13. Vertebrates (V)

What is the flexible cartilaginous rod that provides internal support in chordates and gives the phylum Chordata its name?

Notochord (a flexible cartilaginous rod).

What is the tail feature that extends posterior to the anus in chordates?

Post-anal tail.

What are pharyngeal pouches, and what do they become in fish?

Pharyngeal pouches; in fish they develop into gill slits.

What is meant by the hollow dorsal nerve cord in chordates?

A hollow nerve cord located on the back (dorsal side) that forms the brain and spinal cord.

In vertebrates, what happens to the notochord during development?

It is replaced by vertebrae that enclose the spinal cord.

Which subphylum includes the tunicates or sea squirts?

Urochordata.

Which subphylum includes the lancelets?

Cephalochordata.

What is the common name for Myxini?

Hagfish.

What is the common name for Petromyzontida?

Lampreys.

What is the outer covering of tunicates called and what is it made of?

Tunics; made of cellulose.

In tunicate larvae, which chordate features are present?

Notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail.

What major evolutionary event is associated with the development of jaws and a mineralized skeleton?

The evolution of jaws and a mineralized skeleton.

What is the amniotic egg and why is it important?

An egg with membranes that allows vertebrates to reproduce on land; a major evolutionary step.

Name two key mammalian traits mentioned in the notes.

Milk and fur.

In Cephalochordata, how far does the notochord extend?

Through to the head (cephalo- meaning head).

In Urochordata, where is the notochord located in the larva?

Along the tail of the larva.

Which two subphyla of Chordata were discussed as evolving before vertebrates?

Cephalochordata and Urochordata.

What skeletal characteristics define the subphylum Vertebrata?

An internal skeleton (bone or cartilage) with vertebrae enclosing the spinal cord.

What genetic feature is extra in Vertebrata and why is it important?

Extra sets of Hox genes due to gene duplication, enabling mutations that drive new features in development.

What are the two main vertebrate clades mentioned, and what are their common names?

Jawless fishes (Cyclostomata) and jawed vertebrates (Gnathostomata).

What does 'Cyclostomata' mean and which animals have circular mouths?

Circular mouth; includes hagfish and lampreys (jawless vertebrates).

What are the key features of lampreys?

Jawless vertebrates with circular mouths and embedded teeth; parasitize large fish and feed on scales and flesh.

What is unique about hagfish and their defense mechanism?

Hagfish have slime glands that release protein threads forming slime when in contact with water, deterring predators.

Where are hagfish typically found and what is their feeding behavior?

Deep in the ocean on the sea floor; scavengers that may feed on dead animals or rotting material, sometimes entering carcasses.

From which anatomical structures did jaws evolve in jawed vertebrates?

From the anterior gill arches that enlarged, fused, and modified to form jaws; teeth could then embed in the jaws.

What are the major benefits of jaws evolving in vertebrates?

More powerful prey capture due to larger, fused jaw bones and muscles; teeth embedded in jaws.

What is the cartilaginous fish clade called, and what are its common examples?

Chondrichthyes; sharks, stingrays, and ratfish.

What distinguishes Chondrichthyes from bony fishes in terms of skeleton and gill ventilation?

A cartilaginous skeleton (cartilage) and a need to swim to push water over the gills for respiration.

Can cartilaginous fish rest without swimming, and what evidence is given?

They generally must keep moving to ventilate gills, though some (like nurse sharks) can rest by moving jaws to pump water.

What are the two major groups of bony fishes mentioned?

Ray-finned fishes (Actinopterygii) and Lobe-finned fishes (Sarcopterygii).

How old is the jawed vertebrate clade estimated to be?

Around 400 million years ago.

What classes are included in the jawed vertebrate clade as listed, and what caveat is mentioned about Aves?

Amphibia, Reptilia, Aves (often placed with Reptilia but traditionally separated), and Mammalia.

What adaptation do bony fish use to counteract their heavier skeletons and prevent sinking in water?

A swim bladder, an internal gas-filled balloon that provides buoyancy and helps regulate depth.

What is the function of the operculum in bony fish?

It acts as a valve to pump water over the gills, reducing the need for constant swimming.

Why are most fish called ray-finned fish?

Because their fins are supported by thin bony rays or spines.

What are the two major groups of lobe-finned fish and how are their fins characterized?

Coelacanths and lungfish; they have fleshy, lobed fins with internal bones and muscles, unlike the slender rays of ray-finned fish.

What is a coelacanth and why is it notable in evolution?

A living lobe-finned fish thought extinct for a long time; considered a living fossil with two living species.

From what ancestral structure did the swim bladder originate, according to the notes?

Simple lungs attached to the esophagus of ancestral bony fishes that gulped air.

How are the swim bladder and tetrapod lungs connected evolutionarily?

Primitive lungs evolved into a closed swim bladder separate from the esophagus in bony fish, while in tetrapods the primitive lung evolved into more complex lungs.

What is the gas gland and what does it do?

A structure in the swim bladder where gases are released from blood to increase buoyancy, and removed to decrease buoyancy.

What distinguishes ray-finned fish from lobe-finned fish in terms of fins?

Ray-finned fish have fins supported by thin bony rays; lobe-finned fish have fleshy, lobed fins with bones and muscles.

What unique dry-season adaptation do African lungfish possess?

They can dig into mud, encase themselves in mucus, and survive for months up to about four years without water.

Why are lungfish considered part of the lobe-finned fish group?

Because they have fleshy fins with internal bones and muscles, not just simple ray-supported fins.

Approximately how many living lobe-finned fish species exist today, and which two are highlighted in the notes?

About eight living species; two are coelacanths, with lungfish among the other surviving lobe-finned fishes.

