Gallimimus ( ) is a genus of theropod dinosaur that lived in what is now Mongolia during the Late Cretaceous period. Several fossils in various stages of growth were discovered by Polish-Mongolian expeditions in the Gobi Desert of Mongolia during the 1960s; a large skeleton discovered in this region was made the holotype specimen of the new genus and species Gallimimus bullatus in 1972. The generic name means "chicken mimic", referring to the similarities between its neck vertebrae and those of the Galliformes. The specific name is derived from bulla, a golden capsule worn by Roman youth, in reference to a bulbous structure at the base of the skull of Gallimimus. At the time it was named, the fossils of Gallimimus represented the most complete and best preserved ornithomimid ("ostrich dinosaur") material yet discovered, and the genus remains one of the best known members of the group.
Gallimimus is the largest known ornithomimid; adults were about long, tall at the hip and weighed about . As evidenced by its relative Ornithomimus, it is highly likely it would have had feathers. The head was small and light with large eyes that faced to the sides. The snout was long compared to other ornithomimids, although it was broader and more rounded at the tip than in other species. Gallimimus was toothless with a keratinous (horny) beak, and had a delicate lower jaw. Many of the vertebrae had openings that indicate they were pneumatic (air-filled). The neck was proportionally long in relation to the trunk. The hands were proportionally the shortest of any ornithomimosaur and each had three digits with curved claws. The forelimbs were weak while the hindlimbs were proportionally long. The family Ornithomimidae is part of the group Ornithomimosauria. Anserimimus, also from Mongolia, is thought to have been the closest relative of Gallimimus.
As an ornithomimid, Gallimimus would have been a fleet (or cursorial) animal, using its speed to escape predators; its speed has been estimated at 42–56 km/h (29–34 mph). It may have had good vision and intelligence comparable to ratite birds. Gallimimus may have lived in groups, based on the discovery of several specimens preserved in a bone bed. Various theories have been proposed regarding the diet of Gallimimus and other ornithomimids. The highly mobile neck may have helped locate small prey on the ground, but it may also have been an opportunistic omnivore. It has also been suggested that it used small columnar structures in its beak for filter-feeding in water, though these structures may instead have been ridges used for feeding on tough plant material, indicative of a herbivorous diet. Gallimimus is the most commonly found ornithomimosaur in the Nemegt Formation, where it lived alongside its relatives Anserimimus and Deinocheirus. Gallimimus was featured in the movie Jurassic Park, in a scene that was important to the history of special effects, and in shaping the common conception of dinosaurs as bird-like animals.
History of discovery
thumb|upright=1.4|left|[[Cretaceous-aged dinosaur fossil localities of Mongolia; Gallimimus fossils were collected in area A]]
Between 1963 and 1965, the Polish Academy of Sciences and the Mongolian Academy of Sciences organised the Polish-Mongolian palaeontological expeditions to the Gobi Desert of Mongolia. Among the dinosaur remains discovered in sand beds of the Nemegt Basin were numerous ornithomimids at different growth stages from the Nemegt, Tsaagan Khushuu, Altan Ula IV and Naran Bulak localities. Three partially complete skeletons, two with skulls, as well as many fragmentary remains, were collected. The largest skeleton (later to become the holotype of Gallimimus bullatus) was discovered by palaeontologist Zofia Kielan-Jaworowska in Tsaagan Khushuu in 1964; it was preserved lying on its back, and the skull was found under its pelvis. One small specimen was also found in Tsaagan Khushuu the same year, and another small specimen was found in the Nemegt locality. A small skeleton without forelimbs was discovered in 1967 by the Mongolian palaeontological expedition in Bugeen Tsav outside the Nemegt Basin. The fossils were housed at the Mongolian, Polish and USSR Academy of Sciences. The Polish-Mongolian expeditions were notable for being led by women, some of whom were among the first women to name new dinosaurs. The fossils discovered in these expeditions shed new light on the interchange of fauna between Asia and North America during the Cretaceous period.
