Vertebrate Zoology Chapter 14 Synapsids and Sauropsids PDF

Synapsids and Sauropsids Chapter 14 Amniote Synapomorphies 1. Amniotes – Amniotic egg with 4 “extra- embryonic membranes” – Amnion – Amniotic sac in live-bearers – Allantois – Gas exchange and waste – Chorion – Becomes placenta in mammals; also gas exchange - Yolk sac – Provides nutrien...

Synapsids and Sauropsids Chapter 14 Amniote Synapomorphies 1. Amniotes – Amniotic egg with 4 “extra- embryonic membranes” – Amnion – Amniotic sac in live-bearers – Allantois – Gas exchange and waste – Chorion – Becomes placenta in mammals; also gas exchange - Yolk sac – Provides nutrients 2. Fertilization is always internal and there is no larval stage Amniote Synapomorphies 3. Skin covered by keratinized “water- proof” structures of epidermal origin – scales, hair, feathers, etc., epidermis itself more keratinized & has a high lipid concentration to slow water loss  4. 12-pairs cranial nerves Amniote Synapomorphies 5. Rib-ventilated aspiration (negative pressure, augmented in some by cloacal or pharyngeal gas exchange) How do turtles breathe underwater? | Surprising Science (youtube.com) 6. Complete absence of gills at all life stages (paired pharyngeal pouches present in embryos)  7. Skeleton well ossified, ribs with Amniote sternum Synapomorphies 8. Ventricle partially or completely divided 9. Males of most species with true copulatory organ 10. Ankle with distinct plane of motion Anthracosauria† - amphibian clade that includes amniote ancestors Origins of Amniota By late Carboniferous/Permian there were 4 amniote radiations: - Anapsida - earliest group, skull with solid dermal plates, & no temporal fenestrae; turtles + early reptiles - Diapsida – large Mesozoic radiation (“Age of Dinosaurs”); 2 temporal fenestrae; ancestors of all extant reptiles + birds - Synapsida – 1st large radiation, Permian (280 – 210 MYA); single temporal fenestra (below po-sq suture) includes ancestors of mammals - Euryapsida† - single temporal fenestra (high up on skull); several extinct marine groups (ichthyosaurs, plesiosaurs) Locomotion and Respiration Early tetrapods moved like modern salamanders, bending the body side to side Only sustainable for short dashes – Compresses one lung and pushes air into the other lung, which interferes with airflow in and out of the trachea Changes in Synapsid Anatomy  Synapsid Breathing While Walking/Running Major innovation was the development of a diaphragm – Sheet of muscle that separates the abdomen; parachute-shaped – Bulges anteriorly when it is relaxed, and flattens when it contracts – Flattening pulls air into the lungs Along with expanding the ribs No interference with locomotion Synapsid Breathing While Walking/Running Evolution of a diaphragm correlates to changes in the vertebral column – Most mammals don’t have more than 20 vertebrae in axial portion Divided into thoracic and lumbar – Most have 7 cervical vertebrae Diaphragm develops at the thoraco- lumbar boundary – Linked to the loss of ribs on lumbar vertebrae Sauropsid Breathing While Running/Walking Many birds and dinosaurs developed bipedal locomotion –Only use their hindlimbs –Some used gastralia bones (ventral ribs) for lung ventilation Phylogenetic Pattern of Tetrapod Lung Ventilation  Amniote Lungs Synapsids have alveolar lungs – Treelike branching pattern with alveoli that have dense capillaries Sauropsids have faveolar lungs – Cuplike chambers (faveoli) line the walls of the airways (parabronchi) Synapsid Lungs  Sauropsid Lungs Many different lung structures –Some lizard lungs are sacs at the ends of the bronchi with cups lining the walls of the lungs –In other lizards and turtles the bronchi continue into the lungs and can branch into secondary and tertiary bronchi –Birds and crocodylians have parabronchi that connect the secondary bronchi –Crocodylians also have a diaphragm –Unidirectional air flow  Avian Respiratory System Birds have 2 sets of air sacs – anterior and posterior –Large, but don’t participate in gas exchange –Store air during the respiratory cycle Avian Respiratory System Parabronchi branch across the lungs Air capillaries, where gas exchange occurs, branch from the parabronchi Cross-current exchange between blood and airflow Air takes 2 cycles to get through the lung 1.Inhale 1: Fresh air is inhaled and goes to the posterior air sacs 2.Exhale 1: Air gets pushed into the parabronchial lung 3.Inhale 2: Air gets pulled into the anterior air sacs 4.Exhale 2: Air gets pushed out through the trachea  Amniote Ankle Joint Evolution Tarsus (ankle) – Proximal bones connect to tibia/fibula bones – Distal bones connect to the metatarsals Basal amniotes lost many of the small proximal bones in basal tetrapods and retained two: – Calcaneum (connects to the fibula) – Astragalus (connects to the tibia) Original point of articulation was at the mesotarsal ankle joint  Amniote Ankle Joint Evolution Mesotarsal ankle joint is retained in many extant reptiles –Modifications exist Modifications in derived mammals –Allow the foot to turn inward and outward –Important for climbing mammals Evolution of Endothermy Physiological implications Endotherms maintain body temperatures that are higher than ambient temperatures Mass-specific metabolic rate of an endotherm is ~10x higher than an ectotherm Behavioral and ecological implications Endotherms can be active on cool nights and at colder temperatures Can engage in long periods of foraging and sustained flight and running Models of Endothermy Evolution Direct Selection for a High and Stable Body Temperature Thermogenic opportunity model – Basal mammals may have been nocturnal Warmer is better model – Everything from the cellular to the whole-organism level happens faster and more forcefully at higher temperatures Indirect Selection for Characters that Depend on High and Stable Body Temperature Aerobic scope model – Early synapsids might have been more active, so they had higher metabolic rates while they were moving and needed higher metabolic rates at rest Parental Care Model – Higher and more stable temperatures can increase the rate of embryonic development, increase the viability of embryos, mother can influence phenotype of her offspring through temperature, and providing food for young requires sustained activity Getting Rid of Wastes: The Kidneys Mammalian Kidneys All mammals excrete urea as their chief nitrogenous waste Urea requires much more water to be excreted than uric acid Mammals produce large amounts of nephric filtrate but are able to reabsorb most of this Kidneys are made of millions of nephrons, which filter blood and make concentrated urine  Convert waste nitrogen compounds into uric acid Reptile Kidneys Uric acid can be excreted using only a small amount of water Reptile glomeruli are small, and some reptiles have no glomeruli at all Those with glomeruli filter just enough fluid to wash the uric acid, which is secreted by the tubules, into the cloaca Most of this moisture is reabsorbed in the cloaca Emptying the cloaca deposits feces (brown) and uric acid (a white paste) These water conservation mechanisms can allow the reptile to forgo drinking water The water content of its food plus the water produced by cellular respiration is usually sufficient Nitrogen Secretion by Sauropsids Renal – Uric acid followed by reabsorption of sodium and potassium ions to the bloodstream Extra-Renal Route – Salt glands; allows for excess ions in blood to be secreted as salt while conserving water Vision Vertebrate retinas have rod and cone cells - Rods are sensitive to low-light levels, but do not provide visual acuity - Cones are sensitive to different wavelengths of light (red, green, blue) Most non-mammalian vertebrates have cones that are sensitive to three colors and UV light - Seems to be the ancestral gnathostome condition Mammals usually have green-blue color vision - Humans and other apes have added red sensitivity Taste