fossil morphology jurassic dinosaur footprint, cloughton wyke, scarborough
TRANSCRIPT
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 UMBOTEETH
PALLIAL LINEMUSCLE 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 bivalvesUMBO
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
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.
CORALSIn 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 ENVIRONMENTSCoral 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
GRAPTOLITESThe 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
TetragraptusAs 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
MonograptusLater, 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
TRILOBITESTrilobites 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 sedgwickiiThis 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 interiorEach 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
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
PLANTSThis 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
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.