Lecture 4: A N I M A L E V O L U T I O N :F R O M T H E C A M B R I A N T O T H E C E N O Z O I C

Question 1

what Eon, era, period and epoch are we in?

Answer 1

We are in:
*Phanerozoic Eon
*Cenozoic Era
*Quaternary Period
*Holocene Epoch

Question 2

how is life spread across geological time?

Answer 2

*Earth is ~4.5 Billion years old
*Not a lot happened for the vast majority of that

*Events within the last ‘3 hours’:
*540MYA -Cambrian Explosion
*360MYA –Vertebrates on land
*65MYA –Dinosaur extinction
*2MYA –Human evolution

Question 3

what happened in P R E-C A M B R I A N L I F E?

Answer 3

*For the majority of 3bn yrs -Microbial films growing on sediment surface *These did build up on top of each other to form reef like structures
*Snowball earth event terminates the period of microbial dominance due to anoxia
*Mid Ediacaran 580Ma –Gaskier’sglaciation opening of ecological niches

*Ediacaran biota: A glimpse into early complex life which sit at the base of the animal evolutionary tree
*Generally soft-bodied and feed through absorption from water

Question 4

what is biomineralization?

Answer 4

550Ma: Very early evidence for animals making shells (biomineralization

560Ma: Trace fossils from worm-like animals

Question 5

what are the features of the Cambrian explosion?

Answer 5

*Cambrian explosion 541 Mya –diversification of most modern taxa but also lots of evolutionary dead ends with strange shapes and features that haven’t been seen since

*Land was still barren but oceans became diverse and complex ecosystems

*Lots of evidence from Burgess Shale in Canada

*beginning of “hard bodied” animals, generally all very small (<15cm)

*Development of first apex predators and active hunting –Anomalocaris(60cm)

*Common after mass extinctions to get many strange animals quickly adapting to fill nich

Weird “mistakes?”e.g. Opabiniaand Hallucigenia

Mouth parts that are not seen on any modern arthropod

Question 6

D E F I N I N G C A M B R I A N E X P L O S I O N- Taxonomic

Answer 6

Taxonomic
*Animals represent highest level of bodily organisation
*Sudden explosion in number of different body plans that are present
*Not the origin of animals but the start of diversification and origin of body plans we still recognise today
*Stabilises in Ordicivica

Question 7

D E F I N I N G C A M B R I A N E X P L O S I O N- ecological

Answer 7

Ecological
*Animals and their interspecies interactions become much more dynamic –food web development
*E.g. burrowing and ecosystem engineering –higher diversity of trace fossils
*New lifestyles e.g. pelagic, planktonic

Question 8

D E F I N I N G C A M B R I A N E X P L O S I O N- anatomical

Answer 8

Anatomical
*Diversification of biomineralization
*Different groups used different minerals (calcium, silica, etc)
*Evolution of skeletons for protection from predatio

Question 9

C A U S E S O F T H E C A M B R I A N E X P L O S I O N

Answer 9

Oxygenation Event
Lack of Oxygen was holding back animal evolution pre-CambrianOxygenation event happens and larger and more complex animals able to evolve.
*At the end of snowball earth -> nutrients into water -> more photosynthetic algae -> oxygen increases
*Also end of snowball earth -> glacial erosion -> minerals into water -> more bioavailable minerals for shells

Result of a Mass Extinction
*Niches created by a suspected end-Ediacaran Mass extinction event
*Rapid evolutionary arms race between predator/prey interactions
*e.g. vision occurs right at the start –is this the trigger?
*Huge selection on soft bodied animals to evolve hard defensive parts and faster locomotion

Question 10

what are characteristics of vertebrates?

Answer 10

*Extremely simple to complex
*Increased germ layers
*Radial/bilateral symmetry
*Development of digestive system
*Open/closed circulatory systems
*Deuterostome development
*Notochord structure

Question 11

what are the characteristics of jawless fish?

