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When Darwin wrote On the Origin of Species, no transitional fossils had been discovered, but Darwin predicted that some would be found. On which of the following concepts was Darwin basing his bold prediction?
Individual animals do not change into different species. The formation of new species occurs over thousands and millions of years and involves entire groups of organisms, not individuals. Try again.
Correct! The history of life shows that a major group of organisms can change over long periods of time and a new group can form. Transitional fossils that have some characters of the new group and some from the ancestral group are a logical prediction. Select another correct answer. You selected all the correct answers.
Darwin did not expect that every single fossil would be discovered. It is extremely rare for any organism to become fossilized, and even when a fossil does form, it may never be discovered. However, as scientists unearthed more fossils, Darwin predicted that some transitional forms would be found among them. Try again.
Correct! Life has been evolving on this planet for at least 3.8 billion years, and in that time, major changes have taken place. Groups with different combinations of ancestral and new traits show the changes that occurred during the history of life. Select another correct answer. You selected all the correct answers.
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The 150-million-year-old Archaeopteryx has many birdlike characteristics such as feathered wings, but it also has characteristics that we associate with living reptiles. Which of the following are considered reptilian characteristics of Archaeopteryx? Select all that apply.
An elongated fourth digit supported the wings of pterosaurs, a group of Mesozoic reptiles. In Archaeopteryx, feathers were attached to each of its three digits on each hand. Try again.
Correct! Unlike their reptilian cousins, living birds have forelimbs adapted for flight, not grasping, digging, or defense. Select another correct answer. You selected all the correct answers.
Correct! Many living birds have feathers that extend past their hips, but bones do not support the feathers. Select another correct answer. You selected all the correct answers.
Correct! Living birds have beaks in all shapes and sizes, but they all have one thing in common: they lack structures usually associated with the mouth such as teeth. Select another correct answer. You selected all the correct answers.
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Which discovery finally overturned the prevailing perception that all dinosaurs were large, slow, and lumbering?
Pterosaurs are not dinosaurs. Try again.
Correct! Deinonychus' anatomy, including its sickle-shaped claw, indicated that it was a very agile and quick predator. After its discovery by John Ostrom, most scientists began to see dinosaurian biology and behavior differently. Select another correct answer. You selected all the correct answers.
Darwin's colleague, Thomas Huxley, compared Compsognathus to Archaeopteryx, but his findings failed to convince the scientific community of the kinship among birds and dinosaurs or that dinosaurs could be quick and agile predators. Try again.
Archaeopteryx was a stunning discovery but failed to change the prevailing view that dinosaurs were large and slow. Although clearly suggesting a link between reptiles and birds, scientists had not yet concluded that birds had evolved from a group of dinosaurs. Try again.
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How did Dr. Jack Horner's discovery of dinosaur nesting grounds support the hypothesis that birds evolved from a group of dinosaurs?
Correct! Dr. Horner's discovery of "Egg Mountain" in Montana led to the conclusion that some dinosaurs returned annually to nesting grounds, brooded, and cared for their young—all behaviors associated with birds. Select another correct answer. You selected all the correct answers.
Paleontologists already knew that some dinosaur species lived in groups. Try again.
Paleontologists knew that dinosaurs hatched from eggs before Dr. Horner's discovery. Try again.
There is a lot of debate about whether dinosaurs were ectothermic, like living amphibians and reptiles, or endothermic, like birds and mammals. Dr. Horner’s discovery of nests did not contribute to this debate. Try again.
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Which of the following pieces of evidence supports the hypothesis that birds evolved from theropod dinosaurs? Select all that apply.
Correct! Theropods and birds walk on two legs, which requires adaptations to other parts of their anatomy. Select another correct answer. You selected all the correct answers.
Although many theropods had feathers, they most likely could not fly. Additionally, not all modern birds fly, such as penguins or ostriches. Try again.
Correct! It took a long time for paleontologists to find theropods with this key piece of bird anatomy. Select another correct answer. You selected all the correct answers.
Correct! Reexamination of fossil evidence, as well as new fossil discoveries, has revealed many theropods with this characteristic—once thought to be associated only with birds. Select another correct answer. You selected all the correct answers.
Correct! Even the largest theropods had this trait, which helps enable flight in birds. Select another correct answer. You selected all the correct answers.
Living birds don't have long bony tails, which would impede flight. The few tail (caudal) vertebrae that they have are fused into a structure called the pygostyle. Try again.
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Which of the following statements about bird evolution are accurate based on the evidence presented? Select all that apply.
Correct! Some theropods had feathers with a structure similar to those of duck down. Select another correct answer. You selected all the correct answers.
Archaeopteryx lived before the mass extinction that killed off nonavian dinosaurs. Try again.
The evolutionary history of birds includes species with different combinations of traits. Try again.
Correct! There is increasing evidence that early theropod feathers came in a range of colors. Feather color and pattern help living birds to signal to one another. Select another correct answer. You selected all the correct answers.
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Which of the following pieces of evidence led scientists to propose that the first feathers served a purpose other than flight?
Correct! Some living birds use their feathers for functions other than flight, such as insulation or communication. This evidence suggests that theropods may have used feathers for other functions too, and later lineages co-opted them for flight. Select another correct answer. You selected all the correct answers.
Flight arose independently multiple times in different lineages of organisms. The origin of flight in bats does not provide insights into the function of feathers. Try again.
Correct! A rich diversity of theropods with various feather structures and from different ages supports the hypothesis that feathers evolved long before flight. Select another correct answer. You selected all the correct answers.
Archaeopteryx had asymmetrical feathers that probably enabled flight. This discovery did not indicate that feathers had a function other than flight. Try again.
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Why is the discovery of organisms such as Archaeopteryx that have a mix of traits usually associated with two different groups considered validation of Darwin's theory of evolution?
Correct! Intermediate forms, such as Archaeopteryx, support the hypothesis because they have some features of the descendant species and some features of the ancestral species. This suggests that within a single lineage, some descendant features evolved before ancestral features were lost. For example, wings (a descendant feature of modern birds) evolved before long bony tails (an ancestral feature of nonavian theropods) were lost, as seen in Archaeopteryx. Select another correct answer. You selected all the correct answers.
To date, the oldest genome sequenced is from a 700,000-year-old horse fossil. DNA would not have been available in fossils as old as Archaeopteryx. Try again.
Intermediate fossils are not needed to establish the long history of life on Earth. Try again.
Even if every fossil that exists were found, it still would not provide a complete history of life on Earth. Most organisms that have lived were never fossilized. Of the ones that were, countless fossils have been lost to erosion or tectonic plate movements, or are buried too deep to be found by scientists. Try again.