UNIT 4 DAY 5 - OUR FAMILY TREE Flashcards
chordates are defined by possession of the following 4 derived characters
- dorsal hollow nerve chord –> transmits information across the body
- notochord –> stiff but flexible rod, supports the body
- pharyngeal sites –> food particles in water are collected here as they pass from mouth through slits and out again
- post anal tail –> muscle in tail provides propulsion
original chordate possessed
- one set of hox genes –> controls head to tail organisation during development
living example of chordate
- amphioxus
- buried in sand
- amphioxus sedentary filter-feeders
- sister group of craniates –> active hunters
craniates
- buried in sand
- amphioxus sedentary filter-feeders
- sister group of craniates –> active hunters
craniates are defined by possession of the following derived characters
- sense organs: (nose, eyes, inner ears), products of the outgrowth of the front end of dorsal hollow nerve cord
- brain: evolved in front part of the nerve to process the information coming from sense organs and to send instructions to the muscles
- skull: a sensitive equipment needed for protection
- neural crests: skull comes from new embryonic tissue derived from the neural tube
craniates
- need more genes to control early development, became available when gene duplications arose by mutations
- entire set of Hox genes were duplicated
- have high metabolic rate –> need more efficient ways of extracting oxygen from water and delivering this oxygen to the body
craniates delivering oxygen
- pharyngeal slits of amphioxus, used to filter food particles from water evolved into pharyngeal gill slits, instead extract oxygen from water by diffusion to capillary bed
- 2 chambered heart delivers oxygenated blood via circulatory system to capillary beds, when oxygen diffused from blood into body cells
living example of craniates
hagfish
vertebrates derived characteristics
- improvements in skeleton and gills
- vertebral column replaces notochord –> surrounds and protects dorsal, hollow nerve cord
- different set of developmental genes (DIx genes) are duplicated
vertebrate groups that are still alive
- hagfish
- lampreys
- gnathostomes
Gnathostomes derived characteristics
- jaws, with teeth
- 2 sets of paired fined (stability in swimming)
- second duplication of hox genes
- lateral line
cartilaginous fishes
skeleton made from cartilage
Bony “fishes” derived character
- possession of a lung
living example of bony “fish”
polypterus
ray-finned fish derived traits
- possession of a swim bladder
- an organ of buoyancy
- swim bladder lost connection to esophagus air can’t be added by gulping with the mouth
- gas secreted into it via circulatory system
“lobe-finned fishes” derived characters
- paired fins with a strong support of bone and muscles, with a single basal bone called the humerus
- a three-chambered heart
tetrapod derived characters
true limb with toes
amniotes
- amniotic egg
- ribcage ventilation
- dry, impermeable skin
reptiles
scales
modern birds lost 3 ancestral characters of a true tail, claws on wings and teeth
- tal consists of feathers only, with modern vertebral core of tail remaining only as vestigial stub at back end of pelvis
mammals
- sister group = monotremes
- mammary glands
- hair
- 4 chambered heart
- endothermy
- shelled eggs (not on all)
marsupials
have a placenta where Offspring develop only partly in the uterus; once born they crawl along their mother’s body, attaching to one of her pouch in which the offspring nestles as it develops
Eutherians
Their placenta, evolved independently from that of marsupials, allows complete development of the embryo in the uterus
which chordate possess a 4 chambered heart
mammals and birds
