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