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Vertebrate Origins

Wk1 Lec2
by

Bee Dale

on 8 July 2015

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Transcript of Vertebrate Origins

Chordata

Protochordata

Filter-feeding ancestor with tentacles

loss of tentacles
evolution of free swimming larval stage
evolution of pharyngeal gill slits
Chordate origins
Chordate characteristics
Ostracoderms
Earliest Vertebrates

1st & 2nd

Gnathostomata
Evolution of jaws
What’s the evidence?

Ontogeny
Why did jaws evolve?
Respiratory efficiency - one way flow and larger mandibular arch
Feeding efficiency - crushing force, food manipulation, mechanical digestion

Dunkleosteus armour from The Devonian Period
Placoderms
Early jawed vertebrates
large - low competition?
An Australian placoderm – 380 mya

Materpiscis attenboroughi
Acanthodians
Contemporaries of placoderms
Earliest fossils only sardine-size
Fins supported by large spines
Early forms may be ancestors of modern fish
Group disappeared in the middle of Carboniferous


Cartilaginous fishes
Early separation from stem lineage
Lost heavy dermal armour and adopted cartilage as the skeleton
Flourished during the Carboniferous
Increased again in the early Mesozoic

Evolution of modern jawed fish

Cartilaginous fishes (around 850 living species) – lack “bone” in skeleton

Chondrichthyes
Bony endoskeletons
Three features unite bony fishes and tetrapod descendants:
Endochondral bone is present – replaces cartilage developmentally
A lung or swim bladder is present
Several cranial and dental characters unique to this clade

Osteichthyes
Transition onto land
Lungs developed as out-growths of the pharynx
Increased vascular system – including a network of capillaries
Double circulation – arterial (oxygenated) and venous (deoxygenated) blood flow -
countercurrent exchange
Terrestrial adaptations
jointed limbs
stronger vertebrae
pectoral and pelvic girdle muscles to lift body off ground
ribs vertical
ears
olfactory organs - suitable for life on land
finned tail
Intermediate between fish and amphibians
Well-preserved fossils were found in 2004
Unlike many of the more fish-like transitional fossils, Tiktaalik's "fins" – basic wrist bones and simple fingers – weight bearing

Tiktaalik – The Missing Link?

Living Amphibians
chorion
surrounding membrane – gas exchange
amnion
“the pond"
allantois
waste storage
gas exchange
Placental mammals:
– suppressed the egg shell and yolk sac
– modified the amniotic membranes – nutrients and wastes to pass directly between mother and developing embryo (placenta)
Evolution of mammals
First mammals characterised by:
very small body size
enlarged brain and expanded sensory organs
complex teeth
Mammals have
precise occlusion
–teeth must fit jaw!
two sets of teeth
nourish young until the jaw is big enough for the teeth
lactation is a pre-condition for the evolution of precise occlusion
retain many “primitive” features of skull and limb girdles, oviparous
have mammary glands but not teats
Living Mammals
Invasion of modern placentals in Australia wiping out native marsupials
“Great American faunal interchange” of Pliocene when North America-South America connected by isthmus of Panama - many marsupials went extinct in Sth America, but few placentals went extinct in Nth America
chorus:

It's a long way from amphioxus
It's a long way to us…
It's a long way from amphioxus
To the meanest human cuss.
It's good-bye, fins and gill slits,
Hello, lungs and hair!
It's a long, long way from amphioxus,
But we all came from there!

A fish-like thing appeared among the annelids one day;
It hadn't any parapods or setae to display.
It hadn't any eyes or jaws, or ventral nervous chord,
But it had a lot of gill slits and it had a notochord.

(chorus)

It wasn't much to look at, and it scarce knew how to swim.
And Nereis was very sure it hadn't come from him.
The molluscs wouldn't own it, and the arthropods got sore,
So the poor thing had to burrow in the sand along the shore.

He burrowed in the sand before a crab could nip his tail.
He said "Gill slits and myotomes are all to no avail.
I've grown some metapleural folds, and sport an oral hood.
And all these fine new characters don't do me any good!"

