The Descriptive, Engaging History of the Trilobite

Done by: Boys Who Cry (Tommy, Shane, Jonathan, and David)

Tommy putting the finishing touches on our cladogram.

Figure 1: The Picture of Trilobite Tree.

From the given tree that our group made (figure 1), it is concluded that [3] is the outgroup of the tree. There are multiple reasons for this, firstly being that the organism has the strangest anatomy out of every other species. Observing the body, it has 2 similar looking head and tails, which we can’t tell where it poops or eats. Unlike many other trilobites, this fella does not have any spines that resemble rings, and it has a rather “slim” thorax (though it may look more converged than slim) compared to other trilobites.

Looking at their characteristics, it can be seen perfectly well that [8] is the most basal species out of all. Unlike others, its axial lobe and ring does is not as obvious as many other trilobites. However, it does have some distinguishable characteristics that are shared with its descendants. Firstly, it has a noticeable head and tail like many other trilobites. Followed by the rings on its thorax down to tail, which is shared among many other trilobites (except for our beloved outgroup). Lastly, it follows the pattern of having a larger head, followed by a slightly smaller body. I suppose the most derived characteristic of all that are shared are the rings that it possesses from the thorax down to its tail.

From comparing [6] and [14]’s rear spine, we would say that they are homologous to each other. They may have looked different, but from our deduction, [14] and [6] came down from an earlier common ancestor, which means they are closely related to one another.  The spines seem to have almost equal in number, only [6] has one that is longer. Since they are closely related, it may support the idea that the spines are made of the same cartilages/components, only they have different functions.

Regarding the various trilobite traits, it appears that characteristics lost on the population never evolved again independently.  Traits that ever evolved in our tree were either lost completely or thrived among descendents.  A prime example of this can be seen in the observation of our trilobite spines.  At a certain point, most groups of trilobite organisms evolved with spines in some way without ever losing and evolving with them once more sometime in the future.  As a matter of fact, figure 1 shows that [1] evolved into organisms that either lost their spine like [10] or organisms that gave rise to those like [6] who have long, flourishing spines.  

Figure 2: The Picture of Trilobite From Other Group

Compared to other groups, our cladogram seems to have more branches and is thus more complex. As shown in figure 2, this group not only has fewer branches, but each Trilobite seen has fewer common ancestors, which means that their group has lesser changes. In general, when Biologists look at cladogram trees, they often use the logical principle of parsimony which postulates that the least amount of change is the most likely explanation or pattern for that evolutionary history. So the other group’s tree will most likely to be the correct evolutionary path for the Trilobite since it is the simplest explanation for how they changed over time.