Vertebrate Zoology Lecture Notes

• Introduction to the subphylum Vertebrata, Chapter 26
• Additional grouping of the subphylum Vertebrata:
• Adaptations
• Fossil Record of Vertebrate Animals
• The Fishes
• The Amphibians

Introduction to the subphylum Vertebrata, Chapter 26

Additional grouping of the subphylum Vertebrata:

• group pisces (fish)
  Classes
1. Myxini
2. Cephalaspidomorphi
3. Chodrichthyes
4. Osteichthes
• group tetrapoda
  Classes
1. Amphibia
2. Reptilia
3. Aves
4. Mammalia
• group anamniota
  Classes
1. Myxini
2. Cephalaspidomorphi
3. Chodrichthyes
4. Osteichthes
5. Amphibia
• group amniota
  Classes
1. Reptilia
2. Aves
3. Mammalia

Adaptations

• Living Endoskeleton
1. Advantages

Growth

can grow with the body, thus allowing very large size and nearly unlimited body size.

Jointed scaffolding for muscles

provides jointed attachment structure for muscles which in turn support, protect, and cushion the skeleton.

1. Composition

Cartilage

translucent elastic tissue; the basic form is called hyaline cartilage which has a clear, glassy appearance; is composed of cartilage cells called chondrocytes surrounded by a firm, complex protein gel interlaced with a meshwork of collagen protein fibers. The endoskeleton of some spp. is composed exclusively of cartilage.

Bone

living tissue having significant deposits of inorganic calcium salts laid down as an extracellular matrix.
Most bones develop from cartilage (endochondral bone).
Embryonic cartilage gradually erodes away; bone-forming cells deposit calcium salts around strand-like remnants of the original cartilage.
Bone is the major component of most vertebrate endoskeletons with some cartilage present as well.

• Advantages of bone over cartilage:
1. Bone serves as a reservoir of phosphate in the form of calcium phosphate; phosphate is important for energy production (ATP), membrane formation (phospholipids), and nucleic acids (DNA and RNA).
2. Bone is extremely strong.
• Pharynx and efficient respiration
1. Circulation to the internal gills of aquatic animals is more efficient through the pharyngeal gill slits and openings over most invertebrate forms of aquatic respiration which occurs by variously modified means.
2. The ventral heart, closed circulatory system, and distinct pulmonary and systemic components of the circulatory system allow for more efficient aquatic and terrestrial gas exchange and eventual circulation of oxygenated blood throughout the body.
• Advanced nervous system
1. Centralization of the nervous system:
1. Cephalization - anterior, true head of a cranium containing and protecting the brain and certain external, paired sense organs.
2. Sense organs suited for distance perception.
2. Specialization of paired sense organs:
1. Eyes with lenses and specialized retinas.
2. Pressure receptors such as paired ears designed for equilibrium and sound reception.
3. Chemical receptors, such as taste receptors and olfactory organs for smell.
• Paired limbs
  Pelvic and pectoral appendages are present in most vertebrates in the form of paired fins or jointed limbs. Jointed appendages are suited for life on land because they permit levering motions against a substrate.

Fossil Record of Vertebrate Animals

Jawless Ostracoderms (shell, skin)

Deepest vertebrate fossils are fragments of bony armor discovered in Ordovician rock [geological period corresponding to approx. 500 million to 425 million years before present (BP) in geological or atomic years based on radioisotope dating] in Russia and in the US.

The fossils represented organisms that were small, jawless forms collectively called ostracoderms (shell, skin).

The ostracoderms belong to the Agnatha superclass and consisted of three groups:

• Heterostracans - lacked paired lateral fins.
• Cephalaspids (head, shield) - had paired lateral fins; largest genus was Cephalaspis - had a bony shield around head and a bony armor protecting the remainder of the body.
• Anaspids (without shield) - had paired lateral fins but lacked the bony shield around the head.

