Chordate Origins

  • Created by: rosieevie
  • Created on: 17-01-17 16:29

Chordate Phylum - Cambrian period (535mya)

  • Closest relatives - Echinodermata and Hemichordata (acorn worms, pterbranchs)
  • Key traits:
  • Notochord 
    • Longitudinal flexible chord between nerve chord and digestive tube
    • Large-fluid filled cells
    • Maintain hydrostatic presssure, provide support and act as structure for muscles to act against
    • Replaced by vetebral column in higher vertebrates
  • Dorsal nerve chord (spinal column)
    • Develops by invagination of dorsal ectoderm
    • Hollow nerve chord develops into CNS
  • Pharyngeal slits (throat slits)
    • Allow water to exit body and nutrients remain - filter feeding
    • Slits -> gills -> jaws -> ear bones
  • Muscular post-anal tail
    • No digestive tract in tail
    • Propelling force -> concentration of sensory organs (cephalisation)
  • Segmentation
    • Only key trait if evolved independently
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Subphylum Urochordata

Sea squirts, tunicates (2000 species)

  • Either this or cephalochordata most pirimitive chordates
  • Sessile filter feeders
  • Adults - pharyngeal slits
  • No CNS 
  • Larva have all other traits - disappear during metamorphosis when settles
  • One group free living and retains traits

(http://lh5.ggpht.com/_yItZwKwfM-I/TUfmoJMxdhI/AAAAAAAABFY/1RmP6yIo_s4/UROCHORDATA_thumb%5B6%5D.jpg?imgmax=800)

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Subphylum Cephalochordata

 Lancelets (amphioxus)

  • Plankton feeders
  • Burrow in sand
  • Anterior tip of nerve chord swollen - brain beginnings

 

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GROUP Craniata

  • Pharyngeal slits = gill slits (no longer filter feeding)
  • Neural crest cells migrate to head = cephalisation

EXTINCT - Haikouella (oldest crainiate)

  • Eyes and brain
  • No skull
  • More fossils needed to see if brain or skull comes first

(http://palaeos.com/vertebrates/chordata/images/HaikouellaPhotoBranchial.jpg)

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Class Myxini

Hagfish (30-60 species)

  • Pirimative craniates
  • Cartillage skull
  • No jaws
  • No vertebrae
  • Notochord
  • Scavangers or parasites
  • Produces slime as defence

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GROUP Vertebrata

  • More extensive skull - still cartilage
  • Vertebrae in addition to/replacing notochord
  • Fin rays stiffen fins
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Order Cephalaspidomorphi

Lampreys (35 species)

  • Primitive vertebrata
  • Parasites
  • Cartilage skeleton
  • Cartilagionous pipe around notochord - beginnings of vertebral column(http://ichef.bbci.co.uk/naturelibrary/images/ic/credit/640x395/e/eu/european_brook_lamprey/european_brook_lamprey_1.jpg)
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Extinct Class Conodonts

  • Abundant tooth-like fossils
  • Late Cambrian to late Triassic
  • Complex dental system - first instance of mineralisation

(http://www.le.ac.uk/gl/map2/abstractsetc/conanimals.jpg)

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GROUP Gnathostomata

  • Anterior gill slits = jaws
  • Increasing mineralisation
  • Two sets pair fins

Extinct Placoderms

  • <23m long
  • Big bony heads
  • First instance of internal fertilisation

Extinct Acanthodians

  • Smaller
  • Less armoured with bony fin spines

(http://1.bp.blogspot.com/-2ndm9w7H5xQ/Tfe0iD90hEI/AAAAAAAAAGQ/Xf0m8upkUGg/s320/acanthodi.jpg)

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Class Chondrichthyes - Sharks, rays, ratfish (750

  • Mostly cartilage skeleton (suggests anscestors had bone but evolved back)
  • Marine, some freshwater