Answer 11

*508Ma first fish, no jaw, no fins or gills
*Stuck sucking prey and generally limited on how to feed
*Some later developed teeth but without the leverage that comes from a jaw
*Most likely had strong muscles to help close mouth
*Some extant species like hagfish and lamprey

Question 12

how did fish evolve jaws

Answer 12

*Most fish have jaws, and are Gnathostomes, including tetrapods. The origins of gnathostomes date back to the Ordovician (450-500 mya) but it was not till the devonian that their diversity expanded

*Entelognathusfirst animal with modern jaw

*Primitive jaws allowed fish to develop into more niches including predatory ones which had previously only been arthropods

*Began with development of gills which acted as a precursor for jaws –theorised first pair of gill arches moved forwards to create a mouth structure

Question 13

what are characteristics of the Devonian age of fishes?

Answer 13

*Explosion in Devonion408Ma into big, heavily armoured fish which dominated over inverts for first time -Placoderms

*First fish with pectoral and tail fins

*Give them stability in water and faster locomotion

*Developed as jaws allowed them to fill more niches e.g. apex predators that required faster swimming

*Dunkleosteus–most powerful bite ever?

*Ancestors of all modern fish and vertebrates

*Evidenced by jaws –shared by all other vertebrates

*Two bones on top jaws (maxilla and pre-maxilla) that we still have

Placoderms go extinct at end-Devonian mass extinction.Also see evolution of cartilaginous fish –sharks and rays

Question 14

what are characteristics of LOBE-FINNED F I S H E S ( S A R C O P T E R Y G I A N S )?

Answer 14

L O B E-F I N N E D F I S H E S ( S A R C O P T E R Y G I A N S )

*Develops as a dominant group by the end of Devonian

*Only 4 extant lobe finned fish (lungfish, coelacanth)

*Primitive lungs -probably also used for buoyancy and later divergent into separate lungs and swim bladders

*The Lobe fin eventually develops to the tetrapodlimb and all land-based vertebrate groups descend from this

*375Ma Tiktaalik –primitive hips, wrist and shoulder joints which enabled to use fins to come out of water somewhat or at least be in very shallow water where it could follow small fish into shallow water without fear of getting stuck. Also feed on beached carcasses

Question 15

what are the problems with water species invading land?

Answer 15

Lots of problems… so why do it?Support –no longer buoyed by water, need muscle strength
*Locomotion –need legs
*Respiration –new breathing system
*Reproduction –eggs need to be in water

Question 16

what is the I N V A S I O N O F T H E L A N D: T R A D I T I O N A L T H E O R Y

Answer 16

*Going to land was a good empty niche
*To escape predators –including the many large jawed fish now present
*To avoid competition for food
*To lay their eggs in a safer condition

Traditional Theory:
*Fish ancestor&raquo_space; Fish with fins invade land&raquo_space; Limbs evolve on land&raquo_space; Some return to water

*The fin is not good at moving around on land, so natural selection modified the fin into a limb so that they had better terrestrial locomotion.

*Fish came to land with fins which were then converted to limbs with 5 fingers.

*Most land vertebrates retain these primitive 5 digits (including humans).

Question 17

what is the I N V A S I O N O F T H E L A N D: A L T E R N A T E T H E O R Y

Answer 17

*Species called Acanthostega gave an alternative to this theory.

*Early in tetrapod tree -It showed that limbs likely evolved before fish left water, as it was a fully aquatic animal. Acanthostega is basically a modified fish that hadn’t come to land yet

*Other anatomical evidence –e.g. once an animal lives on land they begin to lose their internal gills as they are rubbish for breathing on land and lose water. Acanthostega has internal gills. Some returning animals (salamanders, newts etc) have external gills (branchy things). this suggests that Acanthostega, again, is a fish that evolved limbs before going to land.

