Dinosaurs
Dinosaurs constitute one of the most successful groups of terrestrial vertebrate animals ever to inhabit the Earth. For over 160 million years in the Mesozoic Era, large dinosaurs dominated every terrestrial niche, appearing during the later part of the Triassic, flourishing through the Jurassic, and surviving until the very end of the Cretaceous. A wealth of evidence has been accumulated in support of the notion that a group of carnivorous dinosaurs, theropods known as maniraptorans, contain the predecessors of birds–65 million years after the Cretaceous mass extinction exterminated the last surviving species of large dinosaurs, their living descendants (birds) continue to be a main component of most terrestrial ecosystems.
Origin of Dinosaurs | Evolution and Diversification | Birds: The Late Evolution of Dinosaurs | Dinosaurs and Hollywood
Origin of Dinosaurs
The ancestry of dinosaurs can be traced back some 230 million years ago to the Late Triassic. At this time, all landmasses were united into a gigantic continent called Pangea. The breakup of this enormous landmass together with significant changes in global climate, and the disappearance of primitive lineages of archosaurs provided impetus for the divergence of dinosaurs. Afterwards, the rapid evolution of critical physical innovations equipped these animals with the specializations required to rule over all Mesozoic terrestrial ecosystems.
All dinosaurs belong to a group of reptiles called archosaurs-a group that also includes crocodiles and a variety of Mesozoic reptiles (pterodactyls and others) that are often misinterpreted as dinosaurs. The anatomical characteristics of both the earliest known dinosaurs and their archosaurian relatives suggest that the common ancestor of all dinosaurs was a small bipedal predator, which had forelimbs shorter than hind limbs. This ancestor was probably similar to the 235-million-year-old Lagosuchus from Argentina.
From the most primitive Triassic forms to the most advanced ones of the latest Cretaceous, all dinosaurs share defining traits that distinguish them from their closest archosaurian relatives. Among these innovations, the femur (or upper leg bone) developed a distinct head for a tied attachment into a hollow hip socket. These and other changes resulted in a hind limb that was tucked directly underneath the body, providing upright, pillar-like support of the body and also enhancing locomotive abilities. The changes that led to the erect posture of dinosaurs from the sprawling posture of their reptilian predecessors had a profound effect on the evolutionary success of these animals. These transformations may have also been coupled with the evolution of a higher metabolism (a step towards warm bloodedness) that endowed them with a greater capacity for sustained activities such as running.
Evolution and Diversification
As currently known, all dinosaurs belong to one of two major groups, the saurischians and the ornithischians. From the onset of their long evolutionary history, ornithischians and saurischians already show the features characteristic of these groups. Ornithischians comprise a series of plant-eating dinosaurs such as the armored stegosaurs and ankylosaurs, the duckbills and their kin, and the horned and dome-headed dinosaurs. Saurischians include the meat-eating theropods (the renowned Tyrannosaurus and Velociraptor among them) and the plant-eating sauropodomorphs (such as the gigantic Apatosaurus).
Among the ornithischians (the main dinosaurian group that includes all non-saurischian forms), the 228-million-year-old small Pisanosaurus of western Argentina is usually accepted as the group's earliest known member. The fact that Pisanosaurus walked on two legs and ate plants suggests that the common ancestor of all ornithischians was also a bipedal herbivore. This early dinosaur's anatomy further suggests that all ornithischians evolved from an ancestor whose pubic bone pointed backward.
Familiar among ornithischians are the thyreophorans-the group that includes the stegosaurs and ankylosaurs. All members of this group evolved from an ancestor having armor comprising bony scutes and plates that covered most of the entire surface of the body. The earliest known thyreophorans are primitive forms dating to the Early Jurassic, although the divergence of the group is likely to be much older. The best-known thyreophorans, however, are the stegosaurs and ankylosaurs of the Late Jurassic through Late Cretaceous times. Stegosaurs evolved small, narrow skulls, hindlimbs longer than forelimbs, two characteristic rows of vertical dorsal plates, and sharp spikes that made their tails formidable weapons (a skeleton of the 150-million-year-old Stegosaurus is housed at the Dinosaur Institute). Armor in the ankylosaurs evolved into a dense shield that covered much of the body, the skull incorporated extra bones that gave it a highly compact constitution, and, in the most specialized forms such as the 65-million-year-old Ankylosaurus, the tail developed into a stiffened structure terminating in an immense club.
