The vertebrates and their relatives

• Characteristics of a chordate
– A dorsal hollow nerve cord (spinal cord in vertebrates)
– A notochord (most vertebrates only have a notochord during development – becomes the backbone in vertebrates)
– Pharyngeal Pouches (develop into gills in fish and amphibians)
– Muscular Tail (disappears in humans)

• Tunicates (also known as “sea squirts”)
– Look similar to other chordates during development, but completely different as adults

• Lancelets: live in the ocean with their body buried in sand
– Have a definite mouth and no jaws
– Long pharynx with up to 100 gill slits
– Breathe through their body surface
– Have a simple digestive system, heart, and closed circulation
– Use paired muscles to move

• 99% of chordates are vertebrates
– Fish 24,000 species
– Amphibian
– Reptiles
– Birds
– Mammals
4,000 species
6,000 species
10,000 species
4,500 species

• Aquatic vertebrates characterized by:
– Fins (Movement)
– Scales (Protection)
– Gills (Breathing)
• There are fish with exceptions!
– Can you name any?

• Fish were the first vertebrate to evolve
• Evolved about 540 mya
– Were jawless and covered in armored plates
• Devonian Period = Age of the Fishes
– Fish developed both jaws and fins at this time

• Fish feed in a variety of ways including parasites, carnivores, herbivores, etc.
• Most fish breathe using gills
– Gills are feathery filaments containing a network of capillaries to increase surface area for CO
2
• Fish have closed circulation and O
2 exchange

• Fish digestive systems are similar to that of humans
• Ammonia is excreted by diffusion of water through gills and by use of kidneys
– Salt water fish conserve bodily fluids by having concentrated urine
– Fresh water fish have dilute urine
– Fish that move from fresh to salt water alter their kidney function to adapt to tonicity!

• Fish exhibit cephalization
• Many fish have
Chemoreceptors for an extraordinary sense of taste and smell
• Lateral Line System – allows fish to sense movement and vibration

• Swim Bladder – adjust buoyancy
– How does pulling a fish from 40 feet of water affect the size of its swim bladder?

• Oviparous – egg laying; includes both internal (some sharks) and external (most fishes) fertilization
• Ovoviviparous – eggs develop inside mother’s body and are nourished by egg yolk; young are born alive
• Viviparous – the mother’s body nourishes the developing young which are born alive

• Class Cephalospidomorphi – lamprey
• Class Myxini – hagfishes
• Class Chondrichthyes – cartilaginous fishes
• Class Osteichthyes – bony fishes

• Are jawless fishes
– Have mouths of soft tissue and no true teeth
• Have no bones
• Are the only vertebrates that do not have vertebral columns as adults

• Are filter feeders as larvae and parasites that suck blood and tissues of fish as adults

• Feed on dead and dying fish using a toothed tongue to scrape a hole in the fishes side
• Secrete large amounts of slime
• Have 6 hearts and an open circulatory system

• Includes sharks, rays, skates, sawfishes, and chimaeras
• “Chondros” = Greek word for cartilage
• A typical shark has 3000 teeth arranged in
6 to 20 rows
• Not all are carnivores, the largest sharks are filter feeders
• Some have flat teeth for crushing mollusks and crustaceans

• Skeletons are made of calcified bone
• Includes fish we are most familiar with:
Sunfish, Muskellunge, Northern Pike,
Walleye, Smallmouth Bass, etc.

• Some fish can live in both salt water and fresh water
– Anadromous Fishes – spend most of their life in the ocean but move to fresh water to breed
– Catadramous Fishes – spend most of their life in fresh water but move to the ocean to breed

• Amphibians gave rise to all other land vertebrates
• Amphibian means “double life”
– As larvae they are typically aquatic filter feeders or herbivores breathing through gills
– As adults most species are terrestrial carnivores that breathe through their moist skin and have lungs

• As the amphibians developed in the late
Devonian Period 360 mya they needed to adapt to terrestrial life
– Keep from drying out
– Breathe using lungs, not gills
– Bones in limbs allow movement
– Ribs to support and protect internal organs
• Amphibians dominated the Carboniferous
Period 345 to 285 mya

• Amphibians have a well developed digestive system similar to that of humans
• As most amphibians develop lungs as adults, some are lung-less and only breathe through their skin
• They have closed circulation and a 3 chambered heart with a double loop system similar to that of a human
• Ammonia is disposed of in urine through the use of kidneys

• Most amphibians lay their eggs in water; fertilization is external
• Some salamanders fertilize internally

