Lecture 12: Deuterostomes

• Deuterostome animals


  Large bodied and morphologically complex animals that are divided into two major phyla: Echinodermata and Chordata
• Bilateral animals are divided into two groups: Deuterostomes and protostomes
• Deuterostomes


  • Mouth-second: pore becomes anus during development
  • Molecular evidence confirms they are a monophyletic group

  
• Major groups of deuterostomes

  • Echinodermata
  • Chordata
• Phylum Echinodermata


  • Aquatic
  • Bilaterally symmetric larva, but radially symmetric adults (pentaradial symmetry)
• Phylum Echinodermata


  • Endoskeleton made of calcium carbonate (CaCO3)
  • Water vascular system: branching fluid-filled tubes and chambers
  • Water in system is often seawater that enters through a pore (madreporite)
  • Allows for movement, respiration (gas exchange) and feeding
• Phylum Chordata


  • Possess four morphological features at some stage of life: Pharyngeal gill slits
  • Dorsal hollow nerve cord
  • Notochord
  • Muscular, post-anal tail

  
• In certain chordates, these four features can only be seen in larval or embryonic stages of development (i.e. gill slits in mammals)

  
• Phylum Chordata: three subphyla

  • Cephalochordata (lancelets)
  • Urochordata (tunicates)
  • Vertebrata (vertebrates)

  
• Subphylum Cephalochordata: lancelets


  • Retain all four chordate features through adulthood
  • Notochord functions as an endoskeleton that muscles can pull against to cause movement

  
• Subphylum Urochordata: tunicates


  • Body covered with a polysaccharide "tunic"
  • Water enters and exits body through siphons
  • Use pharyngeal gill slits for suspension feeding
  • Adults are sessile, larvae are motile and can disperse
• Subphylum Vertebrata: vertebrate animals

  • Vertebrae: column of cartilaginous/bony structures along dorsal side of body
  • Cranium: cartilaginous/bony case that encloses brain

  
• Vertebrates have diversified greatly through evolution
• Vertebrate evolutionary adaptations


  • Jaws
  • Limbs
  • Reproductive modifications
  • Amniotic egg
  • Placenta
• Vertebrate groups


  • Jawless vertebrates (Agnathans)
  • Jawed vertebrates (Gnathostomes)
• Jawless vertebrates: Agnathans


  • Hagfish: well developed notochord, can swim by undulating movements, adults lack vertebral column, possess a brain protected by a cranium
  • Lampreys: attach to fish by suction, use rasping tongue to bore hole through skin and fluid feed on fish blood

  
• Jawed vertebrates: Gnathostomes


  • Well-developed cranium and vertebrae
  • Can get food by biting — big advantage in mass feeding!
  • Includes bony fishes, sharks, and tetrapods (amphibians, reptiles, birds, mammals)
• Class Chondrichthyes: cartilaginous fishes


  • Endoskeleton made of reinforced cartilage
  • Evolution of paired fins
  • Some give live birth (unusual in fishes)
• Class Actinopterygii: ray-finned fishes


  • Swim by alternately contracting muscles on the left and right side
  • Have a symmetrical tail
  • Air-filled sac (swim bladder) that aids in buoyancy
  • Most use external fertilization and are oviparous (lay eggs)

  
• Lobe-finned fishes: coelacanths and lungfishes


  • Fleshy, thick fins composed of an array of bones anchored by a single basal element surrounded by a thick layer of muscle
  • Lungfish can walk along pond bottoms using their fins; can breathe using lungs as well as with gills

  
• Fossil record strongly suggests that ancestors of terrestrial vertebrates (tetrapods) were relatives to lungfish, and tetrapod limbs evolved from the fins of ancestral fish

  
• Tetrapods


  • Land-dwelling vertebrates with 4 limbs
  • Include amphibians, reptiles (including birds and dinosaurs), and mammals
• Class Amphibia: frogs, toads, newts, and salamanders


  • Live in aquatic and moist terrestrial habitats
  • Some gas exchange occurs across moist skin
  • Tadpoles live exclusively in water before metamorphosing into land-dwelling adults
• Amniotes


  • Include all reptiles (and birds) and all mammals
  • Produce amniotic eggs or use a placenta to protect the embryo
• Amniotic egg


  Specialized extra-embryonic membranes and a shell that prevent desiccation
• Placenta


  Allows embryo to derive nutrition and oxygen from female parent, embryo is attached via umbilical cord
• Class Reptilia: reptiles and birds


  • Scaly skin with large amounts of the protein keratin
  • Well-developed lungs to breathe air
  • Shelled, amniotic eggs; sometimes leathery (turtles, lizards) or with CaCO3
• Birds


  • Descended from feathered dinosaur ancestors
  • Endotherms - use body heat from metabolism to maintain body temperature
  • Flight adaptations: feathers, hollow bones, keel on sternum, one ovary
• Class Mammalia


  • Monotremes
  • Marsupials
  • Eutherians (placental mammals)
• Monotremes


  • Lay amniotic eggs and lack nipples: females secrete milk from skin glands
• Marsupials


  • Do not lay eggs, have nipples in a nursing pouch (marsupium)
  • Embryo receives nourishment from placenta for a relatively short period, then crawls into maternal pouch and completes development there while suckling milk
• Eutherians (placental mammals)


  • Embryos nourished for a relatively long period of time via the placenta
  • Include many familiar animals: bats, cats, dogs, bears, dolphins, whales, rodents, ungulates, primates, etc.
• Order Primates


  • Forward-looking eyes at the front of the face
  • Hands adapted for grasping
  • Flat nails (not claws)
  • Relatively large brains
  • Complex social behaviors
• Family Hominidae (great apes)


  • No tail, relatively large-bodied
• Genus Homo


  • Includes humans (Homo sapiens) and several other bipedal hominids
  • Characterized by bipedalism, extremely large brains relative to body size, extensive toolmaking and use, relative small size dimorphism between sexes