The Origin and Evolution of Vertebrates

The Origin and Evolution of Vertebrates
Chapter 34 The Origin and Evolution of Vertebrates

Overview: Half a Billion Years of Backbones
Early in the Cambrian period, about 530 million years ago, an astonishing variety of invertebrate animals inhabited Earth’s oceans One type of animal gave rise to vertebrates, one of the most successful groups of animals The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone © 2011 Pearson Education, Inc.

Figure 34.1 Figure 34.1 What is the relationship of this ancient organism to humans? 3

One lineage of vertebrates colonized land 365 million years ago
There are about 52,000 species of vertebrates, including the largest organisms ever to live on the Earth Vertebrates have great disparity, a wide range of differences within the group © 2011 Pearson Education, Inc.

Concept 34.1: Chordates have a notochord and a dorsal, hollow nerve cord
Chordates (phylum Chordata) are bilaterian animals that belong to the clade of animals known as Deuterostomia Chordates comprise all vertebrates and two groups of invertebrates, the urochordates and cephalochordates © 2011 Pearson Education, Inc.

ANCESTRAL DEUTEROSTOME Cephalochordata Chordates Urochordata Notochord
Figure 34.2 Echinodermata ANCESTRAL DEUTEROSTOME Cephalochordata Chordates Urochordata Notochord Myxini Common ancestor of chordates Craniates Petromyzontida Head Chondrichthyes Vertebrates Vertebral column Actinopterygii Gnathostomes Jaws, mineralized skeleton Actinistia Osteichthyans Lungs or lung derivatives Lobe-fins Figure 34.2 Phylogeny of living chordates. Dipnoi Lobed fins Amphibia Tetrapods Reptilia Limbs with digits Amniotes Amniotic egg Mammalia Milk 6

ANCESTRAL DEUTEROSTOME Cephalochordata
Figure 34.2a Echinodermata ANCESTRAL DEUTEROSTOME Cephalochordata Urochordata Notochord Myxini Common ancestor of chordates Petromyzontida Head Chondrichthyes Vertebral column Figure 34.2 Phylogeny of living chordates. Jaws, mineralized skeleton Osteichthyes 7

Lungs or lung derivatives
Figure 34.2b Actinopterygii Actinistia Lungs or lung derivatives Dipnoi Lobed fins Amphibia Reptilia Limbs with digits Figure 34.2 Phylogeny of living chordates. Amniotic egg Mammalia Milk 8

Derived Characters of Chordates
All chordates share a set of derived characters Some species have some of these traits only during embryonic development Four key characters of chordates Notochord Dorsal, hollow nerve cord Pharyngeal slits or clefts Muscular, post-anal tail © 2011 Pearson Education, Inc.

Dorsal, hollow nerve cord Muscle segments
Figure 34.3 Dorsal, hollow nerve cord Muscle segments Notochord Mouth Figure 34.3 Chordate characteristics. Anus Pharyngeal slits or clefts Muscular, post-anal tail 10

Notochord The notochord is 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 © 2011 Pearson Education, Inc.

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 cord © 2011 Pearson Education, Inc.

Pharyngeal Slits or Clefts
In most chordates, grooves in the pharynx called pharyngeal clefts 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 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Lancelets Lancelets (Cephalochordata) are named for their bladelike shape They are marine suspension feeders that retain characteristics of the chordate body plan as adults © 2011 Pearson Education, Inc.

Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes
Figure 34.UN01 Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Actinistia Dipnoi Figure 34.UN01 In-text art, p. 699 Amphibia Reptilia Mammalia 16

Dorsal, hollow nerve cord
Figure 34.4 Cirri Mouth Pharyngeal slits Atrium Digestive tract Notochord Atriopore 1 cm Dorsal, hollow nerve cord Segmental muscles Figure 34.4 The lancelet Branchiostoma, a cephalochordate. Anus Tail 17

Tunicates Tunicates (Urochordata) are more closely related to other chordates than are lancelets Tunicates most resemble chordates during their larval stage, which may last only a few minutes As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles When attacked, tunicates, or “sea squirts,” shoot water through their excurrent siphon © 2011 Pearson Education, Inc.

Dorsal, hollow nerve cord Pharynx with numerous slits
Figure 34.5 Incurrent siphon to mouth Water flow Notochord Dorsal, hollow nerve cord Excurrent siphon Tail Excurrent siphon Excurrent siphon Atrium Incurrent siphon Muscle segments Pharynx with numerous slits Intestine Anus Stomach Intestine Tunic Atrium Figure 34.5 A tunicate, a urochordate. Esophagus Pharynx with slits Stomach (a) Tunicate larva (b) Adult tunicate (c) Adult tunicate 20

Tunicates are highly derived and have fewer Hox genes than other vertebrates
© 2011 Pearson Education, Inc.

