Download What Is a Vertebrate?

Key Concepts
Echinoderms are radially symmetric as adults and have an
endoskeleton and water vascular system. They are among the
most important predators and herbivores in marine environments.
All vertebrates have a skull and an extensive endoskeleton made
of cartilage or bone; their diversification was driven in part by the
evolution of the jaw and limbs. Vertebrates are the most important
large-bodied predators and herbivores in marine and terrestrial
environments.
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Key Concepts
Humans are a tiny twig on the tree of life. Chimpanzees and
humans diverged from a common ancestor that lived in Africa 6–7
mya. Since then, at least 14 humanlike species have existed.
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Introduction
• The deuterostomes include the largest-bodied and some of the most
morphologically complex of all animals.
• Deuterostomes contain four phyla:
– Echinodermata—includes sea stars and sea urchins.
– Hemichordata—burrowing, deposit- or suspension-feeding
acorn worms.
– Xenoturbellida—two recently discovered wormlike species.
– Chordata—includes the vertebrates (animals with
backbones).
• Deuterostomes all share important features of embryonic
development, but have widely variable morphology and behavior.
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What Is an Echinoderm?
• Echinoderms (“spiny-skins”) are named for the spines or spikes
observed in many species.
• All echinoderms are marine animals.
• About 7000 species of echinoderm have been cataloged thus far.
• This phylum is defined by several adaptations.
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The Echinoderm Body Plan
• Larvae are bilaterally symmetric, as are other deuterostomes
– However, adults have pentaradial symmetry (five-sided radial
symmetry).
• Echinoderms have an endoskeleton—a hard protective and
supportive structure inside the body.
• Echinoderms are also defined by their water vascular system, a
series of branching, fluid-filled tubes and chambers that forms a
hydrostatic skeleton.
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© 2011 Pearson Education, Inc.
The Echinoderm Body Plan
• An important part of the water vascular system is tube feet, which
are elongated, fluid-filled structures.
• Podia are sections of the tube feet that project outside the body and
are involved in motion along a substrate.
Radial symmetry in adults, an endoskeleton of calcium carbonate,
and the water vascular system are all synapomorphies—traits that
identify echinoderms as a monophyletic group.
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© 2011 Pearson Education, Inc.
How Do Echinoderms Feed?
• Echinoderms utilize most methods of feeding.
• Podia play a key role in obtaining food:
– Predatory species use podia to pry apart bivalve shells. They
then extrude their stomach through the opening and secrete
digestive enzymes and absorb the resulting molecules.
– Suspension feeders use podia to flick food to the cilia, which
sweep the food into the mouth.
– Deposit feeders use podia to secrete mucus which sops up the
food, and then to move the food into the mouth.
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Key Lineages: Echinodermata
• To summarize their characteristics, echinoderms have bilaterally
symmetric larvae but are radially symmetric adults. All have a
water vascular system with tube feet, and all produce an internal
endoskeleton.
• There are five major lineages of echinoderms living today:
1. Crinoidea—feather stars and sea lilies.
2. Asteroidea—sea stars.
3. Ophiuroidea—brittle stars and basket stars.
4. Echinoidea—sea urchins and sand dollars.
5. Holothuroidea—sea cucumbers.
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What Is a Chordate?
• The phylum Chordata is defined by the presence of four
morphological features:
1. Openings into the throat called pharyngeal gill slits.
2. A dorsal hollow nerve cord that runs the length of the body,
comprised of projections from neurons.
3. A supportive but flexible rod, called the notochord, that runs
the length of the body.
4. A muscular post-anal tail.
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Three “Subphyla”
• The phylum Chordata is made up of three major lineages:
1. Cephalochordates.
2. Urochordates.
3. Vertebrates.
• All four defining characteristics of chordates are found in these
species at some stage in their life cycle.
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Chordate Body Plans
• Cephalochordates (lancelets or amphioxus) are small, mobile
suspension feeders that resemble fish. Their notochord functions as
an endoskeleton in adults.
• Urochordates (tunicates or sea squirts) have pharyngeal gill slits
in both larvae and adults, but the notochord, dorsal hollow nerve
cord, and tail occur only in the larvae.
• In vertebrates, the dorsal hollow nerve cord is elaborated into the
spinal cord. The pharyngeal pouches present in embryos develop
into gills in aquatic species, but not in terrestrial species.
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© 2011 Pearson Education, Inc.
