Trilobite By Shuaiqian (Helen) Men, Deborah Haney, Na Nguyen, Julia Smith
BIOL& 212 Systematics Lab – Trilobite tree questions
By Shuaiqian (Helen) Men, Deborah Haney, Na Nguyen, Julia Smith
This sheet and your group’s tree (which will be photographed in lab) will be graded.
You should have a labeled drawing of your tree in your lab notebook. The tree should include species numbers (the numbers on the fossil cards) at the tips and labeled synapomorphies along the branches.
1. Post a Picture of your tree.
1- Callavia broggeri 11- Alberiella helena
3- Peronopsis interstricta 13- Basilllela barrandei
4- Flesicalymene meeki 14- Dalamnites verrucosus
5- Trimerus dekayi 16- Ogygopsis klotzi
6- Olenellus Clarki 17- Crepicephalus iowensis
7- Paradoxides gracillis 18- Trimerus delphinocepcius
9- Calymere celebra 19- Odontopteura callicera
10- Coronusa aspectanus
Figure 1: The phylogenetic tree of Trilobites based in morphological characteristics
Specie Number
|
2 Spikes on Pygidium
|
Spikey Thorax
|
Spots
(convergent trait)
|
Longer, pointier Body
|
Round Pygidium
|
Segmented Bodies
|
1
|
0
|
0
|
0
|
1
|
1
|
1
|
3
|
0
|
0
|
0
|
0
|
0
|
1
|
4
|
0
|
0
|
0
|
1
|
1
|
1
|
5
|
0
|
0
|
0
|
1
|
1
|
1
|
6
|
0
|
1
|
0
|
0
|
0
|
1
|
7
|
0
|
1
|
0
|
0
|
0
|
1
|
9
|
0
|
0
|
0
|
1
|
1
|
1
|
10
|
0
|
0
|
1
|
0
|
0
|
1
|
11
|
1
|
1
|
0
|
0
|
0
|
1
|
13
|
0
|
0
|
0
|
0
|
1
|
1
|
14
|
0
|
0
|
1
|
0
|
0
|
1
|
16
|
0
|
0
|
0
|
1
|
1
|
1
|
17
|
1
|
1
|
0
|
0
|
0
|
1
|
18
|
0
|
1
|
1
|
0
|
0
|
1
|
19
|
0
|
1
|
1
|
0
|
0
|
1
|
Table 1: The metric table on the characteristic that each individual has
On your tree, which species is the outgroup?
The outgroup species is number 3, Peronopsis interstricta.
Why did you choose this species? Explain.
Because the species has the least characteristics in common compared to others, or the least ancestral trait such as spikey, or round edge butt for example.
2. According to your tree, what is one basal or ancestral characteristic?
According to our tree, one basal or ancestral characteristic is that they had segmented bodies.
One derived characteristic?
According to our tree, one derived spikes on the pygidium.
3. According to your tree, is the rear ‘spine’ of species 6 homologous or analogous (homoplastic) to that of species 14? Explain.
Analogous (homoplastic)
Species Number
|
2 Spikes on Pygidium
|
Spikey Thorax
|
Spots
(convergent trait)
|
Longer, pointier Body
|
Round Pygidium
|
Segmented Bodies
|
6
|
0
|
1
|
0
|
0
|
0
|
1
|
14
|
0
|
0
|
1
|
0
|
0
|
1
|
First of all, homologous means that species who share a common ancestor are morphological resemblance. Analogous (homoplastic) are that who have similar appearance but are not evolved together; in other words, they don’t have a common ancestor.
According to the matrix and the figure 1, it’s obvious that they do have appearance similarity. However, they are on different branch of the tree and are far away from each other. It’s not possible to determine that they share a common ancestor. Because number 14 also has spots, and spots are a convergent characteristic, we did not group number 6 and number 14 together. Therefore, we’d like to say that specie #6 and specie #14 are analogous (homoplastic).
4. Are there any traits that were lost but then evolved again independently?
Yes, there are.
If so, what are they and where do they occur?
Derived trait might be spikes on the pygidium since it's a modified form of the spikes on the thorax.
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?
Figure 1. Jos’ Group’s Trilobite Phylogeny
While both the outgroup and more advanced species (species number 3 and 10) are the same, we kept our trilobites with spikes (or stingers) further separated from species number 10. By structuring our tree the way we did, we were able to avoid having to mark 4 different trait changes along the branch that gives species number 10. However, Jos and his group organized more logical subgroups than what we have in our tree. In sum, we think the “flow” of our tree from more pointy bodies to more rounded ones makes more sense, but Jos’ subgroups seem to work better than ours. For this reason, and also because Jos’ tree is easier to read and interpret than ours, we believe Jos’ tree is a better representation of Trilobite phylogeny than ours.
Haha oh my god! I find it so funny how you guys named your trilobites, I looked at each name and they were perfect. On both of our groups, we grouped together 10 and 14 as well, which I noticed another group did too, they looked exactly similar, while 14 looked a little more developed than 10 because of the spiked tail and more complex look (our reasoning), was that your groups reasoning too? & it's interesting how you even made some of the trilobites show up as common ancestors on the group and then branched off from there too- it made it easier to examine. Overall I think both of our groups had the same tree and idea of what trilobites formed from which other trilobite.
ReplyDeleteGreat post! I had a good laugh from the names of your trilobites. I find it very interesting that you guys chose to put the trilobites that have the extended spines, such as spike, earlier in the tree instead of at the end like most groups did. The way you guys explained it also makes sense for it to be both ways. My group also thinks that the pygidial spines of trilobites number 6 and 14 were analogous since there are many traits that differentiate them from being in the same branch. Thanks for sharing!
ReplyDeleteGood post. I found the greening number a little hard to read, but it was marginalized when listing the individual species along with the name underneath the table. YAY! I also loved how you actually took a part of the tree and reconstructed it for question three. Also I noticed that you used less traits than our group did. My group focused more on the body in that we used more traits to define it.
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