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

Browse echinoids

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

Browse crinoids

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

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

Browse gastropods

External links

Telling planispiral fossils apart

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

Browse trilobites

Links

Learn about types of preservation

Graptolite

Taxonomy

Phylum: Hemichordata

Class: Graptolithina

Diagnostic features

Stick-shape (often branched)

One or both edges may appear serrated

Thecae

Rhabdosome

Stipes

Stratigraphic range

Cambrian to Carboniferous (Dendroids)

Ordovician to Middle Devonian (Graptoloids)

Way of life

Colonial

Planktonic (mostly, although some dendroids were sessile benthonic)

Suspension feeders

Typical preservation

Flattened along bedding planes, normally in shales

Carbonization or pyritization of the animal

Learn about types of preservation

Advanced notes

Graptolites, because of their abundance and variation in morphology are very good index fossils. At a very basic level the angle between the stipes and number of stipes can be used to give a rough age for the fossil, with Early Ordovician graptolites having two stipes with the 'sawtooth' facing each other (pendent), later Ordovician graptolites having a more open oblique or reflex angle between the 'sawtooth' faces, and Siluran graptolites having the 'sawtooth' faces back to back (scandent) or having lost one stipe altogether (for example monograptids).

Specimens

Browse graptolites

Nautiloid

Taxonomy

Phylum: Mollusca

Class: Cephalopoda

Diagnostic features

Simple suture

Chambers

Central siphuncle

Straight, curved or coiled shell

Stratigraphic range

Cambrian to recent

Straight forms: Cambrian to Permian

Coiled forms: Devonian to Present

Way of life

Predatory

Buoyancy controlled by changing gas/liquid contents of chambers

Marine

Preservation

Commonly preserved as internal moulds

Modern nautiloids preserved with original shell material

Learn about types of preservation

Advanced notes

Nautiloids originated in the Cambrian period, and radiated during the Ordovician. These early nautiloids had conical shaped shells. In the Silurian some nautiloids used curved shells, and by the Devonian some were coiled. The evolution of the coiled shell from the straight is thought to be driven, at least in part, by increased mobility of a coiled shell compared to a long straight one.

Nautiloids could be confused with ammonoids. You can distinguish them by the location of the siphuncle and the complexity of the suture pattern. Nautiloids, unlike ammonoids, are not extinct, although only six species remain today (compared to thousands in the Palaeozoic). This means that if presented with modern shell material it is likely a nautiloid and not an ammonoid.

Specimens

Browse nautiloids

External links

Telling planispiral fossils apart

Coral

Taxonomy

Phylum: Cnidaria

Class: Anthozoa

Diagnostic features

Radial or biradial symmetry

External skeleton

Septa

Tabulae

Stratigraphic range

Ordovician to present

Tabulate, rugose: Ordovician to Permian (extinct at P/T extinction)

Scleractinian: Triassic to present

Way of life

Colonial or solitary

Filter feeding

Reef builders

Advanced notes

Remember, although the most well-known modern corals enjoy a symbiotic relationship with photosynthesising algae (Zooxanthellea) many modern corals do not. When thinking about Palaeozoic corals do not assume that they lived as well known corals do now.

Corals built their skeletons out of aragonite (Ordovician to Permian) or calcite (Triassic to recent). They are often preserved as moulds, casts, intact or replaced.

Specimens

Browse corals

External links

Paleosoc coral info

Brachiopod

Taxonomy

Phylum: Brachiopoda

Diagnostic features

Two valves (brachial and pedicle)

Bilateral symmetry

Growth lines

Adductor and ductor muscle scars

Pedicle

Commissure

Gape

Teeth and socket (articulates; no teeth or socket in inarticulates)

Stratigraphic range

Cambrian to present

Way of life

Marine

Attach to hard substrates using pedicle

Filter feeding

Sessile

Infaunal, epifaunal, reclining

Advanced notes

Apparent decrease in diversity over time

Limited to marginal environments in the modern ocean

Adductor muscle used to close shell, ductor muscle used to open shell

Specimens

Browse brachiopods

External links

Yale Peabody Museum of Natural History: differences between bivalves and brachiopods

Cortland Paleo, Brachiopoda: brachiopod morphology and ecology information

Learn about types of preservation

Bivalve

Taxonomy

Phylum: Mollusca

Class: Bivalvia

Diagnostic features

Palial line/palial sinus

Adductor muscle scars

Growth lines

Dorsoventral symmetry (some exceptions, for example Gryphaea)

Two hinged valves

Umbo

Hinge

Gills (rarely preserved)

Stratigraphic range

Cambrian to present

Way of life

Bivalves have occupied many environmental niches, living in a variety of ways:

Epifaunal, infaunal, nektonic

Marine, freshwater, brackish

Filter feeders through gills

Majority of bivalves begin life in a planktonic larval stage

By looking at the shell shape and palial sinus of fossil bivalves it is possible to say something about its mode of life.

Advanced notes

Apparent increase in bivalve diversity over time (or is this just a preservational bias?)

Bivalves makes their shells out of calite, aragonites, or both

The adductor muscles are used to keep the shell of the bivalve closed. This means that when they are relaxed, the ligament between the valves pulls them apart, so the 'relaxed state' for bivalves is 'open'.

The depth at which infaunal bivalves burrowed can be inferred from the palial sinus. The more prominent the palial sinus, the deeper the bivalve burrowed. This is because the size of the palial sinus is indicative of the size of siphon needed, which in turn depends on the depth of the burrow (deeper burrow, larger siphon).

Specimens

Browse bivalves

Links

youtube: scallops swimming

Cambridge University Museum of Zoology: Lifestyles of bivalves

Yale Peabody Museum of Natural History: differences between bivalves and brachiopods

Learn about types of preservation

Also

Go to the front of the 1A Lab. A display on the right hand side (by the window) shows a number of bivalves in life position. Have a look at how they have adapted their shape and other features to their way of life.

Belemnite