Diversity of non-amniotic Paleozoic tetrapods

1. Late Devonian-early Cretaceous

2. Great Permian mass extinction: net loss of marine shelf

3. Mesozoic: age of dinosaurs

4. Non-amniotic tetrapod radiation

5. 200 million years

6. Most amphibian like (Ichthyostega) some had scales

7. Larger than extant amphibians

8. Includes temnospondyls-largest, most diverse, extinct non-amniotic tetrapods

9. Includes Anthracosaurs

10. Most lineages of non-amniotic lineages extinct by mid-Permian

1. By Permian well established

2. Most distinguishing feature: amniotic egg (not bred in water)

3. More terrestrial than non-amniotic tetrapods

4. Feeding on increased diversity and abundance of plants and invertebrates

5. Amniotes completely dominate terrestrial radiation of tetrapods in Mesozoic

Amniotic Paleozoic tetrapods

Amniotic egg: reptiles, birds (have cleidoic/self-contained egg), and mammals

 a. Cleidoic egg shell: leathery (reptiles and monotremes) 

 b. Or egg is rigid (reptiles and birds)

 d. Stored yolk: energy supply for developing embryo

f. Membranes: chorion, allantois, amnion

g. Chorion: surrounds entire egg, provides protection 

Amniotic Paleozoic tetrapods

Extant embryonic egg

a. Chorion

b. Allantois: site of nitrogenous waste

c. Amnion: protection; surrounds embryo with water

d. Adaptation value hypothesis: for amniotic egg; provided moist environment for successful development on land (challenged by the fact that certain amphibians have got their eggs to develop outside of water; also certain fish)

Patterns of amniotic

temporal fenestration

1. Synapsids: mammals vs. sauropsid (all the rest)

2. Fenestration: pattern openings or windows (skulls in this case not eye sockets)

3. Three main amniote fenestration patterns

a. Anapsid: no opening (sauropsid); modern turtles; skull emargination

b. Synapsid: one opening; lower temporal fenestra merged with orbit; mammals and mammal-like reptiles  

c. Diapsid: two openings (sauropsid); snakes, lizards, birds, dinosaurs, sphenodon 

1. Two lives: land and water

a. Lay eggs in water

b. Adults spend time on land

2. Tetrapods almost non-scaly skin

3. Most have four well-developed legs

4. A few salamanders and caecilians are limbless

Amphibians

characteristics

5. Three lineages

a. Frogs and toads: Anurans; tadpoles=larvae

b. Salamanders: Urodelans; long tail

c. Caecilians: Gymnophionans; limbless 

6. All adult amphibians are carnivorous 

7. Jurassic to present

Urodela-caudata: salamanders

characteristics

1. 566 species

2. Gait similar to earliest tetrapods

3. Northern hemisphere especially Appalachian mountains in North America

4. More species of salamander in TN than Europe and Asia combined

5. Some show paedomorphisis: retention of larval characteristics in adults especially gills, tooth and bone structure, lateral line

a. Some use skin as respiratory organ

b. Have no lungs

c. Some eyeless  

Urodela-caudata: salamanders

Plethodontidae: lung-less salamanders

Plethodontidae: lung-less salamanders

a. Adults aquatic/terrestrial

b. Some omit aquatic larval stage: lay eggs on land

c. 369 species in North/Central and South America

d. Plethodon cinereus: redback salamander; woodlands east US

Urodela-caudata: salamanders

Salamandridae 

Salamandridae 

a. Adults terrestrial/aquatic

b. As larvae have gills

c. 68 species in Europe and Asia

Urodela-caudata: salamanders

Ambystomatidae 

Ambystomatidae 

a. Adults terrestrial only

b. Aquatic larvae

c. 35 species in North America

d. Amystoma tigrina- tiger salamander

Urodela-caudata: salamanders

Proteidae 

Proteidae 

a. Aquatic

b. 5 species in North America; 1 in Europe

c. Paedomorphic

d. Necturus maculosus: mud puppy; lakes, streams of North America

Urodela-caudata: salamanders

Biology of Plethodontids

a. Successful and specious of all salamander families

b . Bulitoglossine (tongue) plethodontid: catch moving prey with binocular vision

