ch 31 Flashcards
Backbone functions:
Protect dorsal nerve chord. Central axis for muscle attachment.
Evolution timeline:
First chordates 600 million years ago.
Fish with no jaws or paired fins, were the only vertebrates for 100 million years starting at 500 million years ago, became dominant animals in shallow seas, fed by filters, eventually replaced by predator fish with paired fins,‑ streamlined bodies for catching prey and hinged jaw for grabbing prey.
First predators fish in fossil records 430 million years ago acanthodians.
Larger jawed Placoderms replaced acanthodians.
Eventually, replaced by two types of fish ‑ sharks and bony fishes.
Sharks have cartilage endoskeleton ‑ light and flexible.
Bony fish have swim bladder to counteract weight of bone endoskeleton. Most fish today are bony.
Amphibians ‑ first vertebrates on land. Evolved from lobed‑fined fish. Needed to develop legs to support weight on land, lungs to get oxygen. Still needed water to reproduce because eggs not water tight.
Reptiles evolve from amphibians. Developed better designed legs, more efficient lungs and heart, water‑tight eggs, internal fertilization, watertight skin to conserve water.
Living reptiles are all what
ectothermic
Disadvantage - inactive at low and high temps.
Advantage - Doesn’t have to eat as much or as often.
ectothermic
metabolism to slow to heat body ‑ get heat from environment.
Endothermic animal have what
high metabolism to generate body heat and require 10 times more food.
Advantage - active at low and high temps.
Disadvantage - Has to eat as more and often.
Therapsids, an order of extinct reptile, were probably endothermic and ancestors of mammals. Therapsids replaced by ectothermic thecodonts and then dinosaurs. Some dinosaurs may have been endothermic. Mammals evolved over 200 million years ago but were limited in numbers and nocturnal until the dinosaurs were wiped out probably by a meteor impact that created a dust cloud and cooled the earth 65 million years ago. First mammals laid eggs, later mammals (100 million years ago) were marsupials which have live births but nurtured young in pouches and placental mammals that nurture young for longer time in mother’s body with the placenta.
Therapsids, an order of extinct reptile, were probably endothermic and ancestors of mammals. Therapsids replaced by ectothermic thecodonts and then dinosaurs. Some dinosaurs may have been endothermic. Mammals evolved over 200 million years ago but were limited in numbers and nocturnal until the dinosaurs were wiped out probably by a meteor impact that created a dust cloud and cooled the earth 65 million years ago. First mammals laid eggs, later mammals (100 million years ago) were marsupials which have live births but nurtured young in pouches and placental mammals that nurture young for longer time in mother’s body with the placenta.
Gills of bony fishes are the most efficient __ organs
oxygen-gathering organs to have evolved (because less oxygen in water).
- One way two opening design prevents oxygen rich water from diluting oxygen poor water (less dilution = more diffusion.
- Individual floating filaments have a lot of surface area for more diffusion.
- Countercurrent flow of water in opposite direction of blood maintains concentration gradient past 50% point.
Air has 20x more oxygen than water, but gills do what
collapse in gravity of land greatly reducing surface area
Amphibians evolve what
bag like structure with much internal folded surface area that does not collapse, through which oxygen can diffuse. In lungs fresh oxygen rich air mixes with oxygen depleted air making lungs less efficient machinery than gills but O2 content of air is high.
Reptiles
higher metabolic rate, air tight skin so have larger lungs with alveoli chambers with more surface area.
Mammals have more
increase lung interior surface area.
Birds
have highest demand for O2 and have evolved a separate bag system to eliminate inefficient mixing of O2 rich air with O2 depleted air. In addition they also have blood flow in the opposite direction of air flow.
Simple jawless fish artery pump worked by
creative sequential squeeze (peristaltic wave) along tube to push blood in – not efficient because some blood backflows.
Gill blood vessels so small they create too much resistance for simple pumps. Gilled fish evolved what
4 chambered heart, each with one way valve to block backflow.
- Sinous venosus
- Atrium
- Ventricle
- Conus arteriosus
Sinous venosus
starts first squeeze later reduced to pacemaker function.
Atrium
large chamber to receive blood with little resistance.
Ventricle
strong muscle chamber
Conus arteriosus
long chamber to smooth pulse so as not to have arteries burst.
Fish system not good enough for land because
Blood goes to gills first to oxygenate, but loses force after passing through fine vessels in gills so blood flow sluggish throughout rest of body.
Amphibians needed more oxygen and evolved a what
separate loop to lungs and back to heart to be pumped again with force to rest of body. Septum separates right and left atrium, but some mixing does occur in ventricle
Reptile ventricles are what
almost completely separated and almost eliminates mixing of blood. Conus arteriosus are separated.
Mammal ventricles are what
completed separated and no mixing occurs.
Mammals and birds have what
remnant Sinus venosus tissue that serves as pacemaker where heart beat originates.
2/3 of vertebrate body is
water.
Marine bony fish lose water by
Freshwater fish have
osmosis and need to drink a lot- need to reduce water loss and reduce salt intake.
opposite problem because their bodies have higher solute concentration and attract water – need to reduce inflow of water and reduce salt loss.
Both problems are solve by kidneys which regulate salt and water balance and removes metabolic waste from blood. Made of thousands of small units called nephrons which have the structure of a bent tube.
Pressure forces blood fluid and small metabolic waste molecules past
nephron filter. As fluid passes through nephron tube, useful sugars and ions are recovered. Remaining water and waste form urine.
