Trilobite Tree Lab 6: Trilobite Phylogeny Tree of Fifteen Species by Nancy Nguyen, Robert Barker, Francis Marfo, and Azar.

1. Post a Picture of your tree. On your tree, which species is the outgroup? Why did you choose this species? Explain.

The specimen chosen as the outgroup was specimen 3, because of it’s very neutral and broad features, such as, having a round body, no spikes or frills, and no eyes.  The lack of many distinct features leads us to believe that the other trilobites evolved from this one, by developing unique traits over time, to better suit their environment.

Figure 1. Phylogenetic tree was reconstructed by Robert, Nancy, Francis and Azar.

2. According to your tree, what is one basal or ancestral characteristic? One derived characteristic?

One ancestral characteristic, that is, a characteristic passed down through lineage over time, that both the older ancestors and newer ancestors express, would be the linear spinal feature.  All the specimens seem to have a vertical, spine-like, column running the length of their bodies.  The overwhelming presence of this trait would reinforce the idea that, this trait in particular, was passed down generation to generation, and remained a very prominent trait.

One derived trait, one that developed at some point in time, but is not shared throughout the ancestry of a specimen, would be the presence of head spikes.  Only one specimen, specimen 19, has this trait, and nowhere in its past ancestry, no matter how far back we looked, was this trait observed in another organism.  This lack of prominence shows as evidence that this trait developed very recently, and is unique to specimen 19.

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 is analogous to that of species 14. These species were different from the head, body and tail structures, especially the rear spine. Species 14 did not have pleural spike on its spine, while species 6 had very sharp pleural spikes on its spine.

4. Are there any traits that were lost but then evolved again independently? If so, what are they and where do they occur?

According to our tree, the dome structure first appeared on top of the heads of species 5, 9 and 4. The trait reappeared in species 10 and 14, after a hiatus which evolved round wide spiked head.

Figure 2. Phylogenetic tree was reconstructed by Shery, Na and Fatoumata.

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?

Our first task was to find an outgroup, that way we can focus on more definite  attributes of the rest of the population. While we focused on the head and spikes, the other group focused more on the shapes and spine. The better tree would be our group’s since it shows a higher level of parsimony. Parsimony means that we lumped more traits together with specimen. Shery, Na and Fatoumata’s tree has only two different trilobites attached to many attributes.

Resources Used:

Nguyen, N., Singhateh, F. & Said, S. (2017, January, 23). Trilobite Tree Lab 6: A Brief History of Trilobite Ancestry by Na Nguyen, Fatoumata Singhateh, & Shery Said [Blogger]. Retrieved from http://biol212-majorsanimalbiology-winter17.blogspot.com/2017/01/trilobite-tree-lab-6-brief-history-of.html

Shlichta, G., Hanson, C. & Mcfarland, J. (2017, Winter). Biol& 212 Major Animal Biology Laboratory Manual

Trilobite Tree Lab 6: Top Fifteen Trilobites Your Doctor DOESN’T Want You To Know About! (Beanboozld™) By Kaveena Ranaweera, Toqa Abosabaa, Leah Koung, Jennifer Chin

1. On our tree diagram, the outgroup is Peronopsis interstricta, the first species on the tree. We chose Peronopsis interstricta as our outgroup because this species had characteristics differing from other trilobites.

Figure 1. Phylogenetic tree, depicting the hypothetical evolutionary history of trilobites.

2. One ancestral characteristic of the trilobites is the pygidium, as the pygidium is found in every species on the tree. One derived characteristic is the pointed pygidium, seen in the trilobites from the fourth generation on.

3. The rear spine of species 6 is homologous to species 14 because both trilobites developed a rear spine, derived from a common ancestor.  
4. A trait that was lost but then evolved independently was the pointed pygidium. In the second generation, the Trimerus delphinocephalus developed a pointed pygidium, however, in the third generation, the pointed pygidium was lost, but then evolved again independently in the fourth generation.The Trilobites started out with a round pygidium but then it started to form a pointed pygidium after the Flexicalymene meeki. As time went on, the Basileilla barrandei formed a round pygidium in the fifth generation. Another trait that was lost was the pleuron. The pleuron was lost twice, once in the ninth generation and another in the tenth generation. The Paradoxides gracilis was the first to lose the pleuron in the ninth generation and then the Albertella helena lost the pleuron in the tenth generation.

Figure 2. Najib, Jung Soo, Tara, and Punyarith’s phylogenetic tree of Trilobites, showing a hypothetical evolutionary process.

The difference between our tree and Najib’s tree are the different characteristics used to reconstruct the phylogenetic tree of the Trilobites. We feel that our tree is better than Najib’s tree because it is simple, clean, organized, and has more synapomorphies.

Trilobite Tree Lab 6: A Brief History of Trilobite Ancestry by Na Nguyen, Fatoumata Singhateh, & Shery Said

Figure 1. Phylogenetic tree of a group of Trilobites based in morphological characteristics. From left to right the species are: [3] Peronopsis interstricta, [18] Trimerus delphirocephalus, [5] Trimerus dekayi, [4] Flexicalymene meeki, [9] Calymene celebra, [13] Basiliella barrandei, [16] Ogygopsis Klotzi, [1] Callavia broggeri, [7] Paradoxides gracilis, [6] Olenellus clarki, [19] Odontopleura callicera, [11] Albertella helena, [17] Crepicephalus towensis, [10] Coronura aspectans, and [14] Dalamnites verrucosus. The tree shows which Trilobite species share a common ancestor, and which traits started showing at which point in time.

1. On our tree, Peronopsis interstricts (3) is the outgroup species. We chose this species because it is missing many of the characteristics and traits that are apparent in most of the other Trilobite species in our group such as axial rings and pleural spines.

2. According to our tree, one ancestral trait that showed up in all the Trilobite species is that they had segmented bodies. On the other hand, one derived characteristic that showed up later in the phylogenetic tree is the long tail spikes, which only showed up in a few of the Trilobites..

3. According to our tree, the rear spine/tail that was apparent in species 6 was analogous to that of species 14. The spine showed up as a derived trait that developed separately for each of the two species and was not inherited by both from a common ancestor.  This is due to the fact that there were many other morphological traits that made the two species seem different, so we chose to not place them in the same monophyletic group.

4. Sharp pleural spines is an example of a trait that was lost, but then evolved again separately. Sharp pleural spines initially developed after the 4th node from the root of the tree, but then were lost after the 5th node from the root of the tree, and then evolved again separately for species Albertella helena

5. For comparison, we looked at the tree of the group of Kaveena, Jennifer, Leah, and Toqa. One of the major differences between our tree and theirs is that many of the species that we believed shared an immediate common ancestor they believed that they did not, and that they evolved separately. Upon reflection, it seems like their tree is better, since it follows parsimony more closely. Our tree has a more complicated pattern where almost every taxon has a sister taxa, while theirs is more simplistic and does not involve a lot of unnecessary branching.