Download Vertebrate Biology

Vertebrate Diversity
Phylogeny
I.
P. Chordata
II.
Invertebrate SubPhylum Urochordata
III.
Invertebrate SubPhylum Cephalochordata
IV.
Vertebrate Subphylum Vertebrata
V.
Superclass Agnatha (Jawless)
VI.
A.
B.
C.
D.
E.
F.
Superclass Gnathostomes (Jaws)
C. Chondrichthyes
C. Osteichthyes
C. Amphibia
C. Reptilia
C. Aves
C. Mammalia
Notes:
1.
C-F are tetrapods—possess two pairs of limbs
2.
D-F have additional adaptations for terrestrial life including amniotic eggs (see below)
Chordate Diversity
I.
A.
1.
2.
Distinguishing Characteristics
Background
Chordates are bilaterally symmetrical deuterostomes with three germ layers
Chordates have a segmented body, complete digestive tract and a well-developed coelom
B.
All chordates share four distinguishing characteristics that are exhibited at sometime during the
life cycle:
1.
2.
3.
4.
Notochord
a.
Most primitive support structure of the chordate body
b.
Persists throughout life as the main axial skeletal support in lancelets and lampreys
c.
In fishes, amphibians, reptiles, birds and mammals the notochord is later partially or
completely replaced by the vertebral column
Dorsal hollow nerve cord
a.
Forms on the dorsal surface of the early embryo shortly after the gastrula stage
b.
Anterior end becomes enlarged as a simple "cerebral vesicle" in tunicate larvae and in
lancelets
c.
In all vertebrates it thickens and differentiates into a tripartite brain
Pharyngeal gill slits develop on the sides of the embryonic pharynx
a.
Gill slits function in feeding in primitive chordates and in respiration in more advanced
chordates
Post-anal tail
a.
In most invertebrates the anus is located at the posterior end of the body
b.
In vertebrates a part of the trunk extends posterior to the anus
c.
Provides a mechanism for using the segmented musculature of all vertebrates for more
effective propulsion
5.
Endostyle
a.
Some authors list a fifth character
b.
In cephalochordates the endostyle is a groove in the base of the pharynx
i.
S similar structure is present in tunicates
c.
Mucous passes over the gills, traps small particles of food and passes along the
endostyle into the gut
d.
Endostyle also produces mucous and iodine containing compounds
i.
Thyroid gland is present in all vertebrates and believed to have been derived
from the endostyle
II.
Phylum Hemichordata: (Acorn worms)
A.
1.
2.
3.
4.
5.
Evolutionary significance
Exhibit characteristics of both echinoderms and chordates
Larval form (known as the tornaria larva) is similar to the echinoderm bipinnaria larva
Hemichordates also possess pharyngeal gill slits (a chordate characteristic)
Some classification systems have regarded the hemichordates as a subphylum of the Chordata
a.
Based on the presence in hemichordates of a stomochord
i.
Some authors consider to be homologous with the notochord of chordates
b.
Short dorsal nerve cord which may be hollow
Most taxonomists prefer to place hemichordates in a separate phylum
III.
A.
Phylum Chordata
Subphylum Urochordata (tunicates or sea squirts)
1.
Characteristics
a.
Marine filter-feeders
b.
Sessile
i.
Attach to rocks or some other stationary object
c.
Do not exhibit most chordate characteristics as adults
i.
Only have pharyngeal gillslits
d.
Larval stage has a notochord and other chordate features
B. Subphylum Cephalochordata (Lancelets)
1.
2.
3.
Chordate characteristics as an adult:
a.
Notochord
b.
Dorsal nerve chord
c.
Gill slits
d.
Post-anal tail
Features associated with burrowing lifestyle
a.
Notocord extends to the tip of the rostrum
Similar features as earliest vertebrates
C.
1.
2.
3.
4.
5.
6.
Subphylum Vertebrata
Vertebral column (either bony or cartilaginous)
a.
Replaces the notochord as the axial support for the body
b.
Nerve cord runs through openings in the vertebrae
c.
Axial skeleton permits larger size, and stronger, faster movement
Anterior part of the nerve cord is elaborated into a brain
a.
Divided into three parts
Cranium surrounds brain
Endoskeleton
a.
Jointed
b.
Two pairs of appendages
c.
Functions
i.
Provides support to the body
ii.
Provides surface area for muscle attachment
iii.
Enables an animal to attain large body size
d.
Endoskeleton may be comprised of:
i.
Bone
ii.
Cartilage
iii.
Combination of a & b
e.
Endoskeleton is alive and can grow
f.
Exoskeletons are for protection and are not alive
Closed circulatory system
a.
Ventral heart with two or more chambers that pump blood
b.
Blood is oxygenated in either lungs or gills and transported via arteries and veins
Other distinctive features:
a.
Kidney composed of tubules (of mesodermal origin)
b.
Unsegmented gonads
c.
Paired eyes, ears, and nasal openings
d.
Separate sexes are the rule
D.
1.
Superclass Agnatha (Lamprey)
Characteristics
a.
Most primitive of the vertebrates
b.
Lack jaws and paired appendages
c.
Parasites or scavengers
E.
1.
Superclass Gnathostomata
Characteristics
a.
Jaws
i.
Evolved from skeletal structures that had previously supported the pharyngeal
gill slits
2.
Six classes
a.
Subgrouped I and II
i.
Gnathostomata II are tetrapods
F.
Superclass Gnathostomata I: Class Chondrichthyes (Shark and rays)
1.
Features
a.
Cartilaginous skeleton
i.
Loss of bone is probably secondary, not primitive
b.
Elastic and lighter than bone
c.
Carnivorous (most)
d.
Tough skin covered with minute placoid scales and possesses many mucous glands
e.
