Practical Work - Fossils Flashcards
What anatomical orientations can be drawn?
Dorsal (top view) Ventral (bottom view) Anterior (front view) Posterior (back view) Left Right
By convention, which way is the umbo oriented and pointing for bivalves?
Dorsal and oriented upwards
Pointing towards the anterior
Concentric parallel lines on a bivalve’s shell indicate what kind of growth?
How could something about the past climate be inferred from the shell?
Accretionary
Isotope ratios for oxygen etc
Which labels can be added on an interior sketch of a bivalve shell?
Pallial line Pallial sinus Umbo Tooth and socket zone Adductor muscles (posterior and anterior)
What was the purpose of both the adductor muscles and the ligaments in a bivalve?
Adductors for closing the shell
Ligaments for opening the shell
How did the ligaments of a bivalve open the shell?
Why does this lead to most bivalves being found open or disarticulated?
They were elastic
The natural state of the bivalve was open so unless buried in sediment, they would die like this/open after death
What was the purpose of the tooth and socket zone in a burrowing bivalve?
Keep the valves aligned when burrowing, no rotation
What does the presence of a prominent pallial sinus in a bivalve shell indicate?
Deep burrower
How do bivalves secrete new shell material?
Why are no growth lines apparent on the inside of the shell?
The mantle must extend out beyond the pallial line to lay down new shell, but is not permanently attached at that point
New shell is deposited across the entire inner surface of the shell
How do brachiopods differ from bivalves in terms of movement?
Brachiopods are sessile, they can’t move or burrow
How do brachiopods attach themselves to a surface?
A pedicle, a fleshy stalk at the posterior
It comes out the pedicle valve
What is the symmetry of a brachiopod?
Bilateral symmetry
How do brachiopods open and close their shell?
Diductor muscles open
Adductor muscles close
Why are brachiopods more often found closed than bivalves are?
Different tooth and socket positioning means a larger surface area remains closed
Lower chance of disarticulation
No ligament that automatically opens the valves
What kind of feeders are bivalves and brachiopods?
Suspension feeder
What is the lophophore structure in a brachiopod used for?
Feeding
Gas exchange
What factors have led to the success of bivalves and marginalisation of brachiopods in terms of diversity?
Brachiopods were more susceptible to mass extinction, particularly the end Permian
Bivalves have a greater range of functions such as mobility and burrowing
Which features can be labelled on a trilobite?
Cephalon (head) Pygidium (tail) Thorax (middle part) Glabella Compound eye Facial sutures (lines on the head) Free cheek Thoracic segment
What is the nature of the segmentation of each of the three body parts in a trilobite?
Cephalon: fused, differentiated and highly integrated segments
Thorax: simple unfused segments
Pygidium: simple fused segments
How does the level of integration of each body part in a trilobite relate to its function?
Cephalon: for mechanical integrity
Thorax: allows movement and enrollment
Pygidium: mechanical stability, helps enrollment
How does the segmentation in a trilobite affect the preservation of the fossil?
Thoracic segments are prone to disarticulation
Pygidium and cephalon tend to remain intact
How does a trilobite grow?
What are the two ways it can perform this?
Moulting the exoskeleton and growing a new one (ecdysis)
Exit from underneath, or between the cephalon/thorax
How can you tell if a trilobite fossil is a moult or a carcass?
A carcass will be fully articulated and free cheeks still attached
What may have been the function of the trilobite appendages, both the segmented and the frilled parts?
Frilled part like a gill so gas exchange
Segmented part for movement/burrowing
What are trilobites likely to have done for a living?
Sift the sediment of the sea bed
Process small prey and detritus
Which features can be labelled on an echinoid?
Apical system Ambulacral area Inter ambulacral area Periproct Pore pairs Tubercle Ambulacral pores Peristome
Which features are lost in an echinoid between death and semi-mummification?
If treated with bleach, what else would be lost?
Behaviour, internal soft parts, tube feet
External epidermis, spines, Aristotle’s lantern
How do echinoids grow their skeleton?
Addition of new ossicles and accretionary growth/remodelling of existing ones
How can the ecological habit of an echinoid be inferred from the observable features/missing features?
Ambulacral pores indicate a water vascular system and mobility
Presence of spines indicates whether infaunal/epifaunal
Pentaradial symmetry and Aristotle’s lantern so a grazer/scavenger
What are the three principal parts of a crinoid?
Calyx
Crown
Stalk
Which four kinds of ossicles of a crinoid can be seen in a fossil?
Crown ossicle
Calyx ossicle
Stalk ossicle (penta-radial symmetry)
Stalk-arm ossicle (called cirri)
What did crinoids do for a living?
