4-2 Cambrian explosion

Question 1

geological time line- how long for animal phyla evolution

Answer 1

• Origin of almost all animal phyla evolved shortly in terms of the geological timeline
In Canada, especially western, we have one of the finest collections of these Cambrian fossils

Question 2

cambrian fossils in canada

Answer 2

walcott Quarry - yoho national park BC
-Incredible level of preservation
Marble canyon BC - close to yoho, major find (motherlode)
over 50 sp. found

Question 3

what is largerstatten (marble canyon has this). what conditions cause this?

Answer 3

sites of exceptional fossil preservation
high diversity
• Best fossilization happens when there is
○ Rapid burial
○ Anoxic conditions to prevent scavenging decay
○ No re-working currents to provide physical protection
○ Little or no alteration after burial
○ Marine organisms with hard parts such as, bones, scales, etc.
Lageersatten commonly have several of these features

Question 4

examples of lager statten?

Answer 4

look at them, but important: pre cambrian: mistaken point, edicara hills
cambrian: burgesss shale BC (mid cambrian, walcott query and marble canyon) ,
devonian: tiktaalik in ellesmere island NU canada
Jurassic: solnhofen limestone germany - archaeopteryx

Question 5

when did the cambrian explosion begin? what led to better fossils?

Answer 5

• Cambrian explosion - began ca. 542 mya
• Exoskeleton and endoskeleton led to greater fossil preservation
Most animal phyla had evolved by end of cambrian 488 mya
ex. trilobites, chordata, echinodermata, branchiopoda

Question 6

look at chart of animal phyla and occurance in fossil record. what does it suggest?

Answer 6

thick line past 541 mya for arthropod, priapulida, mollusca, sponges, and branchiopods - suggests that these groups evolved prior to cambrian based on DNA - but fossil record suggests only sponges started before cambrian - argument that the fossils represent some phyla some groups but most came from the cambrian period - but dna suggests otherwise
• Based on time calibrated dna analysis
• Not sure which is right but cont, w idea that most living anima; phyla evolved in cambrian

Question 7

important developments with cambrian explosion?

Answer 7

• Entirely new modes of 
	locomotion - swimming, 
	burrowing, climbing 
	• First segmented body 
	plans, external 
	skeletons, appendages, 
	notochord 
	• Astonishing diversity of 
	body plans! 
	• exs. Anomalocaris, Pikaia, 
	Hallucigenia, Marella, 
and Ottoia

Question 8

describe anomalocaris

Answer 8

• “abnormal shrimp”
• Extinct genis of early arthropods
““split”Mouth structure - probably top predators

Question 9

describe opabinia and hallucigenia

Answer 9

• Opabinia
• Stem group of arthropods - extinct
• Hallucigenia
• Phylum lobopodia
• Articulated fossils from their shells - some from china, and isolated spines worldwide
•
Suggested to be early ancestor of living velvet worms (phylum onychophora) OR ancestor of arthropods

Question 10

describe pikaia. how does it differ from lanclets

Answer 10

• Primitive chordate, lacked a well-defined head, small (1.5 in)
• Once thought to be close ancestor of all vertebrates -
• Antennalike tentacles on head and series of short apendages - maybe linked to gill slits - on each side of head
Differs from lanclet in these ways - closer to hag fish, still definitely a chordate

Question 11

describe the two burgess shale xritters found

Answer 11

• Species of trilobite - early arthropods
• Some of the first groups of arthropods - hard shelled, body segmented + legs
• Paleozoic era
• 8 orders w 150 families - LOTS of species of them - new discovered almost every year
• Most diverse group of any extinct organisms
• Diversity in size + form from 1mm all the way to 2 feet in length
some of the most well known fossils from cambrian

Question 12

describe leanchoilia

Answer 12

• Sp. Arthropod from cambrian site
  
  • Like a shrimp
  • Well presented in burgess shale
  • Also found in china

Question 13

What caused rapid increase in diversity during cambrian

Answer 13

• Rapid change in genes regulating

Question 14

What caused rapid increase in diversity during cambrian: intrinsic causes

Answer 14

§ Change in body plan organization

Exoskeletons/locomotion - predator/prey arms race, grow at faster rate = leads to change in body plan + gene expression

Question 15

What caused rapid increase in diversity during cambrian: extrinsic causes

Answer 15

§ Major climate changes

Increases o2 level = higher metabolisms + growth

Question 16

What caused rapid increase in diversity during cambrian: genetic causes

Answer 16

§ Evolution of hox gene complex
§ Regulation of patterns of anatomical
development
§ - Provided developmental flexibility
§ Contributed in patterns to build bodies capable
of high-energy directed locomotion (Holland,
2015)

Question 17

land mass in late proterozoic? (approx 650 mya)

Answer 17

800 mya supercontient (pangea)

Question 18

look at map of early cambrian continents. what did we see by start of cambrian?

Answer 18

landmasses were breaking up into smaller land masses = increasing area of continental shelfs and producing shallow seas
•
• = higher amount of sunlight = increase in O2

Question 19

What happened to these early ‘experiments’ in body plans?

Answer 19

○ • Normal levels of extinction undoubtedly accounts for some losses
causes could include competition, predation, failure to adapt to environmental change: i.e., natural selection
major extinction event

Question 20

what happened at end of cambrian? what does contingency refer to?

Answer 20

• End of Cambrian was marked by a major extinction event
Stephen Gould used the term ‘contingency’ to refer to the chance loss of
life forms owing to occasional and unpredictable events (such as
bolide impacts), events that natural selection cannot prepare for
Great Ordovician Biodiversification Event: The lesser known but larger sibling of the Cambrian Explosion!!
opabinia and wiwaxia did not survive cambrian