Vertebrate Evolution- Lecture #2 Flashcards
Vetebrate evolution #2
- Amniotes
- Reptiles
- Birds
- Mammals
Ammiotes quickly slip into 2 lineages:
Synapsids and Sauropsids
Sauropsids split into 2 lineages
Archosaurs and lepisosaurs
Branch of extant diapsids
Lepidosaurs (modern reptiles)
Derived characters includee…..
- lepidosaurs hemipenes
- squamates shed skin
- Lizards shed skin in…….
- Snakes shed skin in………
- Pieces
- Whole piece
Diapsid Lepidosaur lineage
Tautara
- Appeared in time of dinosaurs; 2 species, lives only on islands off New Zealand. Lizards-like animals about half a meter long noctornunal, live in seabird holes, contain parietal eye
Diapsid lepidosaur lineage
Squamates
order squamata: there suborders,7000 species
1. Sauria-Lizard,
2. Amphisbaenia- worm lizards
3. Sepentes- snakes- evolved 20 mya
Squamates
- new synapomorphy is paired compulatory organ in males
- lower jaw not joined directly to skull, most are carnivores
- Scaly skin
ExtantReptiles2.DiapsidLepidosuars Order Squamata: (Lizards, Snakes)
*Evolved about 250 mya
*First were lizard-like
*Snakes evolved later, lost limbs specialized for underground and arboreal habitats
*Snakes are unique in having a jaw kinesis - they can eat prey that is larger than their mouth
*Kill prey before eating
Snake Feeding
A. Nonconstrictors
- May have fangs and venom
- snake venom- different components:
- hemolytic, cell lytic, neurotoxins
- some other species make mimic colaboration
- some venomous snakes have “warning colaboration” warns predators to stay away
- evolution mimics
Snake Feeding
B. Constrictors
*No fangs or venom
*Wrap body around prey and prevent it from breathing
*Boas, pythons
Sauropsids a. Anapsid Reptiles: Turtles: Order Chelonia
Unique skull and skeleton
* Branch off from Diapsid lineage before Archosaurs
* Long separate evolutionary history from rest of reptiles – evolved 200 mya and have changed little
* Turtles and tortoises
* bodies are encased within a protective shell (carapace & plastron) which are derived from dermal bone
* 200 species, turtles & tortoises
Archosaur Characteristics
Diapsid skull plus …have:
* Ante-orbital opening in skull * Orbits like inverted triangle * Laterally compressed teeth
Includes:
* Crocodiles
* Pterosaurs†
* Thecodonts†
* Non-avian Dinosaurs† * Birds
extinct†
Diapsid Lineage: Archosaurs
A. Crocodiles & Alligators
Order Crocodilia: crocodiles & alligators, ~25 species
Evolved about 200mya
Relatively unchanged
All carnivores, ambush predators
Closest living reptilian relative of Dinosaurs Ectothermic
Extensive social behavior
Elaborate parental care of eggs and young
Some features convergent evolution with mammals: 4 chambered heart, secondary palate
Diapsid Lineage: Archosaurs
B. Pterosaurs
Archosaur but Not Dinosaur (lack distinguishing dinosaur character, have no hole in hip socket)
* Wings supported by 4th metacarpal
* Unique Pteroid bone * Wing membrane, no
feathers
* Independent evolution of flight from birds and bats
* We know this because although they all have a humerus, radius and ulna they use different bones to support the wing.
* But some characteristics are convergent evolution with birds & bats
* Why?
Diapsid Lineage: Archosaurs (ruling reptiles)
C. Thecodonts
- Ectotherms, lived in warm climate
- Required less food
than endothermic synapsid
therapsids which they replacedas climate warmed 230 mya Dominant through
Triassic and survived for 15
my until replaced by Dinosaur
Diapsid Lineage: Archosaurs
D. Non-avian Dinosaurs
- Dinosaurs evolved from Thecodonts about 220 mya & dominant until
K- T extinction 66 mya. - New derived character is a hole in hip socket (acetabulum)
- Upright stance in some
- body located directly over legs * increased speed and agility
- 2 branches (differ in way hip bones extend for muscle attachment)
- Ornithiscia
- Saurischia **
- Bipedal saurischians called theropods gave rise to the birds
Dinosaur Physiology
- Several lineages of reptiles became homeotherms (endotherms): * Synapsids → mammals
- Diapsid, Saurischians, theropods → birds
- So were dinosaurs warm blooded? Probably some were. Fossils of small
bipedal theropods found with feathers. - Feathers evolved & provided benefit for insulation or aid in capturing prey. Later adapted for flight.
Birds evolved from
- Saurischian Dinosaurs
- Evidence?
Structure of hip
Amino acids in connective tissue found in a fossilized Tyrannosaurus rex most closely matched chickens
Why fly? Theories of evolution of flight Ground up, Trees down
Evolution of Birds
Birds evolved from a group of small bipedal theropod dinosaurs in the Jurassic period (150 MYA). The oldest known bird fossil is Archaeopteryx lithographica which has a mix of “reptilian” and “avian” features.
*Reptilian: long tail, teeth, long clawed fingers
*Avian: wings, feathers, furcula
Diapsid: Saurichian Avian
(Descended from dinosaurs)
Aves listed as separate class because of key evolutionary novelties of:
* Feathers
* Light bones
* Reduced # bones, hollow long bones
* Super-efficient lungs
* Air sacs, cross-current lungs
* Efficient circulation
* Complete separation of oxygenated & deoxygenated blood
* Endothermy
- Flight requires reduction in weight.
