chapter 34

Which of the following correctly lists probable ancestors of modern humans from the earliest to the most recent?

Sahelanthropus, Ardipithecus, Australopithecus, Homo

wat hey have cartilaginous segments surrounding the

notochord and arching partly over the nerve cord

Lancelets

are invert chordates

The notochord persists as the main ________ in adult lampreys

axial skeleton

Which of the following pairs is not a correct match?

Gnathostomata, hagfish

As hominins diverged from other primates, which of the following appeared first?

bipedal locomotion

Which of the following traits distinguishes hominins from other apes?

bipedalism (upright walking)

Nearly all living osteichthyans have

bony endoskeleton

Which of the following animals is an amphibian?

caecilian

chordates develops into the

central nervous system

Based on the phylogeny shown in Figure 34.25, identify the sister group for (a) reptiles, (b) squamates, and (c) the clade that includes crocodilians and birds.

(a) synapsids, (b) tuataras, (c) turtles

All chordates share a set of derived characters that may not persist past the embryo stage

1. Notochord 2. Dorsal, hollow nerve cord 3. Pharyngeal slits or clefts 4. Muscular, post-anal tail

Functions of pharyngeal slits

1. Suspension-feeding structures in many invertebrate chordates 2. Gas exchange in fishes 3. Develop into parts of the ear, head, and neck in tetrapods

chordates that have backbones derived characteristics

1. Two or more more sets of HOX genes 2. vertebrate usually enclosing the spinal cord 3. An elaborate skull 4. A neural crest

Amphibians require water for reproduction; their bodies can lose water rapidly through their moist, highly permeable skin; and amphibian eggs do not have a shell and hence are vulnerable to desiccation.

Amphibians require water for reproduction; their bodies can lose water rapidly through their moist, highly permeable skin; and amphibian eggs do not have a shell and hence are vulnerable to desiccation.

Describe key adaptations of aquatic gnathostomes.

Aquatic gnathostomes have jaws and paired fins and a tail. Aquatic gnathostomes also typically have streamlined bodies for efficient swimming and swim bladders or other mechanisms for buoyancy.

Explain why birds are considered reptiles.

Birds are descended from theropod dinosaurs and dinosaurs are nested within the archosaur lineage one of the two main reptiles. Thus, the other living archosaur reptiles, the crocodilians are more closely related to birds than they are to non- archosaur reptiles such as lizards.

Identify four avian adaptations for flight.

Birds have weight-saving modifications, including the absence of teeth, a urinary bladder, and a second ovary in females. The wings and feathers are adaptations that facilitate flight, as do efficient respiratory and circulatory systems that support a high metabolic rate.

What derived characters do sharks and tuna share? What features distinguish tuna from sharks?

Both are gnathostomes and have jaws, four clusters of Hox genes, enlarged forebrains, and lateral line systems. Shark skeletons consist mainly of cartilage, whereas tuna have bony skeletons. Sharks also have a spiral valve. Tuna have an operculum and a swim bladder, as well as flexible rays supporting their fins.

If an animal has segments, bilateral symmetry, pharyngeal clefts, a post-anal tail, and deuterostomic development, it must be a member of the

Chordata

Identify at least five derived traits of primates.

Hands and feet adapted for grasping, flat nails, large brain, forward-looking eyes on a flat face, parental care, and movable big toe and thumb

Identify some characters that distinguish hominins from other apes.

Hominins are a clade within the ape clade that includes humans and all species more closely related to humans than to other apes. The derived characters of hominins include bipedal locomotion and relatively larger brains.

What was the earliest hominin to have an enlarged brain (relative to body size)?

Homo habilis

Suggest key roles that mineralized bone might have played in early vertebrates.

In armored jawless vertebrates, bone served as external armor that may have provided protection from predators. Some species also had mineralized mouthparts, which could be used for either predation or scavenging.

Provide an example in which different features of organisms in the hominin evolutionary lineage evolved at different rates.

In hominins, bipedal locomotion evolved long before large brain size. Homo ergaster, for example, was fully upright, bipedal, and as tall as modern humans, but its brain was significantly smaller than that of modern humans.