*Fish ancestor&raquo_space; Limbs evolve&raquo_space; Tetrapods with limbs invade land&raquo_space; Some return to water

*There are reasons why fish would want the limbs before leaving water and there are some fish today which have finger-like structures such as for digging, climbing, rowing, gripping

Question 18

what are key characteristics of amphibians?

Answer 18

A M P H I B I A N S

*Still breathed through skin and still needed water to lay eggs –couldn’t spend too long fully on land

*Extant lineage still alive today and live in a very similar way except frogs

*Dominance in carboniferous in steamy swamps –ideal habitat for amphibians

*Much larger variety of body plans and size 2 meters –big predators –no crocodiles yet

*Rapid changes in adaptations as started to explore land niches

*Temnospondyls were most dominant group and thought to be ancestors of modern amphibians

*Some on land almost fully only returning to water to breed -> problem is that amphibian eggs cant retain water as they lack a protective membrane (amniotic sac)

*300MA End Carboniferous rainforest collapse and world becomes much drier –continues to increase into Permian.

*Push towards life that is better adapted for drier conditions Evolution then addresses this problem with the rise of Amniotes

Question 19

explain A M N I O T E S-T H E E G G C A M E F I R S T

Answer 19

*First appear in Late Carboniferous but most early forms come from the Permian.

*In order to full exploit land niches and completely leave the water, needed a mechanism to keep embryos wet on dry land.

*Mix of amphibian/reptile features. Eggs with semi-permeable tough leathery shell to protect embryo. Created a pod to keep embryo hydrated whilst allowing diffusion of gases ”Private Pond”

*Lay less eggs than amphibians/fish because more energy invested in each egg

*Egg gap –we don’t know exactly how eggs went from jelly to shell due to poor preservation

*Hylonomusis the first true reptile (310MYA), so we know eggs must be at least this old.

*Eggs develop into different forms -> hard shells in birds and -> internal in mammals

Question 20

how did we get D I V E R G E N C E I N T O M O D E R N A N I M A L S

Answer 20

*Amniotes dominate the hot, arid Permian and rapidly diversify

*Amniotes form the major groups of modern land-based animals –Mammals, Reptiles and Birds.

*During the Permian we see the divergence of two main groups

*Sauropsids –anapsids and diapsids (Reptiles and birds)

*Synapsids (Mammals)

*Dominance between the two groups changes throughout time

Question 21

what are PERMIAN “MAMMALS”

Answer 21

*Early synapsids (mammal-like reptiles) capable of manipulating body temperature in a primitive warm-blooded way with big body sails.

*Herbivorous taxa feed on conifers

*Dominance during the Permian

*Look like dinosaurs but closer to humans

*Transition from basal synapsids to primitive mammals

*Jaw bones move back and shrink to form ear bones which are defining features of mammals

Question 22

explain the P E R M I A N-T R I A S S I C E X T I N C T I O N

Answer 22

P E R M I A N-T R I A S S I C E X T I N C T I O N

*The “Great Dying” –largest mass extinction event –

*85-95% of marine species and 70% of terrestrial vertebrate species go extinct

*Plants and insects also heavily impacted

*Only 12 tetrapod families survive –only one Synapsid family (Cynodonts)

*Cause of the extinction could have been a large volcanic event in the Siberian Traps.

*The eruptions lasted 500,000yrs -3 million km3of lava

*One of the largest volcanic events in Earth’s history.

*Extinction of large-bodied anapsids and synapsids during the Permian-Triassic extinction

*Huge niche opportunity now available

*Archosaurs became the dominant terrestrial group

Question 23

explain T H E S T A R T O F T H E A G E O F R E P T I L E S

Answer 23

*In the wake of the mass extinction –many niches now available and Diapsids rapidly radiated to fill them.

*Including many land niches and see niches as well, with the death of many families of inverts as well.

*Big climatic changes during the Triassic to replace Permian flora, and previously dominant herbivores died out as herbivorous reptiles evolved to fill the niche floral dietary niches.