What Is a Vertebrate?
The vertebrates are a monophyletic group distinguished by two
synapomorphies:
1. A column of cartilaginous or bony structures called
vertebrae, which form a column along the dorsal sides of
most species, protecting the spinal cord.
2. The cranium (skull) is a bony, cartilaginous, or fibrous case
that encloses and protects the brain.
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What Is a Vertebrate?
• The coordinated movements of vertebrates are possible in part
because vertebrates have large brains that are divided into three
distinct regions:
1. A forebrain, housing the sense of smell.
– Part of the forebrain is elaborated into a large structure
called the cerebrum.
2. A midbrain, associated with vision.
3. A hindbrain, responsible for balance and hearing.
– In the jawed vertebrates, or gnathostomes, the hindbrain
consists of enlarged regions called the cerebellum and
medulla oblongata.
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An Overview of Vertebrate Evolution
• Vertebrates have been the focus of intense research for over 300
years in part because they are large and conspicuous and in part
because they include the humans.
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The Vertebrate Fossil Record
• Fossils of both echinoderms and vertebrates are present in the
Burgess Shale deposits that formed during the Cambrian explosion.
• The earliest vertebrates lived in the ocean about 540 mya, had
streamlined, fishlike bodies, and seem to have had endoskeletons or
at least skulls made of cartilage, a strong but flexible tissue.
– A cartilaginous endoskeleton is a basic vertebrate feature; only
in the bony fishes and their descendants, the tetrapods, does
the skeleton become composed of bone.
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Key Innovations in the Vertebrate Lineage
• Following the appearance of vertebrates, the fossil record
documents a series of key innovations that occurred as this lineage
diversified:
1.
2.
3.
4.
5.
Bony exoskeleton.
Jaws.
Bony endoskeleton.
Limbs capable of moving on land.
Amniotic egg.
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© 2011 Pearson Education, Inc.
Key Innovations in the Vertebrate Lineage
• The first fossils to contain bone are from about 480 mya, and
contained a series of scalelike plates in the form of a protective
bony exoskeleton.
• The first bony fishes with jaws appear about 440 mya. Jaws
opened up a new method of feeding; with jaws and teeth,
vertebrates became armed and dangerous.
• Unlike the dermal bone that had evolved earlier, the bony
endoskeleton functioned to support movement—rapid swimming.
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Key Innovations in the Vertebrate Lineage
• The first animals that had limbs capable of moving on land date to
about 365 mya. These were the first of the tetrapods—animals
with four limbs.
• The first animals with watertight eggs, called amniotic eggs,
appeared about 345 mya. Amniotic eggs have membranes that help
nourish and protect the embryo, allowing for larger, betterdeveloped young. All tetrapods other than amphibians are
amniotes.
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Several Lineages Are Fishes
• There is no monophyletic group that includes all of the fishlike
lineages.
– Instead, “fishy” organisms are a series of independent
monophyletic groups that form a grade—a sequence of
lineages that are paraphyletic.
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Key Vertebrate Innovations
• Among vertebrates, the most species-rich and ecologically diverse
lineages are the ray-finned fishes and the tetrapods.
– Ray-finned fishes occupy most aquatic environments, while
tetrapods occupy most terrestrial environments. About 27,000
species have been identified in each group.
• Several evolutionary innovations contributed to the success of these
lineages, including:
1. The vertebrate jaw.
2. The tetrapod limb.
3. Feathers and flight.
4. The amniotic egg.
5. The placenta.
6. Parental care.
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The Vertebrate Jaw
• Vertebrates were unable to harvest food by biting until jaws
evolved.
– Modern hagfish and lampreys still lack jaws.
• Jaws most likely evolved from the cartilage in the anterior-most gill
arch:
– Jaws and gill arches have similar bony or cartilaginous
morphology.
– The muscles that move both structures have the same
embryonic origin.
– Both structures are derived from neural crest cells.
• Diversity in ray-finned fish feeding methods results from
modifications to the jaw.
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The Tetrapod Limb
• The lungfish is the closest-living relative to the tetrapods.
– Some species have fleshy fins supported by bones and are
capable of walking short distances.
– Fossils provide strong links between the ancestors of today’s
lungfish and the earliest land-dwelling vertebrates.
• The hypothesis that mutation and natural selection gradually
transformed fins into limbs as the first tetrapods became more and
more dependent on terrestrial habitats is supported by both the
fossil record and molecular genetic evidence.