Together, the dome-headed dinosaurs, or pachycephalosaurs, and horned dinosaurs, or ceratopsians, make up the ornithischian group called marginocephalians. These dinosaurs are united by the presence of a bony shield that projects from the rear margin of the skull. Ceratopsians are further united by the presence of a wedge-like rostral bone covering the tip of the snout. Among the largest ceratopsians is the renowned three-horned Triceratops (fossils of 65-million-year-old pachycephalosaurs and Triceratops are housed in the Dinosaur Institute's collections).
The ornithischian group called ornithopods seems to be more closely related to the marginocephalians than to the thyreophorans. Ornithopods evolved sophisticated dental batteries that must have been highly efficient in grinding plant matter. The earliest records of this group date back to the Early Jurassic, continuing on through the end of the Mesozoic. Primitive ornithopods like the 190-million-year-old Heterodontosaurus were small and agile bipeds with prominent fangs in their lower jaws. Among the more advanced ornithopod groups, iguanodontids were generally larger and although bipedal, could have also walked on all fours. One well-known iguanodontid is the 150 million-year-old Camptosaurus (a mount of which can be seen at the museum). Later iguanodontids called hadrosaurs had a cosmopolitan distribution. These so-called "duckbilled" dinosaurs became particularly abundant in the latest Cretaceous ecosystems of Asia and North America. Some duck-bills, such as the lambeosaurines, developed extravagant headgears (as in the helmet-like crest of Corythosaurus, a specimen of which is also exhibited at this museum) that may have played a role in communication.
Within the saurischian group of dinosaurs (the main group that includes all non-ornithischian forms) are the sauropodomorphs, plant-eating dinosaurs that include a series of small-headed, long-armed dinosaurs usually called prosauropods and the colossal, long-necked sauropods, the largest terrestrial animals of all time. As in the case of other main dinosaur groups, the earliest known examples of both prosauropods and sauropods date back to the Late Triassic. With bodies significantly smaller than those of the sauropods, the prosauropods were able to walk on either two or four legs. The 200-million-year-old Plateosaurus is a well-known example of these dinosaurs. By Early Jurassic times, some 125 million years ago, sauropods were already diversifying globally into various subgroups, each distinguished by its own set of features. By the Late Jurassic, groups like the diplodocids (including the well-known Diplodocus, possessing a long "whiplash" tail that may have served as a weapon or to produce sound) and the brachiosaurids (including enormous forms with longer front than hind legs, such as Brachiosaurus) constituted the world's dominant herbivores. While the predominance of sauropods lessened in the Cretaceous as other kinds of plant-eating dinosaurs took over their niches, one sauropod group, the titanosaurs, impressively diversified and flourished, especially in South America and Europe.
The saurischian family tree. (click to expand)
Theropods constitute the second major saurischian group. The evolutionary history of these animals also dates back 230 million years, when dinosaurs first appear in the fossil record. As with other dinosaurian groups, the earliest theropods already exhibit features typical of this entire group - a movable joint at the center of the lower jaw, powerfully clawed hands, and sharp, knifelike teeth. All theropods descended from a bipedal dinosaur that had feet with three main forwardly pointing toes, of which the central one was the longest. Herrerasaurus, a 230 million-year old dinosaur from western Argentina, is generally accepted as one of the earliest theropods, although some researchers regard it as a more primitive saurischian outside the group.
Theropods break down into numerous subgroups, two main groups being the ceratosaurs and the tetanurans. Ceratosaurs, the most primitive of these assamblages, range in size from very small, long-necked forms such as 190-million-year-old Coelophysis of southwestern North America (several specimens of which are housed at the Dinosaur Institute), to the much larger and more advanced Ceratosaurus, from this continent's Late Jurassic. Some ceratosaurs are distinguished by skull ornamentation, such as the spectacular double crests of Dilophosaurus and the nasal horn of Ceratosaurus.
Most known theropods are tetanurans, a large group whose members all have hands with three or fewer fingers. Tetanurans subdivide into three basic groups, the spinosaurs, carnosaurs, and coelurosaurs. The Late Jurassic to Late Cretaceous spinosaurs, known to date from all continents except Antarctica, include apparently fish-eating forms like the huge 190-million-year-old, sail-backed Spinosaurus of Egypt and 127-million year old, long-snouted Baryonyx of England and Niger.