*The main group that emerged were the Archosaur

Question 24

what is a key feature of early reptiles?

Answer 24

One of the key features of the skulls of early reptiles is an increase in the strength of the jaws when compared with basal tetrapods, sufficient to penetrate the tough arthropod cuticle

Question 25

who were the ARCHOSAURS OF THE TRIASSIC

Answer 25

*Branch into two main lineages during the Triassic –Crurotarsi(Crocodiles) and Ornithodira(Dinosaurs and Birds)

*Triassic Archosaurs characterised by evolution of hindlimbs and posture:
*Spawling-Lizardsand extant crocodiles
Semi-erect–Basal dinosaurs and extinct crocodilesFully Erect -Advanced archosaurs including most dinosaurs and birds

*development of Different stances better for different lifestyles.

*Sprawling -> more stable, use less energy, good for amphibious animals

*Erect -> enables increased stride length, better support body weight,long distance movement

*Convergently evolves in mammal

Question 26

what are T H E O R I G I N S O F D I N O S A U R ?

Answer 26

*Basal dinosaurs looked like quite generic dinosaurs, i.e. Elongated tail as counterbalance

*Dinosaur hips evolve to necessitate erect stance

*Shift from quick burst ambush predation to more active long-distance pursuit predation.

*Allows them to get larger

*Two Theories of Origin in Late Triassic:

*Successful competition with Synapsids and other basal archosaurs

*Thought that they arose several times over second half of Triassic through extensive and long-term competition
*“Superior” due to erect gait and physiological advances and their evolution was a progression

*OR Opportunistic radiation after extinction events

*Fossil record shows two rapid expansions after extinction events
*Some archosaurs with same adaptations die out
*Herbivores disproportionately affected –floral/climatic shifts at the same time.

Question 27

what are the ORNITHISCHIA AND SAURISCHIA?

Answer 27

*The two major groups of Dinosauria are differentiated by their pelvic bones.

*Ornithischia-bird hipped dinosaurs
*All are herbivores -> Larger digestive system -> Risk of losing bipedal posture
*Pelvic configuration accommodates for bigger digestive organs.
*Did NOT evolve into birds

*Saurischia-lizard hipped dinosaurs
*Theropods –carnivores
*Don’t require the additional digestive system space
*Do evolve into birds (hips are convergent evolution not shared ancestry).

*Sauropods -large herbivores
*Give themselves extra gut space by sheer size
*Balance through having long tails
*Mostly quadrupedal

Question 28

D I N O S A U R S -O R N I T H I S C H I A N S

Answer 28

All herbivorous
*Needed defensive adaptations
*Structures for social and mating behaviours
*Evidence of herding and parental care
*Developed social behaviours for the tim

Question 29

D I N O S A U R S-S A U R O P O D S

Answer 29

Characterised by elongated necks, large size and generally quadrupedal

*First radiation of Tetrapods to become high browsers -> unexploited food niche

*Large diversity -12-15 species in same area -> Adaptive radiation

*Fossils evidence different teeth for feeding on different types of plant and different browsing heights.

*Camarasaurus -spoon shaped teeth -ripping and tugging.

*Titanosaurs –small, sharp intersecting teeth -cutting.

*Diplodocus -many narrow peg-like teeth –raking

Question 30

W H Y D I D T H E Y G E T S O B I G ?

Answer 30

Stance -Erect limb stance allows better support of body weight

*Scaling and thermoregulation -Big objects take longer to heat up but hold heat a lot better. Small objects heat up fast but lose heat fast. Having a bigger body means you can better survive environmental temperature changes.

*Defence -Bigger means they are protected from predation by sheer size. Arms race of increasing body size between predator and prey.

*Energy preservation –Fat and water stores to better survive long periods without food.

*Digestion –Generally ate poor-quality nutrition that takes a long time to digest. A small animal cannot wait 4 days for their food to give them energy, larger animals can.

