TT 3 15-20

Lecture Notes on Agnatha and Chondrichthyes

Evolutionary Relationships

• Bilaterally symmetrical: Body has a left and right side that are mirror images.

• Triploblastic: Three germ layers (ectoderm, mesoderm, endoderm).

• Coelomate: Body cavity (coelom) is present, allowing for more complex structures.

• Deuterostome: The mouth develops secondarily to the anus.

• Segmented: Organisms have repeated units in their body structure.

• **Derived Characteristics:

  1. Vertebrae

  2. Jaws

  3. Lungs

  4. Amniotic egg (in tetrapods)

Superclass Agnatha

• Most primitive of the early fishes.

• Characteristics:

  • Contains extinct ostracoderms (paraphyletic)

  • Extant species: lampreys and hagfish.

  • Notochord persists throughout life.

  • Slender, eel-like, with fins, but lacks paired appendages.

  • 7 paired gill openings.

  • Simple heart (single atrium and ventricle).

  • No stomach in their digestive system (very basic).

  • Dorsal nerve cord with a differentiated brain.

  • May have a cartilaginous skeleton not fully developed.

Class Myxini (Hagfish)

• Produce large amounts of slime for protection.

• Entirely marine scavengers, smell is their primary sense for locating food.

• Unique feeding adaptation: attach to food using toothed plates and a rasping tongue.

• Lack a complete skeleton but have a cartilaginous skull and rudimentary vertebrae.

• Little known about reproduction; some species are hermaphrodites.

Class Hyperoartia (Lampreys)

• More derived than hagfish.

• Complete cartilaginous skeleton.

• Parasitic behavior: rasp through fish flesh to siphon body fluids, utilizing an anticoagulant.

• Lifecycle includes spawning in fresh waters where they die shortly after; the eggs develop into larvae (ammocoetes) with a lengthy larval period (3-17 years), eventually undergoing metamorphosis.

Evolution of Jaws

• Jaws represent a significant evolutionary achievement for vertebrates (characterizes Gnathostomes).

• Advantages of jaws:

  • Enhanced foraging capabilities (ability to consume larger chunks of food).

  • Improved manipulation of objects for feeding.

• Development process:

  • Originated from modifications of two bony gill arches, which became displaced forward.

  • Ability to pinch gill arches together, with a bottom arch swiveling while the upper remains attached.

General Characteristics of Chondrichthyes (Cartilaginous Fishes)

• Exhibit various foraging modes and have highly developed sensory organs, particularly in vision.

• Separate sexes with internal fertilization; reproductive modes vary significantly among species.

Subclass Elasmobranchii (Sharks and Rays)

• Originated around 400 million years ago.

• Transitioned from bony skeletons to cartilaginous structures for increased buoyancy.

• Approximately 1000 species identified with about 300 species found in Australia looking across marine and freshwater habitats.

• Size range:

  • Sharks: 20 cm to 12 m length.

  • Rays: < 25 cm to > 7 m width.

• The notochord gets replaced by vertebrae as they mature.

Anatomical Features of Elasmobranchii

• Stomach divided into cardiac and pyloric sections for digestion.

• Digestive traits: short intestine with a spiral valve to maximize nutrient absorption.

• Efficient gas exchange facilitated by spiracles; sharks utilize continuous swimming for ventilation, whereas rays use spiracles to facilitate water flow over gills.

• 2-chambered heart structure indicates a single circulation.

Sensory Systems in Elasmobranchii

• Hearing: Generally not highly developed.

• Vision: Fairly good, especially in low-light conditions.

• Smell: Excellent olfactory capabilities.

• Lateral line system:

  • Located along the sides of the body; detects pressure changes indicating moving prey.

• Ampullae of Lorenzini:

  • Specialized structures in the head that detect electrical fields from potential prey.

Sharks (Superorder Selachimorpha)

• Comprising 6 orders with approximately 400 species. Predominantly marine, with one family of freshwater sharks.

• Characterized by a fusiform body shape that allows for efficient swimming in open water.

• Typically have 5-7 gill slits and one to two dorsal fins along with a large heterocercal caudal fin for propulsion.

• Locomotion:

  • Use paired fins for lift, with pectoral fins that do not swivel, allowing for rapid movement.

