week 11 lectures biol1020h
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BioTRANSCRIPT
Overview: Lost Worlds • Past organisms were very different from those now
alive • The fossil record shows macroevolutionary
changes over large time scales, for example: – The emergence of terrestrial vertebrates – The impact of mass extinctions – The origin of flight in birds
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• The origin of life: hypotheses • Early earth condi5ons and synthesis of
organic compounds on early earth • Fossil record • Single‐cell to mul5‐cellular organisms • Origin of mammals • Plate tectonics (evidence of related
organisms on different con5nents) • Mass ex5nc5ons (past and future)
Week 11: The History of Life on Earth (Chapter 25)
First, some background about early earth:
The earth formed about 4.6 billion years ago, probably condensing from a vast cloud of dust and rocks surrounding a young sun.
No life could have existed for first 2‐3 million years as collisions from comets from outer space would have bombarded the earth, crea5ng far too much heat (think like Venus today)
First atmosphere probably mostly water vapor that, as
the earth cooled, condensed into oceans with most hydrogen escaping into space. Atmosphere also contained chemicals from volcanic erup5ons
What is recent newsworthy event that has as its aim, understanding the origin of earth’s founda5on?
• In the 1920s, A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a ‘reducing’ environment (i.e., electron-adding). Energy came from lightning and intense UV radiation
• In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules including amino acids, in a reducing atmosphere was possible
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Mas
s of
am
ino
acid
s (m
g)
Num
ber o
f am
ino
acid
s
20
10
0 1953 2008
200
100
0 1953 2008
Amino acid synthesis in a simulated atmosphere of early earth based on 1953 (by Miller) and 2008 (by others) experiments
Amino acids have also been found in meteorites. These could have acted as a source for early life. Fragments of a metor that fell in Australia in 1969 contained 80 amino acids.
Results of ‘volcanic atmosphere test’ in 1953 and 2008 (where more control over expt)
• However, early atmosphere may not have been reducing • Instead of forming in the atmosphere, the first organic
compounds may have been synthesized near volcanoes or deep-sea vents (first discovered in 1977 near Galapagos Islands)
• Miller-Urey–type experiments demonstrate that organic molecules could have formed with various possible atmospheres
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Amino acids are not sufficient to produce life, because you also need replica5ng organisms
The dawn of the RNA World: Toward func5onal complexity through liga5on of random RNA oligomers. Briones et al. 2009 RNA. 15: 743–749.
1. RNA monomers have been produced spontaneously from simple molecules 2. Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock. 3. These could have been early catalysts for chemical reactions
Did life start from material from Mars?
Benner (2013) has argued that Molybdenum must have arrived from Mars through Meteorites or volcanoes, as only oxidized mineral form of Molybdenum could have catalyzed reac5ons to start the process of replica5on. Only Boron and Molybdenum can stop organic molecules from turning to tar
"It's lucky that we ended up here nevertheless, as certainly Earth has been the be8er of the two planets for sustaining life. If our hypothe=cal Mar=an ancestors had remained on Mars, there might not have been a story to tell."
Stephen Benner in 29 August 2013 Guardian states…
Protocells • Replication and metabolism are key properties of
life and may have appeared together (but scientists are divided on this point)
• Protocells may have been fluid-filled vesicles with a membrane-like structure
• Evidence: In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer (especially when adding soft mineral clay from volcanic ash!)
