Vertebrate Evolution and Classification

Lecture 1: Introduction

• Vertebrates are animals that possess a spinal column.
• Evolution allows the organization of organism diversity and an understanding of their origins and functions.
• There are 70,000 known species of extant vertebrates.
• Most vertebrates are extinct.
• Modern vertebrate groups are less diverse than in the past.
• Life is not constant through geologic time.
• The Cambrian explosion saw the emergence of the earliest chordates.
• Taxonomy was established by Carolus Linnaeus.
• An important part of taxonomy is the Linnaean system: Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Taxonomy uses binomial nomenclature; Genus species, e.g. Tyrannosaurus rex → T. rex.
• Evolutionary change happens through "descent with modification."
• Natural selection is the differential survival and reproduction between individuals in a population.
• Populations, not individuals, are the unit of evolution.
• Natural selection acts on phenotypes.
• Heritable allelic variation produced by mutation is the raw material of evolution from which speciation can occur.
• Allopatric speciation occurs when there are physical barriers to gene flow within a population.
• Example of Allopatric speciation includes salamanders in California separated by the central valley.
• Sympatric speciation occurs when there is no physical barrier to gene flow.
• Some persistent mechanism prevents individuals from reproducing in the same place.
• Reproductive isolation leads to the evolution of new species.
• Example: northern pacific orcas are now considered 2 different species because they live in the same waters but do not breed or interact and have morphological differences.
• Adaptive radiation is the diversification of a group of organisms into forms filling different ecological niches.
• Example: Darwin and his finches.
• Phylogenetic trees: each node unites tips/terminal taxa into a clade.
• Clades are relative, for example: We are all fish, birds are dinosaurs.
• Methods of classifying organisms in a tree are based on similarities shared by the included species.
• Shared characteristic based on homology.
• Homology is the similarity between different taxa based on shared ancestry.
• Example: forelimbs of humans, whales, bats, and cats.
• Analogy is the independent evolution of similar traits and is not based on shared ancestry.
• Example: dorsal fins in marine vertebrates.
• Captures convergent evolution.

