Bio Unit 3 Chapter 29

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Vertebrate

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Vertebrate animals are those that have a backbone (vertebral column). Vertebrate animals are categorized taxonomically within the phylum Chordata along with two non-vertebrate animals discussed early in the chapter.
All Chordates, both non-vertebrates and vertebrates are deuterostomes (eusterostomes) and have a true coelom. Most Chordates will have an internal (endo) skeleton made up of bone and cartilage that muscles attach to.
2 Advantages: Chordates in general have a great capacity for freedom of movement (flying, swimming, running, climbing) and can attain much larger sizes (Blue whales and Elephants!!!

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The Chordates (phylum Chordata)

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All Chordates have the following traits at least during embryo development. Some organisms lose one or more of these traits when they become adult, and others retain them. It is important to know which types of organisms within the phylum Chordate have all four main chordate features as adults.
• Notochord: dorsal supporting rod. In vertebrate animals, this is replaced during embryo development with a vertebral column.
• Dorsal tubular nerve chord: Previously referred to as the dorsal hollow nerve cord. The position of this nerve is dorsal in chordates. This nerve cord is called the spinal cord in most vertebrates and it is protected by the vertebral column. In the anterior end, (the head) it becomes the brain in most chordates.
• Pharyngeal pouches: seen only during embryo development, they go on to be different structures in different animals. In fishes, they become the gills. In humans, the first pair of pouches becomes the auditory tubes.
• Postanal tail: A tail that in the embryo, if not in the adult, extends beyond the anus. In other groups of organisms, the anus is terminal.

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• Notochord

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dorsal supporting rod. In vertebrate animals, this is replaced during embryo development with a vertebral column.

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• Dorsal tubular nerve chord

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Previously referred to as the dorsal hollow nerve cord. The position of this nerve is dorsal in chordates. This nerve cord is called the spinal cord in most vertebrates and it is protected by the vertebral column. In the anterior end, (the head) it becomes the brain in most chordates.

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• Pharyngeal pouches

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seen only during embryo development, they go on to be different structures in different animals. In fishes, they become the gills. In humans, the first pair of pouches becomes the auditory tubes.

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• Postanal tail

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A tail that in the embryo, if not in the adult, extends beyond the anus. In other groups of organisms, the anus is terminal.

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Non-Vertebrate Chordates

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There are two groups of non-vertebrate chordates that do not have a spine made up of boney vertebrae.

Cephalochordates: Lancelets
Urochordates: Tunicates

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Cephalochordates: Lancelets

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These are marine chordates that do not have vertebrae but do retain all four chordate characteristics as adults. They are filter feeders, found in coastal water and are only a few centimeters long. Lancelets are important for study of the evolution of chordates because they retain all four characteristics.
a) Notochord extends from head to tail; they have gill slits, and a dorsal tubular nerve cord. They also have a post anal tail with a caudal fin.
b) ALSO they show segmentation which in chordates, allows for specialization of body parts.
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Urochordates: Tunicates (Sea Squirts!).

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Named for the tunic like covering the adults have that make them look like short, fat, sacs.
Sea Squirts live on ocean floor and squirt water as a defense mechanism to startle predators.
The larvas are free-swimming and have bilateral symmetry and all four chordate features.
Go through metamorphosis.
The adults only have the gill slits and the adults become sessile filter feeders with incurrent and excurrent siphons. Also, (not in your book) we start seeing the beginning of beat timing mechanisms in the hearts in sea squirts so they are much studied in the cardiac field.

Scientists hypothesize that sea squirts are directly related to vertebrates and that an ancestor may have been a sea squirt larva that happened to retain all the chordate features instead of losing them by time sexual maturity occurred.

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Characteristics of Vertebrates:

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Have all four chordate features as embryos.
In addition, all vertebrates have the following features:
• Vertebral column: embryonic notochord is replaced by vertebral column composed of individual vertebrae. Flexible, strong, and shows segmentation.
• Skull: Main axis of internal skeleton is composed of the vertebral column and the skull, a strong structure made of bone that encases the brain and protects it. High degree of cephalization is accompanied by complex sensory organs.
• Endoskeleton: The vertebrate skeleton (bony or cartilage) is a living tissue that grows with the animal. It also protects the internal organs and serves as a surface for muscle attachment.
• Internal organs: a large coelom and complex digestive tract. Closed circulatory system (blood is transported in enclosed vessels throughout the body. Respiratory systems is gills or lungs which obtain oxygen from environment. Excretory systems with kidneys. Kidneys are water regulating organs and conserve or rid the body of water when needed.
Sexes are generally separate and reproduction is mainly sexual.