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(b) Reproduction
20 µm
(c) Absorp5on of RNA
Some of these vesicles can perform metabolic reac5ons using external sources. Orange is RNA coated clay par5cles
Figure 25.3a
Time (minutes)
Precursor molecules plus montmorillonite clay
Precursor molecules only R
elat
ive
turb
idity
, an
inde
x of
ves
icle
num
ber
0 20 40 60 0
0.2
0.4
(a) Self-assembly
Abio5cally produced vesicles: structure needed for replica5on processes
1. Early natural selec5on would have favoured forms of RNA best suited to the environment and best able to self‐replicate (i.e., natural selec5on..if it didn’t
reproduce it would not be there through 5me!) 2. RNA could have provided template for some informa5on that was passed on (e.g., gene5c informa5on) and eventually, DNA nucleo5des, a more stable molecule to encode gene5c informa5on. RNA molecules could then have taken on roles as regulators and intermediates in the transla5on of genes
A two‐step process towards DNA replica5on and then all further life on earth
The Beginnings of the RNA WORLD
p‐RNA (pyranosyl‐RNA) pep5de nucleic acid)
Review: Conditions on early Earth made the origin of life possible
• Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages:
1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into
macromolecules 3. Packaging of molecules into protocells
(maintaining internal chemistry different than surroundings, e.g. vesicles)
4. Origin of self-replicating molecules © 2011 Pearson Education, Inc.
The Fossil Record • Sedimentary rocks are deposited into layers
called strata and are the richest source of fossils
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• Few individuals have fossilized, and even fewer have been discovered (often fortuitous, e.g., northern Alberta pipeline discovery, Oct 2013, fisherman finding another species of duck-billed dinosaur in Castle River, AB after flood, Aug 2014)
• The fossil record is biased in favor of species that – Existed for a long time – Were abundant and widespread – Had hard parts
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Main take‐home messages from fossiliza5on
Tail of 10 m hadrosaur (Duck‐billed Dinosaur)
Dimetrodon
Stromatolites
Fossilized stromatolite
Coccosteus cuspidatus
4.5 cm
0.5 m
2.5 cm
Present
Rhomaleosaurus victor
Tiktaalik
Hallucigenia
Dickinsonia costata
Tappania
1 cm
1 m
100 mya
175 200
300
375 400
500 525
565 600 1,500
3,500
270
How Rocks and Fossils Are Dated: with difficulty because fossils do not incorporate
elements with long half lives
If volcanic ash above is aged at 525 million years ago, and below is 535 mya then the fossils are assumed to be roughly from 530 mya
How Rocks and Fossils Are Dated • Sedimentary strata reveal the relative ages of fossils
(older occur deeper in sediments) • The absolute ages of fossils can be determined by
radiometric dating • A “parent” isotope decays to a “daughter” isotope at a
constant rate • Each isotope has a known half-life, the time required
for half the parent isotope to decay • Igneus rock and older sediments aged with uranium
and potassium isotopes that degrade more slowly (e.g., has a half life of 4.5 billion years)
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Accumulating “daughter”
isotope
Frac
tion
of p
aren
t is
otop
e re
mai
ning
Remaining “parent” isotope
Time (half-lives) 1 2 3 4
1 2
1 4 1 8 1 16
Figure 25.5
Carbon‐14 has a half life of 5,730 years‐ use ra5os of carbon‐14 to carbon‐12 (non‐decaying), ages fossils up to 75,000 years old; otherwise use age of sediments surrounding fossil or other isotopes
• The geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons
• The Phanerozoic encompasses multicellular eukaryotic life
• The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic
Key events in life’s history include the (1) origins of single-celled and multi-celled
organisms and (2) the colonization of land
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Table 25.1a Ph
anerozoic
Table 25.1b Ph
anerozoic
• Major boundaries between geological divisions correspond to extinction events in the fossil record (e.g., Mesozoic/Cenozoic boundary) or periods of rapid radiation (e.g., the Cambrian explosion at beginning of Paleozoic)
© 2011 Pearson Education, Inc.