Lecture 2: Phylogenetics and Genetic Mechanisms

• Fitness means some phenotypes yield better fitness in a population.
• Darwinian fitness is the genetic contribution of an individual to succeeding generations relative to the contributions of other members of its population.
• Genotypes producing phenotypes have a higher likelihood to reproduce.
• Positive selection results in an increase in the frequency of a genetically based trait in successive generations.
• Positive selection can lead to speciation.
• Gene regulatory networks: gene expression can be activated or repressed via transcription factors.
• Transcription factors are proteins/signaling molecules that bind to DNA and say express, don't express, express a lot, express a little, don't express until this time... etc.
• Changing gene expression can cause a feedback loop in the original cells.
• Gene families: genes that produce structurally related forms of the same protein.
• Developmental regulatory genes are gene families that control developmental processes.
• Examples: bone morphogenetic proteins (BMPs), Sonic Hedgehog (Shh), Gremlin.
• Genes yield proteins, which then dictate the phenotype upon which natural selection acts.
• Example: selective breeding in bull terriers (skull and head shape via Bmp protein associated with accelerated bone growth).
• Heterochrony is defined as descendants retaining juvenile ancestral features.
• Paedomorphism is when descendants retain juvenile ancestral features.
• Progensis is when growth stops earlier and is a way that small animals evolve.
• Neoteny is when horns, wings, and tails grow at a slower rate and is a way smaller/less complex features evolve.
• Postdisplacement is when horns, wings, and tail start growing relatively later and is away for later reproductive/mature development to evolve.
• Examples: adult ostriches retaining juvenile features in their heads, axolotl adults expressing juvenile traits.
• Peramorphism is when descendents develop “beyond” the ancestor.
• Hypermorphosis is when growth stops later and is a way that big animals and exaggerated features evolve.
• Acceleration is when the horns, wings, and tails grow faster and is a way that exaggerated features evolve like tusks and saber teeth evolve.
• Predisplacement is when the horns, wings, and tails start growing earlier and is a way that independent young evolve.
• Heterotropy means "different place"; a change in the location of a gene's expression during development.
• Example: webbed feet and bat wings.
• Heterometry means "different measure"; a change in the intensity of a gene's expression during development resulting in changes in the amount of the gene product (either quantity or size).
• Example: Darwin's finches → beak size controlled by a gene that yields an x amount of beak development.
• Epigenetic effects are modifications of gene expression during development by non-genetic factors, such as temperature, diet, stress, and the environment.
• Can modify behavior, physiology, or morphology → phenotypic plasticity.
• Types of epigenetic effects: Intragenerational effects are limited to one generation, offspring do not inherit any phenotypic changes.
• Example: chemicals in the water causing changes in tadpoles that improve their chances of escaping predation.
• Intergenerational effects are those that affect the next generation.
• Example: exposing adult stickleback fishes to predators modified the offspring's behavior responses to predators.
• Transgenerational effects are those that affect subsequent generations.
• Example: inducing postnatal stress in the mother of lab mice was documented to have extended into her grandchildren.
• Organisms are organized by clades.
• Clades are monophyletic groups that share a single evolutionary origin and include all descendants of a common ancestor.
• The common ancestor is the most recent individual from which all taxa in a monophyletic group are descended.
• Synapomorphies are derived characters shared by 2 or more taxa and presumed to be inherited from their common ancestor.
• Synapomorphies are the characters that make a clade a clade.
• Example: Upright posture for humans and mammary glands for mammals.
• Apomorphy is a derived character that has changed from its ancestral state.
• Plesiomorphy is characters that clade members inherited and share, but are unchanged from their ancestral state.
• All clade members inherited it, but it's not their special feature.
• Examples: humans have four limbs, mammals have lungs, and vertebrates have a vertebral column.
• Synapomorphies and plesiomorphies are relative.
• Topology is the arrangement of branches and taxa on a tree.
• Sister taxa/sister group are 2 clade members that are each other's closest relatives on a particular tree and share a more recent common ancestor.
• Paraphyly refers to a named group of organisms that does not include an ancestor and all of its descendants.
• Example: "fish” → all tetrapods are sarcopterygian, bony fish are derived, but "fish" also means non-tetrapod, conventional fish.
• Types of characters include the following: Molecular - compares all life, directly based on genotype, better for more recent evolutionary divergences, functional significance of DNA differences which can't always be seen, homoplasy.
• Types of characters include the following: Morphological - easy to obtain, can be applied to the fossil record, phenotypic plasticity is a disadvantage, ambiguously defined, continuous and not discrete, easier for older things (like in rock layers).
• Merging genetics and phylogeny, example: spots of a panthers coat.
• Ancestors probably had some types of spots, lions can be expressing some type of heterochrony where spots turn off as they age, and tigers may be experiencing some type of heterometry where spots are ultra-expressed, resulting in stripes.

Lecture 3: What's a vertebrate?

