Trilobite

Taxonomy

Phylum: Arthropoda

Class: Trilobita

Distinctive features

Pygidium (tail)

Thorax (body)

Cephalon (head)

Paired appendages (not often preserved)

Three lobed longitudinal division of body (2x pleural, 1x axial)

Calcitic exoskeleton

Segmented body

Glabella

Eyes (holochroal or schizochroal; only present in some groups)

Eye ridges

Occipital ring

Axial rings

Stratigraphic range

Cambrian to Permian (most common Cambrian to Silurian)

Way of life

Trilobites lived as planktonic, nektonic, epifaunal and infaunal organisms in deep and shallow marine environments. They lived as predators, filter feeders, deposit feeders, particle feeders, scavengers and even symbiotically.

By looking at the functional morphology of the trilobite in question you can be more specific about how it lived, by looking at body shape, size, legs, eyes and other characters.

Advanced notes

Trilobites were very abundant during the Palaeozoic. Their preservation potential was increased further as they moulted their exoskeletons periodically as they grew. This means that one trilobite left numerous hard skeletons or partial skeletons as it grew, each of which has the potential to fossilise.

Specimens

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Links

Learn about types of preservation

Gastropod

Taxonomy

Phylum: Mollusca

Class: Gastropoda

Diagnostic Features

Coiled shell - planispiral or helical - consists of body whorl and spire

Mostly aragonitic shell

Shell consists of one large chamber (no septa)

Aperture

Siphonal notch

Way of life

Marine, non-marine, land-dwelling

Carnivorous, scavenging, deposit feeding and more

Advanced notes

Because of their conservative shell shape it is difficult to use gastropods as environmental or stratigraphic indicators.

Specimens

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External links

Telling planispiral fossils apart

Crinoid

Taxonomy

Phylum: Echinodermata

Class: Crinoidea

Diagnostic Features

Crown

Stalk

Pentaradial symmetry

Ossicles

Calyx

Pinnule

Holdfast

Way of life

Benthic (some pseudoplanktonic)

Filter feeders

Stratigraphic range

Ordovician to present

Advanced Notes

The heyday of the crinoids was the Palaeozoic, where they dominated shallow marine environments. Modern crinoids are exclusively deep marine, and the diversity of forms is far less than it was during the Paleozoic.

Were they victims of the increased grazing and predation pressure of the Mesozoic Marine Revolution?

Specimens

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Links

youtube: modern crinoid behaving pseudoplanktonically. You can see the pinnules, crown and multiple stalks.

flickr: beautiful photographs of both living and fossil crinoids. Compare the levels of detail you can see, admire the colours, and spot the distinctive features that make these crinoids identifiable.

Learn about types of preservation

Echinoid

Taxonomy

Phylum: Echinodermata

Class: Echinoidea

Diagnostic features

Ambulacra (tube feet)

Periproct (opening for anus)

Peristome (opening for mouth)

Pentaradial symmetry (regular echinoids)

Bilateral symmetry imposed upon pentaradial symmetry (irregular echinoids)

Stratigraphic range

Ordovician to Present (Irregular Echinoids from Jurassic to Present)

Way of life

Regular echinoids:

Grazers with functional jaw apparatus

Long spines for protection and movement

Epifaunal at a wide range of depths

Use tube feet for respiration and movement

Irregular echinoids:

Feed on organic matter in sediment, front shaped to funnel sediment into mouth

Use fine spines to move

Infaunal burrowers

Use tube feet for respiration

Advanced notes

Grazing echinoids leave a distinctive pentagonal feeding trace Gnathicnus pentax.

Learn about types of preservation

Specimens

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TF1101

Halysites

TF1102

Isastraea explanata

Specimen Age

TF1103

Rugose coral

TF1104

Tabulate coral

TF1120

Solitary rugose coral

TF1122

Scleractinian coral (modern)