Blog #3: Systematics by Alanna Barnett, Aziz Bajouri, Melanie Nguyen, Morgan Howell, and Robert Barker

Blog #3 - Lab 5: Systematics by Alanna Barnett, Aziz Bajouri, Melanie Nguyen, Morgan Howell, and Robert Barker

In this lab, we were assigned to create a hypothetical phylogenetic tree based off anatomical features as shown in Figures 1 - 2, given a set of trilobite pictures. Trilobite pictures along with their scientific names and ID numbers are shown in Figures 3 - 17.

Figure 1. Trilobite Anatomy


Figure 2. Generalized Trilobite Structure


Figure 3. Callavia broggeri (#1)


Figure 4. Peronopsis interstricta (#3). After comparing this species with the list of features being studied, it was determined that this species only had segmentation and a glabella.


Figure 5. Flexicalymene meeki (#4)


Figure 6.Trimerus dekayi (#5)


Figure 7. Olenellus clarki (#6)


Figure 8. Paradoxides gracilis (#7)


Figure 9. Calymene celebra (#9)


Figure 10. Coronura aspecians (#10)


Figure 11. Albertella helena (#11)


Figure 12. Basiliella barrandei (#13)


Figure 13. Dalamnites verrucosus (#14)


Figure 14. Ogygopsis klotzi (#16)


Figure 15. Crepicephalus towensis (#17)


Figure 16. Trimerus delphinocephalus (#18)


Figure 17. Odontopleura callicera (#19)


Trilobite Species #
Segmentation
Glabella
Eye
Pointed Cephalon
Axial Ring
Genal Spine
Spiked Pleura
Spiked Pygidium
2 Elongated Spikes on Pygidium
Spots
Spiked Cephalon
1
x
x
x
-
x
x
x
x
-
-
-
3
x
x
-
-
-
-
-
-
-
-
-
4
x
x
x
-
x
-
-
-
-
-
-
5
x
x
x
x
-
-
-
-
-
-
6
x
x
x
-
x
x
x
x
-
-
-
7
x
x
x
-
x
x
x
x
-
-
-
9
x
x
-
-
x
x
x
-
-
-
-
10
x
x
x
-
x
x
x
x
-
-
-
11
x
x
x
-
x
x
x
x
x
x
-
13
x
x
x
-
x
x
x
-
-
-
14
x
x
x
-
x
x
x
x
-
x
-
16
x
x
x
-
x
x
x
-
-
-
-
17
x
x
x
-
x
x
x
x
x
-
-
18
x
x
x
x
-
-
-
-
-
-
-
19
x
x
x
-
x
x
x
x
-
x
x
Table 1. Trilobites and by their features. An “x” means that the trilobite species has the feature. A “-” means that the trilobite species does not have the feature.


Figure 18. Hypothesized Phylogenetic Tree for Trilobites Based off Features. Numbers at the top represent the Trilobite species number.


Figure 19. Hypothesized Phylogenetic Tree for Trilobites Based off Features by  Cammie Edwards, Thea Muljadi, Mark Malabuen, and Mackenzie Whittall


Conclusion:

By comparing the features of the trilobites shown in Figures 3-17 to the diagrams in Figures 1-2, we were able to identify which features were present in which trilobite. We then compared the features of each trilobite to each other to analyze which were more closely related. This data is shown in Table 1. From this data, we were able to produce a hypothesized phylogenetic tree that shows the possible relationships between the different trilobite species, as shown in Figure 18. We chose Peronopsis interstricta (#3), shown in Figure 4, as our outgroup because it  looked very different and had the least amount of similar traits compared to the rest of the trilobites among the set. A couple of basal or ancestral characteristics on our tree were the presence of segmentation and a glabella. This is the case, because all the trilobites above had those traits.  A derived trait on our tree was the presence of a spiked cephalon. This is the case, because this trait is unique to only the Odontopleura callicera (#19), whose most recent common ancestor with the other trilobites did not have this trait. Also according to our tree, the rear “spine” of Olenellus clarki (#6) in Figure 7 is considered homologous with that of Dalamnites verrucosus (#14) in Figure 13 since their most recent common ancestors both had this trait. Also, our tree does not show any traits that were lost and then evolved again independently. When comparing to the tree that Cammie, Thea, Mark, and Mackenzie did in Figure 19, there are quite a bit of differences. First, we used a cladogram while the other group used a conventional “forked” phylogenetic tree format. Second, we used a total of 11 different traits to help differentiate the trilobites from each other, while the other group used a total of 6-7 different traits. We determined “different” traits that are unique and not related to the other structurally. For example, we categorized “spiked pleura” and “rounded” pleura as one aspect of a trait since they are both traits that describe the pleura and the pleura can only be described as either one or the other. In our tree, we assumed that the original pleura was “rounded” and that the “spiked” feature evolved later. Hence why we did not mention “rounded” pleura. Anything below the marked trait is assumed to not have the trait, while everything above the marked trait is assumed to have that trait. We believe that overall, our tree is a more accurate representation of the trilobite phylogeny because it makes sure to have the least amount of traits “lost” and does not have any traits that appear before and are regained later. In the other group’s phylogenetic tree, there are some traits that they mention that appeared before but were not labelled, yet were labelled later. For example, the Basiliella barrandei (#13) in Figure 12 clearly has a genal spine, but the phylogenetic tree from the other group did not mention any sort of absence or presence of a genal spine before it, and actually mentions it later. This could have been remediated by ordering the traits so that the traits that had the larger number of trilobites with those traits were closer to the bottom of the tree, while the traits with a smaller amount of trilobites with those traits were closer to the end branches of the tree.

Comments

  1. My group's tree and your guys' tree are pretty similar! I think your guys' tree may be more accurate given that your similarity matrix encompasses more traits than ours, and we didn't pay as much attention to the characteristics of the eyes and other important developments as we probably should have. One difference is that we labeled species number 10 as the most evolved because we thought having more fragile looking spikes wouldn't be favorable. What about that trait did you guys find more favorable?

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  2. Hi guys,

    What a great post! It is really complete, all the photos of trilobite species allow us to understand your tree really well and you're one of the only group that posted the hypothesized tree. Concerning your tree, it is really clear and we came to the same conclusion for specie #19, both of our groups believe that #19 is the more evolved specie. However, I don't understand why you always paired species in your tree. For example, why does specie #13 is next to #4 while it has such huge genal spines?

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  3. your matrix is very well organized and reveals all the common traits to less common traits as they disappear which is where you get to see them develop into different species. i am curious as to what you identified as the spots that 11,14, and 19 had and how that effected your decision making in the phylogeny tree.

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  4. Hi all! It is a great post. It is very easy to follow. I like it when you guys include the structure, names, and numbers of the trilobites tree. Your matrix is also easy to look at and interpret. Great job!

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