• Directional terms: axial skeleton includes the vertebrae, ribs, spinal column, and median fins.
• Appendicular skeleton includes the pectoral and pelvic girdles, and associated fin or limb bones.
• Cranial skeleton consists of the skull and jaw.
• Postcranial skeleton is everything else (not the head).
• Vertebrate plesiomorphies include heterotrophs and bilateral symmetry.
• Triploblastic includes 3 layers: The ectoderm (outermost layer) forms superficial layers of the skin, linings of the digestive tract, and most of the nervous system; The mesoderm (middle layer) forms the muscles, skeleton, deeper layers of the skin, connective tissues, circulatory system, kidneys, and develop in a segmented fashion from anterior to posterior; The endoderm (innermost layer) forms rest of digestive system, portions of urinary system, gills and lungs, taste buds, germ cells (gametes).
• Gastrulation is the movement of undifferentiated cells of the early embryo into these 3 layers.
• Coelom is a body cavity that contains internal organs like the heart and gut tube.
• Coelom divided: into the Pericardial cavity (contains the heart); Peritoneal cavity (contains the GI tract, liver, pancreas, gallbladder).
• Both cavities separated by the transverse septum.
• Divisions get more complex in more derived vertebrates to accommodate lungs → Pleural recesses.
• Coelomic cavities are lined by thin sheets of mesoderm; Pericardium is found on the surface of the heart and lining the pericardial cavity; Peritoneum is found in the peritoneal and pleural cavities.
• Blastopore is the original opening of embryonic gut formed during gastrulation.
• Protostomes; blastopore becomes mouth; Deuterostomes: blastopore becomes anus (vertebrates).
• Chordate synapomorphies include notochord, dorsal neural tube, muscular post anal tail, and endostyle.
• Notochord is a dorsal stiffening rod for attachment for swimming muscles.
• Dorsal neural tube coordinates muscle activity for swimming.
• Muscular post anal tail provides more swimming power.
• Endostyle is a glandular groove on the pharynx (throat), homologous to thyroid, secretes mucus for trapping food particles for filter feeding, and takes up iodine.
• Annelids (worms) and chordates have flipped locations of their nerve cord and their heart (an example of heterotropy).
• Extant nonvertebrate chordates: Lancelets (cephalochordata); not the sister group to vertebrata despite retaining all ancestral chordate characters.
• Tunicates (urochordata); sister group of vertebrata; quite derived (larvae become non-moving, lose post-anal tail, and reduce the neural tube).
• Vertebrate synapomorphies include vertebrae, cranium, head with sense organs (tripartite brain), complex endocrine organs, muscularized gut tube, and multichambered heart.
• Vertebrae provides support, protection, and locomotory muscle origins and are cartilaginous or bony.
• Cranium serves as the "brain case", or a bone/cartilaginous/fibrous structure surrounding the brain.
• Tripartite head includes the forebrain, midbrain, and hindbrain to integrate sensory information.
• Complex endocrine organs produce hormones to regulate body functions.
• Muscularized gut tube has muscles in the wall of the gut tube for processing of large amounts of food.
• Multichambered heart distributes gases and nutrients to all cells of the body.
• Mineralized tissues include i) Calcium deposits in tissues; ii) Calcified cartilage and bone as well as teeth (dentine, enamel, etc).
• Gills are derived from endoderm and allow for efficient respiration.
• Neural crest provides differentiation.
• W-shaped myomeres; Produce lateral undulations for swimming in fish and Six-pack.

Chordate and vertebrate homology

• Chordate characters and what they turn into in vertebrates: Notochord is replaced by vertebral column and remain as intervertebral discs in the spine; Neural tube becomes central nervous system; Postanal tail becomes tails in vertebrates that have them; Endostyle becomes the thyroid. Development of pharyngeal region:
• Pharyngeal arch: segmentally organized tissues between the gill slits.
• Derivatives of the pharyngeal arches are strongly conserved through vertebrate history and gene expression.
• Pharyngula is the developmental stage in vertebrate embryos characterized by the presence of pharyngeal arches and slits.
• Pharyngeal arch #2 and #3 contribute to the hyoid bone.
• Arch #1 associated with bones in the ear and muscles of mastication.
• Mammals don't have a 5th arch as it was lost.
• Development of the brain involves the neural plate being the early embryonic structure that gives rise to neural tube; precursor to CNS, primary neuron generating tissue.
• Evolved into the forebrain (olfaction), midbrain (vision), and hindbrain (motor functions, respiration, circulation).
• Neural crest is embryonic tissue that gives rise to unique structures in vertebrates like neurogenic tissues (sometimes considered a 4th germ layer).
• Neural crest cells are migratory and versatile.
• Neurogenic placodes: thickenings in the embryonic ectoderm that give rise to nerves and sensory receptors of the nose, ear, and other sensory systems.
• Neurogenic placodes also migrate.
• Some are not neurogenic and give rise to structures like feathers and hair.
• Vertebrate characteristics are far more powerful and efficient in feeding, respiration, and locomotion.
• Bones evolved as mineral storage to “act like batteries” and became internal protective mechanisms.
• Important to convince your body that you need that bone for more than just storage (weightlifting super important).

