BIO 200, Test #1

Animals after the Cambrian that are different

-Boedaspis trilobite (russia) -Erbenochile trilobite (clearly segmented w complex compound eye that could see 360 degrees --> suggests predators were a concern) -Anamolocarus "anomalous shrimp" (16,000 lenses, complex eye, predator)

Just before Cambrian Explosion...

-Ediacaran Period (635-541 Mya) -unambiguously multicellular life existed but it is unclear how this life relates to other things (is it animal, plant, neither?)

Taxonomy

-a way of organizing things -Kingdom, phylum, class, order, family, genus, species

Cocnlusions about FR

-imperfect nature of fossil record as explanation for the rarity of animal fossils before the Cambrian does not stand up to scrutiny -trace fossils prove that fossilization was possible -features of Cambrian animals evolved in large bodied organisms -difficult to imagine how large bodied organisms could have been present but infreq. preserved

Cambrian

-larger forms rapidly appear in f.r. -abundant body fossils easily recognizable as animals -suggests that bilaterally symmetrical animals acquired skeletons during Cambrian

Charnia Masoni

-lived @ the bottom of the ocean, beneath the photic zone (not plant) -set in motion searches for other fossils in Pre-Cambrian sediments around the world

Lecture 4 Conclusions

-phylogenies depict lines of descent, not similarity -mutation=fundamental source of biological innovation -evolution drives variation & produces biological diversity -to understand the role of evolution in the Cambrian explosion, we need language to discuss living & extinct groups

Up to this point

-pre-cambrian multicellular life=simple -post-cambrian organisms interacted w environment and eachother using complex structure

Cambrian Explosion

-singular event in history of complex life -appearance of animal life in fossil record

Holocene

.012 ma, glaciation (ice age)

Pleistocene

.05 ma, megafaunal extinctions (large animals, due to human migrations) max sea level = Pleistocene Interglacial

How to find monophyletic group

1) find the most recent common ancestor (down the tree) 2)locate all descendants (back up)

How to find pan group

1) go down tree to just before the branch leading to the next most closely related living relative that is not a member of the crown group 2) everything up tree from this point = pan group

Why are stem group fossils not in FR?

1) maybe very small -key features of bilaterian ancestors developed in large organisms (like blood vascular system) -also there are extremely small trace fossils 2) maybe ancestral bilaterians were so simple that no phylum level distinctions arose suddenly @ base of Cambrian -change in Dev @ base of Cambrian... what then caused this change (Acceptable as an explanation but not an ultimate one!) 3. maybe ancestral bilaterians were large and arose prior to the cambrian but have not been located due to rarity -sampling problem -unlikely bc there is an extensive trace fossil record that includes some bilaterian animals

Assumptions of evolution by natural selection

1.traits are heritable 2.traits impact fitness 3.traits that positively impact fitness are selected for, traits that negatively impact fitness are selected against

Early Cretaceous

120 ma, first flowering plants

Late Jurassic

150 ma, continents begin to look recognizable

Mid Jurassic

170 ma, first birds

Early Miocene

20 ma

Late Triassic

220 ma, first dinosaurs, first mammals 200 ma

Mid Triassic

240 ma

Late Permian

260 ma, biggest mass extinction about to occur

Early Permian

280 ma, world dried out

Life originated

3.77-4.28 bya

Late Pennsylvanian

300 ma

Mid Mississippian

340 ma, first reptiles

Late Eocene

35 ma, just prior to first apes

Late Devonian

370 ma, first amphibians

The earth originated

4.54 bya

Early Devonian

400 ma, first vascular plants, insects shortly afterwards

Early Silurian

440 ma, plants diversify

Late Ordovician

450 ma, first land plants

Mid-Ordovician

470 ma, early vegetation

Early Eocene

50 ma, horses, whales

Late Cambrian

500 ma

Early Cambrian

540 ma

Cambrian Period

541 mya -defined by first appearance of trace fossil: Treptichnus pedum

unambiguous animal fossils appear

541 mya (relatively recent)

Spiggina

550 Mya, Ediacaran, segmented organism, early animal?, could be arthropod?, among first bilaterally symmetrical w head and tail

Ikaria Warioota

560-551 Mya, earliest bilaterally symmetrical animal that predates the base of the Cambrian

Late Proterozoic

600 ma, no vegetation, southern pole=ice shallow seas (good for life) show modern day fossil beds (light blue)

Cretaceous-Tertiary Boundary

65 ma, extinction of non-avian dinosaurs

Late Cretaceous

90 Ma

genetic drift

A change in the gene pool of a population due to chance

Clade

A group of species that includes an ancestral species and all its descendants.

The event to cause disparity only happened once

Cambrian Explosion

Pan group

Crown group & all organisms that share an ancestor w the crown group more recently that w other living organisms

Before Cambrian organisms were

Ediacaran (Dickinsonia)

Fossils discovered in Pre-Cambrian rocks are called

Ediacaran Fauna -named derived from hills in Australia -Fauna is a misnomer b/c not animals -no appendages, eyes, body openings -but they often have telltale bilateral symmetry

Dickinsonia

Ediacaran, bilateral symmetry

Kimberella

Ediacaran, mollusk like muscular foot, clearly bilateral symmetry, known from about 1000 fossils... is it a primitive mollusk?