Jawed Placoderms (plate skin)

Deepest jawed vertebrate fossils are of two placoderm groups:

• Devonian placoderms - large bony plates below epidermis; few, large fins.
• Acanthodians - several, small bony plates below epidermis; several, small fins.

The Fishes

Jawless Fish, Chapter 27

Phylum Chordata

Subphylum Vertebrata

• Cartilaginous fishes: Class Chondricthyes (page 471)
  Sharks, skates, and rays.
  Characteristics:
• 1. Fins: (Figure 23-5)
  a. Caudal fin - tail or posterior fin.
  b. Paired pectoral fins - ventral and posterior to external gill openings.
  c. Paired pelvic fins - ventral and posterior to pectoral fins.
  d. 2 dorsal median fins
  2. Mouth: ventral with jaws; olfactory sacs do not open into the oral cavity.
  3. Placoid scales on skin - scales that are composed of dentin and are covered with enamel-like substance (denticles sp.); modified placoid scales serve as teeth.
  4. Endoskeleton entirely cartilaginous; notochord persists in adult; vertebral column is complete and separate from the notochord.
  5. Digestive system of a "J"-shaped stomach, intestines, liver, gallbladder, and pancreas.
  6. Circulatory system of several pairs of aortic arches; dorsal and ventral aorta, capillary and venous systems, hepatic (liver) portal and renal (kidneys) portal systems; 2-chambered heart; high []'s of urea and trimethylamine oxide in blood (nitrogenous waste products typical of carnivorous animals which take in more nitrogen than needed): protein (polymer of amino acids) -----> Single amino acids.
  7. Gaseous respiration by means of 5 to 7 pairs of gills with separate, external gill slits.
  8. NO SWIM BLADDER!
  9. Brain of 2 olfactory lobes, 2 cerebral hemispheres, 2 optic lobes, a cerebellum, and a medulla oblongata; 10 pairs of cranial (skull) nerves. (page 644)
  Cerebellum - controls balance and coordination - small region that lies just above the medulla.
  medulla - most posterior region of the brain that is really a conical continuation of the spinal cord; together with the midbrain, makes up the "brain stem" or medulla oblongata. Regulates subconscious activities such as heartbeat, respiration, etc.
  10. Sexes are separate; paired gonads (sex organs: ovaries in females and testes in males); reproductive ducts open into the cloaca (excretory structure); sex organs and excretory organs.
• Sharks
  Reproduction:
  Sperm from the testes of the male is carried by the wolffian ducts to the cloaca and is excreted during intercourse; The male uses specialized modifications in the pelvic fins (claspers) to deposit the sperm into the female oviduct; The oviduct retains unfertilized eggs from the ovary until they are fertilized; After fertilization, the zygotes develop within a modified portion of the oviduct which becomes the uterus; Within the uterus, a primitive placenta may form and attach developing embryos to the uterus wall and to the mophenus (coelom wall) until the shark is born; Following birth, the uterus and newborn shark are both released from the mother; The uterus may remain attached to the young shark for a short time; This type of reproduction where the embryo is attached to the mother's uterus wall is called viviparous reproduction; In some species of sharks, the mother retains the developing embryos within the uterus without attachment to the uterus wall ovoviviparous reproduction; Some other shark spp. will lay large, yolky eggs immediately after fertilization. this is called oviparous reproduction.; Finally, some sharks and rays deposit fertilized eggs in a capsule called a "mermaid's purse" which is often attached to seaweed. The young sharks or rays will later emerge from this structure.
• Rays
  includes skates, electric rays, sawfishes, stingrays, eagle rays, and manta rays. All are bottom dwellers (benthic)
  have greatly-enforced pectoral fins that are fused to the head and used like wings for swimming; external gill openings are on the ventral side of the body; water (for breathing) is taken through the spiracle on the dorsal side; feed on mollusks, crustaceans, and occasionally, fish.
  Sting rays have a slender whip-like tail that is armed with one or more saw-edged spines with venom glands. The wounds are very painful and heal very slowly.
  Electric rays produce a high-amperage current by the simultaneous discharge of electricity. The voltage output is very low, but the power output may reach several kilowatts. This is enough to stun prey or ward off predators.
• Chimaeras
  small subclass of cartilaginous fishes such as ratfish, rabbitfish, spookfish, and ghostfish; 25 spp. today; anatomically appear as an odd mixture of shark-like and bony fish features; instead of a toothed mouth, their jaws bear large, flat plates; The upper jaw is completely fused to the cranium, which is very unusual in fish; eat seaweed, mollusks, echinoderms, crustaceans, and other small fish; not a commercial sp. and are seldom caught; despite their ugly appearance, they are rather colorful. (page 475, Figure 23-14)
