Intro to Amniotes & Reptiles Flashcards
How did they go from sea to land?
- Amphibian development is linked to water
Shell-less eggs
Thin, moist skin
Often gilled larvae - An ancestor of amniotes evolved an egg that is better adapted to dry terrestrial conditions
What are Amniotes?
- Monophyletic group within vertebrata
- Includes
Nonavian reptiles
Birds
Mammals - Amniotic membrane around the embryo
- Lack gilled larvae
- Internal fertilization
- Lay eggs on land or retained within the mother
What are anamniotes?
- Vertebrates that lack an amniotic membrane
- Informal group that includes fishes and amphibians
- Tend to lay their eggs in water
- Smaller, slower growing embryos compared to amniotic egg of same size
Are eggs in water or on land?
- In general Amniotic egg is a terrestrial egg Anamniotic egg is an aquatic egg - Exceptions Some amphibians lay their eggs on land (moist environment) Even fish can lay their eggs on land
What are the adaptations of Amniotes?
1) Amniotic egg
2) Thicker and more waterproof skin
3) Rib ventilation of the lungs
4) Stronger jaws
5) High-pressure cardiovascular systems
6) Water-conserving nitrogen excretion
7) Expanded brain and sensory organs
Explain the amniotic egg
- Has four extra embryonic membranes Amnion Chorion Allantois Yolk sac
What is the amnion?
- Encloses embryo in fluid (aqueous medium for growth)
- Cushions embryo
What is the chorion?
- Surrounds the entire egg and is highly vascularized
- Participates in gas exchange
- In most mammals, it contributes to the placenta
What is the allantois?
- Participates in gas exchange and stores metabolic waste (uric acid) in birds and nonavian reptiles
- Role in development of the placenta in most mammals
What is the yolk sac?
- Also found in anamniotes (tend to be larger in amniotes)
- Stores nutrients
- In marsupials and placental mammals the yolk sac doesn’t store yolk, but contributes to the placenta
What is the shell?
- Many amniotic eggs have a shell
Eggs of some lizards, some snakes, and most mammals lack a shell - Shell is mineralized but often flexible
- Provides mechanical support
- Semipermeable barrier
Allows passage of gases but limited water loss (especially in birds)
Explain their waterproof skin
Amphibians
Thin, moist skin to permit effective gas exchange
Vulnerable to dehydration and physical trauma (on land)
Amniotes Change is skin morphology Thicker, tougher, more waterproof Few use skin for respiration Protected by hair, feathers, scales
Explain their rib ventilation of the lungs
- Amniotes have better developed lungs than amphibians
Reflects an increase in metabolic demands and a reduced ability to breathe through skin - Amphibians use positive ventilation breathing
Amphibians push air from oral and pharyngeal cavity into lungs - Amniotes use negative ventilation breathing
Expand thoracic cavity to pull air into lungs
Explain their stronger jaws
- Fish jaw is designed for suction feeding
Have teeth but don’t chew - Tetrapods have tongue and strong jaw
Amphibians and some reptiles have teeth but don’t chew (swallow prey whole)
Mammals have strong jaw adapted for mastication (chewing)
Explain their high pressure cardiovascular system
- Adaptive for terrestrial organisms
Higher metabolic needs
Heart must pump blood uphill
- Heart is segmented
Fish: 2 chambers
Amphibians & most nonavian reptiles: 3 chambers
Birds & mammals: 4 chambersExplain their water conserving nitrogen excretion
- Most aquatic organisms (ammonia)
Toxic at relatively low concentrations - must be diluted with water (not adaptive for dry terrestrial environments) - Mammals (urea)
Concentrated in the kidneys, reduces water loss - Birds and nonavian reptiles (concentrated uric acid)
Bladder receives diluted urine
Water and many salts are resorbed in the bladder
Voided as a semi-solid mass of uric acid
