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Children and adults continue to be fascinated by dinosaurs. What was the fastest dinosaur? The largest? The oldest? The smallest? The smartest? Paleontologist and noted dinosaur expert Dale A. Russell, author of Odyssey in Time: The Dinosaurs of North America (1992), comes to the rescue with answers that will satisfy not only the beginning learner but also the longtime student. You’ll even learn why cement has been found in the feces of Tyrannosaurus rex.
Q: How much food would a typical Apatosaurus eat in a day?
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A: The amount of food an animal consumes depends on the animal’s body weight and metabolism and the energy content (calories) of the food it eats. The body weight of a dinosaur can be calculated from a scale model or from the dimensions of its limb bones.
Models suggest that the large Apatosaurus whose skeleton is in the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, weighed between 17,000 and 30,000 kg (37,000 and 66,000 lb), whereas the same animal’s long bones suggest a weight of 35,000 kg (77,000 lb). For comparison, a large elephant weighs about 6,000 kg (13,000 lb). The posture of the neck of Apatosaurus and the nature of wear on teeth in the related Diplodocus suggest that Apatosaurus browsed on low-growing plants such as ferns. The foliage of such plants has a low caloric content, only about 1.1 calories per gram.
If an Apatosaurus weighing 35,000 kg (77,000 lb) had a metabolic rate similar to that of reptiles that live today, it would have required 86 kg (190 lb) of food per day. If it had a metabolic rate similar to that of today’s mammals, it would have required 415 kg (915 lb) of food per day. Based on the general anatomy of Apatosaurus, it seems that adult animals would have tended to eat like reptiles, while young animals might have eaten at rates approaching those typical of mammals, to support a high growth rate.
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Q: I’m interested in becoming a paleontologist, and would like to hear firsthand what it is like. What are the positive and negative aspects of the profession?
A: We might consider Dr. Alan Grant in the film Jurassic Park as an example of what it is like to be a paleontologist. As an academic, he is charmingly awkward in a social context but very much part of the scene in the movie. He is intellectually surprised by what he encounters in the Mesozoic world created in the movie, but he has a preconception of what it should be like.
The wonderful side of the life of a paleontologist is in imagining the worlds of the past and understanding one’s place in the stream of life. It is, as one aviator wrote, like reaching out and touching the face of God. And the past gives one a perspective from which the beauty of the present can more easily be appreciated.
The difficult side of being a paleontologist is the search for funding to support one’s students and carry out a program of teaching and research.
I think we need paleontologists to orient ourselves in space and time–our life spans are too brief to provide measures on grand scales. Paleontologists also help us judge global changes in the present by comparing them to changes that have occurred in the past.
Q: Did birds evolve from dinosaurs?
A: A small birdlike dinosaur, called the archaeopteryx, lived in what is now southern Germany about 150 million years ago. About the size of a crow, it had a shortened tail, long hands, a perching toe slightly turned backward, and wing feathers that were adapted for flight. This creature has long been considered the most ancient bird known. However, despite its birdlike characteristics, its body more closely resembled those of small meat-eating dinosaurs than those of more birdlike dinosaurs. Many paleontologists identify the archaeopteryx as the so-called missing link between early reptiles and modern birds.
Preserved within lake deposits in northeastern China dating to 125 million years ago are skeletons of small dinosaurs covered with hairlike filaments and/or feathers unsuited for flight. With them are found the remains of numerous small and medium-sized birds that obviously could fly. Remains of birdlike dinosaurs also occur in sediments deposited from 85 million to 65 million years ago in Asia, North America, and South America. All of these birdlike dinosaurs are included within a group of meat-eating dinosaurs called coelurosaurs. Although these animals occur too late in time to have been ancestral to birds, their skeletal anatomy suggests that they were closely related to the archaeopteryx.
The similarities between the archaeopteryx and the coelurosaurs strongly suggest that birds evolved from dinosaurs.
Q: Why are coprolites important in the study of dinosaurs?
A: Coprolites are fossilized fecal material. Any coprolite that is recovered from sediments deposited on land between 200 million and 65 million years ago and that is larger than the feces of a small dog was probably produced by a dinosaur. However, fecal material deposited on land decomposes rapidly, and dinosaur coprolites are uncommon.
Coprolites provide evidence of the food and digestive processes of dinosaurs. This evidence, in turn, yields important information about how dinosaurs affected the plants and animals with which they shared their world.
Pellets resembling sheep dung and containing cellular material of cycad-like plants from the middle Jurassic Period (165 million years ago) have been found. They were probably deposited by a small plant-eating dinosaur.