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Feathers and Flight
• Once the tetrapod limb evolved, natural selection elaborated it into
structures that are used for running, gliding, crawling, burrowing,
or swimming.
– Wings and the ability to fly evolved independently in three
lineages of tetrapods:
1. Pterosaurs, extinct flying reptiles.
2. Bats.
3. Birds.
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Feathers and Flight
• A series of adaptations made powered, flapping flight increasingly
efficient:
– The bird sternum has a projection called the keel, which
provides a large surface area to which flight muscles attach.
– Birds are extraordinarily light for their size because of a
drastically reduced number of bones and because their larger
bones are thin-walled and hollow.
– Birds are endothermic—they maintain a high body
temperature by producing heat in their tissues.
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The Amniotic Egg
• Fish and amphibians must lay their eggs, which only have a single
membrane, in water.
– On the other hand, reptiles, birds, and the egg-laying mammals
are able to lay their amniotic eggs, which have an external
membrane and three internal membranes, on the land.
– The additional membranes provide mechanical support and
increase surface area for gas exchange.
• The amniotic egg has a watertight shell or case enclosing a
membrane-bound food supply, water supply, and waste repository.
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The Amniotic Egg
• The embryo develops within a protective inner membrane called
the amnion.
• The yolk sac contains nutrients for the embryo.
• The allantois contains waste, and the chorion allows gas exchange.
• The egg contains a membrane-bound supply of water in a proteinrich solution called albumen.
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The Placenta
• Egg-laying animals are oviparous; species that give birth are
viviparous. In ovoviviparous species, the female produces an egg
with a nutrient-rich yolk, and retains it within her body. The yolk
nourishes the developing embryo.
• Viviparous mammals have an organ called the placenta that is rich
in blood vessels and facilitates the flow of oxygen and nutrients
from mother to embryo.
• After a development period called gestation, the offspring emerges
from the mother’s body.
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Evolution of Viviparity and the Placenta
• Retaining the embryo within the body has several advantages:
1. Offspring develop at a more constant, favorable temperature.
2. Offspring are protected.
3. Offspring are portable—mothers are not tied to a nest.
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Parental Care
• Parental care encompasses any action by a parent that improves
the ability of its offspring to survive.
• Among animals, mammals and birds provide the most extensive
parental care.
– Female mammals also lactate—they produce milk and use it to
feed their offspring after birth.
• Among large animals, the evolution of extensive parental care is
hypothesized to be a major reason for the evolutionary success of
mammals and birds. In both lineages, mothers produce relatively
small numbers of large, high-quality offspring.
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The Primates
• The primate lineage consists of two main groups:
– Prosimians (“before-monkeys”)
– Includes lemurs from Madagascar, and tarsiers, pottos, and
lorises from Africa and south Asia.
– Most prosimians are small-bodied, arboreal, and nocturnal.
– Anthropoids ("human-like")
– Includes New World monkeys from Central and South
America, Old World monkeys from Africa and Asia,
gibbons from southeast Asia, and the Hominidae or great
apes—orangutans, gorillas, chimpanzees, and humans.
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What Makes a Primate a Primate?
• Primates have many defining characteristics:
– Hands and feet for grasping.
– Flattened nails on the fingers and toes instead of claws.
– Relatively large brains.
– Color vision.
– Complex social behavior.
– Extensive parental care of offspring.
– Forward-facing eyes.
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What Makes a Great Ape a Great Ape?
• Great apes are also called hominids and are relatively large bodied
with long arms, short legs, and no tail.
• Hominids have distinct ways of walking:
– Orangutans live primarily in the trees, but fist-walk when on
the ground.
– Gorillas and chimpanzees knuckle-walk.
– Humans are the only great ape that is fully bipedal (“twofooted”), walking upright on two legs.
Bipedalism is the synapomorphy that defines the hominins, the
monophyletic group comprising Homo sapiens and more than a
dozen extinct, bipedal relatives.
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The Out-of-Africa Hypothesis
• Fossils of Homo sapiens, Homo erectus, and Homo
neanderthalensis are present in different locations during the same
period, from about 160,000 to 100,000 years ago.
• Data suggest that modern humans originated in Africa.
– A population that left Africa split into three broad groups that
spread throughout the world.
• This scenario for the evolution of Homo sapiens is called the outof-Africa hypothesis.
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