  • Cruise speed: 2-5 km/h; capable of burst speeds up to 30 km/h.

Reproduction in Elasmobranchii

• Dioecious with internal fertilization; notable adaptations include claspers for sperm transfer.

• Generally, few offspring born, featuring high survival rates and precocial pups.

• Types of reproductive strategies include:

  • Viviparous: young fed by placenta.

  • Oviparous: eggs deposited and nourished by yolk until hatching.

  • Ovoviviparous: eggs hatch within the female's body without a placenta.

Subclass Holocephali (Rat/Rabbit Fishes and Elephant Fishes)

• Known for their primitive characteristics. Limited species remaining in the order Chimaeriformes.

• Features include a single gill slit, fusion of teeth, and absence of placoid scales in their anatomy, with habits being predominantly benthic.

• All representatives show a degree of oviparity in reproduction.

Summary Points

• Agnatha: jawless fishes with a notochord, cartilaginous skeletons, simple hearts, and no paired appendages.

• Chondrichthyes: possess jaws and are characterized by internal fertilization, various reproductive methods, and unique adaptations like a cartilaginous skeleton and complex sensory systems.

• Subclass Elasmobranchii: prominent features such as a divided stomach, short intestine with a spiral valve, and advanced locomotion and feeding strategies.

• Subclass Holocephali: more primitive, with unique anatomical and reproductive adaptations distinct from Elasmobranchii.

Lecture 16

General characteristics of Osteichthyes

• Classification: Paraphyletic group, largest and most diverse taxon of vertebrates (~25,000 species).

• Origins: Evolved around 410 million years ago.

• Habitat: Found in both marine and freshwater environments.

• Morphology: Exhibit diverse shapes and sizes.

• Circulatory System: Possess a 2-chambered heart.

• Structural Features:

  • Operculum:

    • Pumps water over gills.

    • Made of bony plates from the first gill arch.

    • Operates via an opening and closing mechanism with the mouth to control water flow.

  • Bony Skeleton: Provides structural support.

Gills and Respiration

• Efficiency: Gills are adept at extracting oxygen from water, thanks to:

  • Four gill arches with filaments covered by numerous lamellae for increased surface area.

• Counter-Current Exchange System:

  • Oxygen-rich water flows over oxygen-poor blood, facilitating efficient gas exchange, allowing fish to extract over 80% of available oxygen.

  • Comparisons of oxygen concentration demonstrate superiority over concurrent flow where oxygen saturation levels would equalize.

Lungs and Buoyancy

• Evolution of Lungs: Some fish developed lungs to survive in poorly oxygenated waters.

• Buoyancy Control:

  • Swim bladder aids in maintaining neutral buoyancy.

  • Depth regulation involves gas exchange to adjust buoyancy, with mechanisms for gulping air.

Flashy Fins

• Fin Structure and Function:

  • Fins supported by pectoral and pelvic girdles, allow for independent movement.

  • Dorsal and anal fins provide stability.

  • Tail or caudal fins are essential for thrust and lift, some tails are adapted for signaling during mating rituals.

Feeding and Foraging Specializations

• Diversity in Feeding Modes:

  • Classified based on mouth morphology:

    • Superior/Supraterminal Mouth: Positioned near the water surface.

    • Inferior/Subterminal Mouth: Located close to the substrate.

    • Terminal Mouth: Found in the water column.

• Examples of Specialized Feeding Techniques:

  • Suction Feeding: Tiger fish utilizes rapid mouth expansion to suck and trap prey.

  • Anglerfish: Utilizes a modified dorsal spine as a lure to attract prey, using light absorption to remain undetectable.

Other Cool Adaptations

• Unique Life Strategies:

  • Tripodfish: Stands on elongated fins to catch prey using tactile cues in a benthic environment.

  • Frogfish: Masters of camouflage and ambush, with skin textures aiding in mimicry.

  • Leafy Sea Dragon and Seahorses: Mimicry for survival.

  • Lionfish: Bright colors act as a warning, possess venom, and are invasive.

Fish Taxonomy

• Clades:

  • Actinopterygii: Ray-finned fishes, largest group (~24,600 species).

  • Sarcopterygii: Lobe-finned fishes, includes lungfish (Class Dipnoi) and coelacanths (Class Actinistia).

