Trilobite Tree Lab 6: By The BioBeads (Heidi and Lily)

Systemics Lab

For Lab 5 here is the phylogenic tree of trilobites that Lily and Heidi put together.

 Figure 1. Picture of trilobite tree

1. After reviewing all the species of trilobites we decided that Peronopsis Interstricta was the outgroup for this tree. We came up with this conclusion because this particular organism appeared extremely diverse compared to the other organisms throughout the tree.

2. A basal or ancestral characteristic for all trilobites is that they all have three segments (cephalon, thorax, pygidium) that makes up their physical bodies. A derived characteristic that we noticed was a longer geneal spine later in the tree.

3. When reviewing the rear spine of between species 6 and 14 we concluded from our tree that this trait is analogous. Both of the spines appear different between the two in that the spine of species 6 extends from the axil ring while the spine of species 14 extends from it's plate.

4. In our tree we did have a trait that was lost but then came back again later in evolution. This is seen with the axial ring which first appeared in specie 3, then disappeared in species 18 and 5, then was present again in every specie onwards in the tree.

Figure 2. Other Group's Tree

5. We did observe many differences between our tree and the tree of other lab groups. With our tree we had fewer branches then the tree available in front of the classroom (figure2).   The other tree had many more branches whereas our tree was a bit more linear.  This could be because we only took 4 different traits when building the phylogeny tree.  The 4 traits we looked at were the absent or present of: axial rings, genal spines, longer genal spines, and speckled.  I think ours is easier to look at, while the other group's tree looked more complicated and would need further investigation to pull out the information used to construct it.