• In most cases of external fertilization, the male will attach itself to the female. Eggs and sperm are released simultaneously and encapsulated in a jelly that attaches to aquatic plants.
• The jelly nourishes the developing embryos
• Tadpoles hatch and metamorphose into adults

• Most amphibians abandon their eggs once they lay them.
• Some care for both eggs and young
• Some incubate their eggs in unusual places: in their mouth, on their back, or in their stomach

• Amphibians have a well developed brain and spinal cord similar to that of a fish
• Eye’s are protected by a nictitating membrane
• A tympanic membrane, or eardrum, is located on either side of the head
• Many have a lateral line system similar to that of a fish

• Order Urodela : Salamanders and Newts
• Order Anura : Frogs and Toads
• Order Apoda : Caecilians

• Have long bodies and tails
• Both adults and larvae are carnivores
• Most adults are terrestrial and live in damp forests
• Some salamanders, such as mud puppies, keep their gills and live in water all their lives

• Have the ability to jump
• Frogs have longer legs and can jump farther than toads
• Frogs are closely tied to water; toads are more terrestrial

• Least known of the amphibians
• Are legless and burrow in moist soil or sediment
• Feed on small invertebrates such as termites
• Some have scales

• Most are a great meal for birds and reptiles
• Some have toxins to poison predators
• Some have bright colors to warn of their toxins
• Some mimic the bright colors of others and are harmless

• Amphibian populations are declining worldwide due to several factors:
– Global Warming
– Decreasing Habitat
– Depletion of the Ozone
– Water Pollution
– Introduced Aquatic Predators
– Fungal Infections
– Increasing human population!

• Land vertebrates with a well developed skull, a backbone and tail, and four limbs
– Exemptions: snakes have no legs, and turtles have a shell formed of fused vertebrae?
• Can a turtle lose its shell?

• The oldest reptile fossils date back to the early Carboniferous Period some 350 million years ago
• Dinosaurs of the Triassic and Jurassic
Period ruled the earth until 65 million years ago

• Reptiles are ectotherms – rely on interactions with the environment to control their body temperature
• Reptiles have well developed lungs, four chambered hearts, and a well developed brain and spinal cord
• Reptiles’ legs are rotated farther under their body than amphibians allowing them to carry weight and walk on land more efficiently

• Internal Fertilization – males have a penis to place sperm in the female’s cloaca
• Most are oviparous
– Turtles leave their nests unattended while alligators protect their nest
• Some snakes are ovoviviparous

• Reptiles have amniotic eggs – named after one of the four membranes around the developing embryo
– Amnion : produces watery environment around embryo
– Yolk Sac : contains nutrient rich yolk that feeds embryo
– Chorion : allows gas exchange
– Allantois : stores waste

• Order Squamata : lizards and snakes
• Order Crocodilia : alligators, crocodiles, caimans, and gavials
• Order Chelonia : turtles, tortoises, terrapins
• Order Rhynchocephalia - tuataras

• Most lizards have legs, clawed toes, external ears, and movable eyelids
• Some lizards do not have legs and look more like a snake

• Long broad snout and squat appearance
• Fierce carnivores
• Very protective of their nests
• Alligators and Caimans live only in fresh water and almost exclusively in
North and South America
• Crocodiles live in both fresh and salt water and are native to Africa, India, and Southeast Asia

• Turtles – live in or near water
• Tortoises – are terrestrial
• Terrapins – live in brackish water
– Carapace : Dorsal side of Shell
– Plastron : Ventral side of Shell

• Tuataras are the only living member of the
Order Rhynchocephalia
• Beak headed reptiles that live on a few small islands off the coast of New Zealand
• Differ from lizards as they lack external ears and retain primitive scales
• They have a legendary “third eye” which is part of a complex organs on top of the brain – the function is unknown

• Many are in danger due to loss of habitat
• Humans also hunt them for food, pets, and their skins (for bags and boots)
• Many conservation efforts are underway, but more are needed worldwide

• Characteristics of most birds
– Maintain a constant internal body temperature
– Covered in feathers
– Have two legs for walking and perching
– Front limbs are wings
– Most are adapted for flight

• Used for flight and warmth; several types
– Contour Feathers: provide the lifting force and balance needed for flight
– Down Feathers: trap air close to the body and keep the bird warm
– Powder Down: found on ducks and other birds that live on or in water; release a fine powder that repels water

