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Features of the exoskeleton

Trilobites vary greatly in their size and shape making identification relatively easy although each of the nine groups posses more specific characters that help with classification. As well as sharing the three trilobite exoskeletal divisions widthways and lengthways a typical redlichid has a large, semicircular cephalon (head end) with long genal spines attached at the genal angles (corners) of the cephalon. Large crescent shaped eyes are also found each side of the domed glabella in the middle of the cephalon. The thorax (mid region) has lots of small, sharply pointed segments (pleurae) that gradually decrease in size toward the pygidium (tail). The pygidium is very small sometimes ending with a spine.

The most important feature on the cephalon is the facial suture. This is a line that begins at the front most part of the cephalon, runs along the eyes, ending either in front of the genal angle (proparian), behind the genal angle (opisthoparian), or cutting the genal angle (gonatoparian). The main use of the facial sutures was to help with the moulting process that all arthropods, including trilobites, undergo in order to grow. In redlichids the facial sutures aren’t fully formed although opisthoparian sutures may be found in some redlichids.

basic trilobite terms

Olenellus gilberti (Suborder Olenellina; Superfamily Olenelloidea)

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