Chapter 34: The Origin and Evolution of Vertebrates

Term DefinitionVertebrae the series of bones that make up the backboneChordates have a notochord and a dorsal, hollow nerve cord;

bilaterian animals that belong to the clade Deuterostomia; comprise all vertebrates and two groups of invertebrates (urochordates and cephalochordates)

Key characters:

- Notochord- Dorsal, hollow nerve cord—develops from

a plate of ectoderm that rolls into a tube dorsal to the notochord; develops into the central nervous system (brain and spinal cord)

- Pharyngeal slits or clefts- Muscular, post-anal tail—provides

propelling force in many aquatic speciesNotochord a longitudinal, flexible rod between the digestive

tube and nerve cord; provides skeletal support throughout most of the length of chordate

Pharyngeal clefts grooves in the pharynx; develops into slits that open to the outside of the body

Pharyngeal slits suspension-feeding structures in many invertebrate chordates; gas exchange (except vertebrates with limbs, the tetrapods); develop into parts of the ear, head, and neck in tetrapods

Lancelets Cephalochordota; named for their bladelike shape; marine suspension feeders that retain characteristics of the chordate body plan as adults

Tunicates Urochordata; more closely related to other chordates than are lancelets; most resemble chordates during their larval stage, which may last only a few minutes; “sea squirts”

Craniates chordates that have a headNeural crest feature unique to craniates; a collection of cells

near the dorsal margins of the closing neural tube in an embryo; give rise to a variety of structures

Haikouella most primitive of the fossils from the Cambrian explosion; 3 cm; well-formed brain, eyes, muscular segments; no skull

Myllokunmingia had parts of a skull; a true craniateHagfishes Myxini; most basal group of craniates; have

cartilaginous skull and axial rod of cartilage derived from the notochord; lack jaws and vertebrae; small brain, eyes, ears, tooth-like formations; marine; mostly bottom-dwelling scavengers

Vertebrates craniates that have a backbone

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Derived characters:

- Vertebrae enclosing a spinal cord- An elaborate skull- Fin rays, in the aquatic forms

Lampreys Petromyzontida; represent the oldest living lineage of vertebrates; jawless vertebrates that feed by clamping their mouth onto a live fish; inhabit various marine and freshwater habitats; have cartilaginous segments surrounding the notochord and arching partly over the nerve cord.

Amniotes tetrapods that have a terrestrially adapted egg; a group of tetrapods whose living members are the reptiles, including birds, and mammals

Amniotic egg contains membranes that protect the embryoExtraembryonic membranes amnion, chorion, yolk sac, allantoisMammals amniotes that have hair and produce milk; 5,300

species

Derived characters:

- Mammary glands, which produce milk- Hair- A high metabolic rate, due to endothermy- A larger brain than other vertebrates of

equivalent size- Differentiated teeth

Eutherians placental mammals; have a more complex placenta than marsupials; embryonic development within a uterus, joined to the mother by the placenta

Primates lemurs, tarsiers, monkeys, apes, humans

Derived characters:

- 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- Complex social behaviour and parental

care- A fully opposable thumb (in monkeys

and apes)Living primates 3 main groups:

- Lemurs, lorises, pottos- Tarsiers- Anthropoids (monkeys and apes)

Old world Africa and Asia; first monkeys evolvedNew world South America; monkeys first appeared roughly

25 million years agoApes informal name of primates of a group of

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anthropoids including gibbons, orang-utans, gorillas, chimpanzees, bonobos, and humans; diverged from Old World monkeys about 20-25 million years ago

Humans 200,000 years old; Mammals that have a large brain and bipedal locomotion

Derived characters:

- Upright posture and bipedal locomotion- Larger brains capable of language,

symbolic though, artistic expression, the manufacture and use of complex tools

- Reduced jawbones and jaw muscles- Shorter digestive tract

Paleoanthropology study of human originsHominins formerly hominids; more closely related to humans

than to chimpanzees; 20 species extinct; originated in Africa about 6-7 million years ago; small brains and increasing bipedalism

Australopiths a paraphyletic assemblage of hominins living between 4 and 2 million years ago

Australopithecus afarensis species of australopiths that walked fully erectRobust australopiths that had sturdy skulls and powerful

jawsGracile australopiths that were more slender and had

lighter jawsHomo habilis “handy man”; earliest fossils placed in the genus

Homo; 2.4 to 1.6 million years oldHomo ergaster first fully bipedal, large-brained hominid; existed

between 1.9 and 1.5 million years ago; shows a significant decrease in sexual dimorphism (a size difference between sexes) compared with its ancestors

Homo erectus originated in Africa by 1.8 million years ago; first hominin to leave Africa

Homo sapiens appeared in Africa by 195,000 years ago; all living humans are descended from these African ancestors; first group to show evidence of symbolic and sophisticated thought

Homo floresiensis hominin whose fossils were found in Indonesia in 2004

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