Lecture 19 Flashcards by meira rose

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

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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

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Eggs in water or on land?

In general
Amniotic egg is a “terrestrial egg”
Anamniotic egg is an “aquatic egg”

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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

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Amniotic Egg parts

The amniotic egg has four extraembryonic membranes:
Amnion
Chorion
Allantois
Yolk sac

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Amnion

Part of amniotic egg
encloses embryo in fluid (aqueous medium for growth)
cushions embryo

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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

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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

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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

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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)

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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

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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

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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)

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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)

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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

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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