(http://animalia-life.club/data_images/ratfish/ratfish7.jpg) (http://3.bp.blogspot.com/-jbe2HIAUB_U/UI6Au4WYt5I/AAAAAAAAMZ8/Oeyzhd0wL8Q/s1600/Shark+Wallpapers+1.jpg) (http://images.nationalgeographic.com/wpf/media-live/photos/000/178/cache/rays01-spotted-eagle-ray_17857_600x450.jpg)

Extinct Helicprion shark/ratfish

  • Weird spiral mouthparts like teeth conveyorbelt

(http://blogs.fit.edu/wp-content/uploads/2013/03/helicoprion-4.jpg)

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Class Actinopterygii - ray-finned fish (30,000 spe

  • Fully mineralised endoskeleton
  • Varying lifestyles
  • No notochord - vertebrate instead
  • Skull with lots of bones
  • Swim bladder - same organ as lung

(http://fishbase.sinica.edu.tw/images/species/saitt_u7.jpg)

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GROUP Sarcopterygii

  • Lobe-finned fish
  • Rod-shaped bones surrounded by muscles in pectoral/pelvic fins
  • Yes, we're fish
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Subclass Actinistia - the 'extinct' ones

  • Thought extinct
  • 2 living species near islands

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Subclass Dipnoi - lungfish (6 species)

  • Gills
  • Swim bladder can act as a lung
  • Survive drought in mud cocoon

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GROUP Tetrapoda

  • Limbs/feet
  • Gil slit supports - ear bones
  • First appeared in Devonian period

Extinct Tiktaalik 

  • Canadian fossil 
  • Croocodile fish mutant
  • Intermediate both in time and physiology

(http://bioweb.uwlax.edu/bio203/f2013/raabe_mic2/travelportal/Tiktaalik%20Habitat.jpg)(http://museumvictoria.com.au/pages/17109/imagegallery/2pic-24801.jpg)

Extinct Gogonausus

  • ~380mya 
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Problems with Land Conquest

  • Breathing (no gills)
  • Drying out
  • Egg fertilisation
  • Embryo survival 
  • Body support
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Class Amphibia - frogs, caecilians, salamanders et

  • Adults live on land and breathe with lungs/skin
  • Larvae live in water and breath with gills/skin
  • Metamorphosis

(http://www.caudata.org/forum/attachments/f46-beginner-newt-salamander-axolotl-help-topics/f48-axolotls-ambystoma-mexicanum/f62-axolotl-gallery/21039d1326250880-my-axolotl-buddy-bluegills-cimg5490.jpg)

So magical

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GROUP Amniota

  • Lungs
  • Scales to protect against desication
  • Membranous embryoes
  • No obligatory water stage
  • Early carboniferous ~345mya
  • Extraembryonic membranes surround embryo water
  • Egg shell protection
  • Internal fertilisation
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Class Reptilia

  • Extinct parareptiles - herbivore
  • Extinct pterosaurs - flight
  • Extinct plesiosaurs - swim
  • Extinct ichtyosaurs
  • Dinosauria - dinos, birds
  • Lepidosauria - snakes, lizards
  • Crocodilia - crocodiles
  • Testudines - turtles
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Class Mammalia - mammals (5000+ species)

  • Produce milk from modified sweat glands
  • Endothermic - high metabolism
  • Hair
  • Mostly viviparous - live young
  • 34 bones in skull - 2 main ones cranium and lower jaw (simplification)
  • Tiny ear bones

Extinct Synapsidia:

  • No hair
  • Oviparous - lays eggs
  • Dominant land tetrapods during Permian
  • Few survived and evolved

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Mammalia Groups

Monotremata - platapus and echidana

  • Hair 
  • Produce milk from pores everywhere
  • Oviparous
  • Australia and New Guinea

Marsupalia - opposum, wombat, kangoroo

  • Viviparous - underdeveloped young - move to pouch for second pregnancy
  • Australia, South/North America

Eutheria - cats, humans, dolphins

  • Placental mammals - interface between embryo and mother, feeds embryo
  • Viviparous
  • Embryo develops in uterus
  • Woldwide because of endothermy and efficient circulatory system - environ independence
  • Lrrge brain size - behavioural adaptation
  • Teeth differentiation - evolutionary adaptation
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