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Redlichiida


Fossil record and Life Habits

The fossil record of a group or species is measured by dating the rocks surrounding them, and then by referring the range to the geologic timescale. The range is known scientifically as the stratigraphic distribution.

Geological system Date (millions of years)
Quaternery 1.6 to present day
Caenozoic Pliocene
Miocene
Oligocene
Eocene
Palaeocene
1.6-5
5-25
25-38
38-55
55-65
Mesozoic Cretaceous
Jurassic
Triassic
65-144
144-213
213-248
Palaeozoic Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
248-286
286-354
354-412
412-435
435-492
492-545
Precambrian >545 ma


The Redlichiida are one of nine groups within the trilobites (Clarkson, 1998). Each has a different range in the fossil record but the Redlichiida was the first to appear in the Cambrian followed by the Agnostida, Ptychoparida and Corynexochida. Trilobites were most diverse during the Ordovician although the Redlichiida had disappeared from the fossil record long before. Trilobites survived an extinction event in the Ordovician and in the Devonian through the Proetida, but the entire group disappeared completely by the end of the Palaeozoic.
Order Stratigraphic distribution
Redlichiida Lower to Middle Cambrain
Agnostida Lower Cambrian to Upper Ordovician
Ptychoparida Lower Cambrian to Upper Devonian
Corynexochida Lower Cambrian to Middle Devonian
Lichida Middle Cambrian to Middle Devonian
Asaphida Upper Cambrian to Silurian
Harpetida Upper Cambrian to Lower Devonian
Phacopida Lower Ordovician to Upper Devonian
Proetida Ordovician to Permian


As there are no living trilobites anything about the way they lived is based on modern relatives such as the insects, crustaceans, scorpions and spider, etc or guess work regarding the exoskeletons. Trilobites were restricted to oceans and could either swim through the water or walk on the seabed.

A number of different feeding methods have been suggested for trilobites including filtering particles from the water and predatory or scavenging habits. If you consider the overall shape of a trilobite, those that were more streamlined could move through the water faster, allowing them to catch other animals. Redlichids are generally streamlined and were most likely predatory.

A small plate called the hypostome is present on the underside of some trilobites just behind the mouth. In trilobites that filter fed the hypostome was not attached to the rest of the exoskeleton in a natant condition. In predatory trilobites, the hypostome was stronger to allow manipulation of food against the plate and movement was vertical to push bulky food through the gut. The hypostome for these types are trilobites is called either counterminant, where the front of the plate lines up with the domed glabella on the exoskeleton above, or impendent, where the front of the glabella is much further forward. Redlichida have a counterminant hypostome which again suggests they were predators.


Author: Sue Beardmore
Last updated: 18/11/06

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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2006-7