FOSSIL MORPHOLOGY

FOSSIL MORPHOLOGY

Jurassic Dinosaur footprint, Cloughton Wyke, Scarborough

Fossils • A fossil is a feature which records organisms or plants in rocks. Fossils can include hard parts of the organism such as skeletons, bones, plant material, pollen or shells. • Trace fossils record the activities of animals or plants, but do not include any hard parts. Trace fossils include burrows, footprints and feeding tracks.

TEETH

Bivalves

UMBO

SOCKET GROWTH LINES

RIBS MUSCLE SCARS EVIDENCE FOR MODE OF LIFE?

PALLIAL LINE

THICK SHELL

High energy, intertidal shorelines: Thick shell, large muscle scars, strong teeth and socket arrangements.

Interior of a bivalve UMBO

TEETH AND SOCKETS

PALLIAL LINE MUSCLE SCARS The line of symmetry of bivalves runs BETWEEN the two valves.

Pecten (scallop) Mode of life: Pectens float/swim between periods on the sea bed

EARS

Thin, light shell for floating

Strong ribs to live in high energy water

This bivalve is nearly symmetrical but the ears are not the same and the umbo leans slightly to the left.

Bivalves in their life positions (life assemblage) St Bees sandstone, St Bees, Lake District

Flags on the Pennine Way

Mussels beds on a present day shore

Burrowing bivalves UMBO

TEETH AND SOCKETS

5cm

GROWTH LINES

MUSCLE SCARS

Bivalves which burrow are likely to be more elongated than those which live on the top of the sea-bed. They may also have a gape (the valves do not meet at one end) so that the siphons which enable them to feed can reach the surface of the sea-bed.

BRACHIOPODS LINE OF SYMMETRY CUTS THROUGH THE VALVES

GROWTH LINES

PEDICLE OPENING

Brachiopods differ from bivalves in that they have a sessile mode of life – they live attached to the sea-bed by a pedicle, which is a tough ligament which emerges from the pedicle opening.

Rhynchonella is a very common Jurassic brachiopod, with heavily ribbed valves. UMBO

PEDICLE OPENING

LINE OF SYMMETRY

RIBS Rhynchonella has two valves which close together very tightly, suggesting that they lived on intertidal shorelines which had high energy breaking waves.

Jurassic brachiopods

Picture from the Palaeontological Association

These valves of the brachiopod Productus are not broken up, but they are separated. That suggests that they have been transported by gentle waves or currents into the area of muds without being fragmented.

Carboniferous brachiopods in black shales

CORALS In this Silurian coral, Halysites, the individual corallites have been linked together to form a coral colony, which would have been firmly attached to the sea-bed.

These Carboniferous corals also form a colony, preserved in limestone in their position of growth. Septa are radiating plates of calcite that held the soft body of the coral animal (polyp) firmly inside the corallite. Corals live in high energy conditions with breaking waves where there are plenty of other organisms from which to feed. SEPTA

Picture from the Palaeontological Association

SEPTA

Solitary corals lived with the pointed end stuck into the sea-bed. The coral animal could reach food in the sea with its many tentacles.

CORAL ENVIRONMENTS Coral reef growth is only possible if these requirements are met:

Marine conditions Warm water (over 25oC) Clear water Shallow water (photic zone) High energy (breaking waves)

Present coral reefs

Coral reefs in the Red Sea

Photos from Ellen Spencer

GRAPTOLITES The first graptolites were colonies of animals attached to each other on branches (stipes) and attached to the sea-bed by a hold-fast. They extracted their food from sea-water. STIPES

HOLDFAST

Tetragraptus As time passed, it became more efficient for graptolite colonies to float freely in the oceans to find food (pelagic floating). The number of stipes reduced and the trilobite animals on each colony decreased in number. Their chambers (thecae) became larger and are clearly seen in this picture.

