Chordates Flashcards
Lectures 20-23
What are the 5 unique traits for chordates?
Notochord
Dorsal nerve cord that is hollow
Pharyngeal slits
Muscular post anal tail
What is a notochord?
- Longitudinal flexible rod between nerve cord and digestive tube.
- Provides support and flexibility
- Replaced by vertebral column in higher vertebrates
What is the dorsal nerve cord?
- Develops by invagination (closing) of dorsal ectoderm)
- Develops into central nervous system
What is a Pharyngeal slit?
- Allow water to exit body without going through digestive tract
- In primitive chordates this is used for filter feeding and in lower chordates it is modified for gas exchange (gills)
What is the post anal tail?
- Non chordates digestive tract extends throughout body
- Provides propelling force in aquatic species
- Causes concentration of sensors in opposite end
When and what were the earliest chordates?
Pikaia and Cathamymyrus, 540 mya.
Give a summary of Urochordata.
- Sea squirts
- Sessile filter feeder
- Only have pharyngeal slits but LARVA have nerve cord, notochord and tail
Give a summary of Cephalochordates.
- Lancelets
- Plankton feeders who bury into sand
- Swollen nerve cord in anterior tip (brain sort of)
- On continental shelves
Give a summary of Craniata and the groups within it.
- Pharyngeal slit modified into gills
- Cephalophised
- Include Haikouella (which have eyes & brains, no skull) and Myxini (Hagfishes)
Give a summary of Myxini.
- Hagfishes
- cartilaginous skull but no jaws or vertebrate
- Have a notochord
- Feed on sick/dead fish
- Produce slime
What are the main differences between Vertebrata and Crianates?
- More extensive skull
- Vertebrate either partially or completely replaced notochord
- Fins stiffed by rays
Give a summary of Cephalaspidomorphi.
- Lampreys
- Parasitic to fish
- Cartilaginous skeleton and pipe around notochord which partially closes nerve cord
Give a summary of Conodonts and Agnathes
- First examples of mineralisation
- We have extensive tooth fossils of Conodonts from late Cambrian to Triassic
What are Gnathostomata?
- Have a jaw
- Anterior gull split supports are modified to the jaws
- Increased mineralisation
- Two sets of paired fins
Describe the two major extinct early gnathostomes.
Placoderms: Massive with big bony heads, first evidence of internal fertilisation.
Acanthodians: Smaller, less armoured.
Give a summary of Chondrichthyes.
- Sharks, ratfish, rays
- Cartilage and calcium skeleton
- Helicoprion is a strange extinct shark with a spiral jaw to be able to grow new teeth.
Give a summary of Actinopterygii.
- Ray finned fish
- Fully mineralised
- Homologous lungs and swim bladder
Give a summary of Sarcopterygii.
- Lobe finned fish
- Rod shaped bones surrounded by muscles in fins
- Include Actinistia (Coelacanth) and Dipnoi (Lungfish which can breathe air)
Give a summary of Tetrapoda.
- Have limbs and feet
- Gill slit supports modified into eat bones
What is the first Tiktaalik fossil?
- 375 mya, structure between sarcopterygian and tetrapod fish
- Gogonasus was found 380 mya
What were the issues with conquesting land?
- Cant breathe
- Drying out
- Fertilisation of eggs
- Body weighs more on land
Give a summary of Amphibia.
- Larvae live in water, adults live on land and breathe through skin and lungs.
Give a summary of Amniota.
- Reptiles and mammals
- Breathe through land
- Embryo developed in membranes (eggs or internal) so no need for water stage.
- Scales to protect against dessication.
- Appeared 354 mya (Carboniferous)
What are the scientific names for the groups of snakes, lizards and crocodiles?
Snakes/lizards = Lepidosauria
Crocodiles = Crocodilia
Give a summary of Mammalia.
- Produce milk for offspring
- Endothermic
- Skin covered in hair
- Viviparous (embryo develops in parent)
Give a summary of Synapsida.
- Mammal like reptiles
- No hair and oviparous
- Dominant during Permian, only few survived the Permian extinction and they have become mammals.
Give a summary of Monotremata.
- Have hair and produce milk but no nipples
- Oviparous
- Platypus n that
Give a summary of Marsupialia
- Viviparous but tiny when born. Most of development is done in pouch latched onto nipple.
Give a summary of Eutheria.
- Placental mammals who are viviparous
- Success credit to endothermy allowing independence from environment
- Large brain sizes allow behavioural adaptation
- Differentiation of teeth
What are the five feeding groups of Eutheria?
Carnivores
Piscivores
Herbivores
Insectivores
Omnivores
What is the most morphologically variable animal species on earth?
Dogs. Due to human breeding, not natural selection.
Did feathers or scales evolve first?
Scales. Feathers evolved from scales, first for insulation and then for flight.
Were dinosaurs endothermic?
- Debated but we are sure of at least one group that were.
- Evidence such as bone structure
How did fish shape of mammals evolve?
- Convergent evolution
Give a summary of the order Primates.
- Lemurs, monkeys, apes etc
- Ancestors were small insectivores
- Adapted for grasping with hands, feet and large brain.
- Forward facing eyes
- Omnivorous diet
When did hominoids/ hominids first appear?
Oids: Candidates 20-15 mya. Key hominoid trait is lack of tail but this is hard to ell when the only fossil you have is a skull.
Ids: 76 mya, again not great fossils.
What is the difference between hominids and hominoids?
HominOIDS: Gibbons, gorillas, chimps, human etc
HominIDS: All species more closely related to humans than chimps (Big brain and bipedal possibly due to forests being replaced by savannah)
Give a summary of Ardipithecus.
- 4.4 mya and 1.2m tall
- Small brain size (3-400cm3)
- Upright, grasping hands and feet
- Possible direct ancestor
Give a summary of Australopithecus.
- 4 to 2.5 mya and 1.2-1.4m tall.
- Brain size 4-500cm3
- Fully bipedal so it evolved before large brain size.
- Includes fossil Lucy
Give a summary of Paranthropus.
- 2.5 mya
- 1.3-5m tall.
- Big teeth and strong bones, probably herbivore. Brain size 550cm3.
Give a summary of Homo habilis.
- 2.5 mya
- 600+cm3 brain size
- First evidence of tool making/use
- Later forms known as H. Ergaster (900cm3 brain size)
Give a summary of H. erectus.
- 2mya
- 1100cm3
- Descended from H. habilis and ergaster
- First to migrate out of Africa.
Give a summary of H. Neanderthalensis.
- 350-200,000 years ago
- Descended from H. erectus
- Bigger brain than us (1500cm3+) and really heavy/muscular.
What are the two models of how H. Sapiens populated the world?
Multiregional: One wave out of Africa and into Eurasia
Out of Africa Model: Descended from H. erectus/ergaster in Africa, with H. sapiens leaving Africa and replacing erectus in Asia/Neanderthals in Europe.
Give a summary of H. floresiensis and ‘luzonensis’.
- 1m tall, 400cm brain
- 50-100,000 years ago
- Evidence of fire and tools, as well as island dwarfism
luzonensis: Discovered in 2019, we have no skull so not much info. Roughly same size as floresiensis.
What are the costs of a big brain?
- 18% of energy budget
- Forces premature birth
- Practical and social skills
