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Geology (F1,F2,F3,F4) > Uniformitarism and Fossils (F3) > Flashcards

Uniformitarism and Fossils (F3) Flashcards

1
Q

What is the principle of Uniformitarism?

A

The study of present-day processes and organisms enables understanding of the geological past.

• Fossils provide information on the nature of ancient organisms and palaeoenvironmental and climatic conditions in the past.

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2
Q

How are hard parts of fossils preserved?

A

• mineral replacement
(calcite, silica or pyrite)
• carbonisation – replacement of organic material by a layer of carbon
• moulds (internal and external) and casts.

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3
Q

How are soft parts of fossils preserved?

A

Fossils are preserved by a range of materials.

In terms of soft body remains (e.g. ice, amber), exceptional preservation (Lagerstätte) is rare.

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4
Q

What is a derived fossil?

A

A fossil found in rock that accumulated significantly later than when the fossilized animal or plant died.

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5
Q

What is a life assemblage?

A

Fossils preserved in the position in which they lived

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6
Q

What are death assemblage fossils?

A

Brought together after death by transport

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7
Q

What are the main methods of preservation?

A

Replacement - 👉Petrification (turning to stone)
Impregnation - ☝️

Carbonisation

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8
Q

What is the head of the Trilobite known as?

A

Cephalon
(fused strength for strength and protection)

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9
Q

What is the body (middle part) of a trilobite known as?

A

Thorax
(flexible plates, can enroll)

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10
Q

What is the tail of a trilobite known as?

A

Pygidium
(fused plates)

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11
Q

What is the compound eye of a trilobite?

A

eye made up of hundreds of separate hexagonal calcite lenses

suggests they were a predator

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12
Q

What is the glabella on a trilobite?

A

middle portion of cephalon, typically convex and lobed, the stomach

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13
Q

What are the genal spines of a trilobite?

A

used for support on soft sediment rather like a snow shoe (increases surface area)

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14
Q

What are Pelagic and Benthonic mode of lifes?

A

pelagic: swimming mostly
benthomic: mostly crawling on sea floor

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15
Q

What are the 5 modes of life of trilobites?

A

1: deiphon
not very big
swimmer
thoracic sediments that are separate
lightweight
flat

2: pelagic/planktonic
floated
small size (<1cm)
lightweight exoskeleton
small thoracic sediments

3: burrower
absence of eyes
ribbed/pitted headshield
wide fringe
extended general spine for defence and to spread mass

filter feeding
digs hole (towards current)
current channels through wide fringe
picks up micro-particles

4: benthonic
crawls on sea bed
eye positioned on top of the head
large general spines for support
spike on backside, bends tail spike beneath itself into sediment then used it to launch ( possibly attacking prey [eg worm] )

5: benthonic infaunal
small streamlined shape
eye positioned on top of stalks that project upwards and are level with sea bed

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16
Q

Why did some trilobites lose/gain eyes during evolution?

A

Lost: ocean floor too dark, no need - advanced other senses

Gained: closer to surface, can burrow and look out for predators/prey

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17
Q

When were trilobites in existence?

A

survived on earth from 521->251Ma
during Paleozic period

(specifically Cambrian to Permian)

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18
Q

What are Cephalopods?

A

Group of molluscs

Includes modern day octopuses, squid, cuttlefish, and nautiluses

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19
Q

What are Cephalopods?

A

Group of molluscs

Includes modern day octopuses, squid, cuttlefish, and nautiluses

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20
Q

Why did Nautiloids transition from straight shells to coiled shells?

A

Early forms had a straight shell e.g. Orthoceras
Straight shell: may have posed balance problems - Evolution of coiled nautiloids solved this problem

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21
Q

What was the function of the coil and chambers of a Nautiloid?

A

Nautiloids can move backwards in the water column by sucking in
water and blowing it out at high speed

The chambers are filled with gas to keep the animal buoyant

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22
Q

How deep were Nautiloids found?

A

• Not usually found in waters < 100m deep
• May be found as far down as 500 - 700m

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23
Q

What are Nautiloid shells made of?

A

Shell is usually made of aragonite (+ some calcite / other organic matter

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24
Q

Why are Nautiloids bad zone fossils?

A

It has remained unchanged for over 400Ma!

25
Q

What is the Septum on a Nautiloid?

A

The wall which closes off the body chamber as the nautilus grows

26
Q

What is the Septal neck on a Nautiloid?