Marine, suspension feeder
Water passed through the crown and minerals were picked up
Why did stalked crinoids disappear from shelf settings in the late Mesozoic and Cenozoic?
Permanently attached to a substrate with a long exposed stalk is easily preyed upon
If a surface is well preserved, what does this indicate with respect to burial?
How might crinoids be preserved well?
Buried very rapidly
Rapidly buried in a storm deposit
If crinoids are attached to wood, how might that explain good preservation?
Attached to floating log
Log eventually sunk into anoxic bottom waters so those on the bottom would be preserved, but the ones on top would decay and disarticulate
Why can graptolites and bryozoans be identified as colonial?
How would the soft bits have been distributed?
What is the genetic relationship between individual zooids?
Multiple compartments
Coordinated colony so interconnected soft parts
Genetically identical clones
What is the nature of the bryozoan skeleton?
How did it grow?
Is the colony genetically or environmentally controlled?
Calcite
Accretionary on existing zooids, additive for new zooids
Environmentally controlled
What is the nature of the graptolite skeleton?
How did it grow?
Is the colony genetically or environmentally controlled?
Why is it useful that the colony is controlled this way?
Carbonaceous skeleton
Primarily additive
Genetically determined colony form
Helps with biostratigraphy
What is the palaeoecology of bryozoans?
Why can’t it move?
Marine Benthic Sessile Epifaunal Suspension feeders The calcitic skeleton is massive and immobile
What is the palaeoecology of graptolites?
Marine
Pelagic
Planktic
Suspension feeders
What are some of the ecological or evolutionary advantages of living in a colony? (bryozoans/graptolites)
The colony can survive if some die
Environmental buffer
Large scale forms can generate hydrodynamic properties
Individuals can become specialised
Why are graptolites such great index fossils?
Planktic
Superabundant
Evolved rapidly in Ord-Dev
Taxa are distinctive and easy to identify
Anoxic conditions required for preservation were prevalent at that time
Which features can be labelled on a coral if they are present?
Corallum Calice Septa Columella Epitheca Growth lines (if solitary) Tabulae Dissepiments Apex (if solitary) Coenosteum (if colonial)
What are the three coral types?
Rugose
Tabulate
Scleractinian
How do you tell apart the three coral types?
Tabulate = no septae, Rugose = bilateral symmetry in septae, Scleractinian = hexa radial symmetry in septae Tabulate = always colonial, Rugose/scleractinian = colonial or solitary Tabulate/scleractinian = high level of integration in colony Fossilised = more likely to be rugose or tabulate
What do the coral types mineralise in?
Scleractinian in aragonite
Tabulate and rugosa in calcite
What is the higher-order taxonomy for corals?
Domain - Eukaryota Kingdom - Metazoa Phylum - Cnidaria Class - Anthozoa Order - Scleractinia/Tabulate/Rugose
What kind of integration is expected to be seen in the colonial forms of each coral type?
Scleractinia: highly integrated, often no walls between individual corallites
Rugose: no integration, just loosely packed corallites
Tabulate: substantially integrated, significant amounts of coenosteum
Looking at a fossilised stem in thin section, what would allow you to say it was from an embryophyte?
Tissue differentiation
What were the advantages of growing larger and taller for early plants?
Why aren’t they even taller/larger?
More sunlight exposure, greater distribution of spores
Required structural reinforcement and a good vascular system (wood not evolved yet)
What are the similarities between early spore-bearing plants and mosses?
Terminal sporangia
No vascular system
No real roots
What is the diagenesis of Rhynie Chert?
What makes the colour in the thin section?
Quartz permineralised - from a hot spring - plant nearby
A small amount of organic material left
Why is stomatal density currently on a downward trend in trees?
Rise of atmospheric CO2 since the industrial revolution
Bituminous coal can have a characteristic banded fabric of alternating vitrinite (reflective, conchoidal fractures) and liptinite (duller background material), what may be the sources of these?
Vitrinite derives from mostly solid wood
Liptinite from leaf cuticle, spore walls etc
How do peat and anthracite coal differ from bituminous coal in terms of fabric?
Peat is uncompacted plant material so just has regular vertical layering
Anthracite coal is more homogeneous due to metamorphic overprinting
What is the depositional environment of bituminous coal, including the hydrological regime?
Stagnant
Low oxygen
Low pH
Continuous rainfall
What makes ammonoids useful for biostratigraphy?
Three types - ammonitic, ceratitic and goniatitic
They have distinct suture lines for these species and time frames
What was the likely palaeoecology of ammonoids?
How does the habit make it useful for biostratigraphy
Marine, pelagic, nekton, predator
Remains spread widely
How can the increasingly complex suture lines in ammonoids be explained?
Possibly shell strengthening
What is the biomineral for belemnites?
What is the mode of growth?