c. Nasolabial groove: fine chemoreception 

Anurans: frogs and toads

characteristics

1. Occur on all continents except Antarctica

2 . Short ilium; no urostyle-pre-amphibian 

3. Elongated ilium; urostyle: modern-amphibian; good for jumping (frogs only) 

4. Differences between toad and frog? 

Anurans: frogs and toads

Bufonidae 

Bufonidae  (toad) typical toads

a. 495 species in North/Central/South America

b. Terrestrial

c. Nocturnal

d. Come to yard lights and catch insects

e. American toad: Bufo americanus; small black tadpoles

Anurans: frogs and toads

Pelobatidae 

 Pelobatidae :

spade foot toads; foot to escape predators

Anurans: frogs and toads

Hylidae 

Hylidae : tree frogs

a. Arboreal

b. 830 species

c. Worldwide

d. Toe discs for clinging and climbing

e. Camouflage

f. Only detected with breeding vocalizations

Anurans: frogs and toads

 Dendrobatidae 

Dendrobatidae : poison arrow frogs

a. Small, brightly colored

b. 163 species; Central and South America

c. Highly poisonous skin

d. Poison dart frogs

e. Found on vegetation in rain forest 

Anurans: frogs and toads

Ranidae 

Ranidae 

a. Aquatic (semi)/terrestrial

b. Typical frogs: bull frog-Rana catesbeina; green frog R. clamitans; leopard frog-R. pipiens

c. 400 species

d. Worldwide 

Anurans: frogs and toads

Caecilians 

Caecilians : Gymnophiona

1. 180 species

2. Legless, burrowing, tropical

3. Worldwide tropical

4. Eyes covered by skin or bone

5. Clearly segmented body

Anurans: frogs and toads

Reproductive comparisons

Reproductive comparisons

1. Amphibians: parental care

2 . Caecilians

a. Oviparous/viviparous

b. Matrotrophic

c. Internal fertilization-male intermittent organ

Anurans: frogs and toads

Reproductive comparisons

salamanders

Reproductive comparisons

Salamanders

a. Internal fertilization with spermatophore

b. Behaviors: tail-walk, chin rubbing, pheromones (all species specific)

c. Male deposits spermatophore on substrate and female picks up with cloaca

d. Pheromones: produced by hedonic glands

Anurans: frogs and toads

Reproductive comparisons

frogs/toads

Frogs/toads

a. Two types of mating systems: explosive breeding vs. prolonged breeding

b. Explosive breeding: short but in large concentrations; temporary; vernal (spring) pools; chorusing; number of males=number of females; male reproductive success is equal among males; example is spring peeper; can be mixed choruses (use to measure population size?)

c. Dryer habitats=less specious

d. Prolonged breeding: season lasts up to several months; males territorial; male success unequal; lower number of calling males; example is green frog and bull frog 

Anurans: frogs and toads

characteristics

Anurans: frogs and toads

Poison glands of amphibian

Poison glands of amphibian

1. Thick and glandular skin

2 . Can produce many pharmacological agents

a. Amines

b. Peptides

c. Hemolytic proteins

d. Alkaloids (highly toxic)

3. Dendrobatidae: poison dart frogs 

4 . Hedonic glands: pheromones

5. Full vs. empty poison gland

Anurans: frogs and toads

Declines of amphibian population

General

1 . Many vertebrates have shown recent population decline

a. Is any perceived decline real? (How accurate is census data?)

b. If decline is real, what is/are the cause(s)? (Most of the time more than one cause)

2. Amphibian population declines

a. First realized as possible by International Herpatology conference in ‘89

b. Hypothesized decline began in 50s-60s

Anurans: frogs and toads

Declines of amphibian population

Local Factors

Local factors

a. Loss of forest canopy from logging

b. Moist microenvironment lost

c. Dispersal to breeding sites limited

d. Atrazine: widely used agricultural herbicide; causes feminization of males and oocytes develop in testes 

e. Mine drainage: releases many toxins which leach from soil 

f. Agricultural nitrates: fertilizers; drain from farmlands to breeding ponds and deform development

g. Cattle production: cows trample emerging amphibians and cows create cowpies which smother amphibians