Early Chordate Evolution
Ancestral chordates may have resembled lancelets The same Hox genes that organize the vertebrate brain are expressed in the lancelet’s simple nerve cord tip Genome sequencing suggests that Genes associated with the heart and thyroid are common to all chordates Genes associated with transmission of nerve impulses are unique to vertebrates © 2011 Pearson Education, Inc.

Nerve cord of lancelet embryo
Figure 34.6 BF1 Otx Hox3 Nerve cord of lancelet embryo BF1 Otx Hox3 Brain of vertebrate embryo (shown straightened) Figure 34.6 Expression of developmental genes in lancelets and vertebrates. Forebrain Midbrain Hindbrain 23

Concept 34.2: Craniates are chordates that have a head
The origin of a head enabled chordates to coordinate more complex movement and feeding behaviors Craniates share some characteristics: a skull, brain, eyes, and other sensory organs © 2011 Pearson Education, Inc.

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, 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 structures, including some of the bones and cartilage of the skull © 2011 Pearson Education, Inc.

Dorsal edges of neural plate Neural crest Neural tube
Figure 34.7 Dorsal edges of neural plate Neural crest Neural tube Notochord Migrating neural crest cells (a) (b) (c) Skull bones and cartilage derived from neural crest cells Figure 34.7 The neural crest, embryonic source of many unique craniate characters. 26

In aquatic craniates the pharyngeal clefts evolved into gill slits
Craniates have a higher metabolism and are more muscular than tunicates and lancelets Craniates have a heart with at least two chambers, red blood cells with hemoglobin, and kidneys © 2011 Pearson Education, Inc.

The Origin of Craniates
Fossils from the Cambrian explosion document the transition to craniates The most primitive of the fossils are those of the 3-cm-long Haikouella Haikouella had a well-formed brain, eyes, and muscular segments, but not a skull © 2011 Pearson Education, Inc.

5 mm Segmented muscles Pharyngeal slits Figure 34.8
Figure 34.8 Fossil of an early chordate. Segmented muscles Pharyngeal slits 29

Myllokunmingia had parts of a skull and was a true craniate
In other Cambrian rocks, paleontologists have found fossils of even more advanced chordates, such as Myllokunmingia Myllokunmingia had parts of a skull and was a true craniate © 2011 Pearson Education, Inc.

Hagfishes The most basal group of craniates is Myxini, the hagfishes
Hagfishes have a cartilaginous skull and axial rod of cartilage derived from the notochord, but lack jaws and vertebrae They have a small brain, eyes, ears, and tooth-like formations Hagfishes are marine; most are bottom-dwelling scavengers © 2011 Pearson Education, Inc.

Figure 34.9 Slime glands Figure 34.9 A hagfish. 33

Concept 34.3: Vertebrates are craniates that have a backbone
During the Cambrian period, a lineage of craniates evolved into vertebrates Vertebrates became more efficient at capturing food and avoiding being eaten © 2011 Pearson Education, Inc.

Derived Characters of Vertebrates
Vertebrates underwent a second gene duplication involving the Dlx family of transcription factors Vertebrates have the following derived characters Vertebrae enclosing a spinal cord An elaborate skull Fin rays, in the aquatic forms © 2011 Pearson Education, Inc.

Lampreys Lampreys (Petromyzontida) represent the oldest living lineage of vertebrates They are jawless vertebrates that feed by clamping their mouth onto a live fish They inhabit various marine and freshwater habitats They have cartilaginous segments surrounding the notochord and arching partly over the nerve cord © 2011 Pearson Education, Inc.

Figure 34.10 Figure A sea lamprey. 38

Fossils of Early Vertebrates
Conodonts were the first vertebrates with mineralized skeletal elements in their mouth and pharynx Their fossilized dental elements are common in the fossil record © 2011 Pearson Education, Inc.

Dental elements (within head)
Figure 34.11 Dental elements (within head) Figure A conodont. 40

Other armored, jawless vertebrates had defensive plates of bone on their skin

Pteraspis Pharyngolepis Figure 34.12
Figure Jawless armored vertebrates. Pharyngolepis 42

Origins of Bone and Teeth
Mineralization appears to have originated with vertebrate mouthparts The vertebrate endoskeleton became fully mineralized much later © 2011 Pearson Education, Inc.

Concept 34.4: Gnathostomes are 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 © 2011 Pearson Education, Inc.

Derived Characters of Gnathostomes
Gnathostomes have jaws that might have evolved from skeletal supports of the pharyngeal slits © 2011 Pearson Education, Inc.