Oldest bilateral animal

Ikaria Warioota (trace fossils make it known as animal)

Earth timeline as calendar year

Jan 1: formation of earth Feb-march: origin of life Nov 17 @ 11:10: Cambrian explosion Nov 21: first fish Nov24: first vascular plants, dinos Dec 15: first mammals Dec 25: first primates Dec 31 (11;23;16 p.m.) modern humans Dec 31 (11:59:58.3) industrial revolution

Cambrian Explosion

Onset of morphological diversity onset of disparity unique (541 mya, after 88% of earths history)

What are the 5 animal clades

Porifera (sponges) Ctenophora (comb jellies) Placozoa (flat animals) Bilateria (bilateral symmetry) Cnidaria (jellies)

Not complex life

Pre- cambrian (pre-541 mya) "organisms" kimberella, early mollusk

Taxonomic group

Taxon, plural:taxa

Bilateral animals before the Cambrian

Yes, from new fossil evidence scientists discovered that Dickinsonia is an animal in 2018 Only animals produce cholesteroids Dickinosnia fossils in russia contain cholesteroids but surrounding sediments do not

Stem group

all members of the stem group are extinct, (pan group-crown group)

All living things descend from a common

ancestor

Anomalies in isotopes can cause

big changes in geol. or biol. history of earth!

Features of complex life

bilateral symmetry definitely an animal eyes anterior-posterior axis segmentation

Evolution produces

biological diversity -new species result from evolution

Evolution is the source of

biological innovation

Evolutions is the source of

biological innovation

Reptilia is not a monophyletic group because it includes

birds

Evolution

changes in gene frequency in a population over time -causes changes in traits that organisms possess

If Ctenophora is sister group to all animals

common ancestor of all animals had a nervous or nervous system evolved twice on its own

paraphyletic group

composed of some but not all members descending from a common ancestor (example:reptilia)

The Cambrian Explosion is unique b/c

defines onset of morphological diversity onset of visible life in fossil record/ unambiguous appearance of animals in f.r. first morphological diversification event

Charnwood forrest

exposed rock of pre-cambrian age 600 mya no fossils of large organisms (visible w unaided eye) thought to exist in rocks of this age until 1957 girl discovered Charnia masoni in England

Treptichnus pedum

fossil that defines base of Cambrian, must have had musculature to burrow, among first bilaterally symmetrical animals w vertically and horizontally structured burrows

Recency in a phylogeny is measured in

genealogical time

monophyletic group

group that consists of a single ancestral species and all its descendants

Complex life

immediately recognizable as living multicellular mobile organisms that interact w eachother & environment (animals, plants)

Crown groups appeared in the Cambrian

implies stem group history prior to cambrian

If Porifera (Sponges) sister group to all animals

it means nervous system was gained and lost

Cladograms illustrate

lines of descent step 1= data table of traits (hair, backbone, etc) step 2= venn diagram step 3= use venn diagram to create parsimonious tree

Diversification since the Cambrian has been

long term net positive trend although rate is not constant b/c of extinctions/mass extinctions

What is an animal?

monophyletic group of 5 clades

The 4 mechanisms of evolution

mutation, genetic drift, migration, natural selection

natural selection

non random process by which genes (and therefore traits) become more or less common

mutation is the only source of

novelty

A tree that uses genes as traits=

phylogeny

Paleographic maps

physically accurate renderings of surface of the earth @ diff. past times

The Cambrian explosion was

rapid in geological terms ( tens of millions) increase in DISPARITY of animal -also a diversification event

speciation occurs because of

reduced gene flow

Phylogenies depict lines of descent, NOT

similarity -sometimes organisms that are closely related are dissimilar and vice versa

Phylogenies depict lines of descent NOT

similarity, pay attention to Nodes not tips

After mass extinctions we see

subsequent diversification events

crown group

the group that contains the most recent common ancestor of living forms & all descendants, regardless of whether or not descendants are living (all crown groups=monophyletic)

fossil record

the history of life documented by imprints or remains in sedimentary rock

species are defined as

the most inclusive group of indiv. that can interbreed in nature

Nodes

the point where lines meet on a phylogeny, biological entities that existed in the past (ex: your ancestor os not a chimp, you and chimp share a common ancestor that was neither human nor chimp)

Animals are closely related if

they have the most recent common ancestor

phylo=

tree

Post Cambrian there were

unambiguous animals (trilobites)

Disparity

variation among themes (different animals/plants)

Diversity

variation w/in a theme high diversity=many species low disparity=all beetles ex: mosaic of beetles

Most modern animal phyla

were first observed in the f.r. @ the base of the Cambrian -# of animal phyla= mid to upper 30's - no animal phyla has ever gone extinct