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