Anurans: frogs and toads

Declines of amphibian population

Global Factors

Global factors

a. Global warming: causing rapid declines of high altitude species; warmer and dryer Costa Rica mountains; Australia as well 

b. Acid precipitation: 100x more acidic than pre-industrial revolution 

Acid rain=>acid fog=>acid snow

Cars/power plants=>NOx and Sox (primary pollutants) go into atmosphere=>add water=>H2SO4 and H2NO3 (secondary pollutants)=>moves downwind=>acidifies breeding ponds 

c. When pH<5 amphibian larvae damaged/killed

d. Increases in atmospheric UV radiation reaching earth surface-depletion of ozone layer from human activity; synthesis and release of ODCs (ODCs=CFCs; ozone depleting chemicals; used as cooling agents and to make Styrofoam)

e. UV light kills amphibian larvae

Anurans: frogs and toads

Declines of amphibian population

Amphibian diseases

Amphibian diseases

a . Iridoviruses: at equilibrium with species life history; population fluctuations 

b. Chytrid fungi: newer; Central and South America; life cycle are motile zoospores=>penetrate amphibian skin=>ramify=>produce zoospores=>spores=>kill frogs and froglets because compromised respiration + water imbalance (environmental factors can stress immunity=>can’t repel infectants) 

1 . Early diversification of amniotes produces two separate and very successful lineages that include most extant terrestrial vertebrates

a. Sauropsids: turtles, reptiles, tuatara, birds, snakes, crocodilians, and dinosaurs (pterosaurs)

b. Synapsids: mammals and extinct pelycosaurs; therapsids

2. Solved conflict of running and breathing (separation of two)

1 . Primitive tetrapods: no separation of running and breathing muscles

2. Advanced tetrapods: separation of running and breathing muscles

a. Diaphragm: negative pressure breathing

b. Separation of muscles for running/breathing

c. Shape of upper body changes

3. Sauropsid separation for running/breathing

a. Bipedality: dinosaurs; no diaphragm

b. Quadrapedality: muscles of pelvis/rib cage plus linear movements increase volume of trunk cavity; pelvic muscles used for ventilation 

c. Cuirassal breathing: inspire by body wall moved laterally and ventrally vs. expire by rebounding anteriorly; could not reach certain niches without diversification of running/breathing separation  

Adaptations to land

Increasing Gas Exchange

Increasing gas exchange

1. Required for higher activity lifestyle

2 . Synapsid (alveolar lung) vs. sauropsid (faveolar lung)

a. Synapsid: internal; prevent water loss; many blind sacs, 1 alveolus 0-2mm diameter; gas exchange <1s; humans 70m^2 surface area

b. Tidal volume: strong in alveolar; no flow through

c. Parabronchial lung: air sacs with high volume; pump air through lung; always moving one way; no tidal volume; permanent countercurrent circulation of air and blood-extracts oxygen efficiently from air; air sacs store 9x more air than lungs

3. Amphibians are neither synapsids/sauropsids

Adaptations to land

Turtles

General

 Turtles

1. 300 extant species

2. Ancient lineage of sauropsids

3. Reptiles

4 . Have shell: dermal bone 

a. Upper: carapace

b. Lower: plastron

c. Prevents desiccation 

5. Species diversity limited by shell 

a. No arboreal or flying forms

b. See arboreal or flying in other groups of vertebrates

6. Origin late carboniferous 

Adaptations to land

Turtles

Two main groups

Two main groups

a. Cryptodira: dominant; head retracted into shell in ‘s’ shape 

b. Pleurodira: head retracted by horizontal neck bending; only southern hemisphere