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• Vertebral column

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embryonic notochord is replaced by vertebral column composed of individual vertebrae. Flexible, strong, and shows segmentation.

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• Skull

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Main axis of internal skeleton is composed of the vertebral column and the skull, a strong structure made of bone that encases the brain and protects it. High degree of cephalization is accompanied by complex sensory organs.

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• Endoskeleton:

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The vertebrate skeleton (bony or cartilage) is a living tissue that grows with the animal. It also protects the internal organs and serves as a surface for muscle attachment.

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• Internal organs

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a large coelom and complex digestive tract. Closed circulatory system (blood is transported in enclosed vessels throughout the body. Respiratory systems is gills or lungs which obtain oxygen from environment. Excretory systems with kidneys. Kidneys are water regulating organs and conserve or rid the body of water when needed.
Sexes are generally separate and reproduction is mainly sexual.

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Vertebrate Evolution

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Fossil record indicates the arrival of chordates and vertebrates during the Paleozoic Era.
Special occurrences: Earliest vertebrates where fishes, some without jaws and others with jaws. Animals with jaws are called gnathostomes.
Some of the early jawed fish show evidence of lungs, and fleshy fins, both pre-adaptive to life on land.
The first vertebrates to have limbs where the amphibians. Four limbed organisms are tetrapods.
Another adaptation to land life was the evolution of the amniotes, organisms who produce amniotic eggs. The amniotic egg has the embryo surrounded by an amniotic membrane filled with amniotic fluid.
Water tight skin, seen in reptiles, is also a good feature for life on land.

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tetrapods

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Four limbed organisms

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gnathostomes

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Animals with jaws

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amniotic eggs

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amniotic egg has the embryo surrounded by an amniotic membrane filled with amniotic fluid.

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The Fishes

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The largest group of vertebrates. Some have cartilage skeletons others have bony skeletons. Most have jaws, but some do not.

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Jawless Fishes (Agnathans)

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Earliest fossils in the Cambrian were small, filter feeding, jawless and finless ostracoderms (heavy dermal armor for protection.
Agnathans have
• a cartilaginous skeleton
• persistent notochord.
• Lampreys and Hagfish.
• Smooth skin
• Have gill slits
• Some are filter feeders, others parasitic blood feeders. Hagfish are scavengers dead fish.

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Fishes with Jaws
Characteristics

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• Ecothermy: Must depend on environment to regulate body temperature
• Gills: breath with gills and have a single-looped , closed circulatory system with a heart that pumps blood to the gills first. Heart is two-chambered.
• Cartilaginous or bony skeletons: Endoskeleton includes vertebral column, a skull with jaws, paired pectoral and pelvic fins. Fins help with turning and balance.
• Scales: Skin is covered with scales so not directly exposed to environment.

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• Ecothermy

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Must depend on environment to regulate body temperature

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Cartilaginous Fishes ( Class Chondraichthyes):

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Sharks, rays, skates, chimaeras.
Cartilaginous Fishes have skeletons of cartilage instead of bone. Lack gill cover
Have five to seven gill slits; many have openings to the gill chambers called spiracles that are behind the eyes.
Body covered with dermal denticles, tiny teeth-like scales (so sand paper like feel to skin)
Three well developed senses useful for hunting:
• Ability to sense electric currents in the water
• Lateral line system, a series of pressure sensitive cells which sense pressure caused by swimming movement of nearby fish or other animals
• Very keen sense of smell (sharks can detect 1 drop of blood in 115 liters of water)

Interestingly, the largest shark (whale shark) is a filter feeder!
In rays and sharks the pectoral fins are greatly enlarged and body is flattened dorsoventrally

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Bony Fishes (Class Osteichthyes):

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Majority of fish and majority of living vertebrates.
• Most are ray-finned bony fishes (fan shaped fins supported by a thin bony ray)
• Lack external gill slits, gills are covered by operculum
• Many have swim bladder, a gas filled sac to regulate pressure for buoyancy
• A single-loop, closed cardiovascular system.
• Well-developed brain and nervous system
• External fertilization with females laying eggs and males depositing sperm on the eggs.

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Lobe-Finned Fishes:

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• Fleshy fins supported by bones
• Modern day Lungfish and the Coelacanth (once thought to be extinct).