A

An extension of the septum protruding back towards the protoconch

27
Q

What is the Siphuncle on a Nautiloid?

A

A tube passing through the septal neck which interconnects the chambers

Controls gas & water levels for buoyancy control

28
Q

What are the 3 distinct types of Ammonoids?

A

• Goniatites
Characterised by relatively simple zig-zag suture patterns with smooth lobes and saddles

• Ceratites
Developed frilly or more complex lobes, but the saddles remained simple

• Ammonites
Developed very complex frilly/crenulated lobes and saddles and very long suture lines

29
Q

Why are Ammonoids such good zone fossils?

A

High preservation potential: contain hard parts
• High preservation potential: mostly small organisms, therefore buried quickly
• Were abundant: reproduced many offspring at one time
• Were widespread: wide geographical distribution in a relatively short period of time due to their nektonic mode of life
• Preserved in a range of environments, water depths, and rock types as they’re not facies dependent
• Evolved rapidly: large number of short-lived evolutionary stages
• Easily recognisable evolutionary stages

30
Q

What are Graptolites?

A

Extinct marine organisms that lived in colonies, most floated freely in the oceans, some may have been attached to the sea bed

31
Q

2 main modes of life of Graptolites?

A

Benthonic Pelagic
Epifaunal / infaunal Planktonic /
Nektonic
Vagrant / sessile

32
Q

2 main orders of Graptolites?

A

Dendroidea:
• The colony is a multibranched rhabdosome
• Many vertical stipes in a complex framework
• Horizontal bars (dissepiments) strengthen the structure
• Little use as zone fossils

Graptoloidea:
• Similar to dendroids, but thought to have evolved from the planktonic forms of Dendroid.
•

33
Q

What are Stipes? (Graptolites)

A

Stipe - branch of rhabdosome

34
Q

What are Theca’s {Thecae} (Graptolites)?

A

Theca - individual cup where one zooid lived

35
Q

What is the basic morphology of Graptolites?

A

• Formed organic-walled, stick- like colonies
• Essentially a skeleton of collagen (similar to what our finger nails are made of)
• Some colonies accommodated up to 5000 individual animals (zooids)

36
Q

Are Graptolites good zone fossils?

A

Graptolites are excellent zone fossils

• Contain hard parts that are decay resistant

• Preserved in fine grained black shales in deep water where preservation potential is high (small sediment, low oxygen and energy)

• Evolved rapidly with easily identifiable stages, each of which had a relatively short time range

• Planktonic marine mode of life (floated in ocean surface waters) and not environment-restricted achieving worldwide distribution in a short period of time

• Very abundant

37
Q

What are the evolutionary trends of Graptolites?

A
  1. Changes in number of stipes (reduction)
  2. Stipe Orientation
  3. Theca’s turned from simple cups into complex cups
  4. Theca arrangement
38
Q

What are bivalves?

A

Marine & freshwater molluscs
• First evolved in Cambrian
• Still alive today
• Two calcareous shells, usually equal in size (equivalve)
• Modern examples: cockles, clams, scallops, razor shells, mussels

39
Q

Are bivalves symmetrical?

A

Yes

• Equivalve
• 2 valves, each asymmetrical

• Joined along one edge by a flexible ligament (hinge)

• Plane of symmetry along hinge line
• Mirror image of each other

40
Q

What is dentition? (Bivalves)

A

• Helps to keep valves hinged

41
Q

How do bivalves open?

A

Via a ligament
Pulls valve apart when the internal muscles are relaxed

42
Q

What are the first 5 bivalve modes of life?

A

1: Pecten (scallop)
• Float / actively swim* between periods on seabed
• Strong ribs for high energy water
• Thin, light shell for floating
• Large central adductor muscle for swimming
• Nearly symmetrical, but ears not the same and umbo leans slightly to left

Repeatedly clap valves together
• Expel water out via ears
• Squirt jets of water backwards
• Propels it forwards
• Requires huge
amounts of energy
• Modern bivalves only
swim intermittently

2: Epifaunal cemented
cements to hard surfaces on seafloor using calcareous deposits
cements left valve(not a mirror image of upper right valve)
valve can take on shape of underlying rock
provides continual stable platform for growth
prevents them getting dislodged and destroyed in high energy conditions
sometimes crenulated commissure generally found in-situ
usually a large single adductor scar