thumb|left|Three skeletons, including the holotype (right) and a juvenile (middle), during a temporary exhibition in [[CosmoCaixa]]
The other partially complete skeletons were juveniles; ZPAL MgD-I/1 (from Tsaagan Khushuu) has a crushed skull with a missing tip, damaged vertebrae, fragmented ribs, pectoral girdle and forelimbs, and an incomplete left hind limb, ZPAL MgD-I/94 (from the Nemegt locality) lacks the skull, atlas, tip of the tail, pectoral girdle and forelimbs, while the smallest specimen, IGM 100/10 (from Bugeen Tsav), lacks a pectoral girdle, forelimbs and several vertebrae and ribs. Osmólska and colleagues listed twenty-five known specimens in all, nine of which were only represented by single bones.
thumb|right|Specimens which were repatriated to Mongolia after having been smuggled to the US, in [[Central Museum of Mongolian Dinosaurs]]
Fossil poaching has become a serious problem in Mongolia in the 21st century, and several Gallimimus specimens have been looted. In 2017, Hang-Jae Lee and colleagues reported a fossil trackway discovered in 2009 associated with a clenched Gallimimus foot (specimen MPC-D100F/17). The rest of the skeleton appeared to have been removed previously by poachers, along with several other Gallimimus specimens (as indicated by empty excavation pits, garbage, and scattered broken bones in the quarry). It is unusual to find tracks closely associated with body fossils; some of the tracks are consistent with ornithomimid feet, while others belong to different dinosaurs.
Alternative taxonomic assignments
thumb|left|Specimen informally known as "[[Gallimimus mongoliensis", which probably belongs to a different genus]]
In 1988, the palaeontologist Gregory S. Paul concluded that the skulls of ornithomimids were more similar to each other than previously thought and moved most species into the same genus, Ornithomimus, resulting in the new combination O. bullatus. The species involved have generally been kept in separate genera by other writers.
An ornithomimid vertebra from Japan informally named "Sanchusaurus" was reported in a 1988 magazine, but was assigned to Gallimimus sp. (of uncertain species) by the palaeontologist Dong Zhiming and colleagues in 1990.
Description
thumb|Size compared to a human
Gallimimus is the largest known member of the family Ornithomimidae. The adult holotype (specimen IGM 100/11) was about long and tall at the hip; its skull was long and the femur (thigh bone) was . It would have weighed about . In comparison, one juvenile specimen (ZPAL MgD-I/94) was about long, tall at the hip, and weighed about .
Skull
thumb|left|Reconstructed skull and neck, NHM
The head of Gallimimus was very small and light compared to the vertebral column. Due to the length of its snout, the skull was long compared to other ornithomimids, and the snout had a gently convex sloping upper profile. The side profile of the snout differed from other ornithomimids in not narrowing towards its front half, and the lower front margin of the premaxilla at the front of the upper jaw rose upwards, instead of being horizontal. Seen from above, the snout was almost spatulate (spoon-shaped), broad and rounded at the tip (or U-shaped), whereas it was acute (or V-shaped) in North American ornithomimids. The orbits (eye sockets) were large and faced sideways, as in other ornithomimids. The temporal region at the side of the skull behind the eyes was deep, and the infratemporal fenestra (the lower opening behind the orbit) was nearly triangular and smaller than that of the related Struthiomimus. It had deep muscle scars at the back part of the skull roof, along the parietal bone. The parasphenoid (a bone of the braincase, at the underside of the skull's base) was thin-walled, hollow and formed a pear-shaped, bulbous structure. The structure had a shallow furrow which opened towards the front. The internal nares (internal openings for the nasal passage) were large and placed far back on the palate, due to the presence of an extensive secondary palate, which was common to ornithomimids.
