“Trilobite Tree Lab 5” Reconstructing a Phylogenetic Tree for Trilobites Based on Their Morphological Traits.

“Trilobite Tree Lab 5”   Reconstructing a phylogenetic tree for Trilobites based on their morphological traits.

SAS – Serious About Science

( Rama Tadmori, Asmah Tadmori, and Kevin)

lab5-TrilobiteLab-AB

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

  Peronopsis interstricta is the out-group number 3. We chose this species because it has a distinctively different shape from all other groups of Trilobites. This species didn’t have any eyes and their axial lobe is significantly diminished compared to other species. The shape of their Genal area, glabella, and pleural lobe seem to deviate from all other groups of trilobites. Thereby, since this species share very few traits with other trilobites it can be concluded that this species does relate to the group of trilobites but aren’t part of it meaning it is the outgroup.

Figure1. The Phylogenetic Tree of Trilobites based on their Morphological Traits. 

2.   According to your tree, what is one basal or ancestral characteristic? The ancestral characteristics are Eyes and Genal spine, and the derived characteristic is the loss of Pygidium Spine and the loss of spots. 

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

Analogous trait because we can see that the rear spine trait only appeared in trilobites 6 and 14. Also, trilobites 6 and 14 didn’t share so many traits that we could assume they are close species or they belonged to the same branch. Additionally, if the rear spine trait was a homologous trait we would have seen the appearance of this trait in all the trilobites that share a common ancestor with trilobites 14 and 6. Thereby, it must be that the rear spine trait developed independently as a result of a mutation in trilobite’s numbers 14 and 6.

4.   Are there any traits that were lost but then evolved again independently?  

      If so, what are they and where do they occur?

We didn’t have a trait that was lost but evolved again. Nonetheless, we had a trait that first arose independently, then evolved again and at the end it was lost. It was the appearance of spots that first arose independently in 19. Then it started to evolve before 10 and 14. We see it in both 10 and 14. Eventually, it was lost right after 14.

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?

 After comparing our trilobites tree to Boys Who Cry (Tommy, Shane, Jonathan, and David) trilobite's tree, we found that their phylogenetic tree has a good organisation. However, we've noticed that the shared traits weren't mentioned in their phylogenetic tree diagram. We couldn't figure out what traits have evolved or arisen. Their tree seemed complex, indicating many changes happening. We would think ours is better because we tried to mention all the shared, derived, and basal traits. We chose this way of ordering because we believe that trilobites can evolve from simple to more complex structures and eventually evolve back to being simple since evolution doesn't have to be progressive or directed. We feel that our tree displayed a much simpler hypothesis for trilobites evolutionary history since our tree had fewer lineages within the branches than theirs.

The picture of trilobites tree of Boys Who Cry, Team.