A diversity of theropods: Tyrannosaurus rex, Deinonychus, and the bird Jeholornis (click to expand).
Carnosaurs first appeared in the fossil record during the Middle Jurassic, some 175-161 million years ago. These large-bodied theropods include such predaceous giants as Allosaurus (a skeleton of which is housed at the Dinosaur Institute), from the Late Jurassic of North America, and the even larger Carcharodontosaurus and Giganotosaurus, from the Late Cretaceous of Africa and South America, respectively.
Coelurosaurs comprise the most diverse theropods, this group including small forms like Juravenator, from the Late Jurassic of Germany, to the gigantic Tyrannosaurus (a number of specimens of which are in the Dinosaur Institute's collections), from Late Cretaceous North America. Included among the coelurosaurs are a number of atypically non-carnivorous theropods. Examples of these include the ornithomimosaurs, which superficially resembled ostriches, the therizinosaurs, rather bizarre forms having unusually short tails and long forearms, and the alvarezsaurids, with stout forelimbs resembling those of anteaters. Therizinosaurs and alvarezsaurids are usually classify within the maniraptorans, a coelurosaur group identified by a suite of features, most notably a wrist bone called the semilunate carpal that allowed the hand to be folded back against the body, a condition that, together with an elongated forelimb afforded enhanced reach. Some maniraptoran dinosaurs were remarkably birdlike-in fact, birds are considered to be a subgroup of maniraptorans. Some birdlike maniraptorans include the oviraptorids, odd-looking toothless forms such as Oviraptor. However, the more birdlike were the dromaeosaurids, sickle-clawed (and comparatively large-brained) hunters like Velociraptor, hailing from Late Cretaceous Mongolia. Throughout their long history, theropods developed dozens of highly specialized features, but perhaps none more striking than feathers, which, in time, helped them to become warm-blooded and airborne. Indeed, one coelurosaurian group - the above-mentioned maniraptorans - includes the only dinosaurs living today, the birds.
Birds: The Late Evolution of Dinosaurs
Recently, fossils of early birds and their most immediate predecessors have been collected at an unprecedented rate from Mesozoic-aged rocks worldwide. This wealth of new fossils has settled the century-old controversy of the origin of birds. Today, we can safely declare that birds evolved from a group of dinosaurs known as maniraptoran theropods-generally small meat-eating dinosaurs that include Velociraptor of Jurassic Park fame.
Archaeopteryx
Evidence that birds evolved from the carnivorous predators that ruled the Mesozoic ecosystems is plentiful and it comes from disparate lines of evidence. Traditionally, the prime source of evidence in support of this scientific view was the similar shape of the bones of birds and a variety of maniraptorans but spectacular new discoveries have added other lines of evidence to the table. One of these involves a suite of features from the eggs of these dinosaurs. A host of fossils have shown that not only did maniraptoran dinosaurs resemble birds in the way they laid their eggs but that these eggs also looked like the eggs of birds. Another line of evidence involves the handful of snapshots that tell us about the behavior of the maniraptoran theropods. Fossils of animals in brooding poses or in resting postures also show a startling similarity with the behaviors we see among living birds. Yet, perhaps the most compelling new line of evidence comes from the discovery of soft tissues associated with the skeletons of these predatory dinosaurs, many fossils of these creatures are now known to have been covered by plumage. All this evidence has highlighted the fact that many features that were previously thought to be exclusively avian-from feathers to a wishbone-have now been discovered in the immediate dinosaur predecessor of birds. Even flight is likely to have been an attribute inherited by birds from their dinosaurian forebears! If the new wealth of fossils has clarified the old controversy of the origin of birds, many other fossils have provided a vivid testimony of the early phases of avian evolution. Hidden in these fossils are the clues to how birds perfected their flying abilities and how they evolved warm bloodedness.
A diversity of early birds: Confuciusornis, Sapernornis,
and Longipteryx.(click to expand)
As we know it today, the known history of birds starts with the spectacular Archaeopteryx, a jay-sized creature with toothed jaws, a long lizard-like tail, and flight feathers. Archaeopteryx lived 150 million years ago in today's southern Germany. Although Archaeopteryx stands alone in the fossil record of birds of the end of the Jurassic period, within the last decade a large number and variety of birds have been found in Cretaceous rocks ranging from 130 to 115 million years ago. Some of these fossils show that a great diversity of birds with long bony tails preceded the evolution of birds with the familiar short bony tail.