Gill slits Cranium Mouth Skeletal rods Figure 34.13
Figure Hypothesis for the evolution of vertebrate jaws. 46

Other characters common to gnathostomes
Genome duplication, including duplication of Hox genes An enlarged forebrain associated with enhanced smell and vision In aquatic gnathostomes, the lateral line system, which is sensitive to vibrations © 2011 Pearson Education, Inc.

Fossil Gnathostomes The earliest gnathostomes in the fossil record are an extinct lineage of armored vertebrates called placoderms They appeared in the Ordovician, about 450 million years ago © 2011 Pearson Education, Inc.

Figure 34.14 0.5 m Figure Fossil of an early gnathostome. 49

Another group of jawed vertebrates called acanthodians radiated during the Silurian and Devonian periods (444 to 359 million years ago) Three lineages of jawed vertebrates survive today: chondrichthyans, ray-finned fishes, and lobe-fins © 2011 Pearson Education, Inc.

Chondrichthyans (Sharks, Rays, and Their Relatives)
Chondrichthyans (Chondrichthyes) have a skeleton composed primarily of cartilage The largest and most diverse group of chondrichthyans includes the sharks, rays, and skates © 2011 Pearson Education, Inc.

(a) Blacktip reef shark (Carcharhinus melanopterus)
Figure 34.15 Dorsal fins Pectoral fins Pelvic fins (a) Blacktip reef shark (Carcharhinus melanopterus) (b) Southern stingray (Dasyatis americana) Figure Chondrichthyans. (c) Spotted ratfish (Hydrolagus colliei) 53

A second subclass is composed of a few dozen species of ratfishes

(c) Spotted ratfish (Hydrolagus colliei)
Figure 34.15c Figure Chondrichthyans. (c) Spotted ratfish (Hydrolagus colliei) 55

Sharks have a streamlined body and are swift swimmers
The largest sharks are suspension feeders, but most are carnivores Sharks have a short digestive tract with a ridge called the spiral valve to increase the digestive surface area Sharks have acute senses including sight, smell, and the ability to detect electrical fields from nearby animals © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

The reproductive tract, excretory system, and digestive tract empty into a common cloaca

Ray-Finned Fishes and Lobe-Fins
The vast majority of vertebrates belong to a clade of gnathostomes called Osteichthyes Nearly all living osteichthyans have a bony endoskeleton Osteichthyans include the bony fish and tetrapods Aquatic osteichthyans are the vertebrates we informally call fishes © 2011 Pearson Education, Inc.

Fishes control their buoyancy with an air sac known as a swim bladder
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 © 2011 Pearson Education, Inc.

Swim bladder Dorsal fin Caudal fin Spinal cord Adipose fin Brain
Figure 34.16 Swim bladder Dorsal fin Caudal fin Spinal cord Adipose fin Brain Nostril Cut edge of operculum Anal fin Liver Anus Figure Anatomy of a trout, a ray-finned fish. Lateral line Gills Gonad Stomach Kidney Pelvic fin Intestine Urinary bladder Heart 62

Ray-Finned Fishes Actinopterygii, the ray-finned fishes, include nearly all the familiar aquatic osteichthyans Ray-finned fishes originated during the Silurian period (444 to 416 million years ago) The fins, supported mainly by long, flexible rays, are modified for maneuvering, defense, and other functions © 2011 Pearson Education, Inc.

Yellowfin tuna (Thunnus albacares)
Figure 34.17 Yellowfin tuna (Thunnus albacares) Red lionfish (Pterois volitans) Common sea horse (Hippocampus ramulosus) Figure Ray-finned fishes (Actinopterygii). Fine-spotted moray eel (Gymnothorax dovii) 64

5 cm Lower jaw Scaly covering Dorsal spine Figure 34.18
Figure A reconstruction of an ancient lobe-fin. 66

5 cm Lower jaw Scaly covering Dorsal spine Figure 34.18a
Figure A reconstruction of an ancient lobe-fin. Lower jaw Scaly covering Dorsal spine 67

Three lineages survive and include coelacanths, lungfishes, and tetrapods
Coelacanths were thought to have become extinct 75 million years ago, but a living coelacanth was caught off the coast of South Africa in 1938 © 2011 Pearson Education, Inc.

Figure 34.19 Figure A coelacanth (Latimeria). 69

Concept 34.5: Tetrapods are gnathostomes that have limbs
One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods © 2011 Pearson Education, Inc.

Derived Characters of Tetrapods
Tetrapods have some specific adaptations Four 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 © 2011 Pearson Education, Inc.

The Origin of Tetrapods
Tiktaalik, nicknamed a “fishapod,” shows both fish and tetrapod characteristics It had Fins, gills, lungs, and scales Ribs to breathe air and support its body A neck Fins with the bone pattern of a tetrapod limb © 2011 Pearson Education, Inc.