Class Characteristics

Class Actinopterygii

• Morphology: Homocercal tail, mucous glands in skin, scales present, single operculum, swim bladder for buoyancy.

• Osmoregulation: Differences in osmoregulation strategies in marine and freshwater species including specialized cells for ion transport and kidney function.

• Reproductive Modes: Includes external fertilization and some instances of viviparity, parental care through brooding.

• Locomotion: Uses tail flexing for movement, with specialized uses for pectoral and pelvic fins in maneuverability and stability.

Class Dipnoi - Lungfish

• Habitats: Freshwater species, capable of surviving in low-oxygen environments.

• Anatomy: Two lungs, muscular pectoral and pelvic fins facilitate movement on river beds, long diphycercal tail.

Class Actinistia - Lobe-finned Fish

• Notable Species: Coelacanths, previously thought extinct, are living fossils with vestigial lungs and strong, fleshy fins.

• Evolutionary Significance: Closest relatives to tetrapods, exhibiting features unique to both aquatic and terrestrial life forms.

Summary Points

• Evolution of bony skeletons marks a significant innovation for vertebrates.

• High diversity within aquatic environments, supporting varied physiological and morphological adaptations.

• Significant respiratory and circulatory features enhance survival and efficiency in different habitats.

• Feeding strategies and specialized adaptations reflect evolutionary pressures and ecological niches occupied by Osteichthyes.

Lecture 17

Phylogeny of Chordates

• Vertebrate classes including:

  • Tunicates

  • Lancelets

  • Jawless fishes

  • Cartilaginous fishes (e.g., sharks)

  • Bony fishes (e.g., ray-finned fishes)

  • Lobe-finned fishes

  • Amphibians

  • Reptiles

  • Mammals

• Key characteristics of ancestral chordates:

  • Vertebrae

  • Jaws

  • Bony skeleton

  • Lungs

  • Limbs

  • Amniotic egg (includes birds)

Why Move to Land?

Major Challenges

o Issues faced by organisms transitioning from aquatic to terrestrial life:

• Desiccation

  • Challenges in retaining moisture due to body composition (mostly H2O).

  • Adaptations: skin modifications to minimize water loss.

• Reproduction

  • Sperm require water for movement; egg development needed an aquatic environment.

  • Adaptations: evolved internal fertilization and returning to water for egg-laying.

• Respiration

  • Gills are ineffective in air and collapse when dry.

  • Adaptations: development of moist, vascularized surfaces for gas exchange (lungs).

• Gravity

  • Lack of buoyancy in air necessitates stronger limbs and skeleton structure.

  • Adaptations: evolved a double circulation system to efficiently pump blood.

• Temperature Extremes

  • Air temperature fluctuates more than aquatic environments.

  • Adaptations include behavioral strategies (e.g., basking) and physiological ones (e.g., endothermy).

Benefits of Living on Land

• Diverse habitats available, leading to reduced competition.

• Limited predators (mainly plants and arthropods), enhancing survival rates.

• Easier shelter and reproductive success due to fewer dangers for young and eggs.

Pre-adaptations to Life on Land

• Transition from water was gradual:

  • Early fishes had features like:

    • Simple structures resembling lungs (pharyngeal out-pocketings).

    • Muscular, bony fins facilitating movement.

    • Evolved pelvic and pectoral girdles.

    • Well-developed kidneys for water conservation.

Evolution of Tetrapods

• Emerged around 360 million years ago during unstable environmental conditions (e.g., drought).

• Key adaptations for survival:

  • Ability to breathe air.

  • Strong limbs for supporting body weight on land.

  • Effective kidneys for osmoregulation.

• Defining characteristics of tetrapods:

  • Bony skeletons and distinct necks separating head from body.

  • Fusion of pelvic girdles to the vertebral column.

General Characteristics of Amphibians

• Physical Traits:

  • Limbs (some reduced or absent).

  • Ectothermic (cold-blooded).

  • Paired mesonephric kidneys for excretion.

  • Dependence on water for reproduction; eggs lack a hard shell, making them prone to desiccation.

  • Exhibit metamorphosis in development.

• Reproductive Traits:

  • Separate sexes with either external or internal fertilization.

Respiratory Features

• Heart Structure:

  • 3-chambered heart (2 atria, 1 ventricle) leading to oxygenated and deoxygenated blood mixing.

