THE CHORDATES 30 1 What is chordate A

THE CHORDATES (30 -1)

What is chordate? A chordate (Phylum Chordata) is an animal that has four things at some point during its life cycle: 1) A dorsal, hollow nerve chord 2) A notochord 3) Pharyngeal pouches 4) A tail that extends beyond the anus *** the animal may not keep these for their entire life Hollow Nerve Chord Runs along the dorsal part of the body, has branches at regular intervals that connect to internal organs, muscles, and sense organs.

Notochord- a long supporting rod that runs through the body just below the nerve chord. Most chordates have a notochord only when they are embryos. Pharyngeal Pouches Pharyngeal pouches- paired structures in the throat region: Fishes and Amphibians- develop into gills for gas exchange. Other Chordates- only present when they are embryos Tail At some point in their lives, most chordates have a

hollow nerve chord notochord mouth tail anus pharyngeal pouches

Most Chordates are Vertebrates • 96% of all chordates are placed in the subphylum Vertebrata. • Vertebrates have a strong support column or backbone that originates from the notochord. • The backbone is made up of individual segments called vertebrae that enclose and protect the spinal chord. • In vertebrates, the dorsal hollow chord is called a spinal cord. • The anterior end of the spinal cord develops into the brain in vertebrates.

Compare and Contrast: Endoskeleton (Vertebrates) vs. Exoskeleton (Arthropods) Made of living cells internal Grows as the animal grows Gives muscles a place to attach supports protects Made of non-living material external sheds periodicall y

Vertebrate Phylogeny • Look at Figure 30 -2 on page 768 1) What does this diagram demonstrate? Evolution of major features 2) Where would you place the derived character “vertebrae” on the main branch? between the nonvertebrate chordates and jawless fish 3) What does this say about the relationship between reptiles and birds? they are most closely related to each other 4) What derived character would you put on the branch to birds only? feathers 5) What derived characters do all animals have in common on this cladogram?

There are two groups of Non-Vertebrate Chordates: Tunicates (the other 4%) Lancelets • No fins or legs • Filter feeders • Live in sand • Larva and Adult are quite different • Cephalization • Pharynx- for feeding in form and gas exchange • Larva has all four • Gills are part of chordate pharynx characteristics • CCS- no true heart • Adult is sessile • Paired muscles Common Ancestor Evidence: Fossils from Cambrian Period, Embryological Development

CHORDATE EVOLUTION (33 -1)

Chordate Orgins How do scientists study the origins of chordates? • Studying the embryos of living organisms • Indications that the most ancient chordates are most closely related to echinoderms. • Pikaia- an early chordate discovered by scientists in the Burgess Shale (Canadian Place with many Cambrian fossils). • Scientists also study a nonvertebrate chordate alive today: the tunicate. • Today, biologists study the genes that control the four traits of a chordate: Can you name all four?

Chordate Family Tree • Look at Figure 33 -2 on page 850 1) What does this diagram demonstrate? Evolution of major features 2) What do the colored branches represent? The traditional groupings of these animals 3) Which group is considered the “out group”meaning the one that is outside of the first adaptation? Tunicates and lancelets 4) What animals have amniotic eggs? reptiles, birds, and mammals 5) What derived characters separates lampreys from sharks? jaws and paired appendages 6) What is believed to be the common ancestor of all these

Evolutionary Trends in Vertebrates Adaptive Radiation- the rapid diversification of species as they adapt to new conditions. (notable derived characters) Over the course of evolution, the appearance of new adaptations like jaws and paired appendages has launched adaptive radiations in chordate groups. Convergent Evolution- adaptive radiations that produce species that are similar in appearance and behavior even though they are not closely related. How does this happen? Animals in similar ecological conditions evolved similar adaptations.

