Jawless Fishes: Agnatha and Cyclostomata

• Jawless fishes, or Agnatha, represent some of the earliest vertebrates in fish evolutionary history.
• They are basal to jawed fish groups like cartilaginous fishes (Chondrichthyes) and bony fishes (Osteichthyes).

Ostracoderms

• Armored jawless fishes, characterized by bony head shields and scale-covered bodies.
• The first appearance was in the Ordovician period, approximately 450 million years ago.
• Possessed paired fins and a simple internal skeleton, and lacked jaws.

Cyclostomata

• Consists of hagfishes (Myxini) and lampreys (Petromyzontida).
• Both have elongated, eel-like bodies, lack true jaws, and possess circular, suction-cup-like mouths.
• Hagfish produce slime for defense and scavenging.
• Some lampreys are parasitic, attaching to other fish and feeding on their blood.

Manitoba Diversity of Cyclostomata

• Includes silver lamprey, chestnut lamprey, and northern brook lamprey (the smallest and most widespread).

Conservation Efforts

• Conservation efforts focus on controlling invasive sea lamprey populations in the Great Lakes.
• Barriers, traps, and lampricides are used to reduce their numbers and minimize their impact on native fish species.

Conodonts

• First appeared in the Cambrian period, around 500 million years ago.
• They possessed tooth-like microfossils and are thought to be early vertebrates with eel-like bodies.

Placoderms

• Appeared in the Silurian period, around 430 million years ago.
• Armored fishes with bony plates covering the head and thorax
• They were the first to possess true jaws.
• A notable species is Dunkleosteus, a large predator with powerful jaws.

Jaws Development

• Jaws likely evolved from the modification of anterior gill arches.
• Changes in nostril presentation (from a single nostril to paired nostrils) allowed for more efficient breathing and feeding.

Bone Types

• Endochondral bone forms from cartilage (e.g., long bones).
• Dermal bone forms directly from mesenchyme (e.g., skull bones).

Fin Functionality

• Pectoral fins: Located on the sides, used for steering and stabilization.
• Pelvic fins: Located on the underside, used for stability and maneuvering.
• Dorsal fin: Located on the back, provides stability.
• Anal fin: Located near the anus, provides stability.
• Caudal fin: Located at the tail, provides propulsion.

Cartilaginous Fishes

• Includes sharks, rays, skates (Elasmobranchii), and chimaeras (Holocephali).
• First appeared around 400 million years ago.
• Shared traits of the Elasmobranchii group include cartilaginous skeletons, placoid scales, multiple gill slits, and lack of a swim bladder.
• Hyostylic jaw suspension allows for protrusion and greater mobility of the jaws, enhancing their ability to capture prey.
• The upper jaw is not directly connected to the cranium.
• Selachimorpha: Primitive sharks like dogfish.
• Galeomorphii: Modern sharks like the great white.
• Batomorphii: Rays and skates.
• Squalomorphii: Sharks that lack certain features like angel sharks.

Holocephali

• Single gill opening covered by an operculum, lack of scales, and a fused upper jaw.
• Holocephali have a single covered gill opening, while Elasmobranchii have multiple exposed gill slits.
• Holocephali jaws are fused to the skull, whereas Elasmobranchii jaws are more mobile.
• Holocephali tend to inhabit deep seas, whereas Elasmobranchii are found in a broader range of environments.
• Holocephali have grinding plates, while Elasmobranchii have sharp, replaceable teeth.
• Holocephali lack scales, Elasmobranchii have placoid scales

Special Sense

• Vision: Adapted for low light, excellent night vision.
• Olfaction: Highly developed sense of smell.
• Auditory: Sensitive to low-frequency sounds.

Sensory Input

• Mechanoreception: Lateral line system detects water movements and vibrations.
• Electroreception: Ampullae of Lorenzini detect electric fields produced by living organisms.
• Reproduction: Oviparous lay eggs, ovoviviparous eggs hatch inside the mother, and viviparous have live birth with placental connection.
• Sharks have slow growth, are long-lived, with low reproductive rates, producing a small number of well-developed offspring (K-selected).

Bony Fish

• Actinopterygii (Ray-finned fishes): Largest and most diverse group, fins supported by bony or horny spines.
• Sarcopterygii (Lobe-finned fishes): Contains ancestors of tetrapods, fins are fleshy and lobed, supported by a central bone structure.
• Bony skeletons and swim bladders are similar
• Fin structures and reproductive strategies show differences.
• Bony skeletons, swim bladders, different scale types, and more complex respiratory structures differentiate from cartilaginous fishes.
• Key characteristics of bony fishes are bony skeletons, swim bladders, gills covered by an operculum, and diverse fin structures.
• Coelacanths were thought to be extinct but were rediscovered, while lungfishes possess lungs and gills.
• Tetrapodomorpha fishes arose around 400 million years ago, serving as transitional forms that led to the evolution of tetrapods, capable of moving onto land.
• Cladistia: Bichirs and reedfish.
• Chondrostei: Sturgeons and paddlefish.
• Neopterygii Relic Groups: Gars, bowfin.

