Systematics: Trilobites Tree by Cammie, Thea, Mark, Mackenzie
Lab #5 Systematics: Trilobites Phylogenetic Tree
Cammie Edwards, Thea Muljadi, Mark Malabuen, Mackenzie Whittall
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| Figure 1. Trilobites phylogenetic tree produced by our group according to the
data we obtained in lab by observing specific traits and whether or not they
were present in the species. The oldest ancestors occupy the left of the tree as
time moves from left to right.
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Table 1. The traits we observed of the trilobite species to find similarities/differences in structure and appearance in order to determine their place on our phylogenetic tree are in the leftmost column. The species numbers are across the top row. A "1" represents the presence of the trait, while "0" represents that trait being absent.
Traits
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1
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3
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4
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5
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6
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7
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9
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10
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11
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13
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14
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16
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17
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18
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19
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Glabella
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1
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1
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1
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1
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1
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1
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1
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1
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1
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1
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1
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1
|
1
|
1
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1
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Pleuron
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1
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0
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1
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1
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1
|
1
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1
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1
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1
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1
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1
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1
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1
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1
|
1
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Occipital ring
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1
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0
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1
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0
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1
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1
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1
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1
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1
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0
|
1
|
1
|
1
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0
|
1
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Spiky pleura
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1
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0
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0
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0
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1
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1
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1
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1
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1
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0
|
1
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1
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1
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0
|
1
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Genal spine
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1
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0
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0
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0
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1
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1
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0
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0
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1
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1
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1
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1
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1
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0
|
1
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Pointy pygidium
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1
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0
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0
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0
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1
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1
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0
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0
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1
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0
|
1
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0
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0
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1
|
1
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Elongated pleura
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1
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0
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0
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0
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1
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1
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0
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0
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1
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0
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0
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0
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0
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0
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1
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Texture (bumps)
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0
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0
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0
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0
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0
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0
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0
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1
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0
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0
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1
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0
|
0
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0
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1
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According to Figure 1, a basal (ancestral) trait would be the presence of an occipital ring. The occipital ring is located just between the trilobite spine and glabella and it seems to function as a connector between them. A derived trait would be the presence of pleura. As mentioned earlier, the only species that did not have the presence of pleura is our outgroup, species #3, but the pleura present in all other species evolved slightly different over time.
In Figure 1, the rear spine of species #6, Olenellus clarki, is analogous to that of species #14, Dalamnites verrucosus, because their most recent common ancestor did not have a rear spine, but a pointy pygidium instead. Rear spines evolved independently, not due to common ancestry, so it is a convergent trait.
According to Figure 1, the texture of the exoskeleton in species #19, Odontopleura callicera, was not present in any of the ancestors until this specific species. The trait appeared on species #10 and #14 though, Coronura aspectans and Dalamnites verrucosus, proving that this trait of a textured exoskeleton evolved independently.
After comparing our tree to the tree produced by Alanna Barnett, Aziz Bajouri, Melanie Nguyen, Morgan Howell, and Robert Baker, we noticed that a huge difference was the amount of traits we used when observing and classifying the trilobites. One that stood out was that they chose to look at eyes, whereas our group did not use this trait as some species had less defined eyes that could have also been argued as facial structure. We also set up our trees different visually, which each had their own pros and cons. Our group made our tree spanning from left to right, while the other group made theirs from the bottom to the top using a triangular shape. The triangular tree produced by their group is easier to read and follow, especially with multiple traits, as well as more visually pleasing. Legibility is key when reading a phylogenetic tree with lots of traits and species and makes it easier to check for accuracy.
According to Figure 1, the texture of the exoskeleton in species #19, Odontopleura callicera, was not present in any of the ancestors until this specific species. The trait appeared on species #10 and #14 though, Coronura aspectans and Dalamnites verrucosus, proving that this trait of a textured exoskeleton evolved independently.
After comparing our tree to the tree produced by Alanna Barnett, Aziz Bajouri, Melanie Nguyen, Morgan Howell, and Robert Baker, we noticed that a huge difference was the amount of traits we used when observing and classifying the trilobites. One that stood out was that they chose to look at eyes, whereas our group did not use this trait as some species had less defined eyes that could have also been argued as facial structure. We also set up our trees different visually, which each had their own pros and cons. Our group made our tree spanning from left to right, while the other group made theirs from the bottom to the top using a triangular shape. The triangular tree produced by their group is easier to read and follow, especially with multiple traits, as well as more visually pleasing. Legibility is key when reading a phylogenetic tree with lots of traits and species and makes it easier to check for accuracy.
In class, we learned that the characteristics you use to create a phylogeny determine your result and picking evolutionarily significant traits is key to creating a tree that accurately reflects evolutionary history. In your post, you discussed how you used the presence of an occipital lobe as a significant derived trait. That's easy to agree with; precise vision is often important to any organisms' survival. I'm curious, though, if you thought about whether or not that could be a convergent trait. Did you notice any slight nuances in occipital rings that might indicate a paraphyletic group or convergent evolution?
ReplyDeleteHi everyone!
ReplyDeleteAfter looking through several trilobite posts, I observed that several groups placed the same trilobites at the beginning of their phylogenetic trees, and placed the same trilobites near the ends of their phylogenetic trees. For example, both of our groups decided that Peronopsis interstricta was the outgroup, and that the next two trilobites that Trimerus delphinocephalus and Trimerus dekayi also appeared early in the phylogenetic tree. I found it interesting that both these species have the same genus name! Additionally, both of our groups decided that Odontopleura callicera was the trilobite that emerged from the most recent common ancestor. Even though our phylogenetic trees were similar at the beginning and end, the pathway each of our groups took to get there differed greatly.
Hey,
ReplyDeleteLooking at your groups picture of the phylogenic tree, it is pretty similar to ours. We both had the same outgroup, which I believe everyone got. I like how u labeled the similarities the trilobites shared because it shows us what you were thinking and how you arranged this tree. Nice job!
We used a similar matrix as you did, including the use of 0's and 1's. This matrix was used initially to group them into the different clades and then we distinguished the tails at the end. Some tails were like your characteristic "pointy pygidium" and others were an extension of the axial lobe. Nicely done, we used your tree in our comparison.
ReplyDeleteHi guys,
ReplyDeleteThe way we sorted the traits is pretty similar except for you have more categories than ours. Yet, ours kinda split the characters into two major groups since the beginning, and yours is going from level to level. Another huge difference I noticed is that the structures of the trilobite became more and more complex according to your group, but ours is totally opposite. This is very interesting!
I haven't seen any post so far that start their tree other than the one that you guys have. This kind of ties to the question in the prelab where it asks if species evolve to more complex species. According to your and most of the post it seems to be true. We also don't have much information about their environment, so we cant really assume that they developed something and then it went away. Great post.
ReplyDeleteHey! So one major thing that I noticed in your group's tree was that most of the "splits" are in sister taxa, was that on pupose as a way of showing that the two species could have shared a common ancestor? Very interesting tree and great post overall!
ReplyDeleteHi all ! I like your tree because it is very easy to look at and interpret. It also has the characteristics of the trilobites on the tree. Your tree is somewhat similar to our tree. In you matrix, traits like spines, glabella, pleuron are also on our matrix. I notice that, in your tree, the trilobites are more complex going down the tree. For our group, we have the opposite approach for our tree.
ReplyDelete