8. Most widely diverse through world

9. Limbs attached inside ribs

a. Peripheral shell bones, costal and central + pygal bones

b. Epidermal scutes cover shell bones: marginals and cervical 

c. Vertebral column fused with ribs 

10. All lack teeth

11. Shell kinesis: one or two hinges present in plastron for protection of tail and head/neck

Adaptations to land

Turtles

Ecological Behavior

Ecological behavior

a. Painted turtle: 14 years

b. Box turtle: 50 years

c. Tortoises: 80 years

d. Ectotherm but large sea turtle can achieve transient endothermy with swimming

e. Basking in sun

f. Catching turtles: poop traps with dead fish; put box

next to basking log 

Adaptations to land

Turtles

General (Cont'd)

Unique head and neck patterns

 Limited communication systems

a. Male smaller than female

b. Claw vibration-mating strategies

c. Vocal communication  

d. Sex determination: temperature dependent; warmer nest conditions give rise to females

Adaptations to land

Turtles

Eggs & Nesting

Eggs and nesting

a. Oviparous

b. Fertilization internal

c. Female digs into sandy soil and deposit eggs with cloacal water; then cover eggs back up 

d. Small species: 4-5 eggs; larger species: up to 100 eggs [clutch size]

e. Hatch in 40-60 days

f. Nest failure: nest predation 

g. Mass emergence: sprint to water to survive; greater chance of survival all at one

Adaptations to land

Turtles

Temperature-dependent sex determination 

Temperature-dependent sex determination 

a. Warm nests=females

b. Cold nests=males

c. Opposite in lizards

Adaptations to land

Turtles

Breeding and feeding habitats

Breeding and feeding habitats

a. Migrate between two

b. Large turtles breed every 2-3 years

c. Females return to natal beach 

Adaptations to land

Turtles

  Conservation

Conservation

a. Important life history trait: long-lived and slow reproduction rate; slow growth rate

b. Turtle harvesting: same problem as sharks; can’t recover from high mortality rates

c. Really bad for sea turtles and tortoises

d. Green sea turtles: viral papillomes; causes tumors/warts 

Squamates

Turtles

Conservation

a. Green sea turtles: strong effects of viral papilloma; 58% of turtles in HA, 92% have tumors

b. Desert tortoise: large, terrestrial, SW N. Am (UT, AZ, SC, NM and Mexico); declined 30-70% since 1950; degraded habitat/loss of habitat=loss of body condition 

c. Insidious: turtles also infected by Mycoplasma=>upper respiratory tract disorder (cold)

d. Origin URTD: captive desert turtles released 

Squamates

Turtles

Other threats

Other threats

a. Gallapagos turtles-small populations; compete with sheep/goats/donkeys for minimal vegetation

b. Also cats/dogs/rats prey on eggs and young

c. Every turtle in Asia endangered-eaten 

Squamates

 Lepidosaurs

# of species

1 . 4800 species of lizards

Squamates

 Lepidosaurs

 Reptiles: ectothermic tetrapod

 Reptiles: ectothermic tetrapod

a. Dry, scaly skin

b. Ribs have uncinate processes

c. Inner ear bone: columella

d. Large orbits

e. Lower jaw with several bones

f. One occipital condyle

g. Nucleated blood cells

h. Includes: turtles, crocodilians, lepidosaurs (tuatara), dinosaurs and stem reptiles

Squamates

 Lepidosaurs

Tuatara: S. punctatum biology

Tuatara: S. punctatum biology

a. Mesozoic: diverse; arboreal; terrestrial and marine; herbivorous and insectivorous

b. Two extant species: north and south islands of New Zealand (coastal islands)

c. Cats/rats/dogs prey on eggs and young

d. 0.6m adults, nocturnal, active at low body temperature

e. Live in burrows/sea bird columns; eat dead seabirds and bugs 

Squamates

 Lepidosaurs

Radiation of Squamata

Radiation of Squamata:

Iguania:  Iguanas, chameleons, lizards

Scelonoglassa:  geckos, skinks, lizards, snakes, amphisbaenians

b. Lizards

1. <3cm geckos-3m long Komodo dragon (monitor lizard)