Integumentary System

• Protection, regulation of body temp, sensation, and communication
• Epidermis and Dermis are unique to vertebrates
• Dermis - derived from mesoderm and neural crest
• Hypodermis - Connective tissue layer anchoring the skin to muscles and organs
• Also unique to vertebrates
• Cranial skeleton: Dermatocranium - Bones that cover a portion of the skull, Protect brain, anchor teeth, provide muscle attachment sites, and forms from neural crest and mesoderm.
• Cranial skeleton: Chondrocranium - Surrounds the brain and forms from neural crest and mesoderm.
• Cranial skeleton: Splanchnocranium - Forms from neural crest and contributes to jaws, jaw support, and gills.
• Circulatory system includes arteries, veins, and capillaries.
• Arteries carry blood away from the heart and have higher blood pressure than in veins.
• Veins carry blood back to the heart.
• Capillaries are the smallest vessels, sites of exchange of gases, nutrients, and waste products between blood and tissues.
• Ancestral vertebrate heart has 3 chambers with sinus venosus that receives blood from veins.
• Atrium is an intermediate place for blood.
• Ventricle applies force to eject blood.

Lecture 4: Cyclostomes and Gnathostomes

• Oxygen can be obtained from water using gills.
• Gills are vascularized structures where O2 and CO2 are exchanged between the body and surrounding water
• Internal gills consist of primary lamellae (gill filaments)
• Your classic gills
• Secondary lamellae: microscopic projections from primary lamellae where gas exchange occurs.
• External gills some fish and amphibians have this, they are attached to the sides of the head.
• Example: Axolotls.
• Water flow in unidirectional (unlike lungs)
• Buccopharyngeal (buccal) pumping draws in air or water into the mouth and pharynx and expelling it.
• Buccopharyngeal pumping is more ideal.
• Ram ventilation: where a respiratory current across the gills is generated by fish swimming with its mouth open.
• Ram Ventilation is used by filter feeders and open ocean fish including tuna, mackerel, swordfish, and some sharks.
• Many fish use both, buccopharyngeal pumping at rest and ram ventilation when swimming.
• Gas exchange can occur with countercurrent exchange: when the direction of blood flow through the secondary lamellae is opposite to the direction of water flow.
• Countercurrent exchange allows Max O2 absorption and its like when basketball players say good game at the end of a tournament.
• Many fish breathe air via lunds or other structures.
• Lungs evolved in fish and precede the evolution of tetrapods by millions of years.
• Likely evolved in active fish to supply additional oxygen and then co-opted for breathing in stagnant environments and eventually in tetrapods.
• Buoyancy: Neutral buoyancy is when density is equal to water, neither sink or float (hovering).
• Many actinopterygians (mostly teleost) have neutral buoyancy.
• Gas bladder (swim bladder) is the air filled organ used to regulate buoyancy
• 5% body volume in marine teleosts and 7% in freshwater teleosts because saltwater environments are more dense which makes you more buoyant
• Negative buoyancy is when density is greater than water (sink); seen in Bottom dwellers).
• Positive buoyancy is when density is less than water (float).
• Physostomous fish: has a Pneumatic duct = connection between the gas bladder and gut.
• This allows fish to can gulp air at the surface to fill the bladder and burp gas out to reduce bladder volume.
• The pneumatic duct is present in basal teleosts like eels, herring, anchovies, minnows, and salmon.
• Physoclistous fish are Derived teleost fish where adults lack pneumatic duct.
• Physoclistous fish increase the volume of gas bladder by secreting gas from the blood into the bladder, then decrease volume by absorbing gas from the bladder and releasing it through the gills.
• Rete mirabile is the “wonderful net" that moves O2 from blood into gas bladder