• Breathing Mechanism:

  • Positive pressure breathing through buccal pumping, includes inhalation and exhalation mechanics.

Amphibian Taxonomy

Three Main Orders:

1. Order Apoda (Caecilians)

   • Legless, burrowing amphibians, primarily tropical.

   • Carnivorous, exhibit internal fertilization, and some show parental care.

2. Order Caudata (Salamanders and Newts)

   • Possess tails; can be fully aquatic or terrestrial.

   • Carnivorous, variety of reproductive strategies including metamorphosis.

3. Order Anura (Frogs and Toads)

   • Share various adaptations for jumping; widespread distribution.

   • Dioecious with complex reproduction behaviors including external fertilization.

Unique Frog Stories

• Examples of unusual frogs, including those with unique adaptations like defensive strategies.

Decline of Frog Populations

• Sudden declines noted in late 1970s globally, especially in Australia with many endangered species.

• Contributing factors:

  • Climate change, habitat loss, fragmentation, disease (notably chytrid fungus Batrachochytrium dendrobatidis).

Summary Points

• Movements to land present significant challenges but opportunities exist in the form of reduced competition and diverse habitats.

• Key adaptations and characteristics define amphibians and their evolutionary journey from water to land.

Lecture 18

Phylogeny and Characteristics of Reptiles

Overview of Reptiles

• Reptiles: first truly successful land colonizers.

• Three major innovations that facilitated land adaptation:

  • Amniotic Egg: Faster development of larger offspring, embryo carries its own water.

  • Scales/Bony Plates: Protection from desiccation and support for complex respiratory mechanisms.

  • Strong, Crushing Jaws: Allowed exploitation of new food resources.

Classification of Reptiles

• Non-Monophyletic Group: Reptiles do not share a unique, unifying characteristic across all members.

• Classification based on four primary orders:

  • Order Rhyncocephalia: Tuataras, unique evolutionary history, parietal eye.

  • Order Crocodylia: Crocodiles and alligators, complex social behaviors, nests.

  • Order Chelonia: Turtles and tortoises, characterized by a protective shell.

  • Order Squamata: Snakes and lizards, very diverse.

Amniotic Egg

• Structure:

  • Yolk Sac: Provides nutrition to the embryo during development.

  • Chorion: Outer membrane for gas exchange; fuses with allantois for improved oxygen exchange.

  • Allantois: Waste disposal sac and gas exchange.

  • Amnion: Fluid-filled sac that surrounds and protects the embryo.

• Advantages:

  • Enables development in dry environments without requiring a water medium.

  • Eliminates larval stage, leading to more efficient development.

• Essential for Successful Land Colonization.

Adaptations for Terrestrial Life

• Scales:

  • Protect against desiccation and injury (consist of keratin).

  • Some reptiles shed skin periodically; scales grow throughout life in others.

• Jaws:

  • Strong, capable of crushing, allows diversification of diets.

  • Different muscle arrangements lead to diverse jaw structures (anapsids, synapsids, diapsids).

Temperature Regulation

• Ectotherms: Body temperature regulated by external factors.

• Endotherms: Maintain body temperature through metabolic processes.

• Mechanisms of heat exchange include:

  • Conduction: Transfer of heat through direct contact.

  • Convection: Heat transfer by movement of air or liquid.

  • Radiation: Heat emission as electromagnetic waves.

  • Evaporation: Cooling effect via moisture loss.

• Behavioral adaptations to maintain optimal temperature levels; include basking in sunlight and seeking shade.

General Characteristics of Reptiles

• Physical Traits:

  • Amniotic eggs, scales, strong jaws.

  • Efficient lungs with greater surface area; don’t rely on skin respiration.

• Circulatory System: 4-chambered heart, efficient systemic and pulmonary circulation.

• Reproductive System: Typically dioecious with internal fertilization; most are oviparous with some exceptions (viviparous).

• Nervous System: More complex, better vision; evolved mechanisms for thermoregulation and behavioral adaptations.

Summary Points

• Reptilian evolution marked by the development of amniotic eggs and adaptive features.

• Diversity within reptiles characterized by their classification into four main orders based on anatomical and ecological traits.

• Innovations such as stronger jaws and adapted skin structures have enabled various feeding strategies and environmental adaptations.