Fish Characters Tetrapod Characters
Figure 34.20 Fish Characters Tetrapod Characters Scales Fins Gills and lungs Neck Ribs Fin skeleton Flat skull Eyes on top of skull Shoulder bones Ribs Neck Scales Head Eyes on top of skull Humerus Figure Impact: Discovery of a “Fishapod”: Tiktaalik. Ulna Flat skull “Wrist” Elbow Radius Fin Fin skeleton 73

Tiktaalik could most likely prop itself on its fins, but not walk
The first tetrapods appeared 365 million years ago © 2011 Pearson Education, Inc.

Time (millions of years ago)
Figure 34.21 Lungfishes Eusthenopteron Panderichthys Tiktaalik Acanthostega Tulerpeton Limbs with digits Figure Steps in the origin of limbs with digits. Amphibians Key to limb bones Ulna Radius Amniotes Humerus Silurian PALEOZOIC Devonian Carboniferous Permian 415 400 385 370 355 340 325 310 295 280 265 Time (millions of years ago) 75

(a) Order Urodela (salamanders)
Figure 34.22 (a) Order Urodela (salamanders) (b) Order Anura (frogs) Figure Amphibians. (c) Order Apoda (caecilians) 78

(a) Order Urodela (salamanders)
Figure 34.22a Figure Amphibians. (a) Order Urodela (salamanders) 79

Order Anura includes frogs and toads, which lack tails

Order Apoda includes caecilians, which are legless and resemble worms

Amphibian means “both ways of life,” referring to the metamorphosis of an aquatic larva into a terrestrial adult Most amphibians have moist skin that complements the lungs in gas exchange © 2011 Pearson Education, Inc.

(b) During metamorphosis
Figure 34.23 (a) Tadpole (b) During metamorphosis Figure The “dual life” of a frog (Rana temporaria). (c) Mating adults 83

Fertilization is external in most species, and the eggs require a moist environment
In some species, males or females care for the eggs on their back, in their mouth, or in their stomach © 2011 Pearson Education, Inc.

Figure 34.24 Figure A mobile nursery. 85

Amphibian populations have been declining in recent decades
The causes include a disease-causing chytrid fungus, habitat loss, climate change, and pollution © 2011 Pearson Education, Inc.

Concept 34.6: Amniotes are tetrapods that have a terrestrially adapted egg
Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals © 2011 Pearson Education, Inc.

Ornithischian dinosaurs Dinosaurs
Figure 34.25 Parareptiles Turtles Crocodilians Reptiles Archosaurs Pterosaurs Ornithischian dinosaurs Dinosaurs Saurischian dinosaurs other than birds Diapsids Saurischians Birds ANCESTRAL AMNIOTE Plesiosaurs Ichthyosaurs Figure A phylogeny of amniotes. Tuataras Lepidosaurs Squamates Synapsids Mammals 88

Derived Characters of Amniotes
Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois © 2011 Pearson Education, Inc.

Extraembryonic membranes
Figure 34.26 Extraembryonic membranes Chorion Allantois Amnion Yolk sac Embryo Amniotic cavity with amniotic fluid Yolk (nutrients) Figure The amniotic egg. Shell Albumen 90

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 © 2011 Pearson Education, Inc.

Early Amniotes Living amphibians and amniotes split from a common ancestor about 350 million years ago Early amniotes were more tolerant of dry conditions than early tetrapods The earliest amniotes were small predators with sharp teeth and long jaws © 2011 Pearson Education, Inc.

Figure 34.27 Figure Artist’s reconstruction of Hylonomus, an early amniote. 93

Reptiles The reptile clade includes the tuataras, lizards, snakes, turtles, crocodilians, birds, and some extinct groups Reptiles have scales that create a waterproof barrier Most reptiles lay shelled eggs on land © 2011 Pearson Education, Inc.

Figure 34.28 Figure Hatching reptiles. 96

Most reptiles are ectothermic, absorbing external heat as the main source of body heat
Birds are endothermic, capable of keeping the body warm through metabolism © 2011 Pearson Education, Inc.

The Origin and Evolutionary Radiation of Reptiles
The oldest reptilian fossils date to the Carboniferous period The first major group to emerge were parareptiles, which were mostly large, stocky quadrupedal herbivores © 2011 Pearson Education, Inc.

As parareptiles were dwindling, the diapsids were diversifying
The diapsids consisted of two main lineages: the lepidosaurs and the archosaurs The lepidosaurs include tuataras, lizards, snakes, and extinct mososaurs The archosaur lineage produced the crocodilians, pterosaurs, and dinosaurs © 2011 Pearson Education, Inc.