• The release excess gas they open a sphincter muscle to allow gas to enter the ovale and then Diffuses oxygen into the blood
• Cartilaginous fish (sharks, rays, and chimaeras do not have a gas bladder).
• Cartilaginous fish use Nitrogen containing compounding in the blood and muscle tissue (urea) and their livers which are high in oil content.
• High oil content causes the fish to float
• A bottom dwelling shark would have a less oiler liver compared to a shark that lives closer to the water's surface
• Sensory: Vision
• Air refraction index= 1.00
• Water refraction index= 1.33
• Vertebrate cornea refraction index= 1.37
• Refractive index of the cornea is too close to that of water which is why our vision is blurred
• Aquatic vertebrates have a spherical lens with high refraction which helps them see clearly underwater.
• Olfaction and taste: Jawed fish, have paired nasal sacs.
• Water flows into the incurrent nostril, over the olfactory space in the nasal sac, and out through the excurrent nostril (unidirectional)
• Olfaction and taste: Lampreys, have a Single median nostril.
• Water moves in and out.
• Lampreys smell the way we breathe. Detecting water displacement by hair cells which detect the motion of fluids.
• These hair cells form neuromast organs: clusters of sensory hair cells
• Lateral line system: sensory system on the body surface of fish and aquatic amphibians that detects water movements.
• Lateral line system is only found in aquatic vertebrates because air is not dense enough to trigger neuromast organs.
• Hearing: Hair cells also function in hearing where they respond to sound waves.
• Sound travels faster in water because it goes precisely from water molecule to water molecule, uninterrupted.
• Sound reaches and stimulates by several routes: Chondrichthyians and osteichthyans.
• Sound travels through tissues of the skin and skull to reach the inner ear however Don't have an ear hole and lots of resolution is lost.
• Osteichthyans with gas bladders have sound travels through tissues to the gas bladder, which then vibrates in resonant frequency to be transmitted to the inner ear.
• They can detect high frequency sound this way.
• Some osteichthyans (Catfish, minnows, goldfish) send Vibrations that reach the gas bladder are transmitted to the inner ear by small bones called Weberian ossicles.
• These fish are even more sensitive to high frequency sound and are most efficient.
• Electroreception: Passive electroreception is the ability to detect weak electric fields generated by muscle contractions of aquatic prey..
• Animals with passive electroreception can detect prey with electroreceptors called ampullary organs (ampullae); water conducts electricity.
• Electrically conductive gel fills ampullary organs.
• Ampullae are universal among chondrichthyans who use it to detect and capture prey. Ampullue can be found in in Ampullae of Lorenzini: on the head and are most concentrated in front of the mouth to direct the "final strike" at a prey animal.
• Homeostasis is a tendency of an organism to maintain a stable internal state
• Homeostasis is Achieved via osmoregulation and thermoregulation
• Osmoregulation; process of maintaining both water and salt balance so that body fluids do not become either too dilute or too concentrated.
• Organism; leaky bag of dirty water.
• Exchanges of matter and energy with the environment are essential to survival.
• Osmosis: movement of water across a semipermeable membrane from a dilute solution to a more concentrated solution.
• Solution: Isosmolal has same solute concentration as water and has No osmosis ex Hagfish.
• Solution: Hyposmolal has a lower solute concentration inside the body than the surrounding water.
• This occours in Marine teleosts which has water and salt balance constantly threatened by outflow of water and inflow of ions.
• Water flows out from body into surrounding water.
• Solution: Hyperosmolal has a higher solute concentration inside the body than the surrounding water.