Lecture 19

Phylogeny of Chordates

• Birds belong to the phylum Chordata and are classified as vertebrates, which also include tetrapods, fish, and other groups.

• Evolutionarily, birds are monophyletic with reptiles, sharing a common ancestor with theropod dinosaurs (e.g., Velociraptor).

• The lineage of chordates can be summarized as follows:

  • Tunicates

  • Lancelets

  • Jawless fishes

  • Cartilaginous fishes

  • Bony fishes (ray-finned and lobe-finned)

  • Amphibians

  • Reptiles

  • Birds

General Characteristics of Birds

• Amniotes: Produce strong, inflexible eggs.

• Physiological adaptations:

  • Endothermic: Birds can regulate their body temperature physiologically.

  • 4-chambered heart providing efficient circulation.

  • Unique lung structure allows unidirectional airflow and increased surface area for gas exchange.

• Body Adaptations:

  • Feathers and wings are essential for flight; feathers provide insulation and help in thermoregulation.

  • Tough beak structure without teeth.

  • Nitrogenous waste excreted as uric acid, conserving water.

• Reproductive Traits:

  • Separate sexes, internal fertilization, and oviparous with amniotic eggs.

Origin of Birds

• Birds originated approximately 60 million years ago from Archosauria, closely related to theropod dinosaurs.

• Example of this evolution is Archaeopteryx:

  • Feathered theropod sharing features with both dinosaurs (e.g., teeth and claws) and modern birds (e.g., beak and feathered wings).

Origin of Feathers and Flight

• Feathers evolved about 190 million years ago primarily for insulation before being adapted for flight.

• Flight allowed birds to:

  • Exploit aerial prey such as insects.

  • Escape from ground-based predators.

  • Facilitate migration to favorable climates.

• Hypotheses for the Evolution of Flight:

  • Ground-up hypothesis: Wings evolved from arms for capturing prey or assistance in leaping.

  • Wing-assisted incline running: Wings helped in incline running, leading to gliding.

  • Trees down hypothesis: Wings developed from gliding ancestors learning to flap for thrust.

  • By-product of sexual selection: Wings used as displays in mating rituals.

Adaptations for Flight

• Body Structure:

  • Feather Characteristics:

  • Lightweight, strong, waterproof, and provide insulation.

  • Main shaft (rachis) with barbs; varied feather types aid different functions.

  • Bone Modifications:

  • Fusion and elimination of bones for reduced weight and increased rigidity.

  • Hollow bones (pneumatized) to minimize mass.

  • Muscle Organization:

  • Trunk vertebrae fused for stability; ribs support wing muscles for flapping flight.

  • Large pectoralis and supracoracoideus muscles for powered flight.

Functional Anatomy

• Metabolism and Thermoregulation:

  • High metabolic rate maintained by efficient fermentation of food and muscular contractions.

  • Adaptation to cold environments due to insulation.

• Cardiovascular System:

  • 4-chambered heart for efficient separation of oxygen-rich and oxygen-poor blood.

• Respiratory System:

  • Unidirectional air flow with air sacs aiding in respiration without mixing inhaled and exhaled air.

Feeding and Foraging

• Birds occupy a variety of ecological niches; diet and beak morphology adapted to feeding habits.

• High metabolic rates require substantial food intake; adaptations like crops and gizzards assist in food processing.

Taxonomy of Birds

• Approximately 10,880 species of birds, second most diverse group after fishes.

• Superorders:

  • Paleognathae (ratites): Flightless birds, limited orders (e.g., ostriches, emus).

  • Neognathae: Diverse orders including many species of land and water fowl, core water birds, and terminal land bird clades.

