Trilobite
of the Month
Past
Trilobites of the Month
About
Trilobites
The
trilobites (Phylum Arthropoda, Class Trilobita) first appear
in the fossil record in the Lower Cambrian some 540 million
years ago. When trilobites first appeared in the fossil record
they were already highly diverse and geographically dispersed.
From that time until the last of them died out at the end
in the Permian extinction they attained amazing diversity.
Because their diversity and a readily fossilized calcite
exoskeleton, a prodigious fossil record with some 500 genera
and 17,000 known species spanning Paleozoic time provides
a story about how evolution by means of natural selection
progresses. Trilobites adapted to occupy a broad spectrum
of environmental niches and made a living in concomitantly
diverse ways.
The
number of trilobites families actually peaked in the upper
Cambrian, and thereafter gradually declined. With the exception
of Order Proetida all trilobite orders died during the 
Devonian
extinction that mainly affected marine organisms. The sole
surviving order into the Carboniferous were the proetids that
disappeared finally in the great mass extinction at the end
of the Permian about 250 million years ago. Nonetheless, trilobites
have to be ranked among the among the most successful of the
early animals, swarming in the oceans for over 270 million
years, beginning with the Cambrian Explosion.
How trilobites lived:
Trilobites adapted to occupy many different marine environments,
essentially everywhere, and led corresponding different life
styles. Some lived a benthic life in the lowest level of the
water column, including the sediment surface and some sub-surface
layers. They moved over the sea-bed as predators, scavengers
or filter feeders. Other trilobites lived a pelagic life, swimming
and feeding on plankton. Other trilobites, and notably those
of Family Olenidae are believed to have evolved a symbiotic
relationship with chemotrophic, sulfur-eating bacteria from
which they obtained their food (1). They lived inshore and
in deep water, and at all depths in between. Each niche they
occupied required different adaptation in order to survive,
thrive, compete, and eat before they were eaten. Selective
pressures particularly drove
Why trilobites are important to science:
The study of these trilobites has advanced important contributions
to biostratigraphy, paleontology, evolutionary biology and
plate tectonics.