Ghazal Trilobites blog

Trilobite Tree Lab-AB: Reconstruction of Phylogenetic Tree of Trilobites Based on Morphological Traits. (Ghazal Salehi)

Figure 1. The Phylogenetic Tree of Trilobites based on their Morphological Traits.

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

Peronopsis interstricta (3) is the outgroup. This species is vastly different compared to all the other trilobites. This is only species with cephalic shield with the deep parabolic outline, along with thorax with different segments.

2.According to your tree, what is one basal or ancestral characteristics?

The ancestral trait has the anterior sutures that curve adaxially. Long and clear axial lobe, eyes have developed and its clearly visible on both sides of cephalon. Pygidium and thorax parts of Trimerus delphirocephalus (18), and Trimerus dekayi has clear but simple segments.   

3. According to your tree, is the rear “spine”of species 6 homologous or analogous (homoplastic) to that of species 14?

According to the tree, Olenellus clarki is homologously related to Dalamnites verrucous(14). Dalamnites verrucous pygidium has developed a pagetia(spike), and Olenellus clarki species have developed even more advanced spikes on thorax area. These two species have a common ancestor. Species 6 and 14  are sister taxa groups to one another on the tree because both have the same branch meeting at the same node.

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

I didn’t have any trait that was lost but then evolved again independently.

5. Describe one important differences between your tree and a tree estimated by a different group. Upon reflection, which tree seems better? Why?

I compared my tree to “Chiton Crew”, even though there are obvious differences between our trees I think if I draw my tree in a similar fashion as Chiton Crew our trees are not that far different from one another. This group also added a Data Matrix which makes it much easier to see the similarities and differences.

I like Chiton Crew tree much better because it’s constructed on a white board and therefore very clear to see.

Figure 2. Details added to The Phylogenetic Tree of Trilobites based on their Morphological Traits.