thumb|left|[[Skeletal pneumaticity|Pneumatic structures in the caudal vertebrae of Shenzhousaurus (A), and the cervical (B, C, D), dorsal (E), sacral (F, G) and caudal (H) vertebrae of Gallimimus]]
The back of Gallimimus had 13 dorsal vertebrae, with spool-like centra that were short, but tended to become deeper and longer towards the back. Their transverse processes (processes articulating with the ribs) slightly increased in length towards the back. The two first dorsal centra had deep pneumatic foramina, while the rest only had shallow fossae (depressions), and the neural spines were prominent being somewhat triangular or rectangular in shape. The sacrum (fused vertebrae between the pelvic bones) consisted of five sacral vertebrae which were about equal in length. The centra here were spool-like, flattened sideways and had fossae which appear to have continued as deep foramina in some specimens. The neural spines here were rectangular, broad, and higher than those in the dorsal vertebrae. They were higher or equal in height to the upper margin of the iliac blade and were separate, whereas in other ornithomimids they were fused together. The tail had 36–39 caudal vertebrae with the centra of those at the front being spool-shaped, while those at the back were nearly triangular, and elongated across. The neural spines here were high and flat, but diminished backwards, where they became ridge-like. The only sign of pneumaticity in the tail were deep fossae between the neural spines and the transverse process of the two first caudal vertebrae. All the vertebrae in front of the sacrum bore ribs except for the atlas and the last dorsal vertebra.
thumb|alt=|right|[[Metatarsal footbones of ornithomimosaurs; the foot of Gallimimus (upper left) was arctometatarsalian (see middle bone in white)]]
The following cladogram shows the placement of Gallimimus among Ornithomimidae according to the palaeontontologist Bradley McFeeters and colleagues, 2016:
Ornithomimosaurs belonged to the clade Maniraptoriformes of coelurosaurian theropods, which also includes modern birds. Early ornithomimosaurs had teeth, which were lost in more derived members of the group. In 2004, Makovicky, Kobayashi, and Currie suggested that most of the early evolutionary history of ornithomimosaurs took place in Asia, where most genera have been discovered, including the most basal (or "primitive") taxa, although they acknowledged that the presence of the basal Pelecanimimus in Europe presents a complication in classification. The group must have dispersed once or twice from Asia to North America across Beringia to account for the Late Cretaceous genera found there. As seen in some other dinosaur groups, ornithomimosaurs were largely restricted to Asia and North America after Europe was separated from Asia by the Turgai Strait. In 1998, Holtz instead found that troodontids were basal maniraptorans, meaning that all members of that clade would fall within Bullatosauria, which would therefore become a junior synonym of Maniraptoriformes, and the clade has since fallen out of use.
Palaeobiology
thumb|Skull in [[Central Museum of Dinosaurs of Mongolia]]
The cervical vertebrae of Gallimimus indicate that it held its neck obliquely, declining upwards at an angle of 35 degrees. Osmólska and colleagues found that the hands of Gallimimus were not prehensile (or capable of grasping), and that the thumb was not opposable. They also suggested that the arms were weak compared to, for example, those of the ornithomimosaur Deinocheirus. They agreed with the interpretations of ornithomimid biology by palaeontologist Dale Russell from earlier in 1972, including that they would have been very fleet (or cursorial) animals, although less agile than large, modern ground birds, and would have used their speed to escape predators. Russell also suggested that they had a good sense of vision and intelligence comparable to that of modern ratite birds. Since their predators may have had colour vision, he suggested it would have influenced their colouration, perhaps resulting in camouflage. In 1982, palaeontologist Richard A. Thulborn estimated that Gallimimus could have run at speeds of 42–56 km/h (29–34 mph). He found that ornithomimids would not have been as fast as ostriches, which can reach 70–80 km/h (43–49 mph), in part due to their arms and tails increasing their weight.
thumb|left|Skull cast of the juvenile specimen ZPAL MgD-I/1, [[National Museum of Natural History]]
In 1988, Paul suggested that the eyeballs of ornithomimids were flattened and had minimal mobility within the sockets, necessitating movement of the head to view objects. Since their eyes faced more sideways than in some other bird-like theropods, their binocular vision would have been more limited, which is an adaptation in some animals that improves their ability to see predators behind them. Paul considered the relatively short tails, which reduced weight, and missing halluxes of ornithomimids to be adaptations for speed. He suggested that they could have defended themselves by pecking and kicking, but would have mainly relied on their speed for escape.