• Ex. Sharks and freshwater fish who must cope with inflow of water and outflow of ions Water flows into their bodies.
• Most fish and lissamphibians are stenohaline; inhabit either seawater or freshwater and tolerate only modest changes in salinity (sensitive)
• Marine shark is hyperosmolal in seawater
• Marine teleost is hyposmolal in seawater.
• Freshwater teleost is hyperosmolal in freshwater.
• Some fish and lissamphibians are euryhaline; migrate between freshwater and seawater and tolerate large changes in salinity.
• Anadromous: fish that move from seawater to freshwater to reproduce.
• Ex Atlantic salmon.
• Catadromous: fish that move from freshwater to seawater to reproduce
• Ex American eel.
• Haikouichthys is the Earliest Vertebrate.
• 3 lines of evidence support the hypothesis of a marine origin of vertebrates.
• 1. Earliest fossils found in marine sediment.
• 2. Invertebrate deuterostomes are exclusively marine and are isosmolal.
• 3. Hagfish have concentrated body fluids like surrounding seawater.
• Cyclostomata is Extant jawless vertebrates.
• Clade;Includes hagfish and lampreys.
• Characters that separate cyclostomata from gnathostomes are:-
• Single median nostril
• Branchial basket (simple gills)
• Unarticulated gill arch.
• In gnathostomes, the gill arch has joints between.
• Gill arch lateral (outside of) to the gill tissue.
• In gnathostomes, the gill arch is medial (inside of) to gill tissue
• Velum: membranous flap in the pharynx moved by muscles to pump water over gills Tongue that bears keratinous teeth and is supported by cartilage
• Cyclostome tongue is not homologous to gnathostome tongue
• Hagfish (Myxiniformes) are All marine, living in Deep, cold water habitats They Drawn to carcasses by their sense of smell and Have keratinized teeth arranged front to back and close in the horizontal plane
• Hagfish has a median nostril used to take in water for olfaction and gill ventilation with Pharynx and gill slits are behind (posterior) the head
• Hagfish are Only extant vertebrates with a pre-anal fin
• Lampreys (Petromyzontiformes) are a sister clade to hagfish
• the Shared characters (synapomorphies) of lampreys include:
• Seven pairs of gill pouches
• A round mouth located at the bottom of the buccal funnel The nostril does not connect to the oral cavity or pharynx like it does in hagfish. Eye is well developed with good color vision Cambrian vertebrates and extant cyclostomes lack mineralized tissue Gnathostome synapomorphies Joints between skeletal elements of gill arches Allow double-pump gill ventilation (expand and suck) which results in large volumes of water moving across the gills to enhance the exchange of gases.
• Have Joints between skeletal elements of gill arches which allows for double-pump gill ventilation (expand and suck)
• This results in large volumes of water moving across the gills to enhance the exchange of gases
• Jaws with true teeth (dentine and enamel) 2 dorsal fins A set of pectoral and and pelvic fins Segmental W- shaped axial muscles Hox genes and gnathostome evolution, Hox genes is a group of control genes that determine the body plan of an animal during embryonic development (decides which body parts go where).
• All animals have hox genes, but vertebrates have more hox gene clusters than other animals
• All extant vertebrates have 2 clusters of hox genes resulting from a duplication of the single hox gene complex in nonvertebrate chordates
• Eugnathostomata ( the group that includes chondrichthyes and osteichthyes ) have 4 clusters of hox genes resulting from a second duplication
• Resulted in more refined genetic control of development leading to more anatomical possibilities
• Modify mandibular cartilages into a biting apparatus when you already have mouth parts?
• Ventilation hypothesis; jaws would have allows early gnathostomes to suck in larger volumes of water Improving respiration and gas exchange
• Evolution of paired appendeages, helps to: Spin(roll), move side to side in circle(yaw), do front flips
• Better thrust and acceleration