2. Very diverse in adaptation

3. 80% of lizards are small bodied and insectivorous

Squamates

 Lepidosaurs

lizards

key families

Key families

a. Chamelionidae: prehensile tail; old world; independent eyes; feet permanently zygodactylous (two toes in front and two in back)

b. Iguanidae: diverse in arboreal niches in central and south America; some terrestrial especially on islands; many large species herbivorous

c. Varanidae: monitor lizards; old world; islands; carnivorous; have bacteria in mouth that inject and weaken prey

d. Anguidae: glass lizards; legless; lizard face

e. Amphisbaenians: African; fossorial; rigid skulls; legless; tunnel through layers of soil; two teeth; skin is rigid tube

Squamates

 Lepidosaurs

Venomous lizards

Two venomous lizards: for subduing prey

a. Gila monster

b. Mexican beaded lizard

c. Neurotoxic venom so lizards do not have to overpower prey; have grooved teeth for injecting venom 

Squamates

Snakes

General

 Snakes: 2900 species

1. Very small (blind snakes)-very large

2 . Either constrictor or venomous but not both for subduing prey to avoid damaging sensitive skull

3. Bigger snakes are slower

4. Racer: long and thin; eat small prey; neither constrictor or venomous 

5. Active on hot days

6. If in danger will throw up prey to get away

7. Burrowing vs. fish-like vs. vine-like vs. short and stout (vipers)

Squamates

Snakes

Families

Families

1.  Cranial kinesis: lost QJ and skull capable of more movement

2. Snakes: lost both temporal jaws

a. Eight points of flexibility-jointed

b. 3D movement-no chewing

c. Prey has difficult time escaping

d. Capable of moving jaws to get prey into throat-eat prey whole 

e. Skin stretches

f. Skull delicate: prevent damage with constriction and venom 

3. Boas, pythons, some colubrids: constrictors

4. Venomous snakes 

Ecology and behavior of squamates

Venomation

1 . May have replaced constriction during Miocene

a. Makes smaller, lighter body

b. Reduced muscle mass

c. With warm open grasslands

2 . Dentitions of venomous snakes: Colubridae

a . Aglyphous: no fangs; curving backwards  b. Opistoglyphous: rear-fang snakes; have small rear fangs; may be grooved; venom weak-strong; “chew” prey through grinding (example: African vine snake, Malaysian tree snake, east Indies and Central America false viper, African boomslang) venom from modified salivary glands   c. Protaroglyphous: front-fang snakes; fangs permanently erect on maxilla; fangs hollow; venom made and released from modified salivary glands (Elapidae: cobras, coral and sea snakes)  d. Solenoglyphous: front-fang; hollow but located on hinge-rotating maxilla (example: rattle snakes and pit vipers)

Ecology and behavior of squamates

Categories of Venom

 Categories of venom

a. Neurotoxic: attacks nervous system; causes paralysis; Elapidae

b. Hemolytic: attacks lining of blood vessels; breaks up RBCs and platelets

c. 8k cases of invenomation in US each year

d. Snakes invenomate to avoid ruining delicate skull 

Ecology and behavior of squamates

Olfaction and feeding behavior

B . Olfaction: Jacobsen’s organ; moist tongue + odor molecules = forked tongue inserted into Jacobsen’s organ and olfactory recognized

C. Feeding behavior of lizards

1 . Gradient of activity level: foraging behavior

a. Sit and wait predators: spiny swift (derived)

b. Cruising predators: intermediate activity; Eumeces- skinks (ancestral)

c. Widely foraging predators: Cnemidophorus (6-lined racerunner) (derived) 

d. Applies also to fish, mammals, birds, insects, frogs and zooplankton

2 . Lizards show autotomy: self-amputation of tail 

Ecology and behavior of squamates

Social Behavior of Lizards

. Social behavior of lizards

1. Use olfactory, visual, auditory, chemical cues during social interaction

a . Pheromones-chemical; mate attraction; territorial behavior (Iguanian lizards-Anoles about 400 spp); dominance hierarchies; communications among conspecific. Example: structure and use of gular fans (simple vs. compound vs. complex)          2. Reproduction

a . Ancestral: oviparity; supplied by lecithotrophy; develop outside of body-with yolk as primary nutrition for developing embryo 

b. Derived: viviparity; matritrophy-live birth and supplied from nutrients of female reproductive tract; evolved dozens of times among squamates

c. Parental care: females remain with eggs at nest; pythons coil around eggs to warm with muscular heat; most parental care occur with eggs + adults