3: Epifaunal byssally attached
• secretethincollagenousthreads (byssus) to attach themselves to objects for anchorage
• elongateshellswithflatventralsurface
• streamlinedshape to move with current
• anteriorofshell reduced
• musclescarsinside different sizes, anterior muscle reduced
• smallgapethrough which byssal threads emerge

4: Infaunal deep burrowers
• Burrow for protection
• Equivalve, and generally more
elongate shell
• Adductor muscles roughly equal
• Smoother, thinner shell
• Gapes in commissure; siphons remain outside closed shell
• Dentition reduced

5: Infaunal shallow burrowers Water
Sediment
Venus: shallow burrowing form with short retractable siphons.
Tellina tenuis: deposit feeder, long slender siphons suck up water/particles close to sediment surface
Cardium edule:
suspension feeder that uses its short siphons to draw in and expel water
Internal view of right valve
• Burrow for protection
• Equivalved
• Thick(ish) valves / ribs
• Adductor muscles roughly equal
• Circular forms burrow more slowly than smooth elongate forms •Reduced pallial sinus = short siphons

43
Q

What are Brachiopods?

A

Marine, invertebrate organisms
• Often lived on the seafloor, attached. What
terms would we use for this?
• Benthonic (often epifaunal sessile)
• Others lived free lying on the seafloor or
were burrowers
• Had 2 unequal sized valves
• Valves is the word we use for shells
• Usually made of chitin and calcium phosphate or calcium carbonate
• What size? 5mm to 8cm, some up to 38.5cm!

44
Q

Why do Brachiopods have a crenulated commissure?

A

Currents get separated = Larger surface area

As gape increases, more nutrients can enter, but so can larger particles

45
Q

Where are coral fossils typically found?

A

In Situ in carbonate rocks (limestone)

• When we compare modern and fossil corals, we can use the
principle of Uniformitarianism to deduce the environment

46
Q

What is COWMESS (corals)

A

Coral Reef Environment requirements:
• C clear
• O well oxygenated
• W warm
• M marine
• E high energy
• S normal salinity (3.5% dissolved solids)
• S shallow

47
Q

What do corals consist of?

A

Polyps

48
Q

Which part of corals get preserved?

A

Calcareous skeleton

49
Q

Basic morphology of corals?

A

Usually sack shaped (widest at the top)
• Mouth at centre top
• Attached at narrow base
• Hard calcite outer layer and inner body cavity

50
Q

Function of mouth of corals?

A

Mouth functions include:
1. Taking in food

  1. Discharging waste
  2. Discharging larvae
51
Q

What is the Corallite? (Corals)

A

The skeleton produced by one coral polyp

52
Q

What is a Coral’s Mode of Life?

A

• Symbiotic algae produce CaCO3 coral skeleton

• Algae need sunlight

• Coral polyps need microscopic plankton to feed on, catching them with tentacles

• So corals are constrained by the environmental needs of both algae and plankton

53
Q

What is the Tabula? (Corals)

A

Horizontal plates dividing the corallite skeleton

54
Q

What is a Columnella? (Corals)

A

Axial rod which supports the septa, running up the centre of some corals

55
Q

What is the Septa? (corals)

A

Vertical plates, dividing the corallite skeleton

• Can be major or minor
• Give the skeleton strength

56
Q

What is the difference between Solitary and Compound corals?

A

Solitary - alone
• Coralite (hard outer
skeleton) is conical
• Can be straight or curved (horn shaped)
• Skeleton grew upwards from base attached to sea floor
• One polyp secretes a single skeleton
On its own so no competition = space to grow = rounded shape

Compound - colonies (multiple polyps living together)
• Many coral polyps (corallites) growing together
• Many skeletons or corallites fused together: a colony
• Sometimes skeletons branch outwards
• Usually compete for space
• Competition for food etc.
• Corallites become hexagonal

57
Q

Which corals are fossils and modern?

A

Fossils:
• Tabulata
• Rugosa

Modern:
• Scleractina

Tabulate corals started in the Late Cambrian

Rugosa corals started in the Early to Mid Ordivician

Scleractina corals started in the End of Permian/ Early Triassic

58
Q

Summarise the three coral types we have looked at

A

Rugose
Septa & Columnella, extinct, 6 defined septa initially

Tabulate
Columnella only, extinct, less defined septa, well-defined tabulae

Scleractinian
Septa & Columnella, extant, 6 defined septa and tabulae present

Geology (F1,F2,F3,F4) (9 decks)

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