Pterosaurs were the first tetrapods to exhibit flight
The dinosaurs diversified into a vast range of shapes and sizes They included bipedal carnivores called theropods, the group from which birds are descended © 2011 Pearson Education, Inc.

Debate continues about whether dinosaurs were endothermic or ectothermic
Fossil discoveries and research have led to the conclusion that many dinosaurs were agile and fast moving Paleontologists have also discovered signs of parental care among dinosaurs © 2011 Pearson Education, Inc.

Their extinction may have been partly caused by an asteroid
Dinosaurs, with the exception of birds, became extinct by the end of the Cretaceous Their extinction may have been partly caused by an asteroid © 2011 Pearson Education, Inc.

Tuatara (Sphenodon punctatus)
Figure 34.29 (a) Tuatara (Sphenodon punctatus) Australian thorny devil lizard (Moloch horridus) (b) (c) Wagler’s pit viper (Tropidolaemus wagleri) Figure Extant reptiles (other than birds). (e) American alligator (Alligator mississippiensis) (d) Eastern box turtle (Terrapene carolina carolina) 104

(a) Tuatara (Sphenodon punctatus)
Figure 34.29a Figure Extant reptiles (other than birds). (a) Tuatara (Sphenodon punctatus) 105

Lizards are the most numerous and diverse reptiles, apart from birds
The other major living lineage of lepidosaurs consists of the squamates, the lizards and snakes Lizards are the most numerous and diverse reptiles, apart from birds © 2011 Pearson Education, Inc.

Australian thorny devil lizard (Moloch horridus) (b)
Figure 34.29b Figure Extant reptiles (other than birds). Australian thorny devil lizard (Moloch horridus) (b) 107

Snakes are legless lepidosaurs that evolved from lizards
Snakes are carnivorous; some are also venomous © 2011 Pearson Education, Inc.

Wagler’s pit viper (Tropidolaemus wagleri)
Figure 34.29c Figure Extant reptiles (other than birds). (c) Wagler’s pit viper (Tropidolaemus wagleri) 109

Turtles All turtles have a boxlike shell made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs Some turtles have adapted to deserts and others live entirely in ponds and rivers © 2011 Pearson Education, Inc.

Eastern box turtle (Terrapene carolina carolina)
Figure 34.29d Figure Extant reptiles (other than birds). (d) Eastern box turtle (Terrapene carolina carolina) 111

Alligators and Crocodiles
Crocodilians (alligators and crocodiles) belong to an archosaur lineage that dates back to the late Triassic © 2011 Pearson Education, Inc.

(e) American alligator (Alligator mississippiensis)
Figure 34.29e Figure Extant reptiles (other than birds). (e) American alligator (Alligator mississippiensis) 113

Derived Characters of Birds
Many characters of birds are adaptations that facilitate flight The major adaptation is wings with keratin feathers Other adaptations include lack of a urinary bladder, females with only one ovary, small gonads, and loss of teeth © 2011 Pearson Education, Inc.

Finger 1 (b) Bone structure Palm (a) Wing Finger 2 Forearm Finger 3
Figure 34.30 Finger 1 (b) Bone structure Palm (a) Wing Finger 2 Forearm Finger 3 Wrist Figure Form fits function: the avian wing and feather. Shaft Shaft Barb Vane Barbule Hook (c) Feather structure 116

Flight enhances hunting and scavenging, escape from terrestrial predators, and migration
Flight requires a great expenditure of energy, acute vision, and fine muscle control © 2011 Pearson Education, Inc.

The Origin of Birds Birds probably descended from small theropods, a group of carnivorous dinosaurs Early feathers might have evolved for insulation, camouflage, or courtship display © 2011 Pearson Education, Inc.

Early feathers might have helped dinosaurs
Gain lift when they jumped Gain traction running up hills Glide from trees By 150 million years ago, feathered theropods had evolved into birds Archaeopteryx remains the oldest bird known © 2011 Pearson Education, Inc.

Airfoil wing with contour feathers Long tail with many vertebrae
Figure 34.31 Toothed beak Wing claw Figure Artist’s reconstruction of Archaeopteryx, the earliest known bird. Airfoil wing with contour feathers Long tail with many vertebrae 120

Living Birds Living birds belong to the clade Neornithes
Several groups of birds are flightless The ratites, order Struthioniformes Penguins, order Sphenisciformes Certain species of rails, ducks, and pigeons © 2011 Pearson Education, Inc.

Figure 34.32 Figure An emu (Dromaius novaehollandiae), a flightless bird native to Australia. 122

Figure 34.33 Figure A king penguin (Aptenodytes patagonicus) “flying” underwater. 124

Figure 34.34 Figure Hummingbird feeding while hovering. 125

Figure 34.35 Figure Specialized beaks. 126

Figure 34.36 Figure Feet adapted to perching. 127

Concept 34.7: Mammals are amniotes that have hair and produce milk
Mammals, class Mammalia, are represented by more than 5,300 species © 2011 Pearson Education, Inc.