What key innovation allowed tetrapods to exploit land?

Limbs with digits (four limbs and hind limbs).

Tetrapods evolved from which ancestral group of fishes?

Lobe-finned fish, whose fin bones are similar to tetrapod limb bones.

Why did moving onto land provide an ecological advantage for early tetrapods?

They could access food with less competition, and land has more available oxygen than water.

Name a derived characteristic of tetrapods related to neck movement.

A neck—vertebrae that can support and move the head independently from the pectoral girdle.

What is the role of the pelvic girdle in tetrapods?

It is fused to the backbone and provides stronger support for the hind limbs on land.

Which sense adaptation helps tetrapods detect sound in air?

Ears adapted for detecting airborne sounds (airborne sound detection).

Who is Tiktaalik and why is it significant?

A transitional fossil (~365–375 million years ago) showing both fish-like and tetrapod-like features, bridging the gap between lobe-finned fish and tetrapods.

List the forelimb bones identified in Tiktaalik’s limb.

Shoulder blade, humerus, ulna, radius, carpals, metacarpals, and phalanges.

What skull features did Tiktaalik have that suggest a transition toward tetrapods?

A flat skull with eyes on top of the head and supportive ribs for life on land.

Which fish-like characteristics did Tiktaalik retain?

Fins and scales (fins considered fish-like).

What are the derived characteristics of the class Amphibia?

Quadrupedal (four limbs), moist mucus-covered skin, and cutaneous gas exchange.

What are the three clades of Amphibia?

Anura (frogs and toads), Urodela (salamanders and newts), Apoda (caecilians).

What does Anura mean and which animals does it include?

No tails; frogs and toads.

What does Urodela mean and which animals does it include?

Tail-bearing; salamanders and newts.

What does Apoda mean and which animals does it include?

Without legs; caecilians.

Where do Amphibians typically need to reproduce, and why?

Near water; eggs are laid outside the body and fertilization occurs in water, with larvae developing there.

What is cutaneous gas exchange and why is it important for Amphibia?

Gas exchange through the moist skin, which is a key respiratory route for many amphibians.

How large could early amphibians grow, according to the notes?

Up to a couple of meters in length.

What is the relationship between Amphibia, Reptilia, and Mammalia in the tetrapod phylogeny as described in the notes?

Amphibia, Reptilia, and Mammalia are major tetrapod groups; birds are included within the reptilian clade.

What is notable about caecilians’ eyes and habitat?

They have rudimentary eyes (limited vision) and live in tropical forest floors, often burrowing in litter.

What group includes reptiles, birds, and mammals and is defined by having an amniotic egg?

Amniotes.

Which membrane surrounds the embryo and contains fluid, protecting it during development?

The amnion (amniotic membrane).

What is the evolutionary significance of the amniotic egg for terrestrial vertebrates?

It allows reproduction on land, enabling independence from water and greater diversification.

Name several examples of reptiles mentioned in the notes.

Snakes, lizards (including the Australian thorny devil), turtles, alligators, crocodiles, and the tuatara.

What is a key difference between reptile eggs and bird eggs?

Reptile eggs typically have a leathery outer shell, whereas bird eggs have a hard calcium carbonate shell.

What type of fertilization is essential for the amniotes' reproduction on land?

Internal fertilization (sperm fertilizes the egg inside the female before the shell forms).

Which protein gives reptile skin its waterproof quality?

Keratin.

What does thoracic breathing refer to in the context of these vertebrates?

Breathing by expanding the thorax using the rib cage to ventilate the lungs.

What are the four extraembryonic membranes of the amniotic egg and their general roles?

Chorion (gas exchange and prevents water loss), allantois (gas exchange and waste storage), amnion (protects embryo with fluid), and yolk sac (provides yolk nutrients).

What does the allantois primarily do besides gas exchange?

Stores metabolic nitrogenous waste from the embryo.

What is the function of the chorion in the amniotic egg?

Gas exchange with the outside; contributes to preventing water loss when the shell is present.

What is the role of the yolk sac in the amniotic egg?

Provides food for the developing embryo via the yolk; yolk sacs are vascular to transfer nutrients.

What are the key characteristics of birds discussed in the lecture?

Feathers and flight, internal fertilization, amniotic eggs with hard calcium carbonate shells, and endothermy.

Which fossil is cited as evidence for birds evolving from dinosaurs and as a transitional form?

Archaeopteryx.

From which group did birds evolve?

Reptiles (non-avian dinosaurs).

Is the class Aves considered monophyletic in the notes?

Not strictly monophyletic in the notes (Aves is treated as not monophyletic here).

What major evolutionary insight about dinosaurs is discussed regarding feathers?

Many dinosaurs had feathers; feathers evolved for other functions and were later co-opted for flight.

What class is characterized by milk production and fur, and includes monotremes, marsupials, and placentals?

Mammalia.

What are two defining mammalian traits mentioned in the notes?

Hair or fur and mammary glands that produce milk.

Approximately when did mammals evolve relative to birds?

About 200 million years ago, before birds.

Name the three mammal groups and a key trait for each.

Monotremes (egg-laying; platypus and echidna); Marsupials (short-lived placenta; development in a pouch); Placentals (longer placental development; no pouch).

How do the yolk sac and allantois contribute to the mammalian umbilical cord?

They become part of the umbilical cord with the associated blood vessels; no external yolk sac in newborn mammals.

What happens to the eggshell in mammals (except monotremes)?

The shell is gone; development occurs inside the mother's body (placentals) or, in monotremes, eggs are laid with a shell.

From which embryonic structure do the placenta form in mammals?

Chorion (through its modifications) forms the placenta.