(chorus)

He sulked a while down in the sand without a bit of pep.
Then he stiffened up his notochord and said "I'll beat 'em yet!
Let 'em laugh and show their ignorance; I don't mind their jeers!
Just wait until they see me in a hundred million years!"

"My notochord shall turn into a chain of vertebrae;
As fins, my metapleural folds will agitate the sea.
My tiny dorsal nervous chord shall be a mighty brain
And the vertebrates will dominate the animal domain!"
(chorus)

Gnathostomes (jawed fishes)

pharyngeal gill slits
dorsal nerve chord
notochord
post-anal tail
endostyle
segmented muscles
segmental muscles attach to notochord

thick cell membranes
fluid-filled=turgid
Thanks to my notochord
I can swim fast!
Next up: predation!
evolved early Silurian period
disappeared end of Devonian
armoured - bony plates and scales
paired fins
bony plates for teeth
heterostracans - streamlined
osteostracans - paired pectoral fins
hyomandibular arch
elasmobranchs
batoidea (skates & rays)
holocephali (chimaeras)
squaloids and galeoids
very flexible spinal column
protected with intercalary plates
sharkskin
small brain, sensory integration and processing
cranial kinesis, hyostylic jaw
oviparity, oviviparity, viviparty (lecithotrophy and matrotrophy)
tail with dorsal and caudal fins
oviparous
tail whip-like with barbs
viviparous
deep water (80m)
highly mobile pectoral fins used for swimming thrust
poison gland and dorsal barb
oviparous
actinopterygians
sarcopterygians
lungfishes (6 spp)
autostylic jaw (durophagous)
fused dorsal, caudal, anal fins. homocercal
gill and lung respiration
coelocanths
marine, deep water
fatty swim bladder
electroreception organs like ampullae of Lorenzini
birchirs
dorsal finlets
heterocercal tail
ossified skeleton
ventral lungs
sturgeons
benthic
heterocercal tail
anadromous
gars
fish predator
long narrow jaw
teleosts
marine, freshwater, anadromous
highly specialized jaws
homocercal tail
paired fins flexible and mobile
evolution of birds
diapsids: birds are dinosaurs
body plans
some have parental care
oviparity
body plans variable
resiliency to adverse conditions (heterothermy and tolerance versus homeostasis)
Widespread (absent from poles)
Require moist habitats for reproducton
Anura (frogs & toads)
Caudata (newts & salamanders)
Gymnophiona (caecilians)
Occurred during the Devonian period –
A time of alternating periods of mild weather then droughts/floods – freshwater habitats became low in dissolved O2 – stagnant, or dried up completely
Lead to 2 evolutionary advances:
1. Limbs
2. Lungs
Living Reptiles
Life history characteristics
many have parental care
oviparity, oviviparity, viviparity
longevity
plasticity and development (indeterminant growth)
body plans variable
resiliency to adverse conditions (
poikilothermy
and tolerance versus homeostasis)
The Cleidoic (Amniotic) Egg
internal fertilization
loss of larval stage
nest
yolk
nutrition
Life history characteristics
parental care
sociality, leks, territoriality
monogamy, polygyny, polyandry
oviparity
homeothermy
diverse body sizes
diverse habitats
carnivory, piscivory, insectivory, granivory, frugivory, nectivory
flight
Living Birds
diagnostic features (fur and mammary glands) of mammals don't fossilize
Life history characteristics
vivparous with elaborate, highly invasive placenta
altricial and precocial
greatest mammalian diversity, widespread
homeothermy but also employ torpor and hibernation
diversity of body sizes
diversity of habitats including aquatic, marine, terrestrial
Life history characterisitcs
small, non-invasive, short-lived placenta
viviparous but highly altricial
complete development in pouch
limited distribution/diversity/abundance
low metabolic rate
homeothermy but also employ torpor
diversity of body sizes
Montremata
Metatheria (marsupials)
Eutheria (placentals)
Is Eutherian mode a “better” way to be a mammal?
Marsupials compared to placentals:
lower metabolic rate
super-altricial development
Full transcript