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Chordata - PowerPoint PPT Presentation

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Chordata. Deuterstome coelomates Four features characterize: Dorsal, hollow nerve cord Develops from ectoderm > develops into CNS: brain and spinal chord Notochord Fluid-filled cells encased in stiff, fibrous tissue Pharyngeal slits/pouches Filter feeding Postanal tail

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  • Deuterstome coelomates
  • Four features characterize:
    • Dorsal, hollow nerve cord
      • Develops from ectoderm > develops into CNS: brain and spinal chord
    • Notochord
      • Fluid-filled cells encased in stiff, fibrous tissue
    • Pharyngeal slits/pouches
      • Filter feeding
    • Postanal tail
  • Urochordata and Cephalochordata are nonvertebrate subphyla
in tetrapods
In tetrapods…

Notochord develops into the nucleus pulposus in invertebral disks

  • Tunicates and salps
  • Larvae have notochord and nerve cord
    • Plainly exhibit all of the basic characteristics of chordates
  • Difficult to discern evolutionary relationship by examining an adult
  • Secretes tunic, a tough sec composed mainly of cellulose

Tail and notochord are resorbed; nervous system degenerates

  • Informal name “sea squirts” b/c some species shoot a jet of water through excurrent siphon
  • Lancelets – resemble a lancet – a small, two-edged surgical knife
  • Notochord runs entire length of the dorsal nerve cord and persists throughout the animal’s life
  • Retains chordate characters as adult
  • Filter feeders
  • Closest relatives to vertebrates
  • Hox genes for swollen tip of anterior dorsal nerve cord are expressed in the same anterior-to-posterior order in lancelets and vertebrates
    • Vertebrate brain an elaboration of simple nerve cord tip?

Chordates with a head = craniates

    • Brain at anterior end of dorsal nerve cord, eyes and other sensory organs, and a skull
  • Possess two clusters of Hox genes
  • Neural crest – a collection of cells that appears near the dorsal margins of the closing neural tube
    • Cells give rise to teeth, some bones and cartilage of the skull, inner layer of skin of facial region, several types of neurons
transition to craniates
Transition to craniates

Haikouella – 530 million years old (Cambrian explosion), 3-cm-long; suspension feeder; resembled craniates in that it had a small brain, eyes, and muscular segments, tooth-like denticles. Did not have a skull.

  • Skull of cartilage but lack jaws and vertebrae
  • Use segmented muscles to exert force against notochord
  • Small brain, eyes, ears, and a nasal opening
  • Tooth-like formations of keratin in mouth
  • Secretes mucus as defense
  • Not considered fishes
vertebrates cephalaspidomorphi
  • Gene duplication allowed development of innovations in the nervous system and skeleton
  • Vertebrae takes over mechanical role of notochord
  • Lampreys are oldest living lineage of vertebrates
  • Mostly parasitic
  • Skeleton of cartilage with no collagen
  • Pairs of cartilaginous projections partially enclose nerve chord
conodonts cone teeth
Conodonts“cone teeth”
  • 3-10-cm-long; soft-bodied with prominent eyes controlled by numerous muscles
  • Barbed hooks made of mineralized dental tissues
    • Dental elements used to date strata
  • Other innovations such as paired fins, an inner ear with two semicircular canals, and armor made of mineralized bone
  • Extinct by end of Devonian

Vertebrate skeleton evolved as a structure made of unmineralized cartilage

  • Mineralization began after lampreys diverged from other vertebrates, and mineralization began in the mouth (conodont dental elements)
gnathostomes jaw mouth
Gnathostomes“jaw mouth”
  • Grip food, slice it up.
  • Evolved from skeletal rods that supported anterior pharyngeal slits
  • Remaining slits used for respiration (since suspension feeding was no longer necessary)
  • Additional duplication of Hox genes (four, as opposed to one cluster)
  • Lateral line system – organs sensitive to vibrations

Paired fins and tail allowed more efficient swimming

  • Jaws enabled gnathostomes to grab prey or bite off chunks
  • Earliest gnathostomes (placoderms and acanthodians) are extinct
chondrichthyes cartilage fish
Chondrichthyes“cartilage fish”
  • Sharks, rays, and relatives (ratfish)
  • Skeleton composed predominately of cartilage
    • Does not mean lineage is primitive in the evolution of vertebrates
  • 750 living species
  • Large amount of oil in liver for buoyancy, but sinks of stationary
  • Locomotion and respiration, although some have spiracles that force water across shark’s gills
  • “sleep swimming”
sharks and rays
Sharks and Rays
  • Largest sharks and rays are suspension feeders
  • Sharks have sharp vision but cannot distinguish colors
  • Nose for olfaction, not breathing
  • Detect electric fields generated by the muscle contractions of animals
  • No eardrums; sound is transmitted by body to hearing organs of inner ear
  • Eggs fertilized internally
  • Oviparous and ovoviviparous – eggs that hatch outside the mother and young that are born after hatching within the uterus
  • Viviparous – develop within uterus and obtain nourishment prior to birth via mother’s blood, or by eating other eggs
  • Sibling rivalry.
  • Cloaca – opening for digestive, urinary, and reproductive tract
osteichthyes bony fish
Osteichthyes“bony fish”
  • Includes bony fishes and tetrapods
  • Aquatic osteichthyans are informally called fishes
  • Osteichthyans have ossified (bony) endoskeleton w/ hard matrix of calcium phosphate
  • Breathe by drawing water over 4 or 5 pairs of gills located in chambers covered by protective bony flap, operculum

Transfer of gas from blood to swim bladder allows control of buoyancy

  • Evidence suggests lungs came first then evolved into swim bladders…
  • Skin is covered by flattened, bony scales and mucus that reduces drag
ray finned actinopterygii ray wing fin
Ray-FinnedActinopterygii“ray wing/fin”
  • Bass, trout, perch, tuna, herring, salmon
  • Maneuvering, defense
  • Originated in fresh water
  • Taste great.
ray finned sarcopterygii
  • Evolved during Devonian
  • Rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins
  • Used fins to swim and walk underwater
  • Three lineages survive: coelacanths, lungfishes, and the lineage that gave rise to tetrapods, including humans!