• Bony fishes: Class Osteichthyes
  General Characteristics:
  1. Bony skeleton (mostly); most primitive or simple skeleton in the vertebrate animals; numerous vertebra; notochord may persist; post anal tail present in adults.
  2. 3 types of dermal scales:
  a. Ganoid scales - diamond-shaped; simple scales with layers of silvery enamel on upper surface and bone on the lower surface.
  b. Cycloid scales - thin, flexible scales of dermal material arranged in roughly, concentric circles with smooth margins.
  c. Ctenoid scales thin, overlapping dermal scales of advanced bony fishes; exposed posterior margins are rough with fine, toothlike spines.
  d. some without scales.
  No placoid scales on any bony fish.
  3. Fins both singly and a median; also paired lateral fins.
  Fins have rays of cartilage or bone.
  4. Mouth with many teeth and movable jaws (some toothless fish do exist.). Olfactory sacs paired and may or may not open into the oral cavity.
  5. Respiration by gills supported by bony gill arches and covered by a common operculum - opening for water passage to outside from internal gill cavity.
  6. Swim bladder usually present with or without a duct connected to the pharynx.
  7. Circulation system of a 2-chambered heart, arterial and venous vessels, and usually four pairs of aortic arches; blood contains nucleated red cells.
  8. Nervous system of a brain with small olfactory lobes, cerebrum. Large optic lobes and cerebellum; 10 pairs of cranial nerves.
  9. Sexes separate (sex reversal in some spp.); gonads are paired; fertilization usually external; larval forms may differ greatly from adults.
  Classification:
  Three distinct groups:
  1. Lobe-finned fishes: have fins and bony rays and lobes of bone-less areas lacking rays.
  Simple, primitive type of fishes:
  The coelacanth is a simple bony, lobe-fin fish which was once thought to be extinct, but was found living off the coast of south Africa in 1938.
  2. Lungfishes: Simple bony fishes represented today by only 3 genera; resemble lobe-fins (have lungs and lobed fins).
  Although they have gills and lungs, they cannot survive outside of water; can come to the surface and gulp air. Another sp. actually can breathe air for long periods of time; can burrow into mud and form a cocoon to survive the summer in tropical regions where some regions dry p. The medial fins are fused to make one large, continuous fin.
  3. Ray-finned fishes: Large (21,000 sp.) group of bony fishes. Most common and familiar type of bony fish. Fins entirely composed and supported by rays; no lobes present.
• Structural and Functional adaptations:
  1) Locomotion in water - driven by powerful trunk and tail muscle that flex and extend in a "zigzag" pattern.
  2) Buoyancy and the swim bladder:
  All fishes are slightly "heavier" (more dense) than water because their skeletons and other tissues contain heavy elements that are present only in trace amounts in natural waters. To keep from sinking, sharks must always keep swimming and moving forward in the water. The asymmetrical (heterocercal) tail (caudal fin) of sharks provides the necessary tail lift as it sweeps back and forth in the water. The broad shark head and flat pectoral fins act as angled planes to provide head lift.
  Sharks also have great buoyancy by having very large, fatty, livers composed of low density squalene(Squalus sp.) = fatty (oily) material that helps provide buoyancy. In bony fishes, buoyancy is provided by an efficient swim bladder - a gas-filled organ that regulates the buoyancy of the fish body.
  The amount of gas (oxygen diverted from gills or lungs (if present)) regulates the degree of buoyancy and the depth at which the fish remains. Can change depth (water level by adjusting the amount of gas in swim bladder. Some fish have to "gulp" air from above the water surface to fill the swim bladder. e.g. trout.
  The gulped air is forced into the swim bladder through a pneumatic duct which connects the swim bladder to the esophagus. The more advanced fishes have a gas gland which secretes gas into the swim bladder.
  3)Fish Respiration:
  A)Gills - respiratory organs which are composed of their filaments covered with a thin epidermal membrane that is folded repeatedly into platelike gill lamellae - tissue richly supplied with blood vessels for gas exchange. The gills are located inside the pharyngeal cavity and are covered by the operculum. Flap of tissue which covers the gill - protects the gills.
  B)Lungs - allow some fish to breathe air, but are not developed enough to provide 100% of the fish's respiratory needs. Most of the oxygen that fish breathe is provided by the dissolved oxygen in the water and therefore must be respired by gills.
  4)Osmotic regulation: Fresh water is very dilute with respect to [salt] (salinity). The fresh water salinity is much lower than that of the blood of freshwater fishes.
  Water: tends to enter the cells osmotically and salt is lost due to diffusion. Most of the water intake and salt loss occurs across the gills.

