
|
1
|
18
|
0
|
0
|
0
|
6
|
1
|
1
|
0
|
10
|
1
|
1
|
1
|
1
|
1
|
1
|
0
|
17
|
1
|
1
|
0
|
7
|
1
|
1
|
0
|
11
|
1
|
1
|
0
|
13
|
1
|
0
|
0
|
14
|
1
|
1
|
1
|
16
|
1
|
1
|
0
|
9
|
1
|
1
|
0
|
5
|
0
|
0
|
0
|
3
|
0
|
0
|
0
|
Hey guys, I enjoyed reading your post. Overall our trees were similar to each other but one interesting difference was that on our tree we grouped together species 11 and 17 due to their similarities with the double tail. You guys put them separately assuming that this was convergent evolution and I wonder what traits made you decide that. Both species are very similar with one difference being the longer middle pleuron in 11, but I wonder did you find other differences that made you separate them.
ReplyDeleteI enjoyed reading your post. I noticed that you focused more on less traits than our group focused on. The two main traits you had were the pleura and and glabella. I found it a little hard to read the species names due to the lighting and how small they were. I would recommend turning off the light to take a picture next time.
ReplyDeleteNice tree guys. I liked the idea of using three main traits for your tree. I remember when I made a rough draft for my trilobite tree, I came across a lot of trouble when I had a large amount of traits. My first tree came out messy, so I really like the approach your group took when manufacturing this tree. Good work.
ReplyDeleteWow, the tree you guys made looks really different from ours. I also notice that eyes is also one matrix. The phenotypes you find are more than what we find. Our group only compared the most obvious characteristics of the trilobites. I think we should think more aspects.
ReplyDelete