Amniotes
- Created by: ValentineDevil
- Created on: 25-03-19 13:02
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- Origin of Amniotes
- Land-dwelling vertebrates: mammals, turtles, lizards, crocs, birds
- General characteristics
- Mostly four-limbed or reduced or lost in some groups
- Water-resistant epidermis with various annexes
- Impermeable skin w/ thick keratinous layer
- Annexes: reptile scales, mammalian hairs, feathers, quills, horns
- 3-4 chambered heart
- 3-chambered (reptiles)
- Lizards
- O2 (left atrium) & CO2 (right atrium) contracted into left chamber of ventricle
- Pressure increases, CO2 forced through gap in partition into right chamber of ventricle
- Ventricle contraction: CO2 into pulmonary artery to lungs & O2 into systemic arteries (aortas) to bodies
- Pressure increases, CO2 forced through gap in partition into right chamber of ventricle
- O2 (left atrium) & CO2 (right atrium) contracted into left chamber of ventricle
- Turtles
- Ventricle is not perfectly divided; some slight mixing of CO2 blood can occur
- Snakes
- All 3 arterial trunks comes out of the chamber of the ventricle that receives CO2 blood from R atrium
- Ventricular contraction: muscular ridge forms a partition that guides the CO2 blood to pulmonary artery
- O2 received by other chamber of ventricle is forced through the opening in the ventricular septum and out to the aortas
- Ventricular contraction: muscular ridge forms a partition that guides the CO2 blood to pulmonary artery
- All 3 arterial trunks comes out of the chamber of the ventricle that receives CO2 blood from R atrium
- Lizards
- 4-chambered (birds, mammals, partially so in crocs)
- Crocs
- Ventricular septum is complete; two aortas come out at different ventricular chambers
- Semilunar valve at entrance to left aorta prevents CO2 blodds in R ventricle from flowing into aorta
- Part of O2 blood from L ventricular chamber pumped into the R aorta flows into L by opening (Foramen of Panizza)
- Semilunar valve at entrance to left aorta prevents CO2 blodds in R ventricle from flowing into aorta
- Ventricular septum is complete; two aortas come out at different ventricular chambers
- Crocs
- 3-chambered (reptiles)
- Internal fertilisation: ovi/vivi/ovoviviparous
- Egg w/ porous leathery or hard shell; embryo surrounded by extra-embryonic membranes; direct development
- Amnion
- Innermost membrane; forms sac where embryo is suspended; filled with fluid; protects embryo from shock and carries out hydration
- Allantois
- Stores nitrogenous wastes produced by embryo, and facilitates resp.
- Chorion
- Permits exchanges of O2 and Co2;
- Formed together w/ placenta in mammals- placenta attached to embryo via umbilical cord
- Mesoderm and ectoderm extend beyond embryo to form chorion and amnion
- Layers fuse below yolk so chorion lines the shell; tissues form allantois
- Amnion
- Robust musculo-skeletal system; complex girdles; differentiated backbones
- Two or more sacral ribs
- NO OTIC NOTCH!!
- Bone in the ankle joint complex (astragalus)- deriving from fusion of originally separate bones
- Elongate and curved ribs (often barrel-shaped)
- Enlarged mid-ventral sternum (may be lost altogether in e.g. turtles and snakes)
- Trachea w/ cartilaginous rings
- Cranial features
- Ventricle
- Pterygoid w/ distinct palatal surface, transverse flange and quadrate ramus
- Caniniform tooth on maxilla
- Dorsal
- Premaxilla w/ palatal maxillary & nasal processes
- Various patterns of fenestration
- Squamosal contributes to margin of postemporal fenestra
- Frontal contacts orbit
- Hemispherical & ossified occipital condyle
- Anapsid Pattern
- Universal absence of skull fenestration
- Modern turtle
- Universal absence of skull fenestration
- Synapsid pattern
- Lower temporal fenestra bordered minimally by the jugal, postorbital and squamosal
- dog
- Lower temporal fenestra bordered minimally by the jugal, postorbital and squamosal
- Diapsid condition
- Lower temporal fenestra generally bordered by jugal, postorbital, squamosal, and occassionally quadratojugal and an upper temporal fenestra bordered by postorbital, squamosal, parietal and often postfrontal
- Modern lizard
- Lower temporal fenestra generally bordered by jugal, postorbital, squamosal, and occassionally quadratojugal and an upper temporal fenestra bordered by postorbital, squamosal, parietal and often postfrontal
- Ventricle
- Complex, in-folded lungs
- Spool-shaped vertebral centra, long neck, separate scapula and coracoid ossifications
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