TR

Vertebrates

  • Chordates have a notochord and a dorsal, hollow nerve cord

Notochord

  • Notochord: a longitudinal, flexible rod between the digestive tube and nerve cord
  • It provides skeletal support throughout most of the length of a chordate
  • In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord

Dorsal, Hollow Nerve Cord

  • The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord
  • The nerve cord develops into the central nervous system: the brain and the spinal chord

Pharyngeal Slits or Clefts

  • Pharyngeal clefts: grooves in the pharynx that develop into slits that open to the outside of the body
  • Functions of pharyngeal slits
    • Suspension-feeding structures in many invertebrate chordates
    • Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods)
    • Develop into parts of the ear, head, and neck in tetrapods

Muscular, Post-Anal Tail

  • Chordates have a tail posterior to the anus
  • In many species, the tail is greatly reduced during embryonic development
  • The tail contains skeletal elements and muscles
  • It provides propelling force in many aquatic species

Craniates

  • Craniates: chordates that have a head
  • Derived Characters of Craniates
    • Craniates have two clusters of Hox genes; lancelets and tunicates have only one cluster
    • One feature unique to craniates is the neural crest
    • Neural crest: a collection of cells near the dorsal margins of the closing neural tube in an embryo
    • Neural crest cells give rise to a variety of the structures, including some of the bones and cartilage of the skull
    • In aquatic craniates the pharyngeal clefts evolved into gill slits
    • Craniates have a heart with at least 2 chambers, red blood cells with hemoglobin, and kidneys

Vertebrates

  • Vertebrates: chordates with a backbone
  • Have chordate features as well as:
    • Vertebral column enclosing a spinal nerve
    • Cranium
    • Endoskeleton of cartilage or bone
    • Diversity of internal organs

Gnathostomes

  • Gnathostomes: vertebrates that have jaws
  • Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates
  • Gnathostomes include sharks and their relatives, ray-finned fishes, lobe-finned fishes, amphibians, reptiles (including birds), and mammals
  • Derived characters of gnathostomes
    • Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits
    • Other characters common to gnathostomes
    • Genome duplication, including duplication of the Hox genes
    • An enlarged forebrain associated with enhanced smell and vision
    • In aquatic gnathostomes, the lateral line system, which is sensitive to vibrations

Class Chondrichthyes

  • Sharks, skates, rays
  • Cartilaginous fish
    • Skeleton of flexible cartilage
    • Derived character within the Chondrichthyes (not ancestral)
    • Developmental change prevented ossification of cartilage
  • Sharks among earliest fish to develop teeth
    • But teeth are not set into jaw
  • Shark eggs are fertilized internally but embryos can develop in different ways
    • Oviparous: Eggs hatch outside the mother’s body
    • Ovoviviparous: The embryo develops within the uterus and is nourished by the egg yolk
    • Viviparous: The embryo develops within the uterus and is nourished through a yolk sac placenta from the mother’s blood

Bony Fish

  • Three living classes
    • Actinopterygii: ray-finned fish
    • Actinistia: coelacanths
    • Dipnoi: lungfish 
  • Three features different from Chondricthyes
    • Bony skeleton
    • Operculum covers gills
    • Swim bladder for buoyancy
  • Most fishes breathe by drawing water over gills protected by an operculum
  • Fishes control their buoyancy with an air sac known as a swim bladder
  • Fishes have a lateral line system
  • Most species are oviparous, but some have internal fertilization and birthing

Tetrapods

  • Tetrapods: gnathostomes that have limbs
  • Derived Characters of Tetrapods
    • Tetrapods have some specific adaptations
    • 4 limbs, and feet with digits
    • a neck, which allows separate movement of the head
    • fusion of the pelvic girdle to the backbone
    • the absence of gills (except some aquatic species)
    • ears for detecting airborne sounds

Amniotes

  • Amniotes: tetrapods that have a terrestrially adapted egg
  • Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals
    • Derived Characters of Amniotes
    • The amniotic egg, which contains membranes that protect the embryo
    • The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois
    • The amniotic eggs of most reptiles and some mammals have a shell
  • Amniotes have other terrestrial adaptations, such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs

Mammals

  • Mammals: amniotes that have hair and produce milk
  • Derived Characters of Mammals
    • Mammary glands, which produce milk
    • Hair
    • A high metabolic rate, due to endothermy
    • A larger brain than other vertebrates of equivalent size
    • Differentiated teeth

Marsupials

  • Marsupials include opossums, kangaroos, and koalas
  • the embryo develops within a placenta in the mother’s uterus
  • A marsupial is born very early in its development
  • It completes its embryonic development while nursing in a maternal pouch called a marsupium

Eutherians (Placental Mammals)

  • Compared with marsupials, eutherians have a more complex placenta
  • Young eutherians complete their embryonic development within a uterus, joined to the mother by the placenta
  • Molecular and morphological data give conflicting dates on the diversification of eutherians

Primates

  • Derived Characters of Primates

    • Most primates have hands and feet adapted for grasping, and flat nails
    • A large brain and short jaws
    • Forward-looking eyes close together on the face, providing depth perception = binocular vision
    • Complex social behavior and parental care
    • A fully opposable thumb (in monkeys and apes)
    • some digits have flat nails (not claws)

  • Strepsirrhini: wet noses, no fur at tip

    • Bush babies, lemurs, pottos
    • Generally nocturnal and smaller-brained

  • Haplorrhini: dry, furry nose

    • Tarsiers
    • Anthropoidea
    • Monkeys
    • Hominoidea - gibbons, gorillas, orangutans, chimpanzees and humans