Trilobites were unique beetle-like arthropods.   Comprising more than 2,500 species, they may be closely related to living crustaceans, spiders, and horseshoe crabs.  The populated the earth's oceans for more than three hundred million years until their disappearance at the cataclysmic extinction that brought an end to the Paleozoic era.  As fossils the multiple variety of trilobites are intriguing, even absorbing.  Their seeing eyed stare out at us; their blind snoop and challenge our imaginations.   I write as an amateur who has been thoroughly entranced.

    The many families of this subphylum are a witness to the dynamic interaction between evolution, punctuation, and extinction.   My own collecting experience has encountered asaphids and onellids from the Ordovician, homalonotids and dalmanitids from the Silurian, phacopids and aulacopleurids from the Devonian, proetids from the Mississipian, and phillipsiids from the Pennsylvanian.  I have found them on numerous outcroppings in four states and three South American countries.

    All in all, however, the most intriguing for me have been the calmoniids.  This family is unique (endemic) to the early Devonian of South Africa, South America, and the Falkland (Malvin) Islands.  By far the richest in number and variety come from the highlands of Bolivia.

    The flowering of the calmoniid genera took place in the isolated environment of the Gondwana supercontinent some 400 million years ago.  The astounding variety provides insight into rapid evolutionary changes made possible by different ecological niches.   The ebb and flow of sealevels that resulted from ancient ice ages caused variations within genera as well as the blossoming of haunting changes in the basic structure of just this one family.  The total extinction of the calmoniid and other trilobite families in middle Devonian is but a sample of a larger devastation that was one of the greater extinction events of earth's life history.