Lecture 5: Chondrichthyans and Osteichthyans

• Living gnathostomes include chondrichthyes and osteichthyes.
• Chondrichthyans are cartilaginous “fish”.
• Elasmobranchii is one chondrichthyan clade that has extant members.
• Extant elasmobranchs are solely in the clade Neoselachii, which includes extant Selachii (sharks) and Batomorphi (rays and skates).
• The 2 clades of extant selachians includes Galeomorphii (such as "Famous” sharks → hammerhead, whale shark, great white) and Squalomorphi (Generally smaller than galeomorphs; such as the spiny dogfish).
• The clades in Batomorphii include Skates → Rajiformes and Rays → Myliobatiformes. They primarily dwelled on the bottom.
• Flattened teeth, mouth is extremely protrusible providing powerful suction to dislodge shells from prey.
• Differences between Skates and rays: Skates have a circular body outline with a strong rostrum; Rays are diamond shaped; Skates have 2 dorsal fins and a terminal caudal fin and are oviparous (lay eggs); Rays have a whiplike tail and the fins are replaced by one or more elongated, serrated, and venomous dorsal barbs; Rays are viviparous, giving birth to live young.
• Euchondrocephalii is a sister clade to Elasmobranchii and includes Holocephalii and Chimaeriformes.
• Chimaeriformes are the only extant members of Euchondrocephalii.
• Characters of Chondrichthyans are Placoid scales composed of dentine and enamel and reduces drag during swimming and helps to resist abrasion.
• Characters of Chondrichthyans includes a cartilaginous skeleton.
• Their skeletons are mineralized with the same mineral as osteichthyans use in their bones, but chondrichthyans deposit the mineral differently, forming calcified cartilage, but they lost bone in their evolution They have Internal fertilization
• Male Chondrichthyans have pelvic claspers used to channel sperm into the female's cloaca Some are oviparous (ancestral) and some are viviparous
• Chondrichthyan teeth form tooth whorls which are continually replaced as they wear and are lost.
• Tooth shape tells us about rolls in feeding: tearing, cutting, and crushing
• Shark sense integration and hearing: Olfaction, Mechanoreception (from lateral line), Vision, Electroreception (via ampullae of Lorenzini) and mechanoreception, Swimming, and Caudal fin shape reflects environment.
• Elasmobranch brains have larger brains for more sensory, motor, and interneurons than smaller animals. Osteichthyes: All extant vertebrate groups other than cyclostomes and chondrichthyes are osteichthyans.
• The 2 clades of osteichthyes are Sarcopterygii (flesh/lobe-finned fish which encompasses tetrapods) and Actinopterygii (ray-finned fishes).
• Osteichthyan characters: Internal skeleton with ossified bones and Gas containing lung
• Osteichthyan derived their lungs from embryonic gut used for breathing and has Many dermal bones in their heads
• Such as Opercular bone , that covers the gills and aids in gill ventilation, Dermal bones that form the palate and bear teeth, Fin rays and Ancestral enamel which is is shiny, enamel like tissue on scales and dermal bones Evolutionary precursor to true enamel
• Actinopterygians:A clade within osteichthyans Most extant actinopterygians are teleosts
• Actinopterygian clades: Polypteriformes - Most basal extant actinopterygian, Diphycercal caudal fin, and series of dorsal finlets instead of a single dorsal fin (kinda looks like the spikes on a stegosaurus)
• Actinopterygian clades: Acipenseriformes Sharply asymmetrical heterocercal caudal fin ex Sturgeons and paddlefish
• Actinopterygian clades: Holostei Abbreviated heterocercal caudal fin Holostei are the Sister group to teleost, both are included in neopterygii Includies lepisosteiformes (gars) and amiiformes (bowfin) Actinopterygian clades: Teleosts Homocercal caudal fin

Lecture 6: Actinopterygians

• Most actinopterygians are teleosts
• Teleost characters: Homocercal caudal fin Oral jaws and Bony elements that surround the mouth opening which May or may not have teeth Pharyngeal jaws Scales
• Lack ganoine
• Much thinner layer of bone than non-teleosts
• Together, these thinner scales make the teleost body more flexible for swimming than that of a gar
• More basal teleosts have round, cycloid scales while more derived teleosts have ctenoid scales
• Teleost characters: Swimming: Gas bladders for buoyancy regulation and the skeleton of the paired fins become simplified → primarily fin rays
• These paired fins are used for social signaling, courtship, braking during swimming... etc Teleost Reproduction which includes Pelagic eggs: float freely in the water
• Teleost clades: Elopomorpha; Tarpons, bonefish, ladyfish, true eels are All but few marine.
• share leptocephalus: a kind of larval stage where they spend a long time drifting near the surface where they can be widely dispersed by currents.
• Teleost clades: Otophysi; Carps, minors, piranhas, catfish, electric eels share a Weberian apparatus.
• They Connect the gas bladder to the inner ear allowing for high frequence pick up (very sensitive to sound).
• Teleost clades: Euteleosti; includes Dragonfish (most abundant), Lanternfish, Cods and allies ,most important wild-caught commercial fish includes Seahorse, barracuda, billfish, flounder, halibut swimming and hydro dynamics high co relation between fish body length and swim speed.