Feeding and diet
thumb|left|Reconstructed skull and neck in front view, NHM
Osmólska and colleagues pointed out that the front part of the neck of Gallimimus would have been very mobile (the hind part was more rigid), the neural arches in the vertebrae of that region being similar to chicken and other Galliformes, indicating similar feeding habits. They found the beak of Gallimimus similar to that of a duck or goose, and that it would have fed on small, living prey which it swallowed whole. The mobility of the neck would have been useful in locating prey on the ground, since the eyes were positioned on the sides of the skull. They assumed that all ornithomimids had similar feeding habits, and pointed out that Russel had compared the beaks of ornithomimids with those of insectivorous birds. Osmólska and colleagues suggested that Gallimimus was capable of cranial kinesis (due to the seemingly loose connection between some of the bones at the back of the skull), a feature which allows individual bones of the skull to move in relation to each other. They also proposed that it did not use its short handed forelimbs for bringing food to the mouth, but for raking or digging in the ground to access food.
In 1988 Paul disagreed that ornithomimids were omnivores that ate small animals and eggs as well as plants, as had previously been suggested. He pointed out that ostriches and emus are mainly grazers and browsers, and that the skulls of ornithomimids were most similar to those of the extinct moas, which were strong enough to bite off twigs, as evidenced by their gut content. He further suggested that ornithomimids were well adapted for browsing on tough plants and would have used their hands to bring branches within reach of their jaws.
thumb|The beak of Gallimimus contained structures which have been compared to the [[Lamella (surface anatomy)|lamellae of, for example, the Northern shoveller, or the ridges in the beaks of turtles and hadrosaurids.]]
In 2001, palaeontologists Mark A. Norell, Makovicky, and Currie reported a Gallimimus skull (IGM 100/1133) and an Ornithomimus skull that preserved soft tissue structures on the beak. The inner side of the Gallimimus beak had columnar structures that the authors found similar to the lamellae in the beaks of anseriform birds, which use these for manipulating food, straining sediments, filter-feeding by segregating food items from other material, and for cutting plants while grazing. They found the Northern shoveller, which feeds on plants, molluscs, ostracods, and foraminiferans, to be the modern anseriform with structures most similar in anatomy to those of Gallimimus. The authors noted that ornithomimids probably did not use their beaks to prey on large animals and were abundant in mesic environments, while rarer in more arid environments, suggesting that they may have depended on aquatic food sources. Makovicky, Kobayashi, and Currie pointed out that if this interpretation is correct, Gallimimus would have been one of the largest known terrestrial filter feeders. In 2007, palaeontologist Espen M. Knutsen wrote that the beak shape of ornithomimids, when compared to those of modern birds, was consistent with omnivory or high-fibre herbivory.
David J. Button and Zanno found in 2019 herbivorous dinosaurs mainly followed two distinct modes of feeding, either processing food in the gut—characterized by gracile skulls and low bite forces—or the mouth, characterized by features associated with extensive processing. Ornithomimid ornithomimosaurs, Deinocheirus, diplodocoid and titanosaur sauropods, Segnosaurus, and caenagnathids, were found to be in the former category. These researchers suggested that ornithomimid ornithomimosaurians such as Gallimimus and deinocheirids had invaded these niches separately, convergently achieving relatively large sizes. Advantages from large body mass in herbivores include increased intake rate of food and fasting resistance, and these trends may therefore indicate that ornithomimids and deinocheirids were more herbivorous than other ornithomimosaurians. They cautioned that the correlations between herbivory and body mass were not simple, and that there was no directional trend towards increased mass seen in the clade. Furthermore, the diet of most ornithomimosaurians is poorly known.