Early creatures: Tubeworms, which were first discovered when the floor of
the Pacific was explored
Mouthless, gutless, legless animals that rely on microbes for food. Seem to have a symbio=c rela=onship with sulfur‐oxidizing prokaryotes
Origin of solar system and Earth
Prokaryotes
Atmospheric oxygen
Archaean
4
3 of y e
Figure 25.7-1
Origin of solar system and Earth
Prokaryotes
Atmospheric oxygen
Archaean
4
3
Proterozoic
2
Animals
Multicellular eukaryotes
Single-celled eukaryotes
1
of y e
Figure 25.7-2
Origin of solar system and Earth
Prokaryotes
Atmospheric oxygen
Archaean
4
3
Proterozoic
2
Animals
Multicellular eukaryotes
Single-celled eukaryotes
Colonization of land
Humans
Cenozoic
1
of y e
Figure 25.7-3
Prokaryotes
1
2 3
4
y
i
o
ll o B
f
Figure 25.UN02
The First Single-Celled Organisms
• The oldest known fossils are stromatolites, rocks formed by the accumulation of sedimentary layers on bacterial mats
• Stromatolites date back 3.5 billion years ago • Prokaryotes were Earth’s sole inhabitants from 3.5
to about 2.1 billion years ago
© 2011 Pearson Education, Inc.
Figure 25.UN03
Atmospheric oxygen
1
2 3
4
y
i
o
B
f
Photosynthesis and the Oxygen Revolution
• Most atmospheric oxygen (O2) is of biological origin
• O2 produced by oxygenic photosynthesis, reacted with dissolved iron and precipitated out to form banded iron formations
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• By about 2.7 billion years ago, O2 began accumulating in the atmosphere and rusting iron-rich terrestrial rocks
• This “oxygen revolution” from 2.7 to 2.3 billion years ago caused the extinction of many prokaryotic groups
• Some groups survived and adapted using cellular respiration to harvest energy
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• The early rise in O2 was likely caused by ancient cyanobacteria (oxygen-releasing photosynthetic bacteria)
• A later increase in the rise of O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts
© 2011 Pearson Education, Inc.
Figure 25.UN04
Single- celled eukaryotes
1
2 3
4
y
i
o
B
f
The First Eukaryotes • The oldest fossils of eukaryotic cells date back 2.1
billion years
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Theory of ‘serial endosymbiosis’
Figure 25.9-1
Plasma membrane
DNA
Cytoplasm
Ancestral prokaryote
Nuclear envelope
Nucleus Endoplasmic reticulum
Serial endosymbiosis
Infolding of plasma membrane
Figure 25.9-2
Plasma membrane
DNA
Cytoplasm
Ancestral prokaryote
Nuclear envelope
Nucleus Endoplasmic reticulum
Aerobic heterotrophic prokaryote
Mitochondrion
Ancestral heterotrophic eukaryote
Infolding of plasma membrane
Cell with nucleus and endomembrane system
Figure 25.9-3
Plasma membrane
DNA
Cytoplasm
Ancestral prokaryote
Nuclear envelope
Nucleus Endoplasmic reticulum
Aerobic heterotrophic prokaryote
Mitochondrion
Ancestral heterotrophic eukaryote
Photosynthetic prokaryote
Mitochondrion
Plastid
Ancestral photosynthetic eukaryote
• Key evidence supporting an endosymbiotic origin of mitochondria and plastids:
– Inner membranes are similar to plasma membranes of prokaryotes
– Division is similar in these organelles and some prokaryotes
– These organelles transcribe and translate their own DNA (e.g., mtDNA)
– Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes
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Origin of Multicellularity • The evolution of eukaryotic cells allowed for a
greater range of unicellular forms • A second wave of diversification occurred when
multicellularity evolved and gave rise to algae, plants, fungi, and animals
© 2011 Pearson Education, Inc.
