FOSSIL MORPHOLOGY

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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
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