Development
thumb|Smallest known Gallimimus, the juvenile specimen IGM 100/10, exhibited in CosmoCaixa
The shape and proportions of the skull changed significantly during growth. The rear of the skull and the orbits decreased in size, whereas the snout became relatively longer; similar changes occur in modern crocodiles. The skull was also proportionally larger in the younger specimens, and the sloping of the snout's upper profile was less distinct. The ribs in the neck were fused to the vertebrae only in adults. The forelimbs appear to have become proportionally longer during growth, whereas the proportional length of the bones in the hind limbs changed very little. In 1991, they reported that the bones of old individuals contained the highest amounts of lead and iron, while those in younger animals were lower. A study of the bone histology of various dinosaurs in 2000, by biologists John M. Rensberger and Mahito Watabe, revealed that the canaliculi (channels which connect bone cells) and collagen fibre bundles of Gallimimus and other ornithomimids were more akin to those in birds than mammals, unlike those of ornithischian dinosaurs, which were more similar to mammals. These differences may have been related to the process and rate at which bone formed.
Palaeoenvironment
thumb|right|Two Gallimimus (right foreground) with contemporary [[dinosaurs of the Nemegt Formation]]
Gallimimus is known from the Nemegt Formation in the Gobi Desert of southern Mongolia. This geologic formation has never been dated radiometrically, but the fauna present in the fossil record indicate it was probably deposited during the early Maastrichtian stage, at the end of the Late Cretaceous about 70 million years ago. The sediments of the Gallimimus type locality Tsaagan Khushuu consist of silts, siltstones, mudstones, sands, as well as less frequent thin beds of sandstones. Large river channels and soil deposits are evidence of a significantly more humid climate than those found in the older Barun Goyot and Djadochta formations, although caliche deposits indicate that periodic droughts occurred. Fossil bones from the Nemegt Basin, including of Gallimimus, are more radioactive than fossils from surrounding areas, possibly because uranium accumulated in the bones, transported there by percolating ground water.
The Nemegt rivers, where Gallimimus lived, were home to a wide array of organisms. Occasional mollusc fossils, as well as a variety of other aquatic animals like fish, turtles, Mammal fossils are rare in the Nemegt Formation, but many birds, including the enantiornithine Gurilynia, the hesperornithiform Judinornis, as well as Teviornis, a possible anseriform, have been found. Herbivorous dinosaurs discovered in the Nemegt Formation include ankylosaurids such as Tarchia, the pachycephalosaurian Prenocephale, large hadrosaurids such as Saurolophus and Barsboldia, and sauropods such as Nemegtosaurus and Opisthocoelicaudia. Predatory theropods that lived alongside Gallimimus include tyrannosauroids such as Tarbosaurus, Alioramus and Bagaraatan, and troodontids such as Borogovia, Tochisaurus and Zanabazar. Herbivorous or omnivorous theropods include therizinosaurs, such as Therizinosaurus, as well as oviraptorosaurians, such as Elmisaurus, Nemegtomaia, and Rinchenia. Other ornithomimosaurs, including Anserimimus and Deinocheirus, are also found, but Gallimimus is the most common member of the group in the Nemegt.
The production team became very enthusiastic as nothing similar had previously been achieved, and Spielberg was convinced to write the scene into the script, and to also use computer graphics for other dinosaur shots in the movie instead of stop motion. Kielan-Jaworowska, who discovered the holotype specimen, called it a "beautiful scene".
thumb|left|1994 stamp from Romania showing Gallimimus without feathers
Emphasising the bird-like flocking behaviour of the Gallimimus herd was a point in Jurassic Parks story, as they were supposed to represent the precursors to birds. The herd was shown moving as a whole, rather than individual animals running around, and the smaller Gallimimus were shown in the middle of the group, as though they were being protected. Despite such theories, Gallimimus and other dinosaurs of the movie were depicted without feathers, in part because it was unknown at the time how widespread these were among the group.
It has been claimed that the Lark Quarry tracks (one of the world's largest concentrations of dinosaur tracks) in Queensland, Australia, served as inspiration and "scientific underpinning" for the Gallimimus stampede scene in Jurassic Park; these tracks were initially interpreted as representing a dinosaur stampede caused by the arrival of a theropod predator. The idea that the tracks represent a stampede has since been contested (the "theropod" may instead have been a herbivore similar to Muttaburrasaurus), and a consultant to Jurassic Park has denied the tracks served as inspiration for the movie.
See also
- Timeline of ornithomimosaur research