Lab #5: Systematics by Parker Lehman, Samuel Robinson, David Rowlett, and Janessa Wangadi

Figure 1. Trilobite phylogenetic tree constructed based on morphology traits from Table 1.  

The outgroup we chose for our tree was number 3, Peronopsis interstricta because it lacked almost all the traits we chose to look at, and had the most noticeable differences from all the other trilobites. According to our tree, one basal or ancestral characteristic we observed from the morphology was the 3-part structure of the cephalon, thorax, and pygidium that makes up the body. Even though number 3 was the least parsimonious to the tree, it still had the same 3 structure like the rest of the trilobites. One derived characteristic from the trilobites that we had were the spiked cephalon seen in trilobite number 19, Odontopleura callicera, as the most recent trait that was developed in our tree.

On our tree, the elongated rear spine was an analogous trait for 6, Olenellus clarki, and 14, Dalamnites verrucosus. 14 and 6 were not put together because 14 lacked the smooth cephalon surface, spiked pygidium, and separated cephalon. It also had a segmented pygidium. Due to all these differences in traits it seemed most logical, or parsimonious, to assume the elongated rear spines were developed separately and were analogous traits. As a group, we thought that most of the traits evolved as a trait passed down to at least 2 trilobites. The glabella on trilobite number 19 was one that we thought that evolved again after mutation was done. This is because we noticed the change on 19 throughout the traits we followed, but the glabella was different from the rest of trilobites we looked at. Another trait that was lost but evolved again independently was the smooth pleuron of trilobite 13, Basiliella barrandei, after the pointed pleurons was already developed after trilobite 4, as shown in Figure 1.

We used Alanna Barnett, Aziz Bajouri, Melanie Nguyen, Morgan Howell, and Robert Barker’s group to compare our trees. We found that both trees were relatively similar in the traits that were used to differentiate trilobites. One big difference between the two trees were trilobites 17 and 11, in which our tree thought the dual tail of the trilobite were a homologous trait while Alanna Barnett, Aziz Bajouri, Melanie Nguyen, Morgan Howell, and Robert Barker’s group thought that the trait was analogous. We think that our interpretation makes more sense since we thought that the pointy pygidium started before 17. Also, we did not use the texture of the trilobite body as a trait since we did not think it was a significant enough trait to use for our tree.

Trilobite Number	Names	Eyes	Genal Spine	Pointed Pleuron	Pointed Axis	Bumped Cephalon	Bumpy Head	Pointed Glabella	Axial Ring
1	Callavia bröggeri	1	1	1	1	1	1	1	1
3	Peronopsis interstricta	0	0	0	1	1	1	0	1
4	Flexicalymene meeki	1	0	0	0	0	1	0	1
5	Trimerus dekayi	1	0	0	0	0	1	0	0
6	Olenellus clarki	1	1	1	1	1	1	1	1
7	Paradoxides gracilis	1	1	1	0	1	1	0	1
9	Calymene celebra	1	0	1	1	0	1	0	1
10	Coronura aspectans	1	1	1	1	1	0	1	1
11	Albertella helena	1	1	1	1	1	1	0	1
13	Basiliella barrandei	1	1	0	0	1	1	0	1
14	Dalamnites verrucosus	1	1	1	1	0	0	0	1
16	Ogygopsis klotzi	1	1	1	1	1	1	0	1
17	Crepicephalus towensis	1	1	1	0	1	1	0	1
18	Trimerus delphinocephalus	1	0	0	1	0	1	0	0
19	Odontopleura callicera	1	1	1	1	1	0	0	1

Key: 0=Trait absent; 1= Trait Present

Table 1. Data Matrix for phylogenetic analysis of various trilobite species with Peronopsis interstricta as the outgroup.