Trilobite Estimated Phylogeny Tree -- A Tale of Two Spines (Lab 6)

Trilobite Estimated Phylogeny Tree -- A Tale of Two Spines (Lab 6)

By: Angry Snow People (Ameena Romani, Horea Oprean, Jonathan Hong, Lien Huynh-Phan)

Figure 1. An estimated phylogenetic tree showing our interpretation of Trilobite evolution in generations through time.

1. We chose Pernopsis interstricta as the outgroup because it’s morphology vastly differs from the rest trilobites, with no clear head, tail, or spines.

2. The basal characteristics are the spine, eyes, and axial rings which were generally present in each generation of Trilobites. The genal spine and tails are the derived traits, appearing first in Ogygopsis klotzi.

3. The rear spines of species 6 and species 14 are analogous to each other because they both evolved from a most recent common ancestor which did not have spines, and the appearance of a tail spine was lost in the trilobites that evolved from ancestors in between the two spined species.

4. The appearance of tail spines first appeared in 14 (Dalamites verrucosus), was lost in 7 (Paradoxides gracilis) and reappeared in 6 (Olenelus clarki), although in a different form. The tail spines of D. verrucosus seem to have evolved out of an outcropping on the posterior of the trilobite, separate from the spine of the animal, whereas the spines of the later species such as O. clarki appear directly as extensions of the central column of the back.

5.

Figure 3. Lily and Heidi’s interpretation of the Trilobite phylogenetic tree throughout generations indicating the evolution.

This group used a different structure of a tree that showed the evolution throughout time. Another distinct feature in their tree is the indication of traits appearing in different generation. However we believe our tree (Figure 1.) is easier to interpret as the structure is easier to follow in a linear manner and is simpler to look at because it is easier to locate certain generations.