Other discoveries include large aggregations of plant-filled material from the late Cretaceous Period (75 million years ago) that were invaded by burrowing dung beetles. These aggregations are also coprolites. They probably came from duck-billed dinosaurs, the skeletal remains of which are abundantly preserved in nearby rock layers.
A very large, relatively well-formed coprolite that was produced 66 million years ago contains broken and partly digested bones of juvenile plant-eating dinosaurs. It almost certainly came from a Tyrannosaurus, the famous giant flesh-eating dinosaur. The shape of this coprolite was preserved by cement derived from the high concentrations of calcium and phosphate in the bodies of the animals that had been eaten.
Q: What animals, if any, preyed on dinosaurs? Or what caused the dinosaurs’ deaths? Surely they didn’t all die of old age or hunger?
A: Because dinosaurs lived on the continents and were—for most of the dinosaurian era—the dominant large land animals, most of the animals that preyed on dinosaurs were other dinosaurs. Abundant evidence of this can be found in tooth marks on the bones and teeth of flesh-eating dinosaurs, which have been preserved near fossilized, dismembered carcasses. In very rare cases, bone fragments of other dinosaurs have been found in the petrified scat of flesh-eating dinosaurs. In tropical regions of North America and Africa, giant crocodiles inhabited rivers and estuaries, and it is thought that they also consumed dinosaurs. Remains of dinosaur carcasses that floated out to sea have been identified in marine sediments. Some of these show evidence of dinosaurs having been attacked by sharks. The most common causes of dinosaurian deaths, apart from other dinosaurs, were droughts and floods, which sometimes killed several thousand animals.
Q: What is the fastest known dinosaur?
A: The fastest dinosaur known was a theropod, or two-legged flesh-eater. This particular animal had feet 38 cm (15 in) long and weighed about 600 kg (1,320 lb). According to a trackway (a series of fossil footprints), the animal could run at the speed of 12 m (40 ft) per second, or 43 km/h (27 mph). The trackway was imprinted on limy mud near a seashore in what is now central Texas about 110 million years ago, during the middle Cretaceous Period.
Q: What is the largest known dinosaur?
A: Specimens of very large dinosaurs exist only in the form of a few bones or fragments of bones. They are so fragmentary because the sediment in which the bones occur seldom accumulated rapidly enough to bury the bones before they were largely destroyed by weathering. Thus, the appearance of a giant dinosaur must be inferred from incomplete skeletal parts.
Arguably, the largest dinosaur known is represented by a fragment of a vertebra that originally measured between 2.4 and 2.7 m (7.9 and 8.9 ft) tall. The bone, from the middle of the animal’s back, came from a Diplodocus-like sauropod that is estimated to have measured between 40 and 60 m (130 and 200 ft) long. The animal probably weighed between 100 and 150 metric tons (220,000 and 330,000 lb).
The name Amphicoelias has been given to this dinosaur. The sediments in which the bone fragment was buried were deposited approximately 150 million years ago, during the late Jurassic Period.
Q: What is the most ancient known dinosaur?
A: No single dinosaur is known to be the most ancient dinosaur. Three different dinosaurs enter the fossil record simultaneously about 228 million years ago, during the late Triassic Period. They were all small, measuring between 1 and 1.5 m (3.3 and 4.9 ft) in length, and all had two legs.
One of these dinosaurs was Eoraptor, a theropod. It was an ancestral flesh-eater. This animal had a relatively large head and jaws lined with sharp teeth.
The second of these dinosaurs was Saturnalia, a sauropodomorph. It was an ancestral plant-eater with a small head and a slightly elongated neck.
The third dinosaur was Pisanosaurus, an ornithischian. It also was a plant-eater, and it had a small beak and a short neck.
Relatively complete skeletons of these animals have been recovered in Argentina and Brazil.
Q: What is the smallest known dinosaur?
A: Very small skeletons are seldom preserved in the fossil record. The bones of small dinosaurs were fragile and easily destroyed by weathering. Tiny animals were often swallowed whole by predators, leaving no traces.
The few small skeletons known are usually those of immature specimens of larger dinosaurs. Skeletons in the range of 1 to 1.25 m (3.3 to 4 ft) have been found. They probably represent subadult specimens of Eoraptor, an ancestral flesh-eating dinosaur of the late Triassic Period, and of Compsognathus, a more evolved flesh-eater of the late Jurassic Period (150 million years ago).
