Chordates 2 Flashcards
Two major lineages of lobe-fined fish
- Coelancanths
- Lungfish
- Lineage diverges from lungfish that eventually leads to tetrapods.
The evolution of legs
- Fossil record shows clean progression from lobe-finned lungfish to tetrapod
- Tiktaalik is a fossil intermediate between lobe-finned fish and tetrapods
- Has many fish-like traits (e.g. fins, scales, primitive jaws)
- Has tetrapod-like traits (e.g. fins with wrist, neck, expanded ribs, flat head)
- Digit number highly variable in early tetrapodomoph legs.
- Successful tetrapods have 5 digits.
Evolution of Amphibians
A. Once tetrapods successfully invade land, two major lineages diverge, one leading to the Amphibians, the other leading to the reptiles and mammals
B. Important traits
- Breath through primitive lungs, juveniles and some adults have gills. Capable of cutaneous respiration (i.e. breath through skin)
- Fertilization external
- Reproduction tied to water
C. Amphibians are closely tied to water for reproduction! This limits their terrestrial range.
a. Evolved from the water but still tied to the water
b. Have not made a clean break from the water yet
c. Always go back to water to reproduce
Evolution of the Amniotes
- Breaks the tie to water and allows creates to live 100% away from water
A. Amniotic egg – extraembryonic membranes
- Amnion - protects and provides shock absorbtion
- Yolk sac- stockpile of nutrients for embryo
- Allantois - disposal sac for metabolic waste
- Chorion - allows for respiration across shell
B. Amniotic egg allows for water independence during reproduction.
C. Water independent reproduction leads to internal fertilization
D. Legs rearranged for carrying weight out of water
a. From sides to underneath to keep body from dragging on ground
- Allows for eggs to be placed away from predators = greater success
Amniotic egg – extraembryonic membranes
- Amnion - protects and provides shock absorbtion
- Yolk sac- stockpile of nutrients for embryo
- Allantois - disposal sac for metabolic waste
- Chorion - allows for respiration across shell
The reptiles
Extant Reptile
- Turtles
- crocodilians
- birds
- tuatara
- squamates
The reptiles
Extinct Reptiles
- Pterosaurs – independent evolution of flight
i. Not a dinosaur - Dinosaurs – terrestrial lineage of large reptiles; likely endothermic; some feathered; give rise to birds
- Plesiosaurs and ichthyosaurs – reinvade the water;
i. are not dinosaurs
ii. aquatic reinvasion in the reptile line
iii. ichthyosaurs - gave life birth
The mammals
produce milk, have hair <- 2 traits not in any other
- Monotremes
- Marsupials
- Eutherians
The mammals
Monotremes
- Lay eggs, produce milk (but no nipples)
- only mammals to lay eggs
- E.g. platypus and echidna
- the only 2 species
The mammals
Marsupials
- Rudimentary placenta, nipples
- Pouch for fetal development
- e.g. kangaroos, opossum
The mammals
Eutherians
where humans are
- Complex placenta
- e.g. rodents, whales, bats, primates, elephants
- primates
The mammals
Eutherians:
Primates(derived traits)
- Opposable thumb
- fingerprints
- large brain
The mammals
Eutherians:
Primates(two groups)
- Prosimians(lemurs and tarsiers)
- Anthropoids
- monkeys
- apes
The mammals
Eutherians:
Primates:
Apes(Five genera)
- Gibbons
- orangutans
- gorilla,
- chimpanzee
- humans
The mammals
Eutherians:
Primates:
Apes:
Genus Homo(humans and others)
- Bipedal
- changes the attachment of neck to body to be upright
- Enlarged cranial cavity / brain
- Reduced lower jaw
- trade jaw power for brain power due to weight
- “morphological tradeoff”
- Many species of homo coexist
