Below is the current reconstruction of the animal. In what part of an ecosystem do you think it might have been found? Why do you think one of the reconstructions below is more credible than the other?
Trilobites were among the most abundant animals at this time. Raup says they were successful for a long time, then went extinct because "they did something wrong." Let us look at them as successful animals for a time, then try to understand what one paleontologist thinks they did "wrong."
There are some animals in the Burgess Shale that bear minimal resemblance to living organisms. Wiwaxia may have been a mollusc-type of creature, because some specimens have been found with a muscular foot and a feeding apparatus called a radula (a long strap with rows of teeth). Sometimes it takes a while to reconstruct an organism because it is found in pieces or with different sides exposed to the collector.
Some animals look like those alive now. Here is a polychaete worm Canadia from the Burgess Shale. It looks much like members of this marine group of worms still living. This is a large an successful group found in the world oceans. Many polychetes today are only known from dredged specimens and we do not know their ecologies because we lack data from their undisturbed habitats.
Here is Olenoides, a remarkably well-preserved trilobite specimen with delicate parts like legs still attached. What do you think it did for a living? Do you think it lived near where it died or was it washed into the site? Would you expect it to be found in the same part of an ancient ecosystem as Hallucigenia?
The range of forms of trilobites reflects their success in becoming numerous in many habitats. Here is an example of a trilobite with bite? from a predator. We will meet the predator candidate later in this series...
In fact, the animal that may have been a major predator on trilobites was found in pieces at first. Its fragments were known by different names until fossils connecting the parts were discovered. Here is its mouth, originally thought to be a jellyfish, Peytoia.
After many years, the various parts of the animal were combined and reconstructed as Anomalocaris. It was an arthropod, vividly illustrated below. The disc-like mouth is seen from the edge. Note the large spiked arms. How might they have been used? What kinds of prey could this animal capture? Is it well adpted to catching soft-bodied prey?
