This is one of the charts I used in the book to help the reader gain
familiarity with trilobites. It is based on a figure in Euan Clarkson's
textbook on invertebrate paleontology.
The Paleozoic era comprised six major time periods spanning from 542 to
251 million years ago, as indicated by the numbers along the bottom of
this chart. The blue lines show when and how long each major trilobite
group lived. Representative drawings of selected group members are
only roughly scaled to size, with smaller species greatly expanded so
they are visible on the chart. The range lines of each family group of
trilobites are clustered according to the order to which they belong,
with the right margin of the chart showing the names of the nine orders
of the trilobites and the order Nektaspida.
The rocks of Black
Cat Mountain were deposited in the lower Devonian, almost 418 million
years ago, represented by the vertical line passing through the middle
of the chart. The blue trilobite range lines crossed by this line
indicate which groups of trilobites should be found at Black Cat
Mountain. Those present in the collections include the Scutelluina,
Odontopleuroidea, Lichoidea, Phacopina and Proetoidea. Missing groups
at Black Cat Mountain include the Cheirurina, Calymenina and Harpina,
but they have been found elsewhere in the world from rocks equivalent
in age to Black Cat Mountain. The remaining twenty groups were extinct
by the end of the Silurian.
A key to the trilobite range chart
is given below. This table lists the names of the trilobite examples,
using the numeric labels next to each drawing shown in the chart.
Formal scientific names are in italics, together with approximate
historical range for each example. Drawings of the trilobites came from
the 1959 Treatise, except Naraoia, which I borrowed from Zhang, Shu, and Erwin, 2007, who presented convincing evidence that the Nektaspida were not trilobites.
The relationship of trilobites to other animals is illustrated in an
excellent poster developed by Neal Olander. To view his poster click
on this link: Tree of Life.
You will find the trilobites between the arachnids and the
crustaceans. This Tree of Life indicates the appearance of each
principal animal group in the appropriate geologic time period,
together with representative photographs. These helpful graphic
features are seldom indicated in cladistic diagrams of animal
relationships. This 2 MB file can be downloaded to your computer for
closer viewing.
Other equally superb phylogenetic resources can
be found at Roger Perkins' Virtual Fossil Museum (see the Related
Websites page), the Tree of Life Web Project, Nature, andScience magazines.
Front view of a specimen of Ceratonurus species from the Haragan formation. See the page on the order Odontopleuroidea for other views of this tiny specimen. (Photograph courtesy of John Moffitt and Neal Immega)
