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

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

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)

Phylogenetics and conservation

Important tool for endangered species conservation e.g. Clouded leopards

1.6a

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

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)

Vertebrate structure

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

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:

Urochordata (tunicates)

Filter food particles from seawater Free-swimming larva have chordate features Most adults are sedentary (probably a derived form)

2.2

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

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

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

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

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

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

Axial muscles sequential muscle blocks overlap, produce body undulations when they contract

Vertebrate skeletomuscular system

2.10

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)

Blood -Oxygen and nutrients through arteries+veins connected by capillaries closed circulatory system) -Removes CO2 and metabolic wastes

Vertebrate cardiovascular system

2.11

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)