Figure 25.UN05
Multicellular eukaryotes
1
2 3
4
y
i
o
B
f
The Earliest Multicellular Eukaryotes • Comparisons of DNA sequences date the common
ancestor of multicellular eukaryotes to 1.5 billion years ago
• The oldest known fossils of multicellular eukaryotes are of small algae that lived about 1.2 billion years ago
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• The “snowball Earth” hypothesis (controversial) suggests that periods of extreme glaciation confined simple multicellular life to the equatorial region or deep-sea vents from 750 to 580 million years ago
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The Cambrian Explosion • The Cambrian explosion refers to the sudden
appearance of fossils resembling modern animal phyla in the Cambrian period (535 to 525 million years ago)
• A few animal phyla appear even earlier: sponges, cnidarians, and molluscs
• The Cambrian explosion provides the first evidence of predator-prey interactions
• The Chinese fossils suggest that “the Cambrian explosion had a long fuse”
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Exam news Exam will consist of mul5ple choice ques5ons (as per mid‐term, NO ESSAY QUESTION)
Exam is worth 30% of the final mark
Mul5ple choice ques5ons: 10% of 30% will be based on first half, and 20% of 30% on the second half
There will be a review lecture on the last day of class (2 December)
Readings for this week: Chapter 25 only. For next week parts of chapters (exact page numbers will be provided by Prof. Dorken)
Figure 25.UN06
Animals
1
2 3
4
y
i
o
B
f
Figure 25.10
Sponges
Cnidarians
Echinoderms
Chordates
Brachiopods
Annelids
Molluscs
Arthropods
Ediacaran Cambrian PROTEROZOIC PALEOZOIC
Time (millions of years ago) 635 605 575 545 515 485 0
Recent fossil evidence from China suggests living phyla were present 10’s of millions of years previous to Cambrian explosion. DNA evidence also supports this earlier radia=on
Burgess shale Yoho Na5onal Park, BC. (2300 m seabed)
Figure 25.8
“Oxygen revolution”
Time (billions of years ago) 4 3 2 1 0
1,000
100
10
1
0.1
0.01
0.0001
Atm
osph
eric
O2
(per
cent
of p
rese
nt-d
ay le
vels
; log
sca
le)
0.001
Chengjiang Mao5anshan Shales
Theory has it that oxygen finally reached a concentra5on in atmosphere where animals could have a higher energy level. Also as eukaryotes engulfed mitochondria to obtain a higher energy level, predators arose, are generally larger and so more likely to leave traces in fossil record!
Figure 25.UN07 Colonization of land
1
2 3
4
y
ago i
o
ll B
f
The Colonization of Land • Fungi, plants, and animals began to colonize land
about 500 million years ago • Vascular tissue in plants transports materials
internally (i.e., vascular plants!) and appeared by about 420 million years ago
• Plants and fungi today form mutually beneficial associations and likely colonized land together (e.g., mycorrhizae aid in absorption of water and minerals from the soil and obtain their organic nutriets from plants)..present in the oldest fossilized plants.
© 2011 Pearson Education, Inc.
Fossilized mychorrhiza‐like associa5ons
• Arthropods and tetrapods together are the most widespread and diverse land animals
• Tetrapods evolved from lobe-finned fishes (around 365 million years ago, Sarcopterygii (name of sub‐class of bony fisho)
‘Living fossil’ lobe‐finned fish: coelocanths Current distribu5on: East coast of Africa and Indonesia of about 1000 individuals
Neanderthal DNA Find Your Inner Neanderthal! Learn About Neanderthal Lineage.
The Origin of Mammals
• Mammals are tetrapods, as are amphibians, reptiles and birds..the first vertebrates to walk on land.