However, a skeleton of a 1.1-m (3.6-ft) long flesh-eater contains a pair of unlaid eggs, indicating that the animal was reproductively mature. This animal is called Sinosauropteryx and is from the Cretaceous Period (125 million years ago). The specimen indicates that adult dinosaurs could be only slightly longer than a meter.
Tiny teeth of flesh-eating dinosaurs from the middle Cretaceous Period have been found in Morocco. They may have come from even smaller animals, raising the possibility of the existence of so-called microdinosaurs.
Q: Did any dinosaurs actually fly?
A: A few dinosaurs are known to have possessed feathers on their arms, but their arms were too small to support them in the air and the arm feathers were not suited for flight. No dinosaur is currently suspected of having had the ability to fly. Pterosaurs, or flying reptiles, were not dinosaurs, but their ancestry was related to that of dinosaurs. Pterosaurs were highly adapted to flight, and some attained immense wingspans.
Q: Did dinosaurs live in groups or alone?
A: In general, it seems that dinosaurs were highly social animals. The most striking indications that dinosaurs formed herds are bone beds, or accumulations of skeletons, dominated by one variety of dinosaur. These bone beds evidently resulted from local catastrophes—such as floods, volcanic ash falls, sandstorms, or droughts—that killed large numbers of animals.
Paleontologists have discovered bone beds containing the bones of small meat-eating dinosaurs, sauropods, stegosaurs, armored dinosaurs, horned dinosaurs, small plant-eating dinosaurs, and duck-billed dinosaurs. They have also found extensive nesting sites, which indicate grouping in small meat-eating dinosaurs, sauropods, and duck-billed dinosaurs.
Relatively small herds of sauropods and duck-billed dinosaurs are indicated by groups of trackways (series of fossil footprints) of animals of different sizes moving at the same speed or of trackways that show evidence of animals interacting with one another. One group of trackways in particular shows that a duck-billed dinosaur slipped, bumping into a nearby animal and causing it to change its course.
Even large meat-eating dinosaurs show unusual indications of interactions—in the form of face-biting, perhaps while devouring the same prey animal.
Q: Some dinosaurs were huge. What evolutionary advantage, if any, did their great size provide?
A: Huge dinosaurs were large for the same reasons that animals in general become large. Pound for pound, large dinosaurs probably required less food than did small ones. They could survive on food that was less nutritious and could resist starvation more effectively. And they probably retained body heat more efficiently.
There are disadvantages to becoming large as well. Large animals require more energy to walk up slopes than do small ones, and they are more prone to injury from stumbling or falling. There is a greater risk of heat stroke. Larger animals are more likely to die off as a result of regional changes in ecology.
The balancing point occurs when the advantages of large size equal the disadvantages. Some dinosaurs probably reached such large sizes because their food requirements were low and food was relatively abundant.
Q: Is it possible that dinosaurs did not go extinct until long after scientists believe they did? Could they have survived into modern times?
A: During the extinction that occurred 65 million years ago, communities of plants and animals on land and in the oceans were so decimated that it stands to reason that the dinosaurian era definitively ended. Among the dinosaurs, only those that had previously given rise to the birds survived. There is no clear evidence that any dinosaurs survived anywhere on Earth. The extinction was as brief as it was severe, and the post-extinction world was so weakened competitively that had any dinosaurs survived, it figures that they would have proliferated, and their presence would have been detected in post-extinction sediments. In the absence of post-extinction dinosaur records during the 65 million years since the extinction, it is highly unlikely that any dinosaurs will be found alive in remote regions of Earth today.
Q: Did meat-eating dinosaurs replace lost teeth like sharks do?
A: Unlike mammals, meat-eating dinosaurs regularly lost and replaced their teeth. Replacement occurred in slow waves along the gum line, and new teeth replaced old ones in a tooth socket from below and behind. The dismembered skeletons of plant-eating dinosaurs are often associated with a few pointed teeth from meat-eaters—teeth that broke off in the process of feeding on the carcass. Shed teeth of small meat-eating dinosaurs are among the commonest of fossils in sediments deposited on land during the dinosaurian era. But meat-eating dinosaurs always retained enough teeth in their jaws to render them efficient predators.
Q: Why do some scientists believe that dinosaurs may have been warm-blooded?
A: The best way to determine whether an animal is warm-blooded or cold-blooded is to measure its metabolic rate—the rate at which it changes food into energy. High metabolic rates indicate a warm-blooded animal. Of course, there is no method for directly measuring metabolic rates in extinct animals, such as dinosaurs. Therefore, scientists cite indirect evidence as suggesting that dinosaurs may have been warm-blooded. Such evidence includes the upright posture of dinosaurs, high growth rates, and the presence of dinosaurs in polar regions.