Derived Characters of Mammals
Mammals have Mammary glands, which produce milk Hair A high metabolic rate, due to endothermy A larger brain than other vertebrates of equivalent size Differentiated teeth © 2011 Pearson Education, Inc.

Early Evolution of Mammals
Mammals evolved from synapsids Two bones that formerly made up the jaw joint were incorporated into the mammalian middle ear © 2011 Pearson Education, Inc.

Biarmosuchus, a synapsid
Figure 34.37 Biarmosuchus, a synapsid Key Temporal fenestra Articular Quadrate Jaw joint Dentary Squamosal (a) Articular and quadrate bones in the jaw Middle ear Inner ear Eardrum Middle ear Eardrum Stapes Inner ear Stapes Figure The evolution of the mammalian ear bones. Incus (quadrate) Sound Sound Malleus (articular) Present-day reptile Present-day mammal (b) Articular and quadrate bones in the middle ear 132

By the early Cretaceous, the three living lineages of mammals emerged: monotremes, marsupials, and eutherians Mammals did not undergo a significant adaptive radiation until after the Cretaceous © 2011 Pearson Education, Inc.

Figure 34.38 Figure Short-beaked echidna (Tachyglossus aculeatus), an Australian monotreme. 135

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 © 2011 Pearson Education, Inc.

(a) A young brushtail possum
Figure 34.39 (a) A young brushtail possum Figure Australian marsupials. (b) Long-nosed bandicoot 137

In some species, such as the bandicoot, the marsupium opens to the rear of the mother’s body

Figure 34.40 Marsupial mammals Eutherian mammals Plantigale Deer mouse Marsupial mole Mole Sugar glider Flying squirrel Wombat Woodchuck Wolverine Figure Convergent evolution of marsupials and eutherians (placental mammals). Tasmanian devil Patagonian cavy Kangaroo 140

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 © 2011 Pearson Education, Inc.

Rodentia Lagomorpha Primates Dermoptera Scandentia
Figure 34.41a Monotremes (5 species) Monotremata ANCESTRAL MAMMAL Marsupials (324 species) Marsupialia Proboscidea Sirenia Tubulidentata Hyracoidea Afrosoricida Macroscelidea Eutherians (5,010 species) Xenarthra Figure Exploring: Mammalian Diversity. Rodentia Lagomorpha Primates Dermoptera Scandentia Carnivora Cetartiodactyla Perissodactyla Chiroptera Eulipotyphia Pholidota 142

Figure 34.41 Exploring: Mammalian Diversity.
Figure 34.41b Orders and Examples Main Characteristics Orders and Examples Main Characteristics Monotremata Lay eggs; no nipples; young suck milk from fur of mother Marsupialia Completes embryonic development in pouch on mother’s body Platypuses, echidnas Kangaroos, opossums, koalas Echidna Koala Proboscidea Long, muscular trunk; thick, loose skin; upper incisors elongated as tusks Tubulidentata Teeth consisting of many thin tubes cemented together; eats ants and termites Elephants Aardvarks African elephant Aardvark Sirenia Aquatic; finlike fore- limbs and no hind limbs; herbivorous Hyracoidea Short legs; stumpy tail; herbivorous; complex, multi- chambered stomach Manatees, dugongs Hyraxes Manatee Rock hyrax Xenarthra Reduced teeth or no teeth; herbivorous (sloths) or carnivorous (anteaters, armadillos) Rodentia Chisel-like, continuously growing incisors worn down by gnawing; herbivorous Sloths, anteaters, armadillos Squirrels, beavers, rats, porcupines, mice Tamandua Red squirrel Lagomorpha Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumping; herbivorous Primates Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous Rabbits, hares, picas Lemurs, monkeys, chimpanzees, gorillas, humans Golden lion tamarin Jackrabbit Figure Exploring: Mammalian Diversity. Carnivora Sharp, pointed canine teeth and molars for shearing; carnivorous Perissodactyla Hooves with an odd number of toes on each foot; herbivorous Dogs, wolves, bears, cats, weasels, otters, seals, walruses Horses, zebras, tapirs, rhinoceroses Coyote Indian rhinoceros Cetartiodactyla Hooves with an even number of toes on each foot; herbivorous Chiroptera Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous Artiodactyls Sheep, pigs, cattle, deer, giraffes Bats Frog-eating bat Bighorn sheep Cetaceans Aquatic; streamlined body; paddle-like fore-limbs and no hind limbs; thick layer of insulating blubber; carnivorous Eulipotyphla Eat mainly insects and other small invertebrates Whales, dolphins, porpoises “Core insectivores”: some moles, some shrews Pacific white- sided porpoise Star-nosed mole 143

Derived Characters of Primates
Most primates have hands and feet adapted for grasping, and flat nails © 2011 Pearson Education, Inc.