• The evolution of unique mammalian features can be traced through gradual changes in skull morphology over time
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Figure 25.6a
OTHER TETRAPODS
†Dimetrodon
†Very late (non- mammalian) cynodonts
Mammals
Synapsids
Therapsids
Cynodonts
Reptiles (including dinosaurs and birds)
Key iden5fica5on feature of mammals is a single bone in the lower jaw (the dentary)(among other features, see BIOL4180H), that hinges differently: can easily see loss of smaller bones in fossils of pre‐mammals
Figure 25.6b
Temporal fenestra
Hinge
Temporal fenestra
Hinge
Synapsid (300 mya)
Therapsid (280 mya)
Key to skull bones
Articular Quadrate
Squamosal Dentary
Figure 25.6c
Hinge
Hinge
Hinges
Temporal fenestra (partial view)
Early cynodont (260 mya)
Very late cynodont (195 mya) (plus early mammals)
Later cynodont (220 mya)
Key to skull bones Articular Quadrate
Squamosal Dentary
Crusafon5a‐ an early true mammal
Thrinaxadon: a late cynodont
• The history of life on Earth has seen the rise and fall of many groups of organisms (e.g., loss of anaerobic prokaryotes, dinosaurs, dominant amphibians, ancient conifers, etc.)
• The rise and fall of groups depends on speciation and extinction rates within the group (e.g., more speciation than extinction leads to dominance of that group).
• Extinction rates have been influenced by plate tectonics (among other things)
The rise and fall of groups of organisms reflect differences in speciation and
extinction rates
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Plate Tectonics • At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago
• Earth’s crust is composed of plates floating on Earth’s mantle
Crust
Mantle
Outer core
Inner core
Figure 25.13
Juan de Fuca Plate
North American Plate
Caribbean Plate
Cocos Plate
Pacific Plate
Nazca Plate
South American Plate
Eurasian Plate
Philippine Plate
Indian Plate
African Plate
Antarctic Plate
Australian Plate
Scotia Plate
Arabian Plate
Tectonic plates move slowly through the process of continental drift Oceanic and continental plates can collide, separate, or slide past each other
Interactions between plates cause the formation of mountains and islands, and earthquakes
Figure 25.14a
135
251
Mes
ozoi
c Pa
leoz
oic
Mill
ions
of y
ears
ago
Laurasia
Gondwana
Figure 25.14b
65.5
Pres
ent
Cen
ozoi
c Eurasia
Africa South America
India
Antarctica
Madagascar
Mill
ions
of y
ears
ago
Consequences of Continental Drift • Formation of the supercontinent Pangaea about
250 million years ago had many effects – A deepening of ocean basins – A reduction in shallow water habitat – A colder and drier climate inland
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The distribution of fossils and living groups reflects the historic movement of continents
– For example, the similarity of modern ratites (non-flying tall birds) in parts of South America, Australia, New Zealand and Africa is consistent with the idea that these continents were formerly attached
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Marsupials originated in what is now Asia and reached Australia via South America while con5nents were s5ll
joined
Sinodelphys szalayi
Mass Extinctions • The fossil record shows that most species that
have ever lived are now extinct • Extinction can be caused by changes to a species’
environment • At times, the rate of extinction has increased
dramatically and caused a mass extinction • Mass extinction is the result of disruptive global
environmental changes
© 2011 Pearson Education, Inc.
25
20
15
10
5
0
542 488 444
Era Period
416
E O S D
359 299
C
251
P Tr
200 65.5
J C Mesozoic
P N Cenozoic
0
0
Q
100
200
300
400
500
600
700
800
900
1,000
1,100 To
tal e
xtin
ctio
n ra
te
(fam
ilies
per
mill
ion
year
s):
Num
ber o
f fam
ilies
:
Paleozoic
145
Figure 25.15
The “Big Five” Mass Extinction Events: loss of 50% of species!
Factors that may have contributed to these extinctions
– Intense volcanism in what is now Siberia – Global warming resulting from the emission of
large amounts of CO2 from the volcanoes – Reduced temperature gradient from equator to
poles – Oceanic anoxia from reduced mixing of ocean
waters – Meteorites
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NORTH AMERICA
Yucatán Peninsula
Chicxulub crater
The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time as the Cenozoic/Mesozoic extinction (65 mya)
Half of all marine species and many terrestrial plants and animals, including most dinosaurs went extinct. Thin layer of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago. Dust clouds caused by the impact would have blocked sunlight and disturbed global climate.
