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About This Drill
ACT Science: Conflicting Viewpoints (Drill 3) is a Science practice drill covering Conflicting Viewpoints. It contains 5 original questions created by Brian Stewart, a Barron's test prep author with over 20 years of tutoring experience.
ACT Conflicting Viewpoints questions require analysis of competing scientific positions. In this drill, two scientists debate dinosaur thermoregulation, endothermy versus ectothermy, asking you to identify key evidence, locate points of agreement, and determine what findings would weaken each scientist's argument.
Questions & Explanations
Scientists 1 and 2
Whether non-avian dinosaurs were endotherms (warm-blooded, maintaining a stable internal body temperature through metabolic heat production) or ectotherms (cold-blooded, relying primarily on external heat sources) has been debated for decades. Scientists agree on several lines of evidence: many dinosaur bones contain fibrolamellar bone tissue, which in modern animals is associated with rapid, sustained growth; some small theropod dinosaurs had feathers, confirmed by exquisitely preserved fossils; dinosaur fossils have been found at high paleolatitudes, including sites in what is now Alaska and Antarctica; and modern birds -- which are endotherms -- are classified as living theropod dinosaurs. How these facts bear on dinosaur physiology is disputed.
Scientist 1
Dinosaurs were endotherms that maintained stable, elevated body temperatures through internal metabolic heat production, much like modern birds and mammals. The strongest evidence is the bone histology: fibrolamellar bone, found in a wide range of dinosaur species from large sauropods to small theropods, is a tissue laid down rapidly and continuously, requiring the high and sustained metabolic rates characteristic of endothermy. The presence of feathers on small theropods such as
Velociraptor and
Microraptor indicates these animals needed insulation to retain body heat -- an adaptation that only makes sense for an endotherm. Oxygen isotope analysis of dinosaur tooth enamel suggests stable body temperatures of approximately 36 to 38°C, consistent with endothermy. Dinosaur fossils are abundant at high paleolatitudes where seasonal temperatures were cold; surviving year-round in such environments almost certainly required the ability to generate internal heat. Finally, because modern birds -- the living descendants of theropod dinosaurs -- are endotherms, endothermy in the broader dinosaur lineage is the most parsimonious interpretation of the fossil and phylogenetic evidence.
Scientist 2
Dinosaurs were not fully endothermic. Large-bodied dinosaurs could have achieved thermal stability through gigantothermy -- a physical process by which a very large body mass slows the rate of heat gain and loss, producing relatively constant internal temperatures without requiring the high metabolic rates of true endothermy. Growth rings observed in the bones of some dinosaur species are more consistent with the periodic, environmentally driven growth patterns of ectotherms than with the continuous growth of endotherms. The metabolic rates inferred from bone microstructure in several large dinosaur species fall between those of modern ectotherms and endotherms, suggesting an intermediate physiology -- sometimes called mesothermy -- rather than full warm-bloodedness. Maintaining the high metabolic rate of full endothermy would have imposed enormous food requirements that may have been unsustainable for the largest herbivorous dinosaurs. The presence of feathers in some theropods may have served primarily for display or brooding rather than thermoregulation, as feathers serve multiple functions in modern birds.
Question 1. According to Scientist 1, what does the presence of fibrolamellar bone in dinosaurs indicate?
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A) Rapid, sustained growth requiring high metabolic rates consistent with endothermy ✓
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B) Periodic, seasonal growth consistent with ectothermic physiology
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C) The ability to regulate temperature through gigantothermy
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D) A close evolutionary relationship between dinosaurs and modern crocodilians, in Scientist 1's account
Explanation: Scientist 1 states: "fibrolamellar bone, found in a wide range of dinosaur species from large sauropods to small theropods, is a tissue laid down rapidly and continuously, requiring the high and sustained metabolic rates characteristic of endothermy." Option B describes Scientist 2's interpretation of growth rings -- a different bone feature. Option C describes Scientist 2's gigantothermy argument. Option D is not claimed by either scientist.
Scientists 1 and 2
Whether non-avian dinosaurs were endotherms (warm-blooded, maintaining a stable internal body temperature through metabolic heat production) or ectotherms (cold-blooded, relying primarily on external heat sources) has been debated for decades. Scientists agree on several lines of evidence: many dinosaur bones contain fibrolamellar bone tissue, which in modern animals is associated with rapid, sustained growth; some small theropod dinosaurs had feathers, confirmed by exquisitely preserved fossils; dinosaur fossils have been found at high paleolatitudes, including sites in what is now Alaska and Antarctica; and modern birds -- which are endotherms -- are classified as living theropod dinosaurs. How these facts bear on dinosaur physiology is disputed.
