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.
Bivalves UMBO TEETH PALLIAL LINE MUSCLE SCARS GROWTH LINES RIBS THICK SHELL EVIDENCE FOR MODE OF LIFE? High energy, intertidal shorelines: Thick shell, large muscle scars, strong teeth and socket arrangements. SOCKET
Interior of a bivalve MUSCLE SCARS TEETH AND SOCKETS PALLIAL LINE UMBO The line of symmetry of bivalves runs BETWEEN the two valves.
Pecten (scallop) This bivalve is nearly symmetrical but the ears are not the same and the umbo leans slightly to the left. Strong ribs to live in high energy water Thin, light shell for floating Mode of life: Pectens float/swim between periods on the sea bed EARS
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 GROWTH LINES TEETH AND SOCKETS 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. 5cm
BRACHIOPODS 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. PEDICLE OPENING GROWTH LINES LINE OF SYMMETRY CUTS THROUGH THE VALVES
Rhynchonella is a very common Jurassic brachiopod, with heavily ribbed valves. PEDICLE OPENING RIBS UMBO Rhynchonella has two valves which close together very tightly, suggesting that they lived on intertidal shorelines which had high energy breaking waves. LINE OF SYMMETRY
Jurassic brachiopods Picture from the Palaeontological Association
Carboniferous brachiopods in black shales 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.
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. 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. SEPTA
CORAL ENVIRONMENTS Coral reef growth is only possible if these requirements are met: Marine conditions Warm water (over 25 o C) 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 HOLD- FAST
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. SINGLE STIPE THECAE ON BOTH SIDES OF THE STIPE
TRILOBITES Trilobites had segmented exoskeletons which allowed some species to roll up to protect themselves. Picture from the Palaeontological Association
Trilobite morphology PYGIDIUM – fused segments THORAX WITH SEGMENTS GLABELLA 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 COMPOUND EYES These were made of many crystals of calcite, like present- day insect eyes. GLABELLA SEGMENT OF THE THORAX
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 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. Trinucleus had long genal spines (broken off in this fossil) which probably helped it to balance in soft mud.
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 BODY CHAMBER WHORLS KEEL Ammonite shells were made of calcite. This specimen has very few ribs or growth lines on its shell.
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
Ammonite suture lines FRILLY SUTURE LINES SURFACE OF THE SEPTA 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 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. 4m
Carbonised leaves in white sandstone
Jurassic Gingko tree leaves fossilised in pale grey shale
Plant branch fossils Calamites has a strongly ribbed trunk. Lepidodendron has leaf scales which give it a diamond-shaped pattern.
Branches in Millstone Grit sandstone Sandstone in Ratten Clough, Todmorden Flagstones on the Pennine Way
Rootlets Carbonised rootlets growing in a silica-rich soil, which would have developed in a tropical climate. 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.
THE END Jurassic ammonite moulds and casts, Dorset