Classification of class Osteichthyes

• subclass Actinopterygii, ray-finned fishes
• superorder Chondrostei, primitive ray-finned fishes
• superorder Neopterigii (Teleostei), modern bony fishes
• subclass Sarcopterygii, fleshy-finned (lobe-finned) fishes, e.g. coelacanth

THE AMPHIBIANS

• Phylum Chordata
  Subphylum Vertebrata
  Class Amphibia
  Amphibia = Gr. amphi - both or double; bios = life
  The Frog Life Cycle:
  Masses of fertilized eggs ---hatching---> limbless, gill-bearing tadpole larvae ---feed and grow--->---transformation(metamorphosis)--->hind legs appear and gradually lengthen.
  The tail shortens; larval teeth are lost; gills are replaced by lungs. Eyelids develop and forelegs emerge.
  In a matter of weeks the aquatic tadpoles has completed its metamorphosis to an adult frog.
  The amphibians themselves are not completely adapted to land and are therefore referred to as quasiterrestrial, hovering between aquatic and land environments. This double life style is reflected by their class name, Amphibia. Structurally, they are similar to both fish and reptiles. Although they are adapted for terrestrial life, they rarely can stray from moist conditions.
  The 3900 spp. of amphibians are grouped into 3 orders:
  1. salamanders (order Caudata or Urodela)
  2. frogs and toads (order Anura or Salientia)
  3. the secretive, earthworm-like tropical caecilians (order Gymnophiona or Apoda) - limbless amphibians
• I. Comparison and contrast of terrestrial and aquatic habitats
  Animals are mostly water; therefore, many structural and functional characteristics are necessary for survival on land. Amphibians have most of these characteristics that all land animals have which allow survival on land.
  1. Difference in water content --aquatic environments always present (available).
  - terrestrial environments -- availability of water (humidity amount of water is extremely variable. Less water overall.
  2. Greater Oxygen content of air.
  -aquatic animals spend more energy extracting oxygen from the water than do land animals from air.
  3. Water is more dense -- provides buoyancy and allows for good support even though more difficult to move through than air.
  -survival on land requires (for large animals) a good, strong skeleton for support.
  4. Constancy of water temperature
  - water has high heat capacity; does not change temperature much unless large amounts of heat are added or removed. Most aquatic animals, especially marine spp. do not have problems with the drastic temperature changes that occur on land.
  5. Higher variety of habitats on land as opposed to aquatic environments.
  6. Greater opportunities for breeding on land. Safe shelter for eggs is more readily available on land than in water.
• II. Origin and relationships of Amphibians
  Land animals must be able to support their own weight, resist drying, cope with rapid temperature changes, and extract oxygen from air .
  Requirements for Land Survival
  A. Lungs - absolutely necessary for respiration (self-supporting and internal) on land.
  - gills, with their fine filaments and gill lamellae require water to prevent collapse and desiccation
  - along with lungs, a more efficient circulatory system is required; all fishes have a 2 -chambered heart which pumps blood through gills to get oxygen and from there to the remainder of the body before returning to the heart. This single circulation system is okay for aquatic animals whose bodies are surrounded by water from which oxygen can diffuse into some parts of the body. Also, aquatic animals are metabolically less active and therefore do not require a highly efficient circulatory system.