Other derived characters of primates
A large brain and short jaws Forward-looking eyes close together on the face, providing depth perception Complex social behavior and parental care A fully opposable thumb (in monkeys and apes) © 2011 Pearson Education, Inc.

Living Primates There are three main groups of living primates
Lemurs, lorises, and pottos Tarsiers Anthropoids (monkeys and apes) © 2011 Pearson Education, Inc.

Figure 34.42 Figure Coquerel’s sifakas (Propithecus verreauxi coquereli), a type of lemur. 148

Lemurs, lorises, and bush babies
Figure 34.43 Lemurs, lorises, and bush babies ANCESTRAL PRIMATE Tarsiers New World monkeys Old World monkeys Anthropoids Gibbons Orangutans Gorillas Figure A phylogenetic tree of primates. Chimpanzees and bonobos Humans 60 50 40 30 20 10 Time (millions of years ago) 150

The first monkeys evolved in the Old World (Africa and Asia)
In the New World (South America), monkeys first appeared roughly 25 million years ago New World and Old World monkeys underwent separate adaptive radiations during their many millions of years of separation © 2011 Pearson Education, Inc.

New World monkey: spider monkey (b) Old World monkey: macaque
Figure 34.44 Figure New World monkeys and Old World monkeys. (a) New World monkey: spider monkey (b) Old World monkey: macaque 152

Apes diverged from Old World monkeys about 20–25 million years ago
The other group of anthropoids consists of primates informally called apes This group includes gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans Apes diverged from Old World monkeys about 20–25 million years ago © 2011 Pearson Education, Inc.

(a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees (e) Bonobos
Figure 34.45 (a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees Figure Nonhuman apes. (e) Bonobos 154

Concept 34.8: Humans are mammals that have a large brain and bipedal locomotion
The species Homo sapiens is about 200,000 years old, which is very young, considering that life has existed on Earth for at least 3.5 billion years © 2011 Pearson Education, Inc.

Derived Characters of Humans
A number of characters distinguish humans from other apes Upright posture and bipedal locomotion Larger brains capable of language, symbolic thought, artistic expression, the manufacture and use of complex tools Reduced jawbones and jaw muscles Shorter digestive tract © 2011 Pearson Education, Inc.

The human and chimpanzee genomes are 99% identical
Changes in regulatory genes can have large effects © 2011 Pearson Education, Inc.

The Earliest Hominins The study of human origins is known as paleoanthropology Hominins (formerly called hominids) are more closely related to humans than to chimpanzees Paleoanthropologists have discovered fossils of about 20 species of extinct hominins © 2011 Pearson Education, Inc.

Figure 34.46 Paranthropus robustus Homo ergaster Homo neanderthalensis Homo sapiens ? Paranthropus boisei 0.5 1.0 1.5 Australopithecus africanus 2.0 Kenyanthropus platyops 2.5 Australopithecus garhi Australo- pithecus anamensis Millions of years ago 3.0 Homo erectus 3.5 Homo rudolfensis Homo habilis 4.0 4.5 Figure A timeline for some selected hominin species. Australopithecus afarensis 5.0 Ardipithecus ramidus 5.5 6.0 Orrorin tugensis 6.5 Sahelanthropus tchadensis 7.0 159

Hominins originated in Africa about 6–7 million years ago
Early hominins show evidence of small brains and increasing bipedalism © 2011 Pearson Education, Inc.

Figure 34.47 Figure The skeleton of “Ardi,” a 4.4-million-year-old hominin, Ardipithecus ramidus. 161

Misconception: Early hominins were chimpanzees
Correction: Hominins and chimpanzees shared a common ancestor Misconception: Human evolution is like a ladder leading directly to Homo sapiens Correction: Hominin evolution included many branches or coexisting species, though only humans survive today © 2011 Pearson Education, Inc.

Australopiths Australopiths are a paraphyletic assemblage of hominins living between 4 and 2 million years ago Some species, such as Australopithecus afarensis walked fully erect © 2011 Pearson Education, Inc.

(a) The Laetoli footprints (b) Artist’s reconstruction of A. afarensis
Figure 34.48 Figure Evidence that hominins walked upright 3.5 million years ago. (a) The Laetoli footprints (b) Artist’s reconstruction of A. afarensis 164

“Robust” australopiths had sturdy skulls and powerful jaws
“Gracile” australopiths were more slender and had lighter jaws © 2011 Pearson Education, Inc.

