• 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