Arthropods
Summary by Jon Tortomasi
Trilobites
- Ecology
- benthic, epifaunal, marine
- primarily deposit feeders, but some filter
feeders
and carnivores
- some varieties were pelagic
- Evolutionary History
- little known about ancestors (as with all
arthropods
- possibly derived from annelids (segmented
worms)
- family diversity was at a maximum in the
Upper
Cambrian and lower Ordovician
- diversity highest in the Ordovician
- Morphology
- cephalon, segmented thorax, pygidium
(tail)
- paired walking legs and gill branches
- hyposome mouth area
- glabella housed stomach
- compound eyes
- Stratigraphic Use
- most of the Cambrian zoned by
trilobites
- much of Ordovician also zoned by
trilobites
Ostracods
- Ecology
- predominantly marine, some freshwater and
terrestrial
types
- benthic or pelagic (mobile)
- primarily filter feeders
- can be attached to substrate
- life habit and body shape reflects the
environment
- depth and salinity controls variation
- tropical areas show more diversity
- Evolutionary History
- first appeared in the early Cambrian, but
true
origins are obscure
- Early Ordivician radiation
- Devonian and Carboniferous most varied, with
first appearance of freshwater types
- since Paleocene, diversity has increased
substantially
Eurypterids
- Ecology
- benthic, mobile, predators
- preyed upon fish and other
eurypterids
- lived in marine, brackish, and
freshwater
- could be from 20 cm to 2 m in length
- developed different appendages for eating,
grasping,
etc.
- can crawl on land for short periods of time
because
of lung books and `kiemenplatlen' (bronchial chamber with dense array
of
spines for retaining water)
- Locomotion
- those with paddles, rowed themselves up to
2.5
times their body length per second (may have turned upside down to
do this)
- others had long legs for walking
- some used telson (tail) as a rudder or to
provide
lift
- Evolutionary History
- lived from the Ordovician to the
Permian
- Eurypterina had the greatest
diversity
- relatively rare as fossils due to nature of
the
cuticle (thin)
Malacostreans
- Ecology
- epifaunal or pelagic
- freshwater or marine (w/ a few
terrestrial)
- mostly predators (clawed forms were the most
successful)
- live at all depths
- Evolutionary History
- first appeared in Cambrian, still exist
today
- shrimp-like crustaceans of more modern type
1st
appeared in Late Devonian
- underwent major adaptive radiation in
Carboniferous
- clawed forms first appeared in Triassic,
most
in early Jurassic
Barnacles
- Ecology
- immobile, attached
- filter feeders which surround themselves in
a
calcite `house' which can survive in the inter-tidal zone by retaining
water inside
- Evolutionary History
- first appeared in Silurian, still exist
today
- well known from Tertiary deposits