You are a chordate, yet you lack most of the main derived characters of chordates. Explain.

In humans, these characters are present only in the embryo. The notochord becomes disks between the vertebrae; the dorsal, hollow nerve cord develops into the brain and spinal cord; the pharyngeal clefts develop into various adult structures, and the tail is almost completely lost.

Describe likely features of the common ancestor of chordates. Explain your answer.

Lancelets are the most basal group of living chordates, and as adults they have key derived characters of chordates. This suggests that the chordate common ancestor may have resembled a lancelet in having an anterior end with a mouth along with the following four derived characters: a notochord; a dorsal, hollow nerve cord; pharyngeal slits or clefts; and a muscular, post-anal tail.

Develop a hypothesis to explain why the diversity of mammals increased in the Cenozoic. Your explanation should consider mammalian adaptations as well as factors such as mass extinctions and continental drift

Mammals are endothermic, enabling them to live in a wide range of habitats. Milk provides young with a balanced set of nutrients, and hair and a layer of fat under the skin help mammals retain heat. Mammals have differentiated teeth, enabling them to eat many different kinds of food. Mammals also have relatively large brains, and many species are capable learners.

Scientists think that amphibian populations may provide an early warning system of environmental problems. What features of amphibians might make them particularly sensitive to environmental problems?

Many amphibians spend part of their life cycle in aquatic environments and part on land. Thus, they may be exposed to a wide range of environmental problems, including water and air pollution and the loss or degradation of aquatic and/or terrestrial habitats. In addition, amphibians have highly permeable skin, providing relatively little protection from external conditions, and their eggs do not have a protective shell.

Contrast monotremes, marsupials, and eutherians in terms of how they bear young.

Monotremes lay eggs. Marsupials give birth to very small live young that attach to a nipple in the mother's pouch, where they complete development. Eutherians give birth to more developed live young.

The vast majority of vertebrates belong to a clade of gnathostomes called ________

Osteichthyes

How are differences in the anatomy of lampreys and conodonts reflected in each animal's feeding method?

Parasitic lampreys have a round, rasping mouth, which they use to attach to fish. Non-parasitic lampreys feed only as larvae; these larvae resemble lancelets and like them, are suspension feeders. Conodonts had two sets of mineralized dental elements, which may have been used to impale prey and cut it into smaller pieces.

Some amphibians never leave the water, whereas others can survive in relatively dry terrestrial environments. Contrast the adaptations that facilitate these two lifestyles.

Some fully aquatic species are paedomorphic, retaining larval features for life in water as adults. Species that live in dry environments may avoid dehydration by burrowing or living under moist leaves, and they protect their eggs with foam nests, viviparity, and other adaptations.

In several different animal lineages, organisms with a head first appeared around 530 million years ago. Does this finding constitute proof that having a head is favored by natural selection? Explain.

Such a finding suggests that early organisms with a head were favored by natural selection in several different evolutionary lineages. However, while a logical argument can be made that having a head was advantageous, fossils alone do not constitute proof.

Describe the origin of tetrapods and identify some of their key derived traits.

Tetrapods are thought to have originated about 365 million years ago when the fins of some lobe-fins evolved into the limbs of tetrapods. In addition to their four limbs with digits—a key derived trait for which the group is named—other derived traits of tetrapods include a neck and a pelvic girdle that is fused to the backbone.

Describe three key amniote adaptations for life on land.

The amniotic egg provides protection to the embryo and allows the embryo to develop on land, eliminating the necessity of a watery environment for reproduction. Another key adaptation is rib cage ventilation, which improves the efficiency of air intake and may have allowed early amniotes to dispense with breathing through their skin. Finally, not breathing through their skin allowed amniotes to develop relatively impermeable skin, thereby conserving water.

Based on fossil evidence, summarize how key hominin features have changed over time.