Ecology and behavior of squamates

Diapsids

 general

. Diapsids: most diverse lineage of amniotic vertebrates

1 . Includes: squamates, dinosaurs, birds, tuatara, pterosaurs, Ichthyosaurs, Pleisiosaurs and Plecodonts

2. Mesozoic fauna: age of reptiles

a. 180 million years-lasted

b. Repeated, adaptive radiation into many niches: herbivores and carnivores; occupied today by non-reptiles

c . Frequent parallel evolution: appearance of similar characteristics in lineages that separated recently (example: long hind legs N. America and African desert rodents)  d. Convergent evolution: separated a long time ago (example: wings of birds and bats)  e. Strong trend toward bipedalism

f . Earliest diapsid: Petrolacosaurus (late Carboniferous)

Ecology and behavior of squamates

Diapsids

Archosaurs

Archosaurs

a. Stem reptiles: thecodonts (extinct); crocodilians, pterosaurs (flying reptiles/extinct); dinosaurs; birds 

b . Diapsid skull: orbit shaped like inverted triangle; unique eye socket; antorbital fenestra (avian skull) 

c. Muscle and bone: caudiofemoral muscle with fourth trochanter

Ecology and behavior of squamates

Diapsids

Crocodilians: living Archosaurs

a. Triassic appearance

b. Semi-aquatic: Amazonian skull 15m and entire body 12m 

c. Tail laterally compressed for swimming 

d. Extant crocodilians: 23 spp; most tropical and sub-tropical with different head shapes depending on diet    1. Includes crocodilians, alligators, caiman and gharial

2. Closing mouth muscles are way powerful 

3. Will make long, overland movements in search of new water

4. Hunt in water

5. 4-chambered heart: 2 atria, 2 ventricles; complete intraventricular separation between oxygen rich/poor blood 

6. Lay eggs in mass of decaying matter; oviparous

7. Nestlings follow adults in mouth and release into water

8. Males territorial 9. Young remain near adults for 1-3 years 

Dinosaurs

General Aspects

1. Very successful diapsids

2. Dinosaur means terrible lizard

3. Cretaceous-height of diversity

4. Strong trend for bipedalism 

5. Many forms secondary quadrupedal 

Dinosaurs

Vertebrate Limb Movement

1. Flexion: reduces angle between adjacent bones

2. Extension: increase angle between adjacent bones

3. Adduction: toward midline

4. Abduction: away from midline

5. Protraction: pushing limb away from its base (rapid running)

6. Retraction: pushing limb toward base (rapid running)

Dinosaurs

Lineages of Dinosaurs

1. Ornithischian: bird-hipped

2. Saurischian: reptile-hipped (birds?); solving problem of moving heavy limb over space 

3. Advantages

a. Run away from predators

b. Reach new environment 

Dinosaurs

Ornithischian dinosaurs

1. Herbivorous

2. Diverse radiation

3. Beak jaw; toothless; quadrupedal and armored; slow moving

4 . Thyrephora

a. Stegosaurs: may have had gizzard with which to grind food; plates on back for temperature control

b. Ankylosaurs: dermal armour; clubbed tail; keen sense of smell 

5 . Ornithopods: bipedal; limited dentition; spine in front foot; fancy horns

a. After appearance of angiosperms

b. Hadrosaurs: duck-billed; ma have had highly developed parental care; fossilized mounded nest

