BIO153 Lec 16-17

two major classes of Deuterostomia

1. echinoderms → sea stars and sea urchins

2. chordates → vertebrates like fish, reptiles, mammals and other invertebrates

Chordata

members of Deuterostomia with four derived traits:

1. notochord

2. dorsal, hollow nerve cord

3. pharyngeal slits or clefts

4. muscular, post-anal tail

• invertebrates (lancelets and tunicates)

• all vertebrates

notochord

longitudinal, flexible rod found between the digestive tube and nerve cord

• provides skeletal support for the body without calcification

• for vertebrates, backbones develop around the embryonic notochord, often replacing the notochord entirely

• in humans, notochords become part of the intervertebral discs

dorsal hollow nerve cord

• in chordate embryo develops from a specific surface of the ectoderm (neural plate) that rolls and internalizes into a neural tube

• develops into brain/spinal cord

• dorsal to notochord

• other animal in the phyla may have hard nerve cords that are ventral instead of dorsal

pharyngeal slits or clefts

• pharynx is posterior to the mouth

• clefts are the arches and grooves that develop on its outer surface

• can become slits for fish gills (breathing) and invertebrate chordates (feeding) → water passes without going through the digestive tract

  • do NOT become slits in ADULT TETRAPODS → differentiate to muscle, nervous and skeletal tissues around face and neck in humans

when do pharyngeal clefts develop in human embryos

around 4 weeks

muscular post-anal tail

• in chordates, this can be greatly reduced or lost during embryonic development

• non-chordates have digestive tracts that extend the whole length of the body

lancelets

• invertebrates with ALL features of chordate

• adult has cilia in mouth → adults burrow tail-ends into sand andd use cilia to draw water into their mouths to capture food

tunicates

• more closely related to vertebrates than lancelets

• larvae resemble chordate with all four traits

• settles at a suitable location to undergo metamorphosis

  1. reabsorbs notochord and tail

  2. degenerates nervous system

  3. filters water through enlarged pharyngeal slits for food

Vertebral advantages

1. skeletal system and more complex nervous system → better hunting and escape from predators

2. enclosed spinal cord replaces mechanical roles of notochord

what were the traits of early diverged vertebra

1. no jaws

2. cartilage skeleton with extracellular matrix proteins like collagen

3. cartilage was calcified for support

example of early diverged vertebra

lamprey → jawless fish → toothed suckers

Gnathostomes start at…

• Chondricythes → sharks, rays

• they are cartilage fish → biggest and best vertebrate ocean predators

• predominantly cartilage skeleton

• limited use of mineralization may be derived

• have jaws → hinged structures for food gripping and slicing

ray-finned fishes

• ossified endoskeleton with a matrix of calcium phosphate

• fines made of bony rays with webs and no muscle

• most extant fish species are ray-finned

how lobe-fins differ from ray-fins

• pectoral and pelvic fins have thick muscle supporting bony fin

• muscular fins can be used to walk along the sea floor

• not a lot of extant species with lobe-fins

lobe-finned

three major groups

1. coelocanths (actinista) → living fossil, unchanged for -400 million years

2. lungfish (dipnoi) → lungs and gills for gas exchange

3. tetrapods → sister group to lung fish that adapted to life on land → muscular pelvic and pectoral fins evolved into digited limbs

tetrapods

• Gnathostomes with digited limbs

• four feet

• diverged about 365 million years ago

• weight support for walking

• limbs changed into hands, wings and flippers

Amphibians

• salamanders, frogs, caecilians

• amphibian refers to dual life stage of frogs

  1. tadpole (herbivore, aquatic, legless, tail, gills)

  2. frog (carnivore, terrestrial, tailless, lungs)

• many amphibians are strictly aquatic of terrestrial that still ned moist habitat and have major gas exchange throug skin → eggs dessication-prone

amniotes

tetrapods with terrestrially adapted eggs

• reptiles and mammals

• amniotic egg contains specialized membranes that nurture the embryo amnion is the membrane filled with amniotic fluid

• other membranes function in gas exchange, transfer of nutrients, and waste storage

• amniotic gg allows terrestrial organisms to nurture embryo without a body of water

amniotic egg parts

• amnion → envelopes human placenta, contains amniotic fluid

• allantois → amniotic sac for waste disposal

• chorion → for gas exchange

• yolk sac for nutrients

reptilles

turtles, tuataras, lizards, snakes, crocodiles, birds

• lizards, snakes and many reptiles are ectothermic (cold-blooded) and cannot regulate their own body temperature (rely on sun and shade)

• need tenth of the energy as mammals need to survive

• birds are endothermic and have metabolic activity to regulate body temperature → less energy efficient but able to withstand harsher conditions

mammals gen char

• amniotes with hair and milk to nurture young

• hair and fat insulation

• milk → fats, sugars, proteins, minerals, vitamins

• endothermic and high metabolism

• larger brain for body size → can learn and transfer knowledge from parents

3 mammal types

• monotremes

• marsupials

• eutherians (placentals)

monotremes

• found in Australia and New Guinea

• Platypus and echnidas

• lay eggs

marsupials

• opossums, kangaroos, koalas

• embryo develops in female and is nurtured by placenta

• shorter gestation, earlier birth, child is nourished in pouch

• most extant are in Australia

• convergent evolution with placentals makes them ocupy similar niches

Eutherians or placentals

• larger and more complex placenta

• longer gestation

• embryonic development completed in uterus

• various food, life forms, habitats (i.e., insects, meat, nuts, grass)

  • accredited to teeth variety

teeth types in mammals

1. carnivores → canines and incisors for biting, jagged premolars and molars for crushing

2. herbivores → broad, rigid molars and premolars for grinding

3. omnivores → combination of all (molars only crushing, premolars only grinding, canines and incisors biting)

mammalian digestive tract

• large, expandable stomachs in carnivores due to long intervals between feeding

• herbivores and omnivores have long alimentary canals for better nutrient absorption and because cell walls of plants are harder to digest

gut microbiome in cows

• cow is ruminant that mixes food with microbes in several stomachs

• gut microbiome → intestinal microbe mutualism

  • important for herbivores

• vertebrates cannot digest cellulose cell walls for energy conversion

• rely on bacteria in fermentation chambers of alimentary canals

three primate groups

• lemurs, lorises and bush baby

• tarsiers

• anthropoids → monkeys and apes

gen char of primates

1. earliest ones were tree dwellers

2. thumbs

3. anthropoids have opposable thumbs (ventral surface of thumb and fingers meet)

4. eyes on one side of face

5. flat face, short jaw, large brain

6. well developed parental care and social behaviour

apes

• gibbons

• orangutans

• gorilla

• chimps and bonobos

• humans

• larger than monkeys

• no tail

• only gibbons and orangutans are primarily arboreal (tree dwellers)

• no bipedal locomotion yet (just two limbs for walking)

hominins

• extinct species more closely related to humans than apes

• multiple lineages of bipedal locomotion (about 6.5 million years ago)

• Homo sapiens are the only hominin lineage that survived (others are extinct)

• use of tools may have developed after bipedal locomotion (usuing bones to slice flesh)

• non-hominin apes can use tools too (orangutans put sicks into holes to fish food)

Homo genus

early Homo spread from Africa to Europe/Asian regions as they diversified

Neanderthals

follow different lineage than humans but there is gene flow between them due to interbreeding

• bury dead

• hunting tools

• extinct 28000 - 40000 years ago

Homo sapiens

• about 0.2 million years old

• bipedal locomotion

• language, tools, symbolic thought, artistic expression

• reduced jawbones, jaw muscles, shorter digestive tract

• cave painting 30,000 years ago