Birds of the early Cretaceous blossomed in a range of shapes and sizes. The crow-sized, stout-beaked Confuciusornis sported enormous claws in its wings while the contemporaneous Sapeornis had very long and narrow wings like those of an albatross. These two birds were much larger than the sparrow-sized Eoenantiornis and Iberomesornis, which like most early birds had toothed jaws similar to those of Archaeopteryx. The different design of skulls, teeth, wings, and feet indicate that already at this early phase of their evolutionary history, birds had specialized into a variety of ecological niches, including seed-feeders, sap-eaters, insect-feeders, fish-eaters, and meat-eaters. At the same time, a host of novel features of the wings and ribcages suggests that soon after Archaeopteryx, birds evolved flying abilities not very different from the ones that amaze us today.
The family tree of birds. (click to expand)
As the rocks of the Cretaceous period become younger, the fossil record includes a great number of bird species with even more diverse lifestyles. The hesperornithiforms-large, flightless, foot-propelled divers-made their debut around 100 million years ago. A few million years later, these supreme fish-eaters would be crowned kings of the aquatic birds with the tiny-winged, 4-foot long, Hesperornis. The hesperornithiforms swam the waters of a warm sea dissecting North America from the Gulf of Mexico to the Arctic. On the shore of this shallow sea, over herds of duck-billed dinosaurs, soared the tern-sized Ichthyornis. Its large head with sharp teeth was designed to catch fish.
Not all the birds that lived during the Mesozoic, the Age of Large Dinosaurs, may have looked as unfamiliar as Archaeopteryx, Confuciusornis, and Hesperornis. The early representatives of today's lineages of birds can also be traced back to this remote era of our geological past. In several continents, rocks from the last part of the Cretaceous period have started to provide the remains of early shore-birds, ducks, and other more familiar birds. Their descendants are the true heirs of the magnificent dinosaurs that ruled the Earth tens of millions of years ago.
Dinosaurs and Hollywood
The dinosaur collections of the Natural History Museum of Los Angeles County are filled with more than true fossil specimens. Unknown to most of our visitors, however, the Museum also preserves an extensive collection of motion picture memorabilia, much of it having to do with Hollywood's dinosaurs.
Hollywood's first dinosaur "star" (also distinguished as the first classic character created for an animated film) was Gertie, given cinematic "life" in 1912 by the much-respected cartoonist Winsor McCay. In this pioneering short subject, Gertie (a copy of which is included in the collection of the Museum's Seaver Center for Western History Research), an Apatosaurus, then generally known to the public as Brontosaurus, performed, through a sequential series of McCay's drawings photographed one at a time, in an anachronistic "prehistoric world" that included a woolly mammoth and other extinct animals. Coincidentally, it seems, McCay gave Gertie a long and low head resembling the one we now know Apatosaurus possessed, rather than boxy Camarasaurus-type head then seen on most skeletal reconstructions and consequently, life restorations of this dinosaur.
A collection of original dinosaur movie posters is housed in the History Department of the Natural History Museum of Los Angeles County.
Just as cartoon dinosaurs like Gertie can be brought to life on the screen photographed one frame at a time, so can model dinosaurs sculpted in three dimensions. The process called "stop motion" or "dimensional animation" had been in use for a number of years when Willis O'Brien began experimenting with it around 1914. O'Brien, a paleontology buff as well as a pioneer film maker, had already made a number of dinosaur-related movies by the time he was hired by First National Pictures to film the dinosaur effects for the 1925 silent-movie version of Arthur Conan Doyle's novel The Lost World.
Although a capable model maker himself, O'Brien brought Los Angeles sculptor Marcel Delgado and others on board The Lost World project to create the dinosaurian menagerie that would populate Doyle's South American isolated plateau that had somehow remained untouched by the passage of time. Delgado used as direct inspiration for his models the paintings, drawings and sculptures of Charles R. Knight, perhaps the greatest of all restorers of prehistoric life (whose 1925 stunning mural of the La Brea Tar Pits and a 1944-46 series of prehistoric animals are housed in our Museum). Knight worked under the guidance of such legendary paleontologists as Edward Drinker Cope, Barnum Brown and Henry Fairfield Osborn; therefore, his life restorations, in their day, were considered to be scientifically accurate. Consequently, Delgado's Knight-based dinosaur models, when placed into historical perspective, may be regarded as some of the most accurate ever to appear on the motion-picture screen. Today, one of Delgado's original models still survive, preserved in our Museum's special collections.