It is also possible that through natural selection dinosaurs tended to become more warm-blooded over the more than 150 million years of their existence. Evidence in support of this theory includes the appearance of insulating filaments (similar to hairs) and feathers to retain heat in the bodies of small meat-eating dinosaurs related to birds, the evolution of complex sets of grinding teeth in some plant-eating dinosaurs to help them rapidly digest food, and chemical evidence of high rates of bodily heat flow in some dinosaurs that lived late in the dinosaurian era. A recent identification in a small plant-eating dinosaur of structures resembling an advanced heart like those in mammals and birds is also suggestive of high metabolic rates.
Q: Did any dinosaurs live entirely in water?
A: No dinosaur lived entirely in water. There were no known plant-eating dinosaurs that resembled, for example, manatees. Like elephants today, large dinosaurs tended to avoid even moist ground where they could become mired. Indeed, several examples of upright limbs of sauropods have been found, indicating that the animals perished by miring. However, trackways (series of fossil footprints) along the edges of shallow marine bays demonstrate that sauropods did enter the water, probably like human bathers do, to cool off.
No meat-eating dinosaur possessed a skeleton that suggests an unusual ability in swimming. Spinosaurs—large, crocodile-like dinosaurs—did have long, narrow jaws resembling those of crocodiles, and scales and bones in their abdominal cavities indicate that they ate fish. Huge freshwater fishes were plentiful in the marshes and shallow lakes of Saharan Africa when the spinosaurs were alive, and these fishes must have provided an abundant source of food. However, the presence of giant crocodiles, large lizards known as mosasaurs, and huge plesiosaurs—the skeletons of which indicate they were efficient aquatic predators—probably deterred flesh-eating dinosaurs from becoming aquatic. Instead of being hunters, they would have been vulnerable to becoming prey themselves!
Q: What caused the mass extinction of the dinosaurs at the end of the Cretaceous Period?
A: The extinction of the dinosaurs at the end of the Cretaceous Period, about 65 million years ago, is a complex and widely debated topic. It was most likely caused by brief but planetwide environmental changes resulting from the impact of a comet or an asteroid on the Yucatan Peninsula of Mexico.
Perhaps the most harmful effect of the impact was a global blockage of sunlight caused by huge quantities of ash blown from the impact crater. That was bad enough, but there were other harmful effects as well. These included widespread forest fires, acid rain, and frosts.
Scientists have adequately studied the geologic record of the extinctions on land only in rock layers that have been exposed on the high plains of the United States and Canada. Those studies indicate that far more than half of the species of green plants became extinct, and plant growth effectively ceased for about a year. An equally large proportion of insects and small backboned animals vanished, as did all of the dinosaurs.
Eventually, ferns spread over the decimated landscape. They were followed by plants that formerly grew in swamps and animals that belonged to a food chain based on decaying vegetation. Many millions of years were required for life on land to recover more or less completely—minus, of course, the dinosaurs.
Q: Were there other mass extinctions of dinosaurs in addition to the one at the end of the Cretaceous Period?
A: The record of life on land is rather incomplete, so that times when large numbers of dinosaurs died off may remain undetected. We know that an important extinction of land animals occurred about 205 million years ago, at the end of the Triassic Period and the beginning of the Jurassic Period.
This extinction was similar in some ways to the mass extinction of the dinosaurs at the end of the Cretaceous Period, about 65 million years ago. Like the latter, the extinction about 205 million years ago was severe, but life on land recovered rather quickly. Both animals and plants died off. However, representatives of all three major groups of dinosaurs—theropods, sauropodomorphs, and ornithischians—survived.
More study is required to identify the cause of the extinction that occurred about 205 million years ago. There are some ambiguous indications that a comet or asteroid impact may have occurred. The plant record suggests the onset of an interval of cooler climates. A few tens of thousands of years after the extinction, a vast outpouring of lava flows began around a great rift valley that eventually grew to become the Atlantic Ocean.
Q: If you find a fossil in the field, how do you know that it is from a dinosaur?
A: Identifications of animals based on fragments of bones are uncertain and often erroneous. However, single complete bones are usually distinctive enough to be accurately associated with specific animals, even long-extinct dinosaurs. A good basic reference book on identifying dinosaur fossils is The Dinosauria.