  On land, however, thick skins are important to prevent desiccation but restrict diffusion of oxygen form the air. Also, many terrestrial animals have a very high metabolic activity. Therefore, a very efficient circulatory system (in addition to the presence of lungs) is needed to meet the demands of terrestrial life. All land vertebrates have a double circulatory system which allows oxygenated blood to be returned directly back to the heart before being pumped to the rest of the body.
• Components of the double circulatory system:
• 1. Pulmonary circulation-supplies the lungs with oxygen and provides a short, quick and efficient way of getting blood from the heart to the lungs where it can "pick up oxygen", supply the lungs with oxygen as well, and then return to the heart so that oxygen can then be transported to the rest of the body.
  2. Systemic circulation-supplies blood with oxygen to all of the body except the lungs.
  B. Limbs for travel on land.
  Requirements:
  a) strong, bony endoskeleton for support.
  b) very well developed muscle system for movement.
  c) well-developed CNS for coordination of muscles used to move the skeletal elements and move the body.
  The fossil record indicates that amphibians appeared abruptly in the record as fully-developed amphibians with all of the characteristics aforementioned present and very well developed: a.) all have (had) lungs b.) all have (had) 3 chambered heart for double circulation c.) all have (had) very well-developed limbs d.) all have (had) very well-developed skeletal system e.) all have (had) very well-developed muscle system f.) all have (had) very well-developed CNS ***** No transitional forms found in fossil record that would indicate any gradual appearance of these necessary, terrestrial vertebrate characteristics.
• Amphibian Characteristics (page 499 in book): 1. . . . . 11.
• Classification (page 499 also in book):
• Structure and Natural History
  1. Caecilians:
  members of an obscure order called Gymnophiona (naked snake).
  160 spp. of burrowing, worm-like amphibians.
  Found in tropical forests of South America (primarily), Africa, and south-east Asia.
  Characterized by long, slender body covered with small scales in some spp., no limbs and no postanal tail.
  Many spp. are blind as adults, have the name caecilians (caecus, blind).
  Because they are burrowers, the eyes are replaced by specialized sensory tentacles on the snout.
  Very rarely seen due to their burrowing nature.
  2. Salamanders, order Caudata (meaning tailed amphibian). Newts are also included in this order; they are a specific type of salamander; Least specialized of all amphibians; found in nearly all northern temperate and tropical regions; Most spp. are found in North America.
  Size: Most of them are small.
  The common North America salamanders are less than 15 cm long. Some species are aquatic and never produce true lungs: the gills are the major respiratory organ for the entire life cycle. these aquatic salamanders have all other amphibian characteristics. They can exist for short periods out of the water; some aquatic spp. are rather large (approx. 1 meter); The Japanese giant salamander reaches lengths > 1.5 meters. Salamanders have simple primitive limbs; most have 4 (tetrapod) but a few spp. have only 2 limbs. Most salamanders are carnivorous preying on worms, small arthropods, and small mollusks; most eat only things that are moving.
  ***Their food is rich in proteins; therefore, they produce lots of nitrogenous wastes, usually urea which is less toxic and requires less water for excretion.
  *** They use the carbon skeletons of the protein-derived amino acids for their catabolic (energy) and anabolic (biosynthetic needs); Therefore, they do not store much fat (lipid) or glycogen (storage form of glucose, similar to starch;*** Basically, the animal form of starch, less branched, is mostly a straight chain of polymerized alpha-glucose).
  ***Salamanders are ectotherms - derive heat from surroundings(external heat sources). Therefore, they have a low metabolic rate.
  Breeding:
