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  3. Dinosaurs and Parental CareP1: "Parental care" refers to the level of investmen

Dinosaurs and Parental CareP1: "Parental care" refers to the level of investmen

游客2024-01-02  20
问题 Dinosaurs and Parental Care
P1: "Parental care" refers to the level of investment provided by a mother and father to insure the development and survival of their offspring. The question of whether or not dinosaurs cared for their young has puzzled scientists for decades. A remarkable Oviraptor fossil shows the dinosaur sitting on its nest of eggs just as chickens do today. Not only is the dinosaur squatting on the nest, but its forelimbs are outstretched, perhaps to shade the eggs. Because behaviors are not preserved in the fossil record, we can only make inferences from indirect evidence. Most of our evidence comes from alleged dinosaur rookeries (places where nests are built). Several have been excavated in eastern Montana, where a dense concentration of dinosaur nests was found at a place now called Egg Mountain, most of which probably belonged to the hadrosaur Maiasaura. Preserved in these nests are the bones of baby dinosaurs. The finds at Egg Mountain and other sites around the world document that dinosaurs laid their eggs in nests.
P2: The nests at Egg Mountain are reported to be equally spaced, separated by a space corresponding to the length of an adult Maiasaura. From this arrangement scientists have inferred that the nests were separated in this way to allow incubation in a tightly packed nesting colony. Although this interpretation is disputable, the discovery of Oviraptor adults on top of egg clutches (as determined by embryos in some eggs) is relatively powerful evidence that at least these dinosaurs incubated their eggs.
P3: Evidence for parental care following hatching is much more controversial. The truth is probably biased by behavioral speculation based on indirect fossil evidence because the data is not always as unambiguous as might appear. At Egg Mountain, many nests contain baby dinosaur bones. Not all the dinosaurs in the nest are the same size, and the preserved partial skeleton was so small that its bones were originally mistaken for those of a fossilized crocodile. Besides, many of those small bones belong to jaws and teeth—teeth that show signs of wear. It seems reasonable to assume that the wear was caused by chewing the coarse plants that formed the hatchlings’ diet. During childhood, the young would never step outside the nest, so it seems reasonable to assume that all the food they consumed must have been brought to the rookery by foraging adults. This line of reasoning suggests that these animals had an advanced system of parental care, but a closer look at the evidence clouds this interpretation. Analysis of dinosaur embryos indicates that worn surfaces are present on the teeth of juveniles even before hatching. Just as a human baby moves inside the mother before birth, archosaurs also ground their teeth before birth, wearing the surface in some spots. Thus, the fossil evidence for an advanced parental care system in extinct dinosaurs is suggestive but inconclusive.
P4: In order to settle this debate for good, much research has been conducted regarding whether extinct dinosaurs had independently evolved parenting behaviors similar to those of modern-day organisms. Examination of the phylogenetic position of dinosaurs indicates that they share a common ancestor with and are most closely related to two living groups of animals—crocodiles and birds—both of which exhibit parental care. Although unappreciated, crocodiles do nevertheless exhibit parental care. Female crocodilians build nests and then remain nearby, guarding them, while the eggs incubate. When they are ready to hatch, the baby crocodiles vocalize; females respond by digging up the eggs and carrying the babies to the water. The young even communicate with each other while still in the egg by high-frequency squeaks (as birds do). Some evidence suggests that this squeaking is a cue to synchronize hatching. Since birds and crocodiles share a common ancestor, the simplest explanation for the characteristics they share (such as nest building and some form of parental care) is that they evolved only once—that these attributes were present in their common ancestor and passed on to its descendants. It appears likely, therefore, that the parental care exhibited by both crocodiles and birds did not evolve separately from different ancestors that did not exhibit parental care; rather, the behaviors are homologous (even though this cannot be directly observed, and we cannot be sure how elaborate early parental care was), inherited by each of these groups from their common ancestor that cared for its young.
P1: "Parental care" refers to the level of investment provided by a mother and father to insure the development and survival of their offspring. The question of whether or not dinosaurs cared for their young has puzzled scientists for decades. ■A remarkable Oviraptor fossil shows the dinosaur sitting on its nest of eggs just as chickens do today. Not only is the dinosaur squatting on the nest, but its foreiimbs are outstretched, perhaps to shade the eggs. ■Because behaviors are not preserved in the fossil record, we can only make inferences from indirect evidence. ■Most of our evidence comes from alleged dinosaur rookeries (places where nests are built). Several have been excavated in eastern Montana, where a dense concentration of dinosaur nests was found at a place now called Egg Mountain, most of which probably belonged to the hadrosaur Maiasaura. Preserved in these nests are the bones of baby dinosaurs. ■The finds at Egg Mountain and other sites around the world document that dinosaurs laid their eggs in nests. [br] The word "alleged" in the passage is closest in meaning to
选项 A、scattered
B、supposed
C、isolated
D、exposed
答案 B
解析 【词汇题】alleged意为“声称的，所谓的”。
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