Early Homo The earliest fossils placed in our genus Homo are those of Homo habilis, ranging in age from about 2.4 to 1.6 million years Stone tools have been found with H. habilis, giving this species its name, which means “handy man” © 2011 Pearson Education, Inc.

Homo ergaster was the first fully bipedal, large-brained hominid
The species existed between 1.9 and 1.5 million years ago Homo ergaster shows a significant decrease in sexual dimorphism (a size difference between sexes) compared with its ancestors © 2011 Pearson Education, Inc.

Figure 34.49 Figure Fossil of Homo ergaster. 171

Homo erectus originated in Africa by 1.8 million years ago
It was the first hominin to leave Africa © 2011 Pearson Education, Inc.

Neanderthals Neanderthals, Homo neanderthalensis, lived in Europe and the Near East from 350,000 to 28,000 years ago They were thick-boned with a larger brain, they buried their dead, and they made hunting tools Debate is ongoing about the extent to which genetic material was exchanged between neanderthals and Homo sapiens © 2011 Pearson Education, Inc.

Hypothesis: Neanderthals gave rise to European humans.
Figure 34.50 EXPERIMENT Hypothesis: Neanderthals gave rise to European humans. Expected phylogeny: Chimpanzees Neanderthals Living Europeans Other living humans RESULTS Chimpanzees Figure Inquiry: Did Neanderthals give rise to European humans? Neanderthal 1 Neanderthal 2 European and other living humans 174

Homo Sapiens Homo sapiens appeared in Africa by 195,000 years ago
All living humans are descended from these African ancestors © 2011 Pearson Education, Inc.

Figure 34.51 Figure A 160,000-year-old fossil of Homo sapiens. 176

Humans first arrived in the New World sometime before 15,000 years ago
The oldest fossils of Homo sapiens outside Africa date back about 115,000 years and are from the Middle East Humans first arrived in the New World sometime before 15,000 years ago In 2004, 18,000-year-old fossils were found in Indonesia, and a new small hominin was named: Homo floresiensis © 2011 Pearson Education, Inc.

In 2002, a 77,000-year-old artistic carving was found in South Africa
Homo sapiens were the first group to show evidence of symbolic and sophisticated thought In 2002, a 77,000-year-old artistic carving was found in South Africa © 2011 Pearson Education, Inc.

Figure 34.52 Figure Art, a human hallmark. 179

Figure 34.UN10 Summary figure, Concepts 34.1–34.7
Clade Description Cephalochordata (lancelets) Basal chordates; marine suspension feeders that exhibit four key derived characters of chordates Urochordata (tunicates) Marine suspension feeders; larvae display the derived traits of chordates Myxini (hagfishes and relatives) Jawless marine organisms; have head that includes a skull and brain, eyes, and other sensory organs Chordates: notochord; dorsal, hollow nerve cord; pharyngeal slits; post-anal tail Craniates: two sets of Hox genes, neural crest Petromyzontida (lampreys) Jawless vertebrates; typically feed by attaching to a live fish and ingesting its blood Gnathostomes: hinged jaws, four sets of Hox genes Vertebrates: Dix genes duplication, backbone of vertebrae Chondrichthyes (sharks, rays, skates, ratfishes) Aquatic gnathostomes; have cartilaginous skeleton, a derived trait formed by the reduction of an ancestral mineralized skeleton Actinopterygii (ray-finned fishes) Aquatic gnathostomes; have bony skeleton and maneuverable fins supported by rays Actinistia (coelacanths) Ancient lineage of aquatic lobe-fins still surviving in Indian Ocean Osteichthyans: bony skeleton Dipnoi (lungfishes) Freshwater lobe-fins with both lungs and gills; sister group of tetrapods Lobe-fins: muscular fins or limbs Amphibia (salamanders, frogs, caecilians) Have four limbs descended from modified fins; most have moist skin that functions in gas exchange; many live both in water (as larvae) and on land (as adults) Figure 34.UN10 Summary figure, Concepts 34.1–34.7 Tetrapods: four limbs, neck, fused pelvic girdle Amniotes: amniotic egg, rib cage ventilation Reptilia (tuataras, lizards and snakes, turtles, crocodilians, birds) One of two groups of living amniotes; have amniotic eggs and rib cage ventilation, key adaptations for life on land Mammalia (monotremes, marsupials, eutherians) Evolved from synapsid ancestors; include egg-laying monotremes (echidnas, platypus); pouched marsupials (such as kangaroos, opossums); and eutherians (placental mammals, such as rodents, primates) 180

The Origin and Evolution of Vertebrates

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The Origin and Evolution of Vertebrates

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