Teleosts

• First appeared around 250 million years ago.
• Osteoglossomorpha (elephant fishes) - most primitive, specialiazed teeth and jaw, Elopomorpha (true eels, tarpons, bonefishes) - eel like, special larval stage, Otocephala (herrings, sardines, catfish, carps), and Euteleosts (pike, carp, perch, salmon)
• Mobile Premaxilla allows for a protrusible mouth, enhancing feeding efficiency.
• Homocercal Tail: Symmetrical tail providing powerful and efficient propulsion.
• Swim Bladder: Gas-filled organ for buoyancy control.
• Diverse Body Forms: Range of shapes and sizes to occupy various ecological niches.
• Advanced Fin Structures: Specialized fins for precise movement and stability.
• Operculum: Bony flap covering gills, enabling efficient respiration.
• Reproductive Diversity: Various strategies including oviparity, viviparity, and diverse parental care.
• Cycloid or ctenoid scales providing protection and reducing drag.

Teleost Reproduction

• Reproductive patterns in the teleosts include Oviparous(Lay eggs), Viviparous(Give birth to live young).
• Parental Care: Varied, including mouth brooding and nest guarding.
• Sex determination in the teleosts can be genetic or influenced by environmental factors.

Teleost Parental Care

• Parental care is displayed within the teleosts through Mouth Brooding, Nest Building and Guarding, Egg Deposition on Substrates, Bubble Nesting, Live Bearing (Viviparity), External Brooding, Parental Role Division
• Example: Cichlids. Parents carry eggs or fry in their mouths for protection in Mouth Brooding
• Example: Sticklebacks. Construct and guard nests to protect eggs in Nest Building and Guarding
• Example: Clownfish. Lay eggs on surfaces and guard them in Egg Deposition on Substrates
• Example: Betta fish. Males build bubble nests and guard eggs in Bubble Nesting
• Example: Guppies. Females give birth to live young in Live Bearing (Viviparity)
• Example: Seahorses. Males carry eggs on their bodies in External Brooding
• Example: Cichlids. Different roles for males and females in caring for offspring in Parental Role Division

Class Tetrapoda

• Includes amphibians, reptiles, birds, and mammals.
• Major adaptations for land include limbs for locomotion, lungs for respiration, and modified sensory systems.
• Early tetrapods like Acanthostega and Ichthyostega showed transitional features for terrestrial life.
• A double circulation system developed with separate pulmonary and systemic circuits for efficient oxygenation.
• Lungs became more complex, with increased surface area for gas exchange.
• vision, hearing, and olfaction were enhanced to adapt to terrestrial environments

Class Amphibia

• Includes frogs and toads (Anura), salamanders and newts (Urodela), and caecilians (Gymnophiona).
• Moist, permeable skin for respiration, metamorphic life cycle, and dependence on water for reproduction are shared traits.

Amphibia Orders

• Anura (Frogs and Toads): Short bodies, no tails in adults, long hind limbs for jumping.
• Urodela (Salamanders and Newts): Elongated bodies with tails, typically four limbs.
• Gymnophiona (Caecilians): Limbless, elongated bodies, burrowing or aquatic lifestyle.
• Anura: Mostly external fertilization, eggs laid in water.
• Urodela: Mostly internal fertilization, eggs laid in water or moist environments.
• Gymnophiona: Internal fertilization, many species give live birth.
• Hibernate or estivate during extreme temperatures, some can tolerate freezing temperatures by producing antifreeze-like substances.
• Habitat loss, pollution, climate change, invasive species, and the chytrid fungus (Batrachochytrium dendrobatidis) which causes chytridiomycosis, a disease devastating amphibian populations.

Amniotes

• Includes reptiles, birds, and mammals.
• First appeared around 312 million years ago and diversified into various terrestrial and aquatic habitats.
• Anapsid: No temporal openings (e.g., turtles).
• Synapsid: One temporal opening (e.g., mammals).
• Diapsid: Two temporal openings (e.g., birds and reptiles).
• Anamniotic Egg: Lacks protective membranes, found in amphibians.
• Amniotic Egg: Has protective membranes (amnion, chorion, allantois) and a shell, allowing for development in terrestrial environments.
• Advantages of the amniotic egg- Provides protection, prevents desiccation allows for gas exchange, and enables development in a variety of environments.
• Keratinized skin provides protection against desiccation, physical injury, and pathogens.
• Costal Ventilation: Air is drawn into the lungs by expanding the ribcage (e.g., reptiles, birds, mammals).
• Buccal Ventilation: Air is pushed into the lungs by movements of the floor of the mouth (e.g., amphibians).