Lecture 19 Flashcards
Amniotes caracteristics
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
Anamniotes
Vertebrates that lacks 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
Eggs in water or on land?
In general
Amniotic egg is a “terrestrial egg”
Anamniotic egg is an “aquatic egg”
Adaptations of Amniotes (7)
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
Amniotic Egg parts
The amniotic egg has four extraembryonic membranes: Amnion Chorion Allantois Yolk sac
Amnion
Part of amniotic egg
encloses embryo in fluid (aqueous medium for growth)
cushions embryo
Chorion
Part of amniotic egg
surrounds the entire egg and is highly vascularized
Participates in gas exchange (02 in, C02 out)
In most mammals, it contributes to the placenta
Allantois
Part of amniotic egg
Participates in gas exchange and stores metabolic waste (uric acid) in birds and nonavian reptiles
Role in development of the placenta in most mammals
Yolk sac
Part of amniotic egg
Also found in anamniotes (tends to be larger in amniotes)
Stores nutrients
In marsupials and placental mammals the yolk sac doesn’t store yolk, but contributes to the placenta
Shell of amniotic eggs
Many amniotic eggs have a shell (e.g. reptiles, birds)
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)
Waterproof Skin for amniotes vs amphibians
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
Rib Ventilation of the Lungs for amniotes
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
Stronger Jaws amniotes
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)
High-pressure Cardiovascular System amniotes
Adaptive for terrestrial organisms
Higher metabolic needs
Heart must pump blood ‘uphill’ (i.e. counteract gravity)
Heart is segmented – more on this later
Fish: two-chambered (1 atrium and 1 ventricle)
Amphibians & most nonavian reptiles: three-chambered (2 atria, 1 ventricle)
Birds & mammals: four-chambered (2 atria, 2 ventricles)
Water-conserving Nitrogen Excretion amniotes
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 dilute urine
Water and many salts are resorbed in the bladder
Voided as a semi-solid mass of uric acid
Expanded Brain and Sensory Organs amniotes
All amniotes have a relatively large brain
Particularly birds and mammals
Better integration of sensory information
Better control of muscles during locomotion
Reptile Taxonomy
A modern definition of Reptilia*
includes ‘nonavian reptiles’ (as listed above) and birds
Crocodilians
Also includes the extinct dinosaurs
(birds also belong to a clade within Reptilia called Archosauria)
Class Reptilia orders
Order Testudines
-Turtles
Superorder Lepidosauria
- Tuataras
- Squamata (lizards, monitors, snakes)
Archosauria (no rank)
- Crocodilians
- Birds
General Characteristics: Non-Avian Reptiles
Ectothermic
Tetrapods
Two paired limbs
However, limbs vestigial or absent in many
Body covered in keratinized epidermal scales
Usually dioceious
Some lizards reproduce by parthenogenesis
Parental care typically absent
Except in crocodilians
No larval stage
keratin in animals
Hagfish and Lampreys: keratinized plates for rasping, chewing
Tadpole has keratinized jaws for scraping vegetation
Non-avian reptiles: body is covered with keratinized epidermal scales
Outer layer of turtle shell is covered in keratin
What is keratin?
Fibrous structural protein
Very tough material
Found in reptiles, amphibians and mammals
Hair, horns, nails, claws, hooves, scales, shells, feathers, beaks, quills
Analogous function to chitin
Testudines - Turtles
Enclosed in shell
Dorsal carapace
Ventral plastron (breastplate)
Outer layer composed of keratin
Inner layer composed of bone
Bony layer is a fusion of ribs, vertebrae and other bone
Unique among vertebrates – turtle limbs are located inside the ribs
Testunides - Reproduction
Oviparous
Internal fertilization
All turtles (even marine) bury shelled, amniotic eggs in the ground
Once nest is constructed, it is abandoned
Lepidosauria
Squamata
lizards,
monitors,
snakes
Tuatara
lizard-like animals
endemic to New Zealand
Kinetic skull
Squamata have them
Skull specializations for swallowing large prey
Snake skulls even more kinetic than lizards
Major factor that enabling diversification of snakes and lizards
Lizards characteristics
A paraphyletic group
familiar animals such as geckos, iguanas, skinks, monitors (e.g. Komodo dragon), chameleons
Most have four limbs A few (e.g. glass lizard) are completely limbless
Moveable eyelids
Lizards temperature
Ectothermic (like nearly all nonavian reptiles)
Adjust body temperature by moving among different microclimates
Few species in cold climates
few opportunities to warm up
successful in warm climates with low productivity (e.g. tropical deserts)
Because of the energy savings associated with being ectothermic
Snakes characteristics
Monophyletic group
Limbless
Vertebrae are shorter, wider, and more numerous than other tetrapods
Differ from lizards in several ways:
No moveable eyelids (snakes eyes covered by a translucent cap)
No external ear openings
Internal ears only hear sounds in a limited range of low frequency
Skull even more kinetic than lizard skull (larger range of motion)
Snakes vs Lizards?
What is the difference between a limbless lizard and a snake?
Different common ancestor!
Lizards have moveable eyelids…snakes don’t
Lizards have ear openings…snakes don’t
Snake skull is more kinetic
Snakes – Capturing Prey
Kinetic skull
Skull bones are loosely articulated
Two halves of the lower jar are joined only by muscle and skin
Jaws have posterior facing teeth that anchor prey and slowly move it in
Snakes can swallow very large prey (several times their own diameter)
How do they breathe?
Tracheal opening is extended forward between the mandibles
Snakes - smell
All snakes and some lizards use their tongues for smell
Employ Jacobson’s organs
Paired organs located in roof of mouth
Line with olfactory epithelium
Forked tongue flicks through air collecting scent molecules
Draws past Jacobson’s organs
Also have olfactory areas in the nose (less well-developed)
Tuataras
Lizardlike animal
Endemic to New Zealand
2 living species
Sole survivors of a lineage that diverged from Lizards and Snakes
Endangered species Threatened by non-native species (e.g. cats, dogs, rats, goats) Slow reproduction rate – 10-20 years to reach sexual maturity Produce eggs once every 4 years
Crocodilians characteristics
Order Crocodilia: alligators and crocodiles
more closely related to birds than other non-avian reptiles
Elongated, robust, well-reinforced skull and massive jaw musculature
Wide gape and powerful closure
Teeth are replaced (like sharks)
Alligator vs Crocodile
Alligator head and jaws are wider and shorter than crocodile
Alligators teeth are less visible with mouth closed
Crocodilians - Reproduction
Oviparous
Female lays 20-50 eggs and buries them in sand
Extensive parental care:
female guards eggs
opens nest when hears vocalizations of the hatchlings
Young are guarded by mother for 2 years after hatching
Incubation temperature determines the sex ratio of the offspring
Low nest temperature produces only females
High nest temperature produces only males
Opposite pattern from turtles (high temp = female, low temp =male)
Temperature-dependent sex determination (TSD)
Genetic sex determination in most snakes and lizards, and some turtles
Z/Z = male, Z/W = female
Same system used in birds
Temperature-dependent sex determination (no sex chromosomes) in all crocodilians, most turtles, and some lizards and snakes