THECAE

STIPE

Didymograptus murchisoni In the Ordovician period the number of stipes per colony reduced to two. Often the thecae became more complex in structure.

THECA

TWO STIPES

Monograptus Later, in the Silurian period the two stipes of Didymograptus united and became one, but with thecae on both sides. Monograptus is only found in Silurian rocks and is therefore an excellent zone fossil to correlate rocks of this age. THECAE ON BOTH SIDES OF THE STIPE

SINGLE STIPE

TRILOBITES

Trilobites had segmented exoskeletons which allowed some species to roll up to protect themselves.

Picture from the Palaeontological Association

Trilobite morphology THORAX WITH SEGMENTS GLABELLA

PYGIDIUM – fused segments

COMPOUND EYE – hidden in shadow

Trilobite exoskeletons were made from protein and therefore were slightly flexible. The soft parts, like brain, breathing gills, guts and reproductive organs were protected by the exoskeleton.

Calymene cephalon GLABELLA

SEGMENT OF THE THORAX

COMPOUND EYES These were made of many crystals of calcite, like presentday insect eyes.

Spiny trilobite Some trilobites developed elaborate spines, perhaps to protect themselves from predators or to stop their exoskeletons from sinking into soft sea-bed muds.

Trinucleus Trinucleus had long genal spines (broken off in this fossil) which probably helped it to balance in soft mud.

Trinucleus had no eyes. But the ribbed headshield is thought to be a sensitive organ which could enable Trinucleus to feel its way through mud to find its food by touch.

Angelina sedgwickii This Lower Ordovician trilobite is always found in slates so has been deformed by metamorphism. It is therefore used by geologists as an indicator of the direction and size of pressure during mountain building periods which metamorphosed the shales, in which Angelina is found, into slates.

AMMONITES WHORLS KEEL This specimen has very few ribs or growth lines on its shell.

BODY CHAMBER

Ammonite shells were made of calcite.

Ammonite morphology RIBS

WHORLS

BODY CHAMBER

KEEL

Ammonite interior Each chamber is separated from the next by a calcite septum secreted by the animal as it grows larger.

These chambers have been filled with coarse calcite crystals when the shell was covered with sediments.

SEPTA

Detail of inside whorl

Outer shell and whorls original shell of the ammonite

Shell broken away to show the infilling of the chambers by sediment

Suture lines in ammonites developed very frilly edges to give the shell more strength. This allowed ammonites to become much larger and more competitive.

6cm

SEPTUM

FRILLY SUTURE LINES

SURFACE OF THE SEPTA

Ammonite suture lines Both lobes and saddles developed frills. On this specimen it is not easy to see which is which because the fossil does not include the body chamber.

GONIATITES Goniatites are the ancestors of the ammonites and were common in the Carboniferous period. They have simple suture lines and are usually small with very few whorls.

Goniatites have simple suture lines LOBES POINT AWAY FROM THE BODY CHAMBER SADDLES POINT TOWARDS THE BODY CHAMBER BODY CHAMBER

PLANTS

4m

This tree trunk was found in its position of growth (in situ) in Appleton Quarry, Shepley. The tree grew in a swamp and became covered with fine muds, which are now laminated fissile black shales. The trunk has become carbonised and there is a thin black layer of carbon around the outside of the tree.

Carbonised leaves in white sandstone

Jurassic Gingko tree leaves fossilised in pale grey shale

Plant branch fossils Lepidodendron has leaf scales which give it a diamond-shaped pattern.

Calamites has a strongly ribbed trunk.

Branches in Millstone Grit sandstone

Flagstones on the Pennine Way Sandstone in Ratten Clough, Todmorden

Rootlets

The thin coal seam represents the plants which have become compressed and carbonised as water and gases have been driven off as the rocks became lithified.

Carbonised rootlets growing in a silica-rich soil, which would have developed in a tropical climate.

THE END THE END

Jurassic ammonite moulds and casts, Dorset