Interest in dinosaurs soared to new heights in the 1990s, thanks largely to the blockbuster film Jurassic Park. So too did dinosaur discoveries. Since 1990, more than 100 new dinosaur genera have been described and named.
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A couple dozen new dinosaurs have been found in western North America. Moreover, paleontologists in South Dakota discovered the most complete Tyrannosaurus rex skeleton ever. The story of "Sue" captivated dinosaur buffs around the globe. Dinosaur discoveries in Patagonia included the vertebrae of one of the largest plant-eaters that ever lived, Argentinosaurus, which may have been over 100 feet long.
Asia, particularly China and Mongolia, has yielded the largest number of newly discovered dinosaurs. The first feathered dinosaurs, long anticipated because of the close relationship between dinosaurs and birds, finally appeared in the fossil record, at Liaoning, China. The evidence for a dinosaur-bird connection has grown very strong; meat-eating dinosaurs and birds share more than a hundred anatomical features. Although the dinosaur-bird connection was first proposed by paleontologists in the 19th century, the new, computer-oriented methods of classification have finally made this relationship clear.
The Story of "Sue"
On a foggy August day in 1990, Susan Hendrickson found a few fossilized dinosaur bones weathering out of a cliff on a ranch near Faith, South Dakota. The ranch belonged to Maurice Williams, who was one-quarter Sioux. Hendrickson's employer, Peter Larson, a founder of the Black Hills Institute of Geological Research at Hill City, South Dakota, was at the time en route to Faith to fix the tires on one of the Institute's vehicles. Hendrickson, driven by a feeling that she would make a great discovery, decided that morning to do some fossil prospecting on the ranch. She could tell at once that the bones visible in the cliff-a few vertebrae and a partial thigh bone-belonged to a large meat-eating dinosaur, almost certainly a Tyrannosaurus rex.
By the time she made her way back to camp, Larson had returned. She showed him a few pieces of the find. Larson agreed excitedly that she had found a Tyrannosaurus, and they began making plans to dig the bones out of the ground. They checked to make sure that Williams was indeed the owner of the land where the bones were found, and they obtained his permission to excavate to see how much of the skeleton was there. In a few days, Larson and his crew realized that they were looking at the most complete skeleton of a Tyrannosaurus rex ever discovered. More than 90 percent of the dinosaur's bones were present, including a huge skull nearly five feet long. It was also the largest Tyrannosaurus rex ever found, and its bones were especially well preserved.
Larson negotiated with Williams to buy the skeleton for $5,000 and started work. Within 17 days the skeleton was out of the ground, jacketed, and on its way to the Institute's preparation laboratory. Larson nicknamed the fossil "Sue," after Susan Hendrickson. He had a theory about how one might tell male and female meat-eating dinosaurs apart, and "Sue," he thought, was a large female.
When Williams saw the tremendous publicity the find received, both he and the Sioux tribe began to have second thoughts about the ownership of the bones. The Sioux tribe also felt that they might be legal owners of the fossil, and they asked the U.S. Government to get involved.
In the ensuing legal struggle, the FBI seized "Sue" from the Institute and locked it away at the South Dakota School of Mines and Technology in Rapid City until the dispute could be resolved. They also seized the Institute's financial and fossil-collecting records-and discovered legal irregularities that eventually placed Larson into a minimum-security federal prison for two years.
Larson never got "Sue" back. The government declared Williams the legal owner and returned the fossil to him. Williams soon contacted Sotheby's in New York City to auction the skeleton. On October 4, 1997, after a huge publicity campaign, "Sue" was sold for a mind-boggling $8.36 million to the Field Museum of Natural History in Chicago, which received corporate backing from Walt Disney World Resort and McDonald's Corporation.
The Field Museum became responsible for preparing "Sue" for public display. Head fossil preparator Bill Simpson and his team worked the bones out of the matrix, and Phil Fraley designed the mount to hold them. Paleontologist Christopher Brochu was hired to write up "Sue's" scientific description. The skull, crushed and flattened when the dinosaur was buried 67 million years ago, was CT-scanned to reveal its internal structure. Too heavy to mount with the rest of the dinosaur, the skull was replaced on the skeleton by a lightweight cast with the crushing straightened out. On May 17, 2000, "Sue" went on permanent public display in Chicago. The real skull was displayed nearby.