• Oldest known fossil is Archaeopteryx which lived during the Jurassic Period 150 mya.
– Had teeth in its beak, a jointed tail, and toes and claws on its wings
• Birds are very closely related to dinosaurs, but scientists disagree on whether birds evolved from dinosaurs – or- birds and dinosaurs evolved from one common ancestor

• Endotherms: can generate their own body heat; warm-blooded
• Smaller birds must eat more in relation to its size due to Surface Area to Volume
Ratio

• They lack teeth and therefore do not chew
• Beaks are adapted to the types of food they eat
• Bird Digestion
– Crop: enlargement of the esophagus used to store food
– Gizzard: has muscular walls and small bits of gravel used to grind food

• Birds have very efficient lungs that provide oxygen rich blood during both inhalation and exhalation
• Inhaled air enters posterior and anterior air sacs it then travels through the lungs and is exhaled
• Therefore the air flows into the air sacs and out of the lungs in one single direction, always providing oxygen rich air

• Two loop circulatory system, similar to that of humans
• Ammonia is removed by the kidneys, converted to high concentration uric acid and defecated
(bird droppings); similar to reptiles

• The brains of birds are very well developed
– Birds can see color very well
– Birds can hear very well
– Smell or taste are not well developed

• Most birds can fly. Others are adapted for swimming and running
• Bones are light, strong, and adapted for flight; many bones are fused to provide a study base for flight adaptations

• Both male and female reproductive tracts open into the cloaca
• The sex organs, internal in both sexes, increase in size during mating season
• Birds rub their cloacas together during mating to transfer sperm

• Eggs are amniotic but unlike reptile eggs have a hard outer shell
• Eggs must be incubated by the parents since they are endotherms
• Young must be cared for after hatching

• There are nearly 30 different orders of birds
• 60% of all birds worldwide are perching birds
• Show many examples!

• Birds are very ecologically important
– Hummingbirds are involved in pollination
– Some birds eat seeds without digesting them and therefore spread the seeds
– Many birds keep insect populations in check
• Many birds migrate by guidance of stars,
Earth’s landmarks, and Earth’s magnetic field
• Birds are good indicators of environmental health; bird numbers dwindled with the use of DDT

• Characteristics of mammals
– Endotherms
– Have mammary glands and nurse young
– Have hair

• The earliest mammals evolved about the same time as the early dinosaurs but remained in the shadows until the giant reptiles disappeared
• First ancestors of mammals appeared during the Permian Period about 290 to
250 mya
• First true mammals appeared during the
Jurassic Period 210 mya

• When the continents split about 60 mya, three groups of mammals were isolated from one another.

• Animals have hair to help insulate their bodies.
• They also have subcutaneous fat to keep them warm and many have sweat glands to cool them off.
• Smaller mammals have higher metabolism than larger ones in order to create enough body heat to keep warm.
• Mammals eat about 10 times as much food as a reptile in order to stay warm.

• When comparing the bones and bone structures of all vertebrates - birds, amphibians, reptiles, and mammals – you can see many of the same bones with very similar functions
• Refer to Figure 32-7 in the text (Page 826)

• Internal Fertilization occurs in mammals
• Mammals are divided into three groups based on methods of development and birth
– Oviparous: egg-laying mammals are called monotremes
– Viviparous: includes both placental mammals and marsupials

• All newborn mammals feed on their mother’s milk
• Some newborns are helpless at birth and must be cared for
• Others are able to see and walk within minutes after birth

• Monotremes are the egg laying mammals
• They share two notable characteristics with reptiles
– Both the reproductive and urinary systems open into a cloaca
– “Monotreme” means single opening
• Only three species of monotremes exist today: they are found in Australia and
New Guinea
– Duckbill Platypus and two species of Spiny
Anteaters

• Monotremes lay eggs that are incubated outside the body
• They hatch into young animals in about 10 days
• The young are nourished by their mother’s milk that they lick from pores on the mother's abdomen

• Marsupials give birth to live young that complete their development in an external pouch
• Examples include kangaroos, wombats, koalas, and Tasmanian devils
• A short time after internal fertilization a small embryo leaves the mother’s body, crawls across the fur, and enters the marsupium (pouch) where it attaches to a nipple to nurse

• Placental Mammals are those that are most familiar to us.
• Placenta – organ in placental mammals through which nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and mother
• Gestation – the time it takes from conception to birth in mammals (can vary from 2 weeks to 2 years depending on the mammal)

• There are 12 orders of placental mammals
• They are classified based on several criteria including
– Feeding
– Teeth and Jaw Structure
– Foot Structure
– Brain Development