Lecture 20

Phylogeny of Chordates

• Classification of mammals within chordates

• Major lineage breakdown:

  • Chordates

  • Tunicates

  • Lancelets

  • Jawless fishes

  • Cartilaginous fishes

  • Bony fishes

• Key clades leading to mammals:

  • Tetrapods

  • Amphibians

  • Reptiles

  • Mammals

• Important mammalian innovations:

  • Mammary glands

  • Vertebrae

  • Jaws

  • Bony skeleton

  • Lungs

  • Limbs

  • Amniotic egg (includes birds)

The Evolution of Mammals

• Over 4800 species; adapts to diverse habitats and climate zones

• Occupies many ecological niches, showcasing high mobility and activity

• Notable trends in body size:

  • Increasing size over evolutionary time

  • Clades include:

  • Eutherians/placentals: 18 orders, largest radiation

  • Prototherians (monotremes): 1 order, more primitive

  • Metatherians (marsupials): 7 orders, debated ties to prototherians

Trends in Body Size

The Largest Mammals

• Paraceratherium:

  • Approx. 10 tons, height over 5.5 m

• Mastodons:

  • Approx. 11 tons, about 3.25 m

• African Elephant:

  • Approx. 6 tons, 4 m tall

• Blue Whale:

  • Over 200 tons, length exceeding 30 m

The Smallest Mammals

• White-toothed Pygmy Shrew:

  • Weight: 1.2 – 2.7 g

• Kitti’s Hog-nosed Bat:

  • Size: 30 mm

• Madame Berthe’s Mouse Lemur:

  • Weight: 30 g

General Characteristics of Mammals

• Cerebral Cortex Development:

  • Allows complex and flexible behaviors

• Endothermic:

  • Maintains constant body temperature

• Evolutionary innovations:

  • Hair/Fur (keratin)

  • Milk production (mammary glands)

• Essential anatomical features:

  • Multicellular, true tissues, bilateral symmetry, triploblastic structure, alimentary canal, coelomate, segmented body plan

Derived Characteristics

Hair/Fur Functions

• Insulation, camouflage, protection

  • Glandular Functions:

  • Sweat Glands:

    • Cooling via eccrine (direct to skin) and apocrine glands (hair follicle)

  • Scent Glands: Communication and territory marking

  • Sebaceous Glands: Lubrication of skin and hair

  • Mammary Glands: Milk production

Hair/Fur Modifications

• Insulation and camouflage, spiny protection

• Adaptations such as scales and horns/antlers for protection and fighting

Organ Systems

Vertebral Modifications

• Complex vertebral column with cervical, thoracic, lumbar, sacral, caudal regions

• Adaptations related to activity and metabolism

Circulatory and Respiratory Systems

• 4-Chambered Heart:

  • Complete separation of pulmonary and systemic circulation

• Ventilation Mechanism:

  • Negative pressure breathing:

  • Inhalation: Active process using muscles to lower thoracic cavity pressure

  • Exhalation: Passive process, cavity volume decreases

Excretory Mechanism

• Metanephric Kidneys:

  • Structure with tubules and capillaries

  • Nitrogenous waste excretion as urea, low toxicity

  • Nephron structure: importance for water conservation

Reproductive System

• Sexual dimorphism (separate sexes)

• Internal fertilization:

  • Monotremes: oviparous

  • Marsupials: viviparous (develop in pouches)

  • Placentals: develop in uteri

• Variable gestation periods, obligatory maternal care

Locomotion Adaptations

• Range of modes: swimming, running, flying, etc.

• Limb adaptations showcasing pentadactyl heritage

Cranial Modifications

General Features

• Single, solid skull structure with specific occipital condyles for neck attachment

• Differentiated teeth types reflecting diet (e.g., heterodont vs. homodont)

Eye and Sensory Adaptations

• Eye placement assisting with habitat adaptation and lifestyle:

  • Aquatic animals with elevated eyes for visibility

  • Prey species with wide lateral vision for predator detection

• Auditory adaptations for varied frequencies, some species developing enhanced hearing capabilities

• Olfactory adaptations across species for detecting chemical stimuli

Taxonomy of Mammals

• Over 20 distinguished orders:

  • Rodentia: Largest order; single pair of incisors

  • Chiroptera: Second largest; echolocation in bats

  • Eulipotophyta: Insectivorous group

  • Primates: Forward-facing eyes, large cerebral cortex, two suborders

  • Carnivora: Diverse families (e.g., dogs, cats, bears)

Summary Points

• Mammals exhibit a vast range of habitats and adaptations.

• Three major clades:

  • Eutherians: Mostly placentals

  • Prototherians: Egg-laying monotremes

  • Metatherians: Marsupials with pouch development.

• Key characteristics include a well-developed cerebral cortex, endothermy, and specialized organ systems for efficiency in various ecological niches.