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Lecture 15

BIOLOGY 1M03 Lecture Notes - Lecture 15: Genetic Drift, Ediacara Hills, Shocked QuartzPremium


Department
Biology
Course Code
BIOLOGY 1M03
Professor
Jon Stone
Lecture
15

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BIOLOGY1M03Lecture15PhylogeniesandtheHistoryofLife(Continued)
MorphologicalInnovation:
● Morphologicalinnovationalsocantriggeradaptiveradiations,aswasseenin
theCambrianexplosion.
○ Manyimportantdiversificationeventsinevolutionaryhistoryinitiated
withtheoriginofakeymorphologicaltraitthatalloweddescendentsto
liveinnewareas,exploitnewfoodsources,ormoveinnovelways.
TheCambrianExplosion:
● Thefirstanimalssponges,jellyfish,andsimple'worms'appearinthefossil
recordapproximately565mya,attheendProterozoiceon.
○ Approximately50millionyearslater,animalsdiversifiedintoalmostall
themajorgroupslivingtoday.Thisdiversificationisknownasthe
Cambrianexplosion.Thisperiodsawwhatisarguablythemost
evolutionarychangeinevolutionaryhistory.
○ TheCambrianexplosionisdocumentedbythreemajorfossil
assemblages,calledtheDoushantuo,Ediacaran,andBurgessShale
fossils.Theseexceptionallyrichdepositsbefore,during,andafterthe
Cambrianexplosionmakethefossilrecordforthisevent
extraordinarilycomplete.
○ FromtheDoushantuoformationinChina,whichdatesto570mya,
researchersidentifiedmicrofossil(tinyfossil)spongesandanimal
embryosinearlydevelopmentalstages.Thesewerethefirstanimal
typesofEarth.
○ TheEdicaranfossils,intheEdiacaraHillsinAustralia,wereidentified
bypaleontologistsasfossilsofsponges,jellyfish,combjellies,and
tracesfromotheranimals(e.g.,burrowsandtracks)datedto544565
mya.
■ Theseweresmall,softbodiedanimalsthatburrowedin
sediments,satimmobileontheseafloor,orfloatedinthe
water.
○ TheBurgessShalefossils:Virtuallyeverymajorlivinganimalgroupis
representedintheBurgessShalefossilsfromBritishColumbia,
Canada,whichdateto515525mya.
■ Thesefossilsindicateatremendousincreaseinsizeand
morphologicalcomplexity,accompaniedbydiversificationin
howanimalslived.Thisdiversificationfilledmanyecological
nichesstillfoundinmarinehabitatstoday.
○ Increasedoxygenlevels,predation,novelnichesandnewgenes
triggeredtheCambrianexplosion.(Newgenes:i.e.,Hoxgenes.They
encodedtranscriptionfactorproteinproduct(turnonoroffgenes),
contained60aminoacidDNAbindingsequence('homeobox'),and
exhibit'colinearity'inexpression.)
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