Vertebrates

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

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 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

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: 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: 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

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

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: 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: 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: 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 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

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

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