Feathered Dinosaurs from Liaoning
In 1994, farmers in Liaoning Province in northeastern China began finding exquisitely preserved fossil birds representing a new species, Confuciusornis. They were discovered in fine-grained Early Cretaceous sedimentary deposits near the village of Sihetun. Many were so well preserved that even their feathers could be seen. Several kinds of fossil birds were found, but Confuciousornis was the most common. Other fossils were also found, including splendid examples of fish and plants. So many fossils were found, and are still being found, that a thriving market has developed in exporting them out of China-a market that the Chinese government considers illegal smuggling.
In 1996, the skeleton of a small dinosaur came to light at Sihetun. Complete practically to the last bone, it belonged to a new kind of theropod about three feet long named Sinosauropteryx prima. In size and anatomy, it closely resembled the small European dinosaur Compsognathus, but it showed distinct traces of short, brushy structures along the neck, back, and tail. After some arguing back and forth, most scientists now believe that the brushy structures are indeed feathers, somewhat different in structure than those of modern birds. Sinosauropteryx is thus the first feathered non-avian dinosaur ever found.
Even as Sinosauropteryx was being studied, more feathered dinosaurs turned up in Liaoning: Protarchaeopteryx, a larger theropod five feet long, with very birdlike feathers visible along the tail; Caudipteryx, a very birdlike theropod about three feet tall, showing good feather impressions along forelimbs and tail; Sinornithosaurus, a troodontid-like theropod about the same size as Sinosauropteryx, with hairlike feathers; and Beipiaosaurus, a theropod more than six feet long, the largest-known theropod with feather impressions (also hairlike). The smallest feathered Liaoning theropod was Microraptor, less than 1.5 feet long, classified as a dromaeosaurid. All these feathered dinosaurs had relatively large, powerful hind legs, obviously suited for fast running, and hands with large claws. None had wings.
The discovery of feathered theropods strongly supports the theory that birds are theropod dinosaurs that evolved the ability to fly. But perhaps the most interesting thing about the Liaoning feathered theropods is that they represent several different theropod families. This means that the origin of feathers is not closely linked to the origin of birds, and offers evidence that many different lines of theropod dinosaurs may have had feathers of some sort, not just those most closely related to birds. Depending on how widespread the structures were among theropods, even such giants as Tyrannosaurus rex may have had feathers.
Early Cretaceous Dinosaurs from Patagonia
Dinosaurs were first found in South America more than 100 years ago, but only in the past 30 years have enough paleontologists been working there for us to appreciate just how many interesting kinds of South American dinosaurs there were. Paleontologists have discovered South American dinosaurs that date from the middle of the Triassic Period to the end of the Cretaceous Period.
In particular, paleontologists are now putting together a picture of South American dinosaurs from the Early Cretaceous epoch, a stretch of time of which we know little about dinosaurs worldwide. Most of the newly discovered South American Early Cretaceous dinosaurs are various kinds of sauropods, but there are also some new kinds of theropods. Some seem closely related to certain Early Cretaceous dinosaurs from Africa, which is not surprising, because at that time South America and Africa were partly connected. Dinosaurs could have walked from one continent to the other.
Andesaurus was a normal-size sauropod about 50 to 60 feet long. Its gigantic relative Argentinosaurus just may be the world's largest known dinosaur. It was about twice the size of Andesaurus, with vertebrae about five feet tall. Both it and Andesaurus, which were both found in Patagonia, are close relatives of the titanosaurids of Late Cretaceous South America.
Another group of sauropods, called Dicraeosauridae, includes the odd-looking Amargasaurus, a tall-spined relative of the African Late Jurassic sauropod Dicraeosaurus. These were rather small sauropods (about 40 feet long) related to the giant North American Apatosaurus and Diplodocus. The vertebral spines of Amargasaurus grew especially tall along the back of the neck, where they may have been covered with webs of skin.
Another South American sauropod, Rayososaurus, is a close relative of the African Rebbachisaurus. Both dinosaurs had tall vertebral spines, but whereas the spines in Amargasaurus were paired, single spines were present in the rebbachisaurids. They may have given the animals a tall ridge along the back. The spines of Rayososaurus were not quite as tall as those of Rebbachisaurus. Both dinosaurs were standard-size sauropods, measuring about 50 to 60 feet long.