- Specializations include:
- reduction in #bones
- hollow long bones
- Unique wrist bone
- loss of teeth and evolution of keratinous beak.
But the more we learn about bird evolution the more we realize that many of these characters evolved in the dinosaur ancestors.
Birds: Avian Dinosaurs Class Aves
key characteristics:
- Wings
*Feathers (modified reptilian scales)
about 8,600 species
– Feathers a unique character among living animals, but also
found in dinosaurs.
*Endothermic
*Skeleton modified for flight. Bones hollow, forelimbs support
the wing,, beak but no teeth, reduced tail.
*Breathing by lungs with unique airflow associated air sacs *Internal fertilization and hard-shelled amniotic egg
Feathers
*Among living animals feathers areauniquely aviantrait.
*Feathers evolve first in dinosaurs and probably used for insulation, coloration, attractionofmate. Later for flight.
*Feathers are what enable birds to fly.
*Feathers are lightweight &strong.
*Feathers are made of keratin - but bird keratin is unique and differsfromthatof modern reptiles
Modern Bird Skeleton
The firmness in the skeleton has been accomplished by fusing groups of vertebrae and fusing the two collar bones, the furcula or wishbone.
A pygostyle
formed by the fusion of the remaining tail vertebrae, support tail feathers.
Keeled sternum
for attachment of flight muscles
Know:
1.Furcula
2.Pygostyle
3.Sternum with keel
4.You can ignore the rest of the image
Avian lung
avian lung must be much more efficient than the mammalian lung.
*They have air sacs contiguousto lung
Figure 27.12a
*In birds air flows in only one direction (in contrasttothetidal flow in mammals).
* Because the air
flow is one-way, gases
can be more efficiently exchanged and
there is no “dead air” in the lungs
avian lung must be much more efficient than the mammalian lung.
*They have air sacs contiguousto lung
Figure 27.12a
*In birds air flows in only one direction (in contrasttothetidal flow in mammals).
* Because the air
flow is one-way, gases
can be more efficiently exchanged and
there is no “dead air” in the lungs
Birds have a tremendous diversity of beaks.
*The beak is a birds principal tool for handling food and its size and shape determine the foods that can be eaten.
Synapsid Lineage
A. Pelycosaur
Sail for thermoregulation (ectotherms)
* Strong jaws first land vertebrates to kill organisms their own size
* Large (200Kg)
* Dominant for 50my
but replaced by therapsids by 250 mya
Synapsid Lineage
B. Therapsids
(Mammal- like reptiles)
* speeding up metabolism *Fur? Probably endothermic *Dominant for 20 my
*gave rise to mammals *Extinct by 170 mya
Therapsid to Mammal transition
- Diaphragm
there is indirect fossil evidence in the rib shape of therapsids that suggests they possessed a diaphragm anotheruniquemammaliancharacteristic.
Heterodont teeth
Differentiation of teeth into multiple specialized types.
Secondary bony palate
separating nasal from oral cavities.
Three inner ear bones and a single jaw bone.
- An excellent seriesoffossilsoverabout40millionyears documents the transition from the multi-boned jaw of Pelycosaurstothe singledentaryofmammals.
- Mammals differentiated from Therapsids by evolution of the 2nd and 3rd inner ear bones (Malleus and Incus) which move from back of jaw/skull into inner ear. Stapes evolved earlier at origin of amniotes.
First mammals
*The earliest mammals first appear in the mid-Triassic (about 210 mya) and most were small mouse-sized animals.
*For about 150 million years they lived in a world dominated by the dinosaurs and underwent large scale diversification only late in the reign and rapid evolution of large body size only after the disappearance of the dinosaurs in the Great Cretaceous extinction 66 mya.
Key mammalian characteristics
- Hair (made of keratin)
- heat loss, camouflage, sensory structures,defense weapon
- Mammary glands and lactation
All female mammals have mammary glands
* about 50% of energy in milk comes from fat
- Since lower jaw bone (dentary) and movement of 2 bones
from
back of jaw into inner ear (become incus and malleus)
- Evolution of diaphragm
(skeletal muscle separates chest and abdominal cavities); enhances breathing ability.
- Endothermy:
crucial adaptation that allowed activity at any time of the day to colonize severe environments
endothermic - generate own heat homeothermic
constant body temperature Powered by efficient heart (4 chambers) and respiratory system (diaphragm)
KeyMammalian Characteristics(cont.)
- Placenta
- specialized organ allowing food, water, and oxygen to pass from mother to child
Teeth
heterodont dentition (different types of teeth for different functions)
Hooves and horns
- hooves specialized pads of keratin
- horns composed of core of bone surrounded by keratin sheat
Digestion of plants
Cellulose major source of food for herbivores, mammals lack enzymes to break down cellulose. some have evolved four-chambered stomachs
* some contain mutualistic bacteria in a cecum
4 chambered heart, separation of oxygenated &
deoxygenated blood; also evolution of diaphragm to improve breathing
Convergent Evolution
of 4- chambered heart in Archosaurs (and descendants) and mammals
Orders of Mammals
Early divergence
*Subclass Prototheria
*Monotremes (lay shelled egg;
Females secrete milk but no nipple; eg duckbill platypus)
*Subclass Theria
Marsupials and Placental mammals
Groups ofMammals
Protheria
A. monotremes:
egg-laying mammals
* lay shelled eggs
* Female produces milk but no
nipple
Theria
B. marsupials:
pouched mammals
* finish development in external pouch
C. placental mammals
*placenta nourishes embryo throughoutentire development