As a rule of thumb, any bone from an animal of human or larger size that is found in floodplain deposits of Jurassic or Cretaceous age almost certainly belonged to a dinosaur, since dinosaurs were the only sizable land-dwelling creatures of their time. The process of bone recognition is based on shape and details of structure, and is analogous to being able to identify the faces of friends. Often it is relatively easy to identify a bone, but it is more difficult to explain the identification: “It just looks like it came from the tail of a horned dinosaur.”
Q: According to the movie Jurassic Park, velociraptors were very smart. I was wondering if they were really as smart as the movie says or if they embellished a little? Who were the smartest dinosaurs?
A: The smartest dinosaurs had intelligence comparable to that of chickens or ostriches. There were only a few, exceptionally large-brained dinosaurs that are known to have possessed the brain-body proportions that would rank them in this level of intelligence.
The behavior of the velociraptors in the movie Jurassic Park suggests their intelligence was comparable to that of parrots, monkeys, and apes. You are correct to suspect the movie might have embellished their cleverness a bit.
Q: How do paleontologists determine how fast a dinosaur could run?
A: The speed of moving dinosaurs is best determined from trackways, which are series of fossil footprints.
In a variety of living animals, there is a relatively stable mathematical relationship between the length of an animal’s foot (revealed through its footprint) and the length of its leg. Mathematical relationships also link the spacing between an animal’s tracks (revealed by a dinosaur’s trackway), the length of its leg, and its speed. These mathematical relationships can be used to estimate the speed of a trackway maker, even though the trackway was made many tens of millions of years ago.
Q: Stegosaurus reportedly had a brain the size of a walnut. How did brain size affect behavior in dinosaurs?
A: In simple terms, an animal’s brain monitors its sensory inputs (sights, sounds, smells) and coordinates the animal’s behavioral responses to those inputs. The parts of the brain that receive sensory inputs scan surface areas, such as retinas, eardrums, and skin. The volume of these parts of the brain is proportional to surface area. The volume of the rest of the brain determines how complex the animal’s behavioral responses are.
The brain, or more properly speaking, the cavity for the brain, of an average dinosaur was small relative to the size of the animal’s body. Thus, most of a dinosaur’s brain tissue was used to monitor sensory inputs, and little brain tissue remained for behavioral responses. As a result, the behavior of most dinosaurs, and especially of Stegosaurus, was probably simple and stereotyped compared to that of modern mammals and birds. Their behavior was rather like that of turtles and lizards.
Q: Did Tyrannosaurus rex raise and protect its offspring? Did T-rexes use their adolescent offspring for hunting, the way lions, when hunting large prey, use the more-agile females to disrupt herds and then the larger, stronger males ambush the prey?
A: Tyrannosaurus nests and infants have never been identified in the fossil record. On average, skeletal remains of juveniles are associated with less than 1 in 10 adults. The young specimens are represented in the fossil record by only one or very few bones, while the adults are represented by a relatively complete skeleton.
There may have been some kind of association between the young and older animals, but it is unknown whether the association represented actual parental care, or just unrelated younger animals surreptitiously following an adult in order to feed at its kills.
Scars from head wounds indicate that adult tyrannosaurs bit each others’ faces; they were obviously capable of killing juveniles. Complex hunting strategies similar to those used by lions seem improbable because the brain cavity of a Tyrannosaurus was relatively much smaller than that of a lion, and similar to that of a crocodile. Tyrannosaurus probably used a simple but brutally effective repertoire of hunting strategies.
Q: Tyrannosaurus had such tiny arms. What did it do with those arms?
A: Compared to a human arm, the arm of Tyrannosaurus seems strong. However, relative to the size of the animal’s body, the arm was quite small. In dinosaurs with large arms, the spinal cord in the chest region is enlarged to support complex arm movements. No such enlargement is present in Tyrannosaurus. In addition, Tyrannosaurus arms often show evidence of damage (breakage or infection), probably caused by erratic movements of the animal’s large body. Lesions suggestive of gout have also been identified in Tyrannosaurus arm bones. It is likely that the forelimbs of Tyrannosaurus, rather than being useful, were often a source of pain.
Q: Did Tyrannosaurus run down its prey or ambush it?
A: How nice it would be to respond authoritatively from observations of living specimens of Tyrannosaurus! Instead, one must make inferences from Tyrannosaurus skeletons. Tyrannosaurus had long, graceful legs and a huge, barrel-shaped chest. Accordingly, it probably could and did pursue prey. But in addition, Tyrannosaurus possessed a “footstool”-like bone (the pubis) upon which it could squat and eye sockets high on its skull. Accordingly, it probably often waited in ambush for prey. Thus, like the gigantic “lion” it was, Tyrannosaurus probably did both.
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Paleontology; Dinosaur
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