Chordate Diversity • 96% are vertebrates that make up 50, 000 species throughout the world. • The six living groups are: nonvertebrate chordates, fishes, amphibians, reptiles, birds, and mammals. Chordate Diversity Nonvertebrate Chordates Jawless Fishes Sharks and Relatives Fishes Amphibians Reptiles Birds Mammals

CONTROLLING BODY TEMPERATURE (33 -2)

Body Temperature and Homeostasis Why is it important for animals to body temperature to maintain a certain range? (think of chapter 2) metabolic processes/chemical reactions only take place within a certain “operating range. ” The control of body temperature is important for maintaining homeostasis in vertebrates, particularly in habitats where the temperature varies with time of day and season. All methods of controlling body temperature incorporate three important features: 1) A source of heat 2) A way to conserve heat

Generating and Controlling Body Heat: Animals are classified in two main groups: 1) Ectotherms 2) Endotherms Ectotherm- body temperature is mainly determined by the environment. • Most reptiles, fishes, and amphibians are ectotherms- they pick up heat from their environment and lose heat to their environment. • Most bask in the sun for heat, and burrow unground to cool down. • Ectotherms have low metabolisms when resting, thus generating little heat. • When active, the heat that is generated is lost to the environment due to the lack of insulation.

Endotherms Endotherm- body temperature is controlled from within. Birds and mammals are endotherms- they can generate and retain heat inside their bodies. Endotherms have high metabolisms even when resting, thus generating a significant amount of heat. • Birds retain heat primarily through their feathers serving as insulation. • Mammals have body fat and hair for insulation. • Mammals also get rid of excess heat through sweating and panting.

Endothermy Ectothermy Pro- move around easily Pro- Need much less during cool nights food to keep metabolic because they generate where it needs to be. and retain their own heat In environments where Con- Requires a lot of temperature is steady, fuel to keep up that ectothermy is more metabolic rate. effcient. Con- But in enviroments where there are swings in temperature, it takes a long time to warm up or cool down.

Evolution of Temperature Control There is little doubt that the first land vertebrates were ectotherms. But there is doubt as to when endothermy developed. Theory #1 - Some dinosaurs were endotherms Theory #2 - Endothermy evolved long after the dinosaurs Theory #3 - Endothermy evolved more than once: Line 1 - Reptiles to Birds Line 2 - Reptiles to Mammals

FORM AND FUNCTION IN CHORDATES (33 -3)

Nonvertebrate chordates represent very simple body systems, but that does not mean they are inferior. Lancelets and Tunicates are simple, but have survived to present day to perform the essential functions of life. Vertebrates exhibit a wide range of organs and organ systems that are specialized to perform many functions and maintain homeostasis. Feeding and digestion help maintain homeostasis by providing the body with a continuous supply of nutrients.

Example of Adaptations for Feeding: • Teeth adapted to strain food from water (filter feeders) or to eat meat (carnivores) • The digestive systems of vertebrates have organs that are well adapted for different feeding habits: - Carnivores: short digestive tracts with enzymes - Herbivores: long digestive tracts with bacteria Respiration As a general rule, aquatic chordates use gills for respiration. Land vertebrates use lungs. However, there are many exceptions to this rule: several fishes have both lungs and gills.

Additional Respiratory Structures that aid in respiration: • Nostrils, mouth, throat • Trachea • Air sac • Operculum How do gills work? Water passes over gill filaments, oxygen molecules diffuse into blood through capillaries. At the same time carbon dioxide diffuses from the blood to the water. Water and carbon dioxide are pumped out of fish through the operculum (gill slits). How do lungs work? Oxygen rich air is inhaled into the trachea then to lungs, oxygen diffuses into blood through capillaries, carbon dioxide diffuses out, oxygen-poor

From amphibians to reptiles to birds to mammalsthe surface area of lungs increases (birds are slightly different in form). • Amphibians- a little sac with ridges for more surface area. • Reptiles- lungs divided into chambers for more surface area. • Mammals- lungs branch extensively, filled with aveoli- bubble-like structures that provide surface area in lungs. Air must travel two-ways (in and out in same passages) • Birds- one-way system of tubes and air sacs that allow birds to fly at high altitudes where there is

Circulation Circulatory systems maintain homeostasis by transporting needed materials throughout the body. Single Loop vs. Double Loop Circulation Single Loop is for animals that use gills for respiration: Blood travels from heart- to gills- to the rest of the body- back to Question: the heart in one circuit. Why do you think the blood goes to the gills first, then the rest of the body? Answer: Because oxygen is picked up from the water and then it is carried to the rest of the body.

