| Gallimimus | |
|---|---|
 | |
| Reconstructed skeleton (based on the adultholotype and a juvenile specimen),Natural History Museum | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Ornithomimosauria |
| Family: | †Ornithomimidae |
| Genus: | †Gallimimus Osmólskaet al., 1972 |
| Species: | †G. bullatus |
| Binomial name | |
| †Gallimimus bullatus Osmólskaet al.,1972 | |
| Synonyms | |
| |
Gallimimus (/ˌɡælɪˈmaɪməs/GAL-im-EYE-məs) is agenus oftheropoddinosaur that lived in what is nowMongolia during theLate Cretaceousperiod, about seventymillion years ago (mya). Several fossils in various stages of growth were discovered by Polish-Mongolian expeditions in theGobi Desert of Mongolia during the 1960s; a large skeleton discovered in this region was made theholotype specimen of the new genus and speciesGallimimus bullatus in 1972. The generic name means "chicken mimic", referring to the similarities between its neck vertebrae and those of theGalliformes. The specific name is derived frombulla, a golden capsule worn byRoman youth, in reference to a bulbous structure at the base of the skull ofGallimimus. At the time it was named, the fossils ofGallimimus represented the most complete and best preservedornithomimid ("ostrich dinosaur") material yet discovered, and the genus remains one of the best known members of the group.
Gallimimus is the largest knownornithomimid; adults were about 6 metres (20 ft) long, 1.9 metres (6 ft 3 in) tall at the hip and weighed about 400–490 kilograms (880–1,080 lb). As evidenced by its relativeOrnithomimus, it is highly likely it would havehad 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 akeratinous (horny) beak, and had a delicate lower jaw. Many of thevertebrae had openings that indicate they werepneumatic (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 groupOrnithomimosauria.Anserimimus, also