The fossil record shows that from 4.5 to 2.5 million years ago, a wide range of hominin species walked upright but had relatively small brain sizes. About 2.5 million years ago, the first members of genus Homo emerged. These species used tools and had larger brains than those of earlier hominins. Fossil evidence indicates that multiple members of our genus were alive at any given point in time. Furthermore, until about 1.3 million years ago, these various Homo species also coexisted with members of earlier hominin lineages, such as Paranthropus. The different hominins alive at the same periods of time varied in body size, body shape, brain size, dental morphology, and the capacity for tool use. Ultimately, except for Homo sapiens, all of these species became extinct. Overall, human evolution can be viewed as an evolutionary tree with many branches--the only surviving lineage of which is our own.

Identify the four derived characters that all chordates have at some point during their life.

The four characters are a notochord; a dorsal, hollow nerve chord; pharyngeal slits or clefts; and a muscular, post-anal tail.

______ arose very early in hominid evolution; _____ evolved more recently

Upright posture; large brains

Some genetic studies suggest that the most recent common ancestor of Homo sapiens that lived outside of Africa left Africa about 50,000 years ago. Compare this date with the dates of fossils given in the text. Can both the genetic results and the dates ascribed to the fossils be correct? Explain.

Yes, both can be correct. Homo sapiens may have established populations outside of Africa as early as 115,000 years ago, as indicated by the fossil record. However, those populations may have left few or no descendants today. Instead, all living humans may have descended from Africans that spread from Africa roughly 50,000 years ago, as indicated by genetic data.

Imagine that we could replay the history of life. Is it possible that a group of vertebrates that colonized land could have arisen from aquatic gnathostomes other than the lobe-fins? Explain.

Yes, that could have happened. The paired appendages of aquatic gnathostomes other than the lobe-fins could have served as a starting point for the evolution of limbs. The colonization of land by aquatic gnathostomes other than the lobe-fins might have been facilitated in lineages that possessed lungs, as that would have enabled those organisms to breathe air.

Are snakes tetrapods? Explain.

Yes. Although snakes lack limbs, they descended from lizards with legs. Some snakes retain vestigial pelvic and leg bones, providing evidence of their descent from an ancestor with legs.

Based on the phylogenetic tree in Figure 34.2, predict which vertebrate groups should have lungs or lung derivatives. Explain.

You would expect the vertebrate groups Actinopterygii, Actinistia, Dipnoi, Amphibia, Reptilia, and Mammalia to have lungs or lung derivatives. All of these groups originate to the right of the hatch mark indicating the appearance of this derived character in their lineage.

notochord

a longitudinal, flexible rod located between the digestive tube and the nerve cord

ratfishes have a skeleton containing

a mix of cartilage and bone as well as a venomous spine in dorsal fin

Vertebrates and tunicates share

a notochord and a dorsal, hollow nerve cord

Which of the following could be considered the most recent common ancestor of living tetrapods?

a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebrates

Humans and lorises share many traits that probably evolved in our early primate ancestors; one such trait is __________.

a thumb that is relatively mobile and separate from the fingers

All species of New World monkeys are __________.

arboreal

Identify the shared features of early fossil vertebrates.

a. Conodonts, among the earliest vertebrates in the fossil record, while jawless their well developed teeth provide early signs of bone formation. Other species of jawless vertebrates developed armor on the outside of their bodies probably to protect themselves from predators. Paired appendages for locomotion and an inner ear with semicircular canals which provided a sense of balance.

Describe the origin and early evolution of mammals.

a. Mammals are members of a group of amniotes called synapsids. Early synapsids laid eggs and had a sprawling gait. The jaw was modified over time in non-mammalian synapsids, eventually coming to resemble that of a mammal. There were many species of early mammals but most of them awere small and they were not abundant or dominant members of their community. Mammals did not rise to ecolofical dominance until after the extinction of the dinosaurs.

How would the appearance of organisms with jaws have altered ecological interactions? Provide supporting evidence.

a. The origin of jaws altered how fossil gnathostomes obtained food which in turn had great ecological impact. Predators could use their jaws to grab prey or remove chunks of flesh, stimulating the evolution of increasingly sophisticated means of defense in prey species. Evidence for these changes can be found in the fossil record which includes fossils of 10 meter long predators with remarkably powerful jaws.