Ancestral mammal
ANCESTRAL CYNODONT
250 200 150 100 50 0 Time (millions of years ago)
Monotremes (5 species)
Marsupials (324 species)
Eutherians (5,010 species)
Adap5ve radia5on of mammals as a result of empty niches created by loss of terrestrial dinosaurs
Consequences of ex5nc5ons
Is a Sixth Mass Extinction Under Way? • Scientists estimate that the current rate of
extinction is 100 to 1,000 times the typical background rate
• Extinction rates tend to increase when global temperatures increase (a weak trend)
• A sixth, human-caused mass extinction is likely to occur unless dramatic action is taken to reduce humans impact on the earth! (‘the emerging Anthropocene’)
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Mass extinctions
Cooler Warmer
Rel
ativ
e ex
tinct
ion
rate
of m
arin
e an
imal
gen
era
3
2
1
0
-1
-2 -3 -2 -1 0 1 2 3 4
Relative temperature
Figure 25.17
Source: NOAA 2013
Modern ex5nc5ons: examples
1970s Acornshell Epioblasma haysiana Cumberland and Tennessee River systems in Alabama, Virginia, Tennessee and Kentucky mollusc
1970 Clear Lake Splirail Pogonichthys ciscoides Clear Lake, California fish 1969 Blackfin Cisco Coregonus nigripinnis Lake Huron and Lake Michigan fish 1969 Tubercled Blossom Epioblasma torulosa torulosa Alabama, Illinois, Indiana, Kentucky,
Ohio, Tennessee and West Virginia mollusc 1968 Striped Bass, St. Lawrence Estuary popula5on Morone saxa=lis sp. 3 Quebec
fish 1967 Angled Riffleshell Epioblasma biemarginata Alabama, Kentucky and Tennessee
mollusc 1967 Narrow Catspaw Epioblasma lenior Tennessee River system in Virginia, Tennessee
and Alabama mollusc 1967 Lined Pocketbook Lampsilis binominata Upper Charahoochee and Flint River
systems in Alabama and Georgia mollusc mid 1960s Turgid Blossom Epioblasma turgidula Alabama, Arkansas and Tennessee
mollusc 1964 Bluntnose Shiner Notropis simus simus Rio Grande River in New Mexico and
Texas fish 1964 Lake Ontario Kiyi Coregonus kiyi orientalis Ontario fish 1964 Bay Springs Salamander Plethodon ainsworthi Jasper County, Mississippi
amphibian
Par5al list of the 31+ North American ex5nc5ons since 1960’s…
More EVO‐DEVO! Evolu5onary transforma5on can result from heterchrony…changes in the rate or 5ming of development events.
Chimpanzee fetus and adult
Human fetus and adult
Figure 25.22
Gills
Axolotl: retains larval features of amphibians (including gills) but can breed. An example of paedomorphosis (from ‘paedos’ meaning child and ‘morphosis’ meaning shape or form. Probably result of change at single locus
Figure 25.27
Holocene
Pleistocene
Pliocene
0
5
10
Anchitherium
Mio
cene
15
20
25
30 Olig
ocen
e
Mill
ions
of y
ears
ago
35
40
50
45
55
Eoce
ne
Equus
Pliohippus
Merychippus
Sino
hipp
us
Meg
ahip
pus
Hyp
ohip
pus
Arc
haeo
hipp
us
Para
hipp
us
Mio
hipp
us
Mesohippus
Prop
alae
othe
rium
Pach
ynol
ophu
s
Pala
eoth
eriu
m
Hap
lohi
ppus
Epih
ippu
s
Oro
hipp
us
Hyracotherium relatives
Hyracotherium
Key Grazers Browsers
Hip
pario
n
Neo
hipp
ario
n
Nan
nipp
us
Cal
lippu
s Hip
pidi
on a
nd
clos
e re
lativ
es
Evolu5onary trends: are they predictable or direc5onal?