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The Amphibians (Class Amphibia)

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Characteristics of Amphibians: Carry out part of life cycle in water and part on land.
• Limbs: Typically four limbs (tetrapods) Well developed pelvis and pectoral girdle promotes locomotion
• Smooth and nonscaly skin: Kept moist by mucus glands, active in water balance and respiration! Also regulates cooling of skin on while on land. Also, most (not all) must stay near water to avoid drying out (don’t lick the toads!)
• Lungs: If lungs are present, relatively small. Respiration is supplemented by gas exchange through skin (cutaneous respiration).
• Double-loop circulatory system: Three-chambered heart. Single ventrical with two atria pumps that pump blood to lungs and body. However, oxygen poor blood mixes with oxygen rich blood (mixed blood)
• Sense organs: sight, smell, hearing are fine tuned for life on land. Brains are larger than that of fish. Specialized tongue for catching prey and eyelids for protecting eyes and keeping eyes moist. Sound producing larynx.
• Ectothermy: body temp is regulated by environment but they can deal with great fluctuations in temp and cool off by evaporation out their skin. Some can hibernate!
• Aquatic reproduction: Most must return to water to lay eggs and for larva to develop and live. Eggs protected by a jelly coat not a shell. Young are tadpoles, aquatic larva with gills. Tadpoles undergo metamorphosis to become adults. Some species have evolved mechanisms to bypass aquatic larval stage and reproduce on land.

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Evolution of Amphibians

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evolved from lobe-finned fish with lungs by way of transitional forms.
Two main hypothesis.

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Diversity of Amphibians

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three groups of amphibians today.
• Salamanders and newts:
• Frogs and toads
• Caecilians: legless, often sightless, worm-like amphibians. Some look like earthworms.

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The Reptiles (Class Reptilia) & Birds

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. Characteristics of Reptiles: a very successful group of terrestrial animals. Over 17, 000 species. Birds, are now starting to be categorized with reptiles. Following characteristics shows that they are fully adapted to life on land.
• Paired Limbs: Two pairs of limbs, usually with five toes (pentadactly). Adapted for climbing, swimming, and running, paddling or flying. Feet tend to be clawed.
• Skin: Thick, dry and impermeable to water. Skin prevents water loss. Skin is usually mostly scaly (at least partly scaly). Many reptiles shed skin several times a year.
• Efficient breathing: Lungs are more developed than in amphibians. Also, many have expandable rib cage to assist breathing.
• Efficient circulation: Heart prevents mixing of blood. Septum divides the ventricle either partially or completely. Most reptiles have a three chambered heart. Crocodiles and birds have a four chambered heart.
• Efficient excretion: Kidneys. Well-developed. Kidneys excrete uric acid, thus less water is required to eliminate waste.
• Ectothermy: Rely on environment to regulate temp but this also means need less food to maintain metabolism compared to birds and mammals. Behavior adaptation to use the sun to warm themselves.
• Well adapted reproduction: Adapted to life on land and reproduction on land. Sexes are separate and fertilization is internal (protects sperm from drying out and don’t need water to get the sperm to where they need to go
Amniotic egg contains membranes that protect the embryo, provide oxygen, food ,water, and help remove nitrogenous wastes. One such sack is the amnion that fills with fluid and provides a “private pond” for the embryo to develop in.

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Evolution of Reptiles

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Amniotes (such as reptiles, birds and mammals) consist of three lineages (look at skulls):
1) The turtles in which the skulls are anapsid; this means has no opening behind the orbit (orbit= the eye socket).
2) The other reptiles including birds: skulls are diapsid; has two openings behind the orbit.
3) The mammals have skulls that are synapsid; one opening behind the orbit


The reptile group is an artificial group because it has no common ancestor
(paraphyletic not monophyletic), so taxonomists are currently in the process of dividing the reptiles into a number of monophyletic groups. The skull anatomy is part of this and we will not focus on this right now.

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Diversity of Reptiles:

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Living Reptiles are represented by turtles, lizards, snakes, tuataras (lizard like creatures that have a third eye and native to New Zealand. Also, basically the most ancient and most dinosaur-like though small). Also crocodilians and birds.

READ OVER diversity of reptiles.

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Birds (Class Aves but increasingly found to be more like reptiles and thus a group in there for now)

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Share a common ancestor with crocodilians and have traits such as the presence of scales (feathers are modified scales), a tail with vertebrate and clawed feet that show they are indeed reptiles. Of course, they are amniotes as previously stated.
Also, almost every anatomical feature can be related to bird’s ability of fly. Examples of this are its light weight bones, feather anatomy, respiration etc.