Swimming and Hydrodynamics

• Strong correlation between a fish's body length and its swimming speed with longer fish swim faster
• Actinopterygian reproduction; most diverse in reproduction than any other vertebrate group.
• Oviparity is most ray-finned fish.
• What eggs in freshwater generally produce relatively small number of large, yolk rich eggs, which they bury in gravel or place in a nest or attach to the surface of a rock
• what eggs in marine is usually large numbers of small, buoyant, transparent, pelagic eggs, are released to float in the water column
• Viviparity; Ex Guppies
• Can Change their sex (in teleosts) Actinopterygian ecology:Photic zone - most bio mass happens here(all tiphotic), Pelagic and Deep sea-Basix ocean food chain

Actinopterygians

• Photic zone has most of the biomass occurs here (top 1000m of water) with Alltiphotic (very most top layer) Includes Coral reef fishes - Very diverse - Almost all vertebrates that live on reefs are teleosts, Mesophotic and Rariphotic)
• Pelagic and deep-sea fish (basic ocean) with Light levels in epipelagic (top 200m) can support photosynthesis, so oceanic biomass is concentrated in the epipelagic and mesopelagic (“twilight zone”) beneath it and Food webs in ocean depths rely on falling detritus and Below the mesopelagic is the bathypelagic
• Epipelagic includes Sardines, herring, tuna and Counter shading in pelagic.
• Mesopelagic: includes Daily vertical migrations and During the nighttime, they come up to the epipelagic zone to feed.
• Higher productivity at night Shallower water is warmer so their metabolic rates increase and they use energy faster
• Daytime descent into cooler water lower metabolism and conserves energy Bahtypelagic have large mouths to to stuff with large food sizes
• does not travel because it is too hard an energy
• Sarcopterygians. What we are-fletchlobe finish to mammals, and are sister to adingoperygion, we can use both gulls and lungs
• Acinista is what we put fish into
• Diapnorpha - longfish

Lecture 7: Sarcopterygians

• Sarcopterygians: Flesh/lobe finned “fish like” fish and tetrapods → amphibians, lizards, birds, and mammals
• Within osteichthyes
• Sister clade of actinopterygians
• “Fish like” sarcopterygians includes Acinistia → Coelacanthiformes and Dipnomorpha → lungfish

Crown tetrapods

• Crown group: composed of all living representatives of the collection, the most recent common ancestor of the collection, and all descendents of the most recent common ancestor
• Members of a crown group have all of the derived characters of the extant members of a clade
• 3 clades of sarcopterygians are extant with more than 99% of the species in tetrapoda Phylogeny,
• Coelacanthiformes and dipnomorpha are not sister clades
• are is most basel- sister to traptod
• Have hard tiisssue called cosmine, (hard skin) on dermal and boney skins to help swim at base Most Basal acanitiodes Had good bone scale base
• In clade actinosia- excellent fossil record
• A,O,S, and more
• Australian is only 15 m
• We eat oxygen here use both gulld and both
• Long is the only use gills here

Australian Lungfish

• Can have long lifespans and grow to 1.5m long
• Uses well developed gills for gas exchange and although it can use it's single lung to obtain oxygen, it does not depend on air breathing
• has a Massiv genome
• Long eel body and uses skin and lungs
• We can use to to stop it. Invert and land we can use lungs Fish are old. Devioan

Early Traprds

• • Come from late Devonian period (about 360 million years ago)
• Were primarily aquatic rather than terrestrial
• Crown tetrapods
• During the early Carboniferous, crown Tetrapoda diversified into clade like Lissamphibia and Amniota
• Time in history called Romer's gap where fossil records from that time are scarce Challengss of landing support breathing air - circ - sensorcy Dfference betweem tetremporh , In fisk neck doesmove in the tetrapod girdles does move
• The chord does reist, tosoio,
• We need to to resist Limb is a synanprpthy for the world
• Our link are advaced finns Torsion needed so we coded for less fin, in that water.

Land Senses

• Eating on land has its harder to get food into your mouth and down your throat with large, muscular, and mobile tongues,some have salmander tounge
• Circulation
• Much more difficult in terrestrial vertebrates, because blood must be pushed uphill into portions of the body higher off the ground than the heart- blood pressure. This calls for high double curclation with oxygenated blood.
• Sense where cornea is focused as opposed to water with a sensory system and
• Teprads Lissaphiban came from lissamanthia and gave them

Questions covering vertebrate evolution, classification, and key characteristics. Topics include the significance of evolution, extant vertebrates, binomial nomenclature, and the emergence of chordates. Also covers the development of jaws, characteristics of Batomorphii and Squalomorphi, paired appendages, Neoselachii, and the adaptations of lungfish and early tetrapods.