The adaptation that freed vertebrates from water for reproduction and allowed them to radiate into diverse terrestrial environments was the

amniotic egg

Habitat loss, the spread of a fungal disease, climate change, and pollution are causing severe population declines and extinction in

amphibians

The first vertebrates to live on land were

amphibians

The cartilaginous skeleton evolved secondarily from

an ancestral mineralized skeleton

Tunicates most resemble

chordates during their larval stage which may last only a few mins

The phylum also includes two groups of invertebrates

chordates, the urochordates and cephalochordates

One of the most ancient surviving vertebrate groups is the __________ the hag fishes

class myxini

Which of the following is among the earliest known vertebrates?

conodonts

Which of the following is an archosaur group?

crocodiles

rays and skates

dorsoventrally flattened bodies with the gills placed underneath

Which of the following can be found in vertebrates but not in lancelets and tunicates?

duplications of genes that produce signaling molecules and transcription factors, two or more clusters of Hox genes, neural crest

In many species, the tail is greatly reduced during:

embryonic development

In most vertebrates a more complex jointed skeleton develops and the adult retains only remnants of the

embryonic notochord

Which of the following characteristics is not shared by extant birds and extant reptiles?

endothermic metabolism

Included among the extant groups of apes are

gibbons, orangutans, gorillas, chimpanzees, and bonobos

Cartilaginous fishes or chondrichthyans

have a skeleton composed primarily of cartilage

Gnathostomes

have jaws that might have evolved from skeletal supports of the pharyngeal slits

Unlike eutherians, both monotremes and marsupials

have some embryonic development outside the uterus

A lamprey, a shark, a lizard, and a rabbit share all the following characteristics except __________.

hinged jaws

Chordates have a

hollow nerve cord that forms from a plate of ectoderm that rolls into a tube dorsal to the notochord

As an adult a tunicate draws in water through an

incurrent siphon, filtering food particles and expelling water through the excurrent siphon

Tunicates

invert. chloroplasts more closely related to each other chlordane's than to lanceletes

Analysis of DNA from a variety of sources has led most researchers to agree that

modern humans emerged from Africa

Hag fishes lack

jaws, have poorly developed vertebrae, have a cartilaginous skull, and retain the notochord as adults

A ______ is a chordate but not a vertebrate.

lancelet

The operculum was an important adaptation for fish because it helps with __________.

maintaining a supply of oxygen

The opossum is an example of a(n) __________ mammal.

marsupial

All mammals ______

nourish their offspring through mammary glands

Most fishes breathe by drawing water over gills protected by an ________

operculum

Primates are distinguished from other mammals by __________.

opposable thumbs, nails, and good depth perception

Most gnathostomes have

paired appendages which allie greater speed and maneuverability

Which of the following chordate characteristics contributes most to the formation of your ears?

pharyngeal clefts

in most chordates, grooves in the pharynx called ________ develop into slits that open to the outside of the body

pharyngeal clefts

Which of the following chordate characteristics contributes most to suspension-feeding devices in many invertebrate chordates?

pharyngeal slits

vertebrates are placed in the

phylum chordata and subphylum vertebrata

Chordates have a tail

posterior to the anus

tail provides a

propelling force in many aquatic species

Which of the following sets of animals contains only gnathostomes?

rays, turtles, pigeons, and tuna

Lampreys

represents 38 species which are jawless and inhabit marine and freshwater habitats

The largest group includes the

sharks, rays and skates; a smaller group includes a few dozen species of rat fishes

notochord provides

skeletal support throughout most of the length of a chordate

Rows of _________ along a hagfishes produce slime to deter a potential predator

slime glands

other animals possess a nerve cord that is

solid and positioned ventral to the digestive system

A feature of bony fish not found in sharks is __________.

swim bladder

Lancelets are marine suspension feeders

that retain characteristics of the chordate body plan as adults

Osteichthyes includes

the aquatic bony fishes and the terrestrial tetrapods

Living vertebrates can be divided into two major clades. Select the appropriate pair.

the cyclostomes and the gnathostomes

Some sharks are viviparous, which means that __________.

the young develop within the female's body