Name any name and then remember everybody you ever knew who bore that name. Are they all alike? I think so. –Gertrude Stein
When unrelated or only distantly related organisms evolve a similar form as an adaptation to a common way of life, you have convergence. And convergence is one of the great patterns in the history of life–and one of the clearest lines of evidence that evolution by means of natural selection is real.
Distinguishing features that are identical by descent (blood relationship) from those that are convergent is the central challenge in reconstructing the evolutionary histories of living things.
Evidence of convergence is to be seen throughout the Trilobita. An easy place to recognize it is among the filter feeders. All the trilobites in this post were likely filter feeders, their large cephalons used as filtration chambers. Aristoharpes and Broggerolithus are not closely-related to each other, and Cordania is only distantly related to the others (they all belong to the Ptychopariida). Their superficial resemblance is likely due to a common way of life.
How many instances of convergence can you recognize in your collection?
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