AEBI - 211 Intro to Amniotes & Reptiles

What is special about the egg that the ancestor of amniotes developed?

It is better adapted to dry terrestrial conditions

Amniotes is a ____ group within vertebrata

monophyletic

What does Amniota include?

Non-avian reptiles, birds, mammals

Membrane surrounding embryo of amniotes

Amniotic membrane

True or false: amniotes have gilled larvae

False

Type of fertilization in amniotes

Internal

Anamiotes

Vertebrates that lacks an amniotic membrane. Informal group that includes fishes and amphibians

Amniotic egg is ____ while anamniotic egg is ____

• Terrestrial

• Aquatic

What are the exceptions to egg laying?

• Some amphibians lay eggs on land in moist environment (Darwins’ frog, some salamanders, etc.)

• Splash tetra jumps out of water to lay eggs on leaf

  • Male guards egg by keeping them mois

Are larval amphibians cannibalistic?

Most herbivores, but some are opportunistic omnivores —> can consume other tadpoles

Do axolotls exhibit direct development

No, still go through larval stages

Name 7 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

Name the 4 extraembryonic membranes of amniotic egg

• Amnion

• Chorion

• Allantois

• Yolk sac

Function of amnion

• encloses embryo in fluid (aqueous medium for growth)

• cushions embryo

Function of chorion

• surrounds the entire egg and is highly vascularized

• Participates in gas exchange (02 in, C02 out)

• In most mammals, it contributes to the placenta

Function of 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

Function of yolk sac

• 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

Amphibian skin vs Amniote skin

• Amphibians

  • thin, mois, allows gas exchange

  • Vulnerable to dehydration and physical trauma

• Amniotes

  • change in skin morphology

  • thicker, tougher, more waterproof

  • few use skin for respiration

  • protected by hair, feathers, scales

Rib ventilation of the lungs - do amniotes have better lungs?

Yes, amniote lungs are more well-developed than amphibians —> reflects increase in metabolic demands + reduced ability to breathe through skin

Type of breathing amphibians use

Positive ventilation —> air is pushed from oral and pharyngeal cavity into lungs

Type of breathing amniotes use

Negative ventilation breathing —> expand thoracic cavity to pull air into lungs

Stronger jaws: tetrapods

Strong jaw adapted for mastication (chewing)

High pressure cardiovascular system - Terrestrial organisms

• Adaptive to their metabolic needs

• Heart pumps blood uphill to counteract gravity

Describe heart of fish, amphibians/nonavian reptiles and birds/mammals

• Fish: two-chambered (1 atrium and 1 ventricle)

• Amphibians/nonavian reptiles: three-chambered (2 atria, 1 ventricle)

• Birds/mammals: four-chambered (2 atria, 2 ventricles

Water-conserving nitrogen excretion: name 3 compounds that are excreted

• Ammonnia

• Urea

• Uric Acid

Ammonia

• Excreted by most Aquatic organisms

• Toxic at low concentrations

• must be diluted with large amounts of water to keep concentrations in the excretory fluid below toxic levels

• not adaptive for dry terrestrial environments

Urea

• Excreted by mammals and amphibians

• Less toxic, less dilution required

• concentrated in kidneys

Uric acid

• Birds and nonavian reptiles

• Least toxic

• Bladder receives dilute urine

• Water and many salts resorbed in bladder

• voided as semi-solid mass of uric acid

Expanded brain and Sensory organs of amniotes

• All have a large brain

• Better integration of sensory info

• Better control of muscles during locomotion

Traditional definition of class reptilia

• included snakes, lizards, tuataras, crocodilians, and turtles

• Also extinct groups: dinosaurs, plesiosaurs, pterosaurs and early mammal-like reptiles

• This is a paraphyletic group, because it doesn’t include birds

Modern definition of Reptilia

• includes ‘nonavian reptiles’ (as listed above) and birds

• Crocodilians and birds belong to a clade within Reptilia called Archosauria

  • Also includes the extinct dinosaurs

3 groups of reptilia

• Order Testudines (turtles)

• Superorder Lepidosauria (tuataras and squamata - lizards, monitors, snakes)

• Archosauria (no rank) —> crocodilians and birds

Are reptiles ectothermic or endothermic

Ectothermic

Number of limbs in reptiles

Tetrapods —> 2 paired limbs

What scales do reptiles possess?