Describe the arrangement of the crystals
Calcite
Accretionary growth (laterally)
Large and radially oriented
What do the growth lines for a belemnite indicate about the position of the secretory tissue and the guard relative to the squid?
Guard was inside the squid
Surrounded by secretory tissue
Why are belemnites suitable for oxygen isotope measurements?
Solid macrocrystalline calcite
Somewhat immune to diagenesis
In the evolution from an epifaunal to an infaunal echinoid, how does the test change?
More flat, more gently curved anterior, steeper posterior
Pentaradial symmetry develops into bilateral symmetry
How do the tubercles change in the evolution from an epifaunal to an infaunal echinoid?
Tubercles decrease in size
Tubercles increase in density
How have the openings moved in the evolution from an epifaunal to an infaunal echinoid?
Why?
Anus moves from the top to the posterior
Mouth moves to the anterior
Feeding on the sediment as they move forward in it
How do the pore pairs change in the evolution from an epifaunal to an infaunal echinoid?
What did the increased surface area provide?
Pore pairs become non-symmetrical
One pore is circular, the other is a thin slit
Increased gas exchange and feeding
If a dead echinoid is encrusted with worms, how can you tell if they were around at death or came after?
If after death, worms encrust over disarticulated spines or cover the mouth/peristome
What do infaunal echinoids feed on?
How has their skeleton been adapted for this?
Detritus feeders
Spines reduced in size (easier movement)
Vertical tube for ventilation
Trailing tube for waste
Why are trace fossils for infaunal echinoids hard to find?
What are the consequences of extensive feeding?
Destruction by bioturbation
Ventilation and mixing of sediments
Why did the rise of infaunal echinoids and bivalves coincide with a decline in free lying brachiopods?
Mud sitting brachiopods didn’t fare well when their substrate was constantly being turned over
Why have infaunal echinoids been so successful since they evolved?
Rise in predators during their evolution like fish and crustaceans, safe in the sediment
Why does the probability of extinction remain constant?
While the prey evolves to be better at avoiding predators, the predators also evolve to get better at catching the prey
No real ground gained
How do benthic forams grow?
Coiled accretionary skeletons with the outer wall enveloping all previously formed shell
How are fusilinids and nummulite LBFs similar/different in terms of overall form, internal compartmentalisation, wall microstructure and mode of life?
Both are large accretionary structures with spiral geometry, but fusilinids are more drawn out
Both have inter-connected compartments, but fusilinids have more open space
The microstructure of fusilinids is granular vs the larger crystalline habit of nummulites
Both live in shallow water carbonates settings
What do benthic forams do for a living?
Why do they have a high level of diversity?
On the seafloor eating detritus etc
A diverse range of environments at the microscopic range
What are the three types of benthic forams?
Agglutinating
Hyaline
Porcellaneous
How do planktic forams differ from benthic forams?
Generally thin-walled
Often porous
Often with inflated chambers
No agglutinating or porcellaneous
When are gastropods index fossils for?
Very common in the Cenozoic (but have been present throughout even as far back as Cambrian)
When are Megalodon teeth index fossils for?
Mid Cenozoic
Outline the shell of an ammonoid
Planispiral coiled shell
Shell has chambers separated by septa that meet the shell wall at a suture
Chambers joined by a tube (siphuncle) through the outer edge of each septum
Chambers contain gas/fluid to control buoyancy
How are ammonoids often preserved?
What is revealed in this preservation?
Why are they preserved this way?
As internal moulds
Suture lines
Aragonite shells
When are the three types of ammonoids index fossils for?
Goniatites: Mid Devonian to end Permian
Ceratites: Triassic
Ammonites: Jurassic and Cretaceous
When are the types of nautiloids index fossils for?
Coiled and straight forms: Ordovician to end Permian
Coiled only: Triassic to now
When are belemnites index fossils for?
Very common in Jurassic and Cretaceous
When are bivalves good index fossils for?
Very common in Cenozoic
Somewhat common in Mesozoic
When are brachiopods good index fossils for?
Very common Ordovician to end Permian
Common Triassic to end Cretaceous
When are the coral forms good index fossils for?
Rugose and Tabulate: early/mid-Ordovician to end Permian
Scleractinian: mid-Triassic to now
When are echinoids good index fossils for?
Regular echinoids: mid-Ordovician to now
Irregular echinoids: Jurassic onwards
Very common from Jurassic to now
When are crinoids good index fossils for?
Carboniferous and Permian
When are graptolites good index fossils for?
Ordovician and Silurian
When are trilobites good index fossils for?
Very common in early Palaeozoic (Cam-Sil)
With trilobites, when would few segments and a roughly equally sized cephalon and pygidium be indicative of?
Early Cambrian