A possible relative of the rebbachisaurids is the very strange sauropod Agustinia, which had a double row of plates and spines resembling those of Stegosaurus along its back. They may have been movable. No dinosaur like Agustinia has been found anywhere else in the world.
From about the same time and place as the gigantic Argentinosaurus comes the correspondingly huge theropod Giganotosaurus. Bigger than Tyrannosaurus, it is presently the largest known meat-eating dinosaur, as much as 50 feet long. In a lagoonal deposit in Brazil was found the man-size, fish-eating theropod Irritator. It was probably related to the much bigger African spinosaur Suchomimus.
Early Cretaceous Dinosaurs from North America
Not much was known about Early Cretaceous dinosaurs of North America until paleontologists discovered new kinds of dinosaurs in Lower Cretaceous rock strata in Utah and Arizona. The North American dinosaurs are more similar to Early Cretaceous dinosaurs of Europe and Asia than they are to those from Africa or South America.
The recent discoveries in Utah and Arizona included two armored dinosaurs: Gastonia and Animantarx. The first was about 12 to 15 feet long and resembled its close relative, the British dinosaur Polacanthus. The second was about half that size and lived several million years later. It was the first dinosaur discovered by tracing the radioactivity of its fossilized bones; they were not visible at the surface where they were buried.
From the same general location where Gastonia was found came the scattered bones of the large meat-eater Utahraptor. About six feet long and built like a giant Deinonychus, Utahraptor was armed with "killer claws" more than a foot long on its feet. It may have used them to tear open its prey. Being a dromaeosaurid, it may have been covered with feathers like an ostrich. Nedcolbertia was a much smaller meat-eating dinosaur, about six feet long, that lived at the same time as Utahraptor.
Sauropods are scarce in the Early Cretaceous of North America, but their partial skeletons are found from time to time. Cedarosaurus and the Sonorasaurus were smaller relatives, about 50 feet long, of the gigantic Late Jurassic sauropod Brachiosaurus. Other Early Cretaceous plant-eating dinosaurs discovered in North America included Zuniceratops, the world's earliest known horned dinosaur with well-developed brow horns, and Eolambia, an ornithopod dinosaur very close to the ancestry of the later duckbilled dinosaurs.
Early Cretaceous Dinosaurs from Africa
Until the 1990s, Africa remained largely unexplored territory for dinosaurs. A few dinosaur-bearing localities were found by German expeditions to Egypt and Tanzania; French expeditions to Morocco, the Niger Republic, and Madagascar; and South African expeditions within their own country. The 1990s saw the first expeditions organized by American paleontologists to some of the localities previously visited by other countries. American paleontologists returned with more material of previously known dinosaurs and also fossils of dinosaurs not known before. Most of the fossils were from the Early Cretaceous age.
The first Carcharodontosaurus remains (teeth) were found by the French in the 19th century, and teeth and jaw fragments continued to turn up in French and German dinosaur digs everywhere across the Sahara Desert during the 20th century. Not until the 1990s did an American expedition, organized by Paul C. Sereno, turn up a good partial skeleton and skull, giving us our first good look at this mysterious giant meat-eater. Closely related to South America's Giganotosaurus, Carcharodontosaurus was about as large as Tyrannosaurus (40 to 45 feet). The American expeditions also found a new, smaller meat-eater about 30 feet long that they called Afrovenator and another new meat-eater, Deltadromeus, which was similar in size to Afrovenator but more slender.
The spectacular Late Cretaceous Spinosaurus aegyptiacus, first found by German expeditions to Egypt before World War I, has so far proved elusive; no more Spinosaurus aegyptiacus fossils have ever turned up. But a few of its Early Cretaceous relatives, which were smaller (about 35 feet) and evidently had much shorter spines along the back, have been found by French and American expeditions to Morocco. Known from fragmentary fossils are Sigilmassasaurus, Cristatusaurus, and Spinosaurus maroccanus. Known from a fairly complete skeleton is Suchomimus. The spinosaurs are currently being restudied, and Suchiomimus may prove to belong to the same species as one of the previously named spinosaurs. A spinosaur hallmark is the elongated, narrow snout with slender teeth, strongly resembling the snouts and teeth of modern fish-eating crocodiles of India. It is the reason we believe spinosaurs were mainly fish-eaters.