Double Loop is for animals that use lungs for respiration: Loop #1: Carries blood between heart and lungs -Oxygen-poor blood goes to the lungs - Oxygen-rich blood goes back to heart Question: Loopblood #2: Carries blood between the heart and the How does become body. “oxygen-poor? ” - Oxygen-rich blood goes to body Answer: Oxygen diffuses-from the poor blood goes back to heart vessels out to body blood tissues and organs to be used for cellular processes.

Heart Chambers During the course of chordate evolution, the heart developed chambers and partitions that help separate oxygen-rich blood from oxygen-poor blood. Fishes and Larval Amphibians: 2 -chambered heart Atrium: receives blood from the body Ventricle: pumps blood to the gills and then the rest of the body. Adult Amphibians: 3 -chambered heart Left Atrium : receives oxygen-rich blood from lungs Right Atrium: Receives oxygen-poor blood from the body *Both Atria: Empty into the ventricle Ventricle: There is a “flow” that dictates that

Reptiles: 3 -chambered heart *Same as Adult Amphibians except: Ventricle: There are partial partitions to allow for less mixing of oxygen-poor and oxygen-rich blood Crocodilians, Birds, Mammals: 4 chambered heart Left and Right Atria- same as 3 chambered Left and Right Ventricles- completely partitioned so there is no mixing of

On the pictures below, first write the type of heart demonstrated on the line, then, outline the oxygen-poor blood in blue and the oxygen-rich blood in red. (see pg. 860 for help) ____________

Excretion Excretory Systems help maintain homeostasis by eliminating nitrogenous wastes from the body. Nitrogenous wastes are produced from the breakdown of proteins and are first in the form of ammonia- toxic until converted or released from body. Nonvertebrate chordates use gills and gill slits to rid themselves of nitrogenous wastes. Most vertebrates use kidneys- system of tubes that filter blood and remove wastes.

Response • Compared to invertebrates, most chordates have elaborate systems that allow them to respond to stimuli in their environment. • Nonvertebrate chordates have a relatively simple nervous system with a mass of nerve cells that form a brain. • Vertebrates have a more complex brain with distinct regions that specialize in function. • Vertebrate brain regions: 1) olfactory bulb 4) cerebellum 2) cerebrum 5) medulla oblongata 3) optic lobe

Structure Function Olfactory bulb Sense of smell Cerebrum “thinking” region of brain, receives, interprets, and determines the response of sensory information, learning, memory, conscious thought. Optic lobe Vision Cerebellum Coordinates movement, controls balance Medulla Oblongata Functioning of many internal organs

Movement • Nonvertebrate chordates: no bones, but they do have muscles. • Vertebrates: the skeletal and muscular systems support a vertebrate’s body and make it possible to control movement. • Skeletons can be bone or in the case of sharks and their relatives: cartilage. • Most vertebrates have ligaments that connect the bones and allow for flexibility without breaking. • Most vertebrates have girdles that support fins or limbs. • Fishes and Snakes: main muscles in blocks on either side of the backbone and contract in waves. • Amphibians and Reptiles: Limbs stick out

Reproduction • Almost all chordates reproduce sexually. • In general, evolution shows a trend from external to internal fertilization. • After fertilization the development of chordates can be: 1) oviparous- eggs develop outside the mother’s body; nutrition for embryo from yolk. ex: fish, amphibians, birds 2) ovoviviparous- eggs develop inside of mother, embryo gets nutrition from yolk in the egg. ex: sharks 3) viviparous- development inside of mother’s body, embryo gets nutrition directly from mother. ex: mammals • Some vertebrates care very little for their young