*Food Access -to physically reach the tops of trees they needed long necks, supported by big bodies.

*Travel –could travel further to reach new resources (food, water, mates).

*We must bear in mind that there a lot of smaller dinosaurs that are often neglected because they don’t preserve as well and they’re not as spectacular

Question 31

D I N O S A U R S-T H E R O P O D S

Answer 31

*Usually bipedal carnivores, often large apex predators

*Diversity of theropods with a variety of body sizes and lifestyles

*Pack hunting to take down larger sauropods/ornithischian

Question 32

what are T H E O R I G I N S O F B I R D S?

Answer 32

*Archaeopteryx was a transitional form between Dinosaurs and Birds from the Late Jurassic.
*Small, pigeon sized animal with feather like structures along wings.
*It also still had reptile characterises, like teeth and a long bony tail.
*~160 characteristics that are unique to birds but have origins in theropods.

*Some of these features are:
*Feathers
*“Bird hips” (Convergent evolution)
*Reduction of the digits, 4/5 fingers -> 3 fused fingers.
*A modified wrist bone (Important for flight stroke).
*Wishbone/fused clavicle (Important role in flight)

There are no other good candidates for origins of birds

Question 33

B I R D S –O R I G I N O F F L I G H T

Answer 33

Several different hypotheses:*Cursorial –running animals develop wings for better leaping at prey in chase
*Arboreal -animals living in trees develop it to travel between trees better and avoid predators.
*Pouncing –ambush predators used to glide down from elevated sites
*Wing-assisted climbing –wings helped ground animals get up high to escape predators

*Recent thinking that they are not mutually exclusive:
*Useful both for escaping predators and being one
*Allows safer travel
*Access distant food sources

*Multitude of selective advantages for animals in different habitats/ecological roles

Question 34

K-T E X T I N C T I O N E V E N T

Answer 34

65MYA Cretaceous –Tertiary Extinction –Most likely a meteor strike which triggered volcanism and climatic change

*Extinct:
*Non-avian dinosaurs (100%)
*Pterosaurs (100%)
*Marine reptiles (100%)
*Marsupial mammals (75%)
*Birds (75%)
*Many marine inverts. E.g. Ammonites

*Survivors
*Basal and placental mammals (9%, 14%)
*Amphibians (0%)
*Fish (12%)
*Some Crocodiles and Turtles (36%, 27%)
*The other 25% of bird

Question 35

what happened during the K-T E X T I N C T I O N E V E N T

Answer 35

Lots of debate but generally thought that the meteor itself was not the cause but the start of a string of events -> tsunamis, volcanism, forest fires, ocean acidification, lack of solar radiation.

*Global devastation of plants from fire and dust -> Collapse of food chains

*Larger animals with limited diets vulnerable to food shortages, knock on from herbivorous dinosaurs to carnivorous

*Lizards and crocodiles have slow metabolisms and able to survive long periods without food

*Birds able to travel long distances to find food

*Oceans –extinction of shelled inverts due to acidity -> food shortages for large marine reptiles

*Other reptile groups (pterosaurs and ichthyosaurs) had already been in decline for a long time

Question 36

what happened during the age of mammals?

Answer 36

Early mammals were characterized by several key features:

*Hair/Fur: Provided insulation and protection.
*Mammary Glands: Developed for nourishing young with milk.
*Endothermy(Warm-Bloodedness): Allowed for increased activity levels.
*Specialized Teeth: Various tooth types for different diets.

Survival strategies in a world dominated by dinosaurs:

*Burrowing:Some were burrowers, seeking refuge underground
*Nocturnal Habits:Activity during the night to avoid diurnal predators.
*Exploiting New Food Sources: Adapting to new diets and niches to minimize competition.
*Small size: to avoid direct competition

All the above meant they were much better equipped to survive the K-T Extinction Event, and their diversity and adaptions set the stage for adaptive radiation in the Cenozoic