6 . Marginocephalians: horny beak; Triceratops (Sarah from LBT)

a. Ceratopsians

b. Pachylcephalosaurs: thick bone cap used for mating defense

Dinosaurs

Saurischians: two main groups

Sauropodomorphs: quadripedal herbivores (little foot from LBT)

a. Jurassic, Cretaceousb. Over 30m long

c. Forelimbs longer and long neck

d. Adaptive significance of long neck and large size: very efficient lateral feedinge. Knees lock when walk so legs don’t collapse-terrestrial characteristicsf. Specialized vertebrae: large with large neural arches but light-pleurocels     

2 . Theropods

a. Large: Tyrannosaurus; enormous but slow; held food between teethb. Small: Coelophysis; active, cursorial, fused clavicle to form furcula (bird-like)c. Dromeosaurs: Deinomychus; slashing claw; group hunting; T. rex size (velociraptor) 

Dinosaurs

Evolution of birds from reptiles

1. Did birds evolve from reptiles: yes

2 . Similarities: birds and reptiles (shared characteristics)

a. Epidermal scales on head

b. Few skin glands

c. Single middle earbone (columela)

d. Large orbits

e. Lower jaw consists of several bones

f. Single occipital condyle

g. Ribs have uncinate processes

h. Nucleated blood cells

i. Similar egg development

j. Cloaca 

Dinosaurs

Evolution of birds from reptiles

Unique avian features, pterosaurs

3 . Unique avian features

a. Forelimb uniquely modified for flight: two free wrist bones (ulnare and radiale), carpometacarpus; feathers inserted in bone

b. Feathers

4 . Pterosaurs: flying reptiles

a. Fifth digit elongated to generate lift

b. Large piece of skin

c. Distal part of wing-thrust

d. Different kinds of skulls for different niches

e. Large brains

f. Hollow bones and strong sternum 

Dinosaurs

Evolution of birds from reptiles

Archaeopteryx lithographica: missing link

a. 135-155 mya

b. Found in limestone deposits: Bavaria (how limestone is formed is important for fossils helps fossils form in great detail)

c. Reptilian claws and wings

d. Ribs with uncinate processes for efficient flight

e. Small cursorial predator or arboreal predator

f. Capable of weak flapping flight-1500m 

B. Birds: successful diapsids

1. Take advantage of ecological opportunities allowed by powered flight

2. Pterosaurs

a. Triassic-Cretaceous

b. Overlap with birds in evolutionary time for 100 million years

Dinosaurs

Evolution of birds from reptiles

Are birds highly modified dinosaurs?

. First theory: Thomas Huxley late 1800s; birds and theropods share derived characteristics such as pneumatic bone (hollow), elongated ‘s’ shaped neck, degitigrade (heel off ground and toes flat on ground), tridactyl foot, feathers/precursors, reduced genome size, similarities in protein characteristics

b . Coelurosaurs and birds: both have furcula (wishbone/fused clavicles), brooding is bird like (shelter), bird like sleeping posture (head tucked under wing), shoulder and wrist motions that does allow flight especially in dromeosaurs

4. Sharing of feathers: many coelurosaurs found with feathers

a. Dromeosaurs: feathers; vane + shaft; if two parts of vane symmetrical then feather in evolutionary history

b. Beta-keratin is unique

c. Caudipteryx and Protoarchaeopteryx

d. Archaeoopteryx: first bird with asymmetrical feather (especially found on wings) means capable of generating thrust 

Dinosaurs

Evolution of birds from reptiles

Vertebrates take to the air: all from trees down except birds 

1 . Gliding: short-long flights but loss of altitude; not powered by a flying apparatus

a. Lizards, snakes, marsupials, phalangers, squirrels, lemurs, monkeys 

2. Flapping: powered flight; stable or gaining altitude

a. Bats, pterosaurs, birds

3. Soaring: stable altitude, gain in altitude but not powered by flying apparatus but by rising air 

(thermals etc)

a. Birds of prey 

Dinosaurs

Evolution of birds from reptiles

Trees Down

Evolution of bird flight: trees down vs. ground up 

1 . Trees down

a. A. lithographica and ancestors were tree climbers/dwellers 

b. Moved branch to branch

c. Selection favored good parachuting

d. Weak to strong powered flight

e. Hoatzins: S. America

f. Why live in trees: food supply, nesting sites, protection

g. Simple-parachute=>intermediate-weak flap=>advanced-strong flap (capable through microevolution)