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Characteristics of Birds

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• Feathers: Soft down keeps birds warm (insulation), wing feathers allow flight, tail feathers for steering. Feathers are modified scales. Nearly all birds molt at least once a year.
• Modified Skeleton: *Unique to birds, collar bone is fused (wishbone) and sternum has a keel. Many other bones are fused, so skeleton is more rigid than reptilian skeleton. Breast muscles are attached to the keel and this helps with ability to fly. Horny beak has replaced jaws and slender neck connects to rounded, compact torso.
• Modified respiration: lobular lungs connect anterior and posterior air sacs. This means that air passes one-way through lungs and gases are continuously exchanged across respiratory tissues!
Also, air sacs are lighten the body and bones. Some also have air sacs present in the bones.
• Endothermy: Generate their own internal heat (so do mammals). Called endotherms. Endotherms use metabolic heat to maintain constant internal temp.
• Well-developed sense organs and nervous systems: Birds have particularly acute vision and very well developed brains (quite intelligent). Reflexes are excellent. Ritualized courtship often precedes mating. Parental care of new hatched chicks (in most). Seasonal migration ability of many species. High vocalization abilities in many.

E. Diversity of Birds : from birds of prey like eagles and hawks, to scavengers like vultures, seed eaters like songbirds. Flightless birds like kiwi, ostrich and emus. Also chickens, turkeys, to waterfowl like ducks and geese. Lots of different birds in many different habitats.

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The Mammals (us! Yeah!)

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This group includes the largest (in size) individuals (the Blue whale =130 metric tons!!) to the smallest mammal (the Kitti’s bat, 3cm long nicked named the “bumblebee bat. SUPER CUTE!). Also the fasted land animal (drum roll please) the cheetah!)

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Characteristics of Mammals

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• Hair: Most distinguishing feature (hair, fur etc, covering outer skin) Provides insulation against heat loss. Hair color can camouflage. Hair can be ornamental and also sensory (whiskers!)
• Mammals are ENDOTHERMS.
• Mammary glands: Glands enable females to feed young milk (nursing) without them having to leave young to collect food. Also creates a bond between female and young and helps ensure parental care of offspring. Also provides antibodies for immune system of very young offspring.
• Skeleton: Skull accommodates a much larger brain than relative to body size. Cheek teeth are differentiated into premolars and molars. Vertebrate are highly differentiated; typically middle of vertebral column is arched, and limbs are under the body rather than out to the sides.
• Internal organs: Efficent respiratory system and circulatory system. Four chambered hearts, no mixing of blood and double loop circulatory pathway.
• Internal development: IN MOST but not all. In most, young develop internally and are born alive from mothers body in an organ called a uterus. Internal development allows for shelter of young and movement of mother actively while young are developing.

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Evolution of Mammals

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are amniotes but most do not lay eggs outside of the body. Some still do lay eggs!!! Have a common amniote ancestor with reptiles!

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) Monotremes

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• Egg-laying mammals
• Example: Duck-billed Platypus and two species Echidna (spiny anteaters)
• Monotreme refers to one urogenital opening, the cloaca (which birds have). Both excretory and reproductive opening.
• No embryonic development occurs inside body of female.
• Echidna’s have a pouch where egg moves to from the cloaca. Milk is produced from special pores in the belly pouch.
• Platypus also lays eggs but in a burrow and produces milk for young from modified sweat glands.

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Marsupials

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• Include kangaroos, wallabies, Koalas, wombats, Tasmanian devils, sugar gliders, and opossums.
• Have a true uterus.
• Some embryonic development inside the uterus but are born in an immature development state.
• Maturity continues in the belly pouch of females where they attach to a nipple to obtain milk until they are developed enough to leave pouch.
• Most abundant in Australia.

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Placental Mammals (us!)

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• Also known as eutherians, are the dominant group of mammals
• Developing placental mammals are dependent on a placenta. This is a very specialized organ for the exchange of substances between maternal blood supply and growing offspring. Nutrients to offspring and wastes to mother who then excretes them for the offspring. (peeing for two!) While the fetus is clearly somewhat parasitic on the female, the female can move around freely (especially to escape predators or find food and shelter)
• Senses are acute , active lifestyle in placental animals and cerebral hemisphere is very large. Brain continues development past birth and in general, young are very dependent on parental care.
• Most mammals live on land but some have returned to water lifestyle (whales etc).
• Bats can fly, some other mammals can glide. Most walk/run or climb.