Median and paired fins are present, all supported by fin rays
f.
Mouth is ventral
i.
Has upper and lower jaws
ii.
Rostrum anterior to the mouth
g.
Heterocercal tail
i.
Vertebral column turns dorsally into the upper lobe of the tail
h.
Internal fertilization
i.
Males have claspers on pelvic fins to transfer sperm into female reproductive
tract
i.
Have a spiracle—take water in and out over gill slits
j.
Lateral line—sensory organ, water pressure and vibrations
Placoid scale
a.
Basal plate embedded in the dermis
b.
Spine projects from this plate
i.
Perforates the epidermis and projects caudally
c.
Dermal denticle resembles a tooth in that it contains a pulp cavity, a thick layer
of dentine and a surface covering of enamel
2.
G.
Superclass Gnathostomata I: Class Osteichthyes (Bony fishes)
1.
Characteristics
a.
Operculum
i.
Flap attached to the first gill arch that covers all of the gill openings
b.
Spiracle is absent in modern bony fish
c.
Scales lack enamel and dentine
i.
Thin and translucent bony structures that are covered by the epidermis
d.
Skin usually contains many mucous glands
i.
Mucous reduced drag
e.
Paired and median fins; modern bony fishes have pectoral and pelvic fins that are
located anteriorly
i.
Paired fins with a bony supporting structure
ii.
Pectoral fins are just behind head; pectoral girdle attached to skull; fish have no
necks.
iii.
In most modern bony fish, pelvic fins are located very anteriorly; in primitive
fishes they were posterior in position
f.
Axial skeleton
i.
Similar vertebrae and ribs all along the body
ii.
No regional differentiation
iii.
Aids in locomotion--series of S-shaped curves
g.
Skeleton is highly ossified in most species
h.
Homocercal tail (symmetrical)
i.
Swim bladder—provides bouyancy
j.
Most are oviparous with external fertilization
H:
1.
2.
3.
4.
I.
1.
2.
Superclass Gnathostomata II: Class Amphibia
Three orders:
a.
Urodela (salamanders)
b.
Anura (frogs)
c.
Apoda
Mode of reproduction
a.
Primitive
b.
Eggs lack protective membranes or a shell
i.
Small with little yolk for the developing embryo
ii.
Eggs are laid in the water and fertilized externally
c.
Embryo hatches at a very immature stage
i.
Water-dwelling larva with gills
d.
Larva undergoes metamorphosis
i.
Gills are lost, lungs develop, and the animal may become completely terrestrial
Amphibians were the first vertebrates to move onto land
a.
Most amphibians are restricted to moist habitats, and need water to reproduce
i.
Skin is used as an accessory breathing organ
Major adaptations of amphibians to land life:
a.
Limbs
i.
Modified to support the body
ii.
Shoulder girdle is no longer tied to the skull
iii.
Pelvic girdle is anchored to the vertebral column
b.
Lungs
a.
Present in the fishes ancestral to amphibians
i.
Preadaptation for land life
Superclass Gnathostomata II: Class Reptilia
Defining feature
a.
Means of reproduction
i.
Amniote or cleidoic egg
ii.
Independent of water
Amniotic egg:
a.
3.
4.
5.
J.
1.
2.
3.
4.
5.
6.
K.
1.
Contains a large amount of yolk so that the young do not hatch as larvae, but as
miniature adults
b.
Egg is surrounded by a shell (prevents desiccation)
c.
Membranes:
i.
Chorion--prevents desiccation
ii.
Amnion—contains the embryo; enclosed watery environment
iii.
Allantois--stores nitrogenous waste as the insoluble, non-toxic compound uric
acid
Fertilization is internal
a.
Reptiles have separate sexes and males have copulatory organs to deposit sperm
Additional characteristics include:
a.
Dry, cornified skin
b.
Ectotherms
i.
Need behavioral adaptations to maintain body temperature
Extant orders:
a.
Chelonia--turtles
b.
Squamata—lizards and snakes
c.
Crocodilia—alligators and crocodiles
Superclass Gnathostomata II: Class Aves (Birds)
Highly modified for flight
a.
Most of the defining characters are related to means of locomotion.
Characteristics
a.
Feathers
b.
Endothermic thermoregulation
i.
Permits enhanced metabolic activity
c.
Modified bones
d.
Four chambered heart
i.
Separate pulmonary and systemic circuits
e.
Amniote egg
Anatomical modifications
a.
Honeycombed bones—strength while reducing weight
b.
Reduced organ systems to minimize weight
c.
No teeth
Metabolic changes that enable energy production
a.
Endothermic
b.
Four-chambered heart (blood segregation)
Advanced nervous system—vision and sensory integration
Skeletal modifications—keel on sternum to anchor pectoral muscles
Superclass Gnathostomata II: Class Mammalia
Characteristics:
a.
Mammary glands—milk for young
b.
Endotherms with active metabolism
c.
Hair—comprised of keratin; did not evolve from scales; insulation
d.
Four-chambered heart—segregates oxygenated and non-oxygenated blood
e.
Differentiated teeth
f.
Separate sexes; viviparous with nutrients across placenta
2.
3.
Most primitive living mammals: monotremes
a.
Lay eggs
b.
Have mammary glands
i.
Nurse their young
c.
Have hair
i.
Insulation
ii.
Sensory
Mammals that give birth to live young
a.
4.
Marsupials
i.
Very immature young and nurse them in a pouch
b.
Placentals
i.
Live young that are much more highly developed
Advantages of live young:
a.
Young are automatically kept warm and protected
b.
Degree of development is not limited by the amount of stored yolk
i.
Degree of development depends on nutrients available
c.
Degree of development not limited by length of gestation
i.
Amount of nitrogenous wastes that build up