  Terrestrial salamanders live in moist places under stones and rotten logs, usually not far from water. They do not show much diversity in regard to breeding habitats, due to the somewhat restricted habitats in which they are found. Fertilization of eggs is internal. The female picks up a packet of sperm Spermatophore) that has been previously deposited by the male on a leaf or stick. Aquatic species lay their fertilized eggs in small, group-like clusters under logs or in holes of soft dirt. Many spp. remain near eggs to guard them. The embryos of salamanders hatch from their eggs resembling their parents. The larvae do undergo metamorphosis during development, but not to the extent that tadpoles of frogs and toads do. American newts often have a terrestrial stage interposed between the aquatic larvae and the aquatic, breeding adults.
  Respiration
  All salamanders hatch with gills, but during development, they are lost in all except aquatic forms or in some spp. which do not undergo complete metamorphosis. Terrestrial salamanders have well-developed, fully functional lungs. Some salamanders have neither lungs nor gills and respire through their skin. The skin contains an extensive vascular network of capillaries which allow for gas exchange to take place just below the epidermis. This type of respiration through the skin is called Cutaneous respiration. Cutaneous respiration is facilitated by pumping air in and out of the mouth where further respiratory gas exchange can take place. The buccal (mouth) cavity has a highly vascularized membrane system that supplements cutaneous respiration in lungless, gill-less salamanders.
• Order Anura
  Frogs and toads; very specialized order of amphibians; very popular for educational purposes, but are actually poor representatives of the vertebrate body plan; why?
1. lack a visible neck
2. the caudal vertebra are fused into a urostyle (coccyx, tailbone) which is found, usually, in the more advanced vertebrates, e.g. mammals
3. Ribs are absent in some spp. and very reduced overall in other spp.; no true rib cage in most spp.
• Hindlimbs are greatly enlarged for leaping
  Salamanders would be a better choice for lab studies if frogs were not so readily available.
• Classification, taxonomy, etc.
  Frogs and toads are divided into 21 families; the most well-known North American families are:
1. Ranidae - most of our familiar frogs
2. Hylidae - the tree frogs
3. Bufonidae - toads; differ from frogs in that toads have:
1. shorter fore- and hindlimbs
2. stout, compact bodies
3. thicker skin
4. usually, skin is covered with prominent "warts" or "bumps (overall rough appearance and texture)
• etc.:
  
  The term toad is used rather loosely to refer to frogs and toads that tend to spend more of their life cycle in terrestrial habitats.
• size:
  
  The largest frog is the West African Gigantorana goliath; no lie, I'm not making this up! See Fig. 24-11, p. 504 of textbook. It is more than 30 cm in length from nose to anus, weighs 7.5 pounds - approx. size of a small baby (my daughter weighed 7.5 pounds at birth - born 3-weeks early); has been known to eat rats and even ducks (the frog, not my daughter).
  The smallest frog recorded is approx. 1 cm long (smaller than a dime); found in Cuba.
  Largest American frog is the bullfrog (genus Rana) which reaches a body length of 20 cm.
• Habitats and distribution:
  
  Most abundant and successful of the frogs are of the genus Rana (Gr. for frog).
  Found all over the temperate and tropical regions of the world except New Zealand, many islands, and southern regions of South America.
• Continuation of order Anura, family Ranidae, genus Rana

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