New African sauropods found by American expeditions included Malawisaurus, a primitive titanosaur from Malawi; Jobaria, a large but primitive sauropod similar to Cetiosaurus from the Jurassic of Great Britain; and Nigersaurus, a peculiar medium-size sauropod perhaps related to the rebbachisaurids. Nigersaurus had rows of hundreds of teeth, packed in its jaws like the dental batteries of duckbilled dinosaurs. Malawisaurus material had been discovered as early as 1928, but only after better fossils were found in the early 1990s was it possible to identify it as a new kind of dinosaur.
When the French expedition to the Niger Republic in 1972 found the sail-backed ornithopod Ouranosaurus, they also found a large, heavily built but otherwise standard iguanodontid in the same general area. This dinosaur was described and named Lurdusaurus in 1999.
Early Jurassic Antartic Dinosaurs
Antarctica was not always covered miles deep with ice. During the Mesozoic, it had a fairly temperate climate in which dinosaurs and other Mesozoic animals and plants thrived. It also served as a land bridge that joined southern Africa, Madagascar, India, and Australia. Unfortunately, today's huge Antarctic ice pack and very cold Antarctica temperatures make it very difficult to collect dinosaur fossils there. But even so, a few scattered dinosaur fossils are now known from Antarctica, one of which, Cryolophosaurus, is complete enough to warrant establishing a new species.
Cryolophosaurus was a theropod 26 feet long, described in 1994. It had a unique, flat crest atop its head between the eyes, shaped like two ruffled potato chips stuck together side by side. Quite a bit of the skull was found, so we have a pretty good idea what this dinosaur looked like. Along with it were found the bones of an unnamed prosauropod, perhaps the kind of dinosaur that Cryolophosaurus preyed upon. Both dinosaurs lived during the Early Jurassic epoch.
Late Cretaceous Dinosaurs from Madagascar
Dinosaurs were first discovered in Madagascar by British and French paleontologists late in the 19th century. The fossils were rather scrappy, but they included Jurassic and Cretaceous sauropod (brachiosaurid and titanosaurid) and theropod bones. In 1926, a fossil tooth from Madagascar was described by the French as belonging to a new species of Stegosaurus; the French named the theropod Majungasaurus. And in 1979, a thickened skull bone was described as a pachycephalosaur called Majungatholus. Every so often a few more scrappy dinosaur bones were found there, but this was essentially where dinosaur paleontology of Madagascar stood as late as the mid-1990s.
In 1996 and following years, American expeditions to Madagascar found fairly plentiful bones of Late Cretaceous dinosaurs, including two kinds of titanosaurids (still undescribed); a large theropod; a new kind of small to medium-size theropod with front teeth that protrude forward almost horizontally; a small, birdlike theropod with a long tail that had large, winglike forelimbs and was probably a good flier; and a "true" bird that was named Vorona. The new material settled some doubts about Madagascar dinosaurs. First, the aforementioned stegosaur tooth was found to belong to a peculiar kind of crocodile and was not stegosaurian after all. Then, the so-called pachycephalosaur turned out to be a theropod with a bumpy, thickened skull roof and a short snout. A good skull showed that Majungatholus was a close relative of the peculiar South American horned theropod Carnotaurus; instead of a pair of horns, it had a single thick knob on top of its head. The earlier name Majungasaurus had to be discarded because the material on which it was based was too scrappy to identify; it may or may not be the same dinosaur as Majungatholus.
The small theropod with protruding front teeth was named Masiakasaurus in early 2001. The available material suggests that it may be related to the small theropod Noasaurus from South America, but further work needs to be done before this identification is secure. Some speculate that it was a fish-eater.
The small, birdlike theropod, called Rahonavis, is perhaps the most interesting fossil found by those expeditions to Madagascar. Although the describers classified it as a bird about as advanced as the Jurassic bird Archaeopteryx, its feet are almost exactly the same as the feet of Deinonychus and other dromacosaurids, right down to the enlarged "killer" claws. The long tail and hips also closely resemble those of dromaeosaurids, but the forelimbs have the long, slender bones of bird wings and little bumps where feathers might have been attached. Thus, Rahonavis seems to be a genuine link between small theropod dinosaurs and "true" birds. Only further study, and some more specimens, will resolve the relationship of theropods, birds, and Rahonavis.