Among O'Brien's animation assistants on The Lost World was Los Angeles sculptor J. L. Roop, of whom the Museum's Seaver Center for Western History Research maintains a collection of scrapbooks, photographs, articles and other items. One of Roop's models from The Lost World is housed in the Museum's History Department. Three years following The Lost World, Roop did the rather crude special dinosaur effects for The Lost Whirl, a comedy inspired by (but not really based on) the original film.
However, new and improved dinosaurs would later emerge from O'Brien and Delgado. In 1931 the team would be back at work again, sculpting dinosaurs and then test them in scenes for the proposed RKO movie Creation, a fantasy-adventure story about a group of people stranded on a prehistoric promontory that rises from the sea. Again working from Knight's life restorations, Delgado produced a number of models of extinct animals, including a family of the horned dinosaur Triceratops. Extant is a sequence in which a submarine's crewmember kills a baby Triceratops, only to be pursued to his death by the dinosaur's angry mother. The sequence was somehow ahead of its time, as there was no recognized evidence for dinosaurian parental care back in the 1930s. Creation was never completed, going far over budget being one of the reasons for its premature termination. The completed Triceratops sequence (now missing the ending shot, wherein the mother dinosaur impales the crewman against a tree with her horns), however, became, for a while after its completion, a popular exhibit at the Natural History Museum of Los Angeles County, clips now housed among our collections of rare film frames.
Model of Velociraptor from Jurassic Park housed in the History Department of the Natural History Museum of Los Angeles County.
Although Creation was never finished, those two creative men mainly responsible for the project - along with some of their dinosaur models - did survive into the project's unofficial successor. Shortly following the cancellation of Creation, movie producer Merian C. Cooper was hired by RKO to salvage what he could of some of the studio's unfinished film projects, among them Creation. Cooper saw Creation as "just a lot of animals walking around," although he was impressed by the special effects work of Delgado and O'Brien. At the time Cooper had been planning his own modern "Beauty and the Beast" movie featuring a performer in a gorilla costume and some Komodo dragon lizards, all photographically enlarged to make them appear gigantic. Now sold on the stop-motion project, Cooper hired Delgado and O'Brien (who brought along some of the dinosaur models built for Creation) for his own motion picture, which became the 1933 classic King Kong. Some props from King Kong, including a miniature articulated hand from the Kong stop-motion puppet that climbed the Empire State Building, now have a permanent home in our Museum's History Department movie memorabilia collection along with a Delgado-created Brontosaurus model also believed to be from King Kong.
King Kong proved to be an enormous hit upon its first release, so successful that - the very same year - RKO rushed out a comparatively inferior sequel, The Son of Kong, which also included, courtesy of O'Brien and Delgado, its share of dinosaurs and other extinct animals. Fortunately O'Brien meticulously recorded his behind-the-scenes work on The Son of Kong through a series of snapshots that he then preserved in a scrapbook now under Seavers Center curatorship.
In more recent than past years, moviemakers have finally paid attention to scientific accuracy in their dinosaur movies. Dinosaurs are now depicted with greater accuracy, based upon current paleontological information. Also, most movie dinosaurs are now portrayed more as real animals rather than, as in the past, lumbering monsters existing only to attack anachronistic "cave people," engage each other in "mortal combat" or destroy cities. Much of this change in appearance and behavior can be attributed to the movie Jurassic Park (1993), based on the 1990 novel of the same title authored by Michael Chrichton. Thanks to the seeming miracles of CGI (computer generated imagery) and to the foresight of director/producer Steven Spielberg, who demanded that his cinematic dinosaurs be portrayed with some accuracy, the paradigm for dinosaur movies has been raised, seemingly forever. Yet, the movie's fearsome Velociraptor is several times bigger than its real inspiration. This bigger-than-life-sized working model of Velociraptor, made by the Stan Winston studios, now proudly resides within our Museum's collections.