Dinosaurs

Evolution of birds from reptiles

Ground Up

 Evolution of bird flight: trees down vs. ground up

 2 . Ground up: insect grabbing forearms

a. Adduction vs. abduction

b. Strongly abducting dromeosaurs during prey capture

c. A. lithographica cursorial predator: forelimbs insect/prey net

d. Feathers also evolve to thermoregulation 

3. Ground up: fluttering-leapinga. Running from predators

b. Engage in leaping: controlled/coordinated by protowing 

c. Running=>leaping=>powered-flapping flight

d. Problems: sticking forearms out while running slows down; small theropods losing velocity while running makes for problem believing ground-up because minimum velocity needed to take flight 

a. Evolve feathers for reason other than flight

b . Dinosaurs not endothermic: supposed endothermy based on four flawed arguments

1. Dinosaurs and modern birds and mammals had erect posture BUT no causal relation; first mammals did not have erect posture but were endotherms

2. Microscopic bone structure of dinosaurs is mammal-like (Haversian subunits) BUT turtles (ectotherms) have Haversian system/subunits and is absent in passerines (perching birds) 

3. Few predators for many prey ratio BUT fossil record incomplete 4. Dinosaurs (like modern birds and mammals) have large brains BUT many dinosaurs had small brains 

1. Dinosaurs may not have been endothermic

2 . Time problem: birds supposedly evolved from theropod dinosaurs (Cretaceous radiation 100-65 million years ago)

B. Avian main radiations

1. New adaptive zone: aerial, terrestrial

2. Attack as predators and avoid predators

3 . Two main radiations

a. Enantiornithes: teeth; kind of loon like

b. Orinithurae: late Cretaceous 

c. Both gave rise to Neornithes: modern birds; 9800 spp; Passeriformes has 5800 spp 

 Features of extant birds

Feathers

a. Modified reptilian scales

b. Grows in tracts: capital, humeral, alar, ventral, spinal, femoral, crural, caudal

c. Apteria: featherless region

d. Different kinds of feathers: down, flight, semiplume, contour, bristles, filoplume

e. Basic components: calamus, rachis, vane; barbs with barbules; distal barbules have hooks to attach to proximal barbules of next barb

f. Down feathers: not many barbs; trap body heat

g. Invest pigment in ends of feathers 

h. Filoplumes help with changes in air temperature while flying 

Features of Extant Birds

more

2 . Four toes and claws: mid-tarsal joint; certain tarsals=tibiotarsals and tarsometatarsus 

3. Specialized hip structure to avoid falling over

4. Uncinate processes with ribs

5. Bird skeleton is very stiff

6. Lost certain digits and phalanges

7. Flexible neck vertebrae

8. Use beak instead of forelimb for grabbing-forelimb only used for flight

a. Primaries: generate thrust

b. Secondaries: generate lift 

c. Different in camber generated force for lift

d. Disturbed high lift and undisturbed high lift

e. Alula: helps with disturbed high lift-less turbulence “secondary wing”

f . Power generating: pectoralis muscles large-creates powerful downstroke; raises wing with weak upstroke with supercoracoideus-pulls humerus back up except in ducks and hummingbirds-generate thrust on down and upstroke both=strong flight 

g. Keeled sternum: for better attachment flight muscles

10 . Strongly soaring: large forearm and small hands; not good flight muscles so soaring instead of flying

11. Hummingbirds: can fly backwards; small forearm and huge hands to support primary flight feathers=extreme amounts of thrust

12 . Wings

a. Dynamic soaring wing: albatross

b. Elliptical

c. Standard-high power: quail

d. High aspect ratio: swallow 

Penguins-Sphenisciformes

a. Southern oceans

b. Dive deep 

c. Flightless

d. Strong keel

e. No feather tracts