how are amniotes divided
- sauropsida (birds, crocodiles, tutles, reptilians and tuatara)
- synasida (mammals)
how did synapsid and sauropsid lineages adapt and develop derived traits? did they evolve together? separately?
lineages separated before many derived characters associated with terrestrial life emerged
lineages independently developed many derived adaptations (endothermy, parental care, social behaviours)
selection pressures for sauropsids and synapsids
- locomotion and ventilation
- uptake of oxygen and release of carbon
- waste excretion that conserves water (nitrogenous waste)
gas exchange adaptations
to support higher levels of muscle activity associated with tetrapod evolution, more gas exchange was needed
more surface area!
sauropsids and synapsids developed complex lungs but lung morphology varied - ex. evolved diff solution to same problem
locomotion and ventilation adaptations - sauropsids
bipedal locomotion of many groups (ex. birds and dinosaurs)
don’t have diaphragm, instead
- pelvic movements
- ventral ribs (gastralia)
locomotion and ventilation adaptations
early tetrapods had short limbs, sprawling posture (bent at elbows) and long tails
lizards lateral axial bending and lung ventilation
- volume decrease raises air pressure in left lung (left foot up, right arm up)
- air moves between lungs as lizard moves but does not move into or out of lungs
locomotion and ventilation adaptations - synapsids
- upright posture with limbs more underneath the trunk
- diaphragm
- bounding gait
- dog: volume decrease raises air pressure (exhale) when front legs are behind, volume increase lowers air pressure in lungs (inhale) when dog leaps, couples locomotion w/ ventilation - trunk vertebrae differentiated into thoracic and lumbar
synapsid lungs
- alveolar lung
- air travels thru trachea to progressively smaller airways via primary pronchi
- air ultimately reaches alveolar sacs: sites of gas exchange
- tidal ventilation brings air in and out of airways to alveoli
- alveoli can be re-inflated due to production of surfactants which reduce surface tension of water lining alveoli
what are 2 ways that bird respiration is unique?
- have small tubules (air capillaries) that radiate from para bronchi for gas exchange - use crosscurrent exchange
- presence of air sacs - 2 grps: anterior and posterior, not used for gas but act as bellows during respiratory cycle
bird require 2 respiratory cycles to pass 1 unit of air thru respiratory system - 1 way passage of air
explain the 2 breath model for lung ventilation
- first inhale - volume of thorax increases, drawing fresh air thru trachea and primary bronchi into posterior air sacs, while air that was in parabronchial lung at the beginning of inhalation is pulled into anterior air sacs
- first exhale - volume of thorax decreases, air from posterior sacs into parabronchial lung and expelling air from anterior sacs to the exterior via trachea
- second inhalation - draws unit of air into anterior air sacs, and a new unit of fresh air into the posterior sacs
- second exhale - sends air out thru trachea and forces air from posterior sacs into parabronchial lung
what was the solution to high blood pressure that is required for circulation but can be problematic for gas exchange
2 blood circuits (pulmonary and systemic) created by a permanent septum in the ventricle
- most likely not seen in ancestral amniot
- transient septum in turtles, lizards, snakes and tuatara
how do sauropsids excrete waste?
produce uric acid, which has low solubility in water and low toxicity
combines with ions (ex. K, Na) in cloaca or bladder and forms a precipitate
water is reabsorbed and precipitate expelled
sensory systems of amniotes, differences between synapsids and sauropsids
diverse within and between synap and saurop
differences in vision, chemosensation and hearing
synapsids rely more on olfaction (smell) than vision
sauropsids have variable olfactory sensitivity but excellent vision
do mammals and bird tend to have higher systemic pressure or pulmonary pressure?
pressure in systemic circuit of mammls and birds is 6/8 times higher than pressure in the pulmonary circuit
why did the problem of waste elimination present itself?
protein metabolism produces NH3, which is toxic but soluble in water
nitrogenous wastes are primarily excreted in urine
terrestrial organisms need to deal with eliminating nitrogenous waste without losing much water
how do synapsids excrete waste?
excrete nitrogenous wastes such as urea, which is more water soluble and less toxic
mammalian kidneys are adapted to producing concentrated urine, conserving water
do synapsids rely more on olfaction or vision
olfaction
do sauropsids rely more on olfaction or vision
variable olfactory sensitivity but excellent vision
