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Taxonomic relationships based on phylogenies -
considerations
Phylogenies are hypotheses can be falsified as new data comes
in
When is a character derived vs. ancestral? Need a good outgroup
(closest relative of the ingroup)
Vertebrate phylogeny reconstruction A continual process Allows
us to formulate hypotheses about the sequence of evolution of
vertebrates
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Fossils and evolutionary hypotheses
Evolution of parental care in crocodiles and birds (closest
living relatives to dinosaurs) did dinosaurs have parental care?
(not universal in earlier evolved, living vertebrate groups)
1.5
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Other challenges to determining phylogenetic relationships
Homoplasy similarities in characters that are not indicative of a
common ancestry
Convergent evolution, parallel evolution characters that have
evolved independently in separate evolutionary lineages (but
impression of common evolutionary origin)
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Phylogenetics and conservation
Important tool for endangered species conservation e.g. Clouded
leopards
1.6a
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Phylogenetics and conservation
Important tool for endangered species conservation, but should
not be the only tool, e.g. Polar bears and brown bears
1.6b
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History of the Earth and vertebrate evolution
Continental shifts Climate change Coalescing, fragmentation of
vertebrate faunas
Paleozoic Cambrian Ordovician Silurian Carboniferous Permian
Triassic
Mesozoic Jurassic Cretaceous
Cenozoic Tertiary Quaternary
(oldest to
youngest periods in descending
order)
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Vertebrate structure
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Vertebrates in relation to other animals Metazoans
Early embryo forms hollow ball of cells (blastula) Sex cells
formed in special organs
Sponges
Cell layers and tissues, nervous system with neurons
Cnidarians ectoderm, endoderm
Triploblasts ecto/meso/endoderm; bilaterally symmetrical gut;
anterior head
Coelomates
Coelom: split in mesoderm forms inner body cavity
Protostomes Blastopore (1st opening in the embryo) becomes the
mouth Mollusca Annelida Arthropoda
Deuterostomes Blastopore becomes the anus (second opening:
mouth)
Chordata Echinodermata Hemichordata
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Chordata Distinct features 1) Notochord-dorsal stiffening rod 2)
Dorsal hollow nerve cord 3) Segmented, post-anal tail 4) Endostyle
ciliated, glandular groove on the floor of the pharynx - secretes
mucus for trapping food particles (generally homologous with the
vertebrate thyroid gland) Other shared features 5) Pharynx feeding
or respiration (fishes) 6) Bilaterally symmetrical (one side mirror
of other) 7) Left-to-right symmetry (e.g. Heart (l) &
liver(r))
Vertebrates Urochordates (tunicates) Small marine animals
Cephalochordates Small marine animals
Three subphyla:
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Urochordata (tunicates)
Filter food particles from seawater Free-swimming larva have
chordate features Most adults are sedentary (probably a derived
form)
2.2
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Cephalochordates Fish-like locomotion due to (i) sequential
contraction of myomeres (striated muscle fibres on the sides of the
body) and (ii) incompressible notochord (prevents body from
shortening when myomeres contract) Respiration through the skin
surface; gill slits used to filter feed Shared features with
vertebrates (but different from tunicates): 1) Myomeres 2)
Analogous circulatory system 3) Specialized excretory cells
(podocytes) 4) Vertebrate-like tail fin
myomeres
2.2
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What is a vertebrate animal? Animals that have vertebrae
serially arranged to form a spinal column*; these replace the
notochord after embryonic period
Other distinguishing features of vertebrates: 1) Cranium (bony
or cartilaginous, surrounding the brain)
*Jawless fishes lack true vertebrae, and some jawed fishes
retain the notochord as adults (e.g. Sharks)
2) Prominent head with complex sense organs 3) Embryonic
feature: neural crest a unique germ layer
that forms many new structures (e.g. head)
4) Large brains having three parts: forebrain, midbrain and
hindbrain
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Basics of vertebrate structure Whole-animal level transition
from non-vertebrate chordate
Increased body size and activity
Need organ systems that can carry out physiological processes at
a greater rate
Evolution towards larger head, muscular pharynx, bigger brain,
sensory system
Need muscles and skeleton (mobility)
2.4
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Vertebrate embryology gill pouch stage
Segmentation
Lining in other vertebrates: Thymus, parathyroid glands,
tonsils
Grooves: gills (fish)
Ventral part of mesoderm: Vascular system, heart, reproductive
system
Kidneys
Dorsal mesoderm: skin, muscle , vertebral column, ribs, limb
muscles in tetrapods
Similar laying down of different anatomical structures
2.5
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Vertebrate adult tissue types Organs comprised of epithelial,
connective, vascular, muscular, and nervous tissues
Mineralized tissues hypoxyapatite (Ca + P) (unique to verts.)
cartilage, bone, enamel, dentine, enameloid (many fishes),
cementum
Integument external covering skin, glands, scales, dermal
armour, hair epidermis: protection, exchange, sensation
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Vertebrate skeletomuscular system
Notochord and gill skeleton
Cranium
Vertebrae, ribs, median fin supports
Appendicular skeleton (limb skeleton bones, limb girdles)
Chondrocranium cartilage around the brain Splanchnocranium gill
supports
Dermatocranium skin as an outer cover
Lamprey Chondrichthyan
Osteichthyan
Cranium-cross-sectional view
teeth notochord gular bones
chondrocranium
dermatocranium
Otic capsule
Lower jaw Branchial basket
2.8
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Axial muscles sequential muscle blocks overlap, produce body
undulations when they contract
Vertebrate skeletomuscular system
2.10
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Vertebrate energy acquisition, metabolism
Feeding/digestion 1) Mouth, pharyngeal processing: chemical and
physical components 2) Enzymes produced by the liver and pancreas
3) Cloaca: common opening for urinary and digestive systems
Respiration/ventilation Through thin skin (many amphibians) Gas
exchange over large surface areas (gills, lungs)
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Blood -Oxygen and nutrients through arteries+veins connected by
capillaries closed circulatory system) -Removes CO2 and metabolic
wastes
Vertebrate cardiovascular system
2.11
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Excretory and reproductive systems
Kidneys Dispose waste products; regulate bodys minerals and
water
Reproduction Gametes (eggs/sperm) Usually two sexes but some
unisexual fishes, amphibians and lizards
No specialized tubes/passages for gametes (lampreys)
Deposited eggs may develop inside/outside the body Intromittent
organs by which sperm are inserted into female reproductive tracts
(e.g. claspers)