Keratinized epidermal

Are reptiles monoecious or dioecious?

• Usually dioecious

• Some lizards reproduce by parthenogenesis

In what reptile is parental care present?

Crocodilians

Do reptiles have a larval stage?

No

Other animals with keratin

• Hagfish and lampreys: keratinized plates for rasping/chewing

• Tadpole has keratinized jaws

• Turtle shell’s outer layer covered in keratin

Keratin

• Fibrous structural protein

• Tough material

• Analogous function to chitin

Chitin

• Nitrogenous polysaccharide

• Very tough material

• FOund in arthropods, molluscs and annelids

Testudines - Turtles: characteristics

• 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 —> limbs located inside the ribs

What makes turtles unique among vertebrates?

Their limbs are located inside the ribs

Where is rib growth directed in turtles vs amniotes?

• Turtles: laterally towards carapacial ridge

• Amniotes: ventrally

Testunides - Reproduction

• Oviparous

• Internal fertilization

• Bury shelled, amniotic eggs in the ground

• Nest is abandoned after being constructed

Lepidosauria: 2 groups

• Squamata

• Tuatara

Tuatara includes:

• Lizard-like animals that are endemic to New Zealand

Squamata includes:

• Lizards

• Monitor lizards

• Snakes

  • 95% of non-avian reptiles

Characteristic features of squamata

• Body covered with scales

• Kinetic skulls

What type of group are reptiles a part of?

Paraphyletic

Kinetic skull

• Highly mobile skull specializations for swallowing large prey

• Major factor enabling diversification of snakes and lizards

Lizards are:

a) paraphyletic

b) monophyletic

a)

Type of lizard lacking 4 limbs

Glass lizard

What is special about lizard eyelids?

They are moveable

Name 3 general characteristics of lizards

• Ectothermic (like nearly all nonavian reptiles)

  • Adjust body temperature by moving among different microclimates

• Fewer 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 are:

a) paraphyletic

b) monophyletic

b)

Do snakes have limbs?

No

Snake vertebrae

Shorter, wider, and more numerous than other tetrapods

How do snakes differ from lizards?

• 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)

Feature that allows snake to capture large prey

Kinetic skull —> loosely articulated bones + 2 halves of lower jaw are joined only by muscle and skin

Jaws of snakes have ____ facing teeth that anchor prey and slowly move it in

Posterior

How do snakes breathe?

Tracheal opening extended forward between mandibles

What do snakes use for smell?

Their tongues + Jacobson’s organs

Paired organs located in roof of mouth that line with olfactory epithelium

Jacobson’s organs

Tuatara

• Lizardlike animal

• Endemic to New Zealand

  • 2 living species

  • sole survivors of lineage that diverged from lizards and snakes

• Endangered species

  • Slow reproduction rate: 10-20 years to reach sexual maturity and produce eggs once every 4 years

Crocodilians

• Alligators and crocodiles —> more closely related to birds

• Elongated, robust, well-reinforced skull and massive jaw musculature

• Wide gape and powerful closure

• Teeth are replaced

Crocodilians are:

a) Viviparous

b) Oviviparous

c) Oviparous

c)

Describe parental care of crocodiles

• Females guard eggs

• Open nest when it hears vocalizations of hatchlings

• Young guarded by mom for 2 years after hatching

What does the incubation temperature of crocodiles determine?

Sex ratio of the offspring

In crocodilians, low nest temperature produces (females/males) while high nest temperatures produce (females/males)

• Females

• Males

In turtles, low nest temperature produces (females/males) while high nest temperatures produce (females/males)

• Males

• Females

Genetic sex determination is found in what type of reptiles?

• Most snakes and lizards

• Some turtles

Temperature-dependent sex determination is found in what reptiles?

• All crocodilians

• Most turtles

• Some lizards and snakes