Scientist 1
Dinosaurs were endotherms that maintained stable, elevated body temperatures through internal metabolic heat production, much like modern birds and mammals. The strongest evidence is the bone histology: fibrolamellar bone, found in a wide range of dinosaur species from large sauropods to small theropods, is a tissue laid down rapidly and continuously, requiring the high and sustained metabolic rates characteristic of endothermy. The presence of feathers on small theropods such as
Velociraptor and
Microraptor indicates these animals needed insulation to retain body heat -- an adaptation that only makes sense for an endotherm. Oxygen isotope analysis of dinosaur tooth enamel suggests stable body temperatures of approximately 36 to 38°C, consistent with endothermy. Dinosaur fossils are abundant at high paleolatitudes where seasonal temperatures were cold; surviving year-round in such environments almost certainly required the ability to generate internal heat. Finally, because modern birds -- the living descendants of theropod dinosaurs -- are endotherms, endothermy in the broader dinosaur lineage is the most parsimonious interpretation of the fossil and phylogenetic evidence.
Scientist 2
Dinosaurs were not fully endothermic. Large-bodied dinosaurs could have achieved thermal stability through gigantothermy -- a physical process by which a very large body mass slows the rate of heat gain and loss, producing relatively constant internal temperatures without requiring the high metabolic rates of true endothermy. Growth rings observed in the bones of some dinosaur species are more consistent with the periodic, environmentally driven growth patterns of ectotherms than with the continuous growth of endotherms. The metabolic rates inferred from bone microstructure in several large dinosaur species fall between those of modern ectotherms and endotherms, suggesting an intermediate physiology -- sometimes called mesothermy -- rather than full warm-bloodedness. Maintaining the high metabolic rate of full endothermy would have imposed enormous food requirements that may have been unsustainable for the largest herbivorous dinosaurs. The presence of feathers in some theropods may have served primarily for display or brooding rather than thermoregulation, as feathers serve multiple functions in modern birds.
Question 2. Which of the following statements would both Scientist 1 and Scientist 2 most likely accept?
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A) All dinosaurs were fully endothermic, with metabolic rates equivalent to those of modern birds
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B) Feathers in theropod dinosaurs functioned exclusively as thermal insulation
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C) Dinosaurs grew faster than modern ectothermic reptiles such as lizards and crocodilians ✓
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D) Gigantothermy fully accounts for thermoregulation in all dinosaur species regardless of body size
Explanation: Both scientists acknowledge that dinosaur bones contain fibrolamellar bone, which is associated with rapid, sustained growth -- faster than modern ectotherms. The intro paragraph establishes this as agreed evidence. Scientist 1 uses this to argue for endothermy; Scientist 2 acknowledges the faster growth but argues it implies mesothermy rather than full endothermy. Both accept the raw observation: faster growth than modern reptiles. Option A is Scientist 1's position only. Option B is contradicted by Scientist 2, who says feathers may have served "primarily for display or brooding." Option D is only part of Scientist 2's claim, and even Scientist 2 does not say gigantothermy applies to all sizes.
Scientists 1 and 2
Whether non-avian dinosaurs were endotherms (warm-blooded, maintaining a stable internal body temperature through metabolic heat production) or ectotherms (cold-blooded, relying primarily on external heat sources) has been debated for decades. Scientists agree on several lines of evidence: many dinosaur bones contain fibrolamellar bone tissue, which in modern animals is associated with rapid, sustained growth; some small theropod dinosaurs had feathers, confirmed by exquisitely preserved fossils; dinosaur fossils have been found at high paleolatitudes, including sites in what is now Alaska and Antarctica; and modern birds -- which are endotherms -- are classified as living theropod dinosaurs. How these facts bear on dinosaur physiology is disputed.
Scientist 1
Dinosaurs were endotherms that maintained stable, elevated body temperatures through internal metabolic heat production, much like modern birds and mammals. The strongest evidence is the bone histology: fibrolamellar bone, found in a wide range of dinosaur species from large sauropods to small theropods, is a tissue laid down rapidly and continuously, requiring the high and sustained metabolic rates characteristic of endothermy. The presence of feathers on small theropods such as
Velociraptor and
Microraptor indicates these animals needed insulation to retain body heat -- an adaptation that only makes sense for an endotherm. Oxygen isotope analysis of dinosaur tooth enamel suggests stable body temperatures of approximately 36 to 38°C, consistent with endothermy. Dinosaur fossils are abundant at high paleolatitudes where seasonal temperatures were cold; surviving year-round in such environments almost certainly required the ability to generate internal heat. Finally, because modern birds -- the living descendants of theropod dinosaurs -- are endotherms, endothermy in the broader dinosaur lineage is the most parsimonious interpretation of the fossil and phylogenetic evidence.
Scientist 2
Dinosaurs were not fully endothermic. Large-bodied dinosaurs could have achieved thermal stability through gigantothermy -- a physical process by which a very large body mass slows the rate of heat gain and loss, producing relatively constant internal temperatures without requiring the high metabolic rates of true endothermy. Growth rings observed in the bones of some dinosaur species are more consistent with the periodic, environmentally driven growth patterns of ectotherms than with the continuous growth of endotherms. The metabolic rates inferred from bone microstructure in several large dinosaur species fall between those of modern ectotherms and endotherms, suggesting an intermediate physiology -- sometimes called mesothermy -- rather than full warm-bloodedness. Maintaining the high metabolic rate of full endothermy would have imposed enormous food requirements that may have been unsustainable for the largest herbivorous dinosaurs. The presence of feathers in some theropods may have served primarily for display or brooding rather than thermoregulation, as feathers serve multiple functions in modern birds.
Question 3. Which of the following findings, if confirmed, would most weaken Scientist 2's hypothesis?
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A) Oxygen isotope analysis of large sauropod teeth indicates body temperatures of approximately 37°C
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B) Small-bodied juvenile dinosaurs, whose mass was far too low for gigantothermy, also exhibit fibrolamellar bone identical to that of adults ✓
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C) Feathered dinosaur fossils are found only in warm, low-latitude environments
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D) Some large dinosaurs show both fibrolamellar bone and growth rings in the same bone section
Explanation: Scientist 2's primary explanation for dinosaur thermoregulation is gigantothermy -- which depends specifically on very large body mass to buffer temperature. A small-bodied juvenile dinosaur, regardless of what species it belongs to, lacks the mass required for gigantothermy. If juveniles show the same fibrolamellar bone (indicating rapid, continuous growth and high metabolic rate) as adults, then gigantothermy cannot explain dinosaur physiology generally -- it would leave the thermoregulation of young, small individuals completely unexplained. This is a significant gap that strongly undermines Scientist 2. Option A is consistent with Scientist 2's mesothermy claim and does not specifically weaken it. Option C would weaken Scientist 1's insulation argument but not directly weaken Scientist 2. Option D is ambiguous and does not directly attack the core of Scientist 2's claim.
Scientist 2
Whether non-avian dinosaurs were endotherms (warm-blooded, maintaining a stable internal body temperature through metabolic heat production) or ectotherms (cold-blooded, relying primarily on external heat sources) has been debated for decades. Scientists agree on several lines of evidence: many dinosaur bones contain fibrolamellar bone tissue, which in modern animals is associated with rapid, sustained growth; some small theropod dinosaurs had feathers, confirmed by exquisitely preserved fossils; dinosaur fossils have been found at high paleolatitudes, including sites in what is now Alaska and Antarctica; and modern birds -- which are endotherms -- are classified as living theropod dinosaurs. How these facts bear on dinosaur physiology is disputed.
Scientist 2
Dinosaurs were not fully endothermic. Large-bodied dinosaurs could have achieved thermal stability through gigantothermy -- a physical process by which a very large body mass slows the rate of heat gain and loss, producing relatively constant internal temperatures without requiring the high metabolic rates of true endothermy. Growth rings observed in the bones of some dinosaur species are more consistent with the periodic, environmentally driven growth patterns of ectotherms than with the continuous growth of endotherms. The metabolic rates inferred from bone microstructure in several large dinosaur species fall between those of modern ectotherms and endotherms, suggesting an intermediate physiology -- sometimes called mesothermy -- rather than full warm-bloodedness. Maintaining the high metabolic rate of full endothermy would have imposed enormous food requirements that may have been unsustainable for the largest herbivorous dinosaurs. The presence of feathers in some theropods may have served primarily for display or brooding rather than thermoregulation, as feathers serve multiple functions in modern birds.
Question 4. Scientist 2 argues that gigantothermy could explain the stable body temperatures inferred from isotope analysis of large dinosaur bones. This argument assumes which of the following?
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A) All dinosaurs were larger than any living ectotherm
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B) Oxygen isotope analysis cannot reliably measure ancient body temperatures
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C) The degree of thermal stability observed in the isotope data could be produced by body mass alone, without internal heat generation ✓
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D) Modern birds are not true endotherms and therefore cannot be used as a comparison for dinosaur physiology
Explanation: Scientist 1 points to isotope data suggesting stable body temperatures of ~36-38°C. Scientist 2 counters by proposing gigantothermy as an alternative explanation. For gigantothermy to work as an explanation here, Scientist 2 must assume that a large body mass can produce the same level of thermal stability that the isotope data shows -- without the animal generating its own metabolic heat. If body mass cannot produce temperatures as stable as the isotope data indicates, then gigantothermy fails as an explanation and endothermy must be invoked. Option A is false -- some dinosaurs were small, and Scientist 2 does not claim all dinosaurs were large. Option B would undermine Scientist 1's isotope evidence but would also remove the very data Scientist 2 is trying to explain with gigantothermy. Option D contradicts agreed scientific consensus that Scientist 2 does not dispute.
Scientists 1 and 2
Whether non-avian dinosaurs were endotherms (warm-blooded, maintaining a stable internal body temperature through metabolic heat production) or ectotherms (cold-blooded, relying primarily on external heat sources) has been debated for decades. Scientists agree on several lines of evidence: many dinosaur bones contain fibrolamellar bone tissue, which in modern animals is associated with rapid, sustained growth; some small theropod dinosaurs had feathers, confirmed by exquisitely preserved fossils; dinosaur fossils have been found at high paleolatitudes, including sites in what is now Alaska and Antarctica; and modern birds -- which are endotherms -- are classified as living theropod dinosaurs. How these facts bear on dinosaur physiology is disputed.
Scientist 1
Dinosaurs were endotherms that maintained stable, elevated body temperatures through internal metabolic heat production, much like modern birds and mammals. The strongest evidence is the bone histology: fibrolamellar bone, found in a wide range of dinosaur species from large sauropods to small theropods, is a tissue laid down rapidly and continuously, requiring the high and sustained metabolic rates characteristic of endothermy. The presence of feathers on small theropods such as
Velociraptor and
Microraptor indicates these animals needed insulation to retain body heat -- an adaptation that only makes sense for an endotherm. Oxygen isotope analysis of dinosaur tooth enamel suggests stable body temperatures of approximately 36 to 38°C, consistent with endothermy. Dinosaur fossils are abundant at high paleolatitudes where seasonal temperatures were cold; surviving year-round in such environments almost certainly required the ability to generate internal heat. Finally, because modern birds -- the living descendants of theropod dinosaurs -- are endotherms, endothermy in the broader dinosaur lineage is the most parsimonious interpretation of the fossil and phylogenetic evidence.
Scientist 2
Dinosaurs were not fully endothermic. Large-bodied dinosaurs could have achieved thermal stability through gigantothermy -- a physical process by which a very large body mass slows the rate of heat gain and loss, producing relatively constant internal temperatures without requiring the high metabolic rates of true endothermy. Growth rings observed in the bones of some dinosaur species are more consistent with the periodic, environmentally driven growth patterns of ectotherms than with the continuous growth of endotherms. The metabolic rates inferred from bone microstructure in several large dinosaur species fall between those of modern ectotherms and endotherms, suggesting an intermediate physiology -- sometimes called mesothermy -- rather than full warm-bloodedness. Maintaining the high metabolic rate of full endothermy would have imposed enormous food requirements that may have been unsustainable for the largest herbivorous dinosaurs. The presence of feathers in some theropods may have served primarily for display or brooding rather than thermoregulation, as feathers serve multiple functions in modern birds.
Question 5. Researchers recover a well-preserved skeleton of a small theropod dinosaur (estimated adult mass: 4 kg) from a site at a high paleolatitude. Oxygen isotope analysis of its teeth indicates a stable year-round body temperature of approximately 38°C. This finding most strongly supports the hypothesis of:
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A) Scientist 2 only, because a 4 kg animal is small enough to gain heat efficiently from its environment
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B) Scientist 1 only, because a small animal at high latitude maintaining a stable 38°C could not do so through gigantothermy or behavioral basking ✓
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C) Both scientists equally, because both predict stable body temperatures in theropod dinosaurs
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D) Neither scientist, because the finding applies only to one individual specimen
Explanation: This finding combines three features that together strongly favor endothermy: small body (4 kg -- far too small for gigantothermy, which requires massive body volume to buffer temperature changes); high paleolatitude (cold environment with limited solar warming); and stable ~38°C body temperature year-round. Gigantothermy works only for animals with very large body mass, so it cannot explain this small animal's thermal stability. Behavioral thermoregulation by basking is ineffective at high latitudes with limited sunlight. The only mechanism that explains a stable warm body temperature in a small animal in a cold, high-latitude environment is internal metabolic heat production -- endothermy -- exactly as Scientist 1 argues. Option C is wrong because Scientist 2 does NOT predict stable warm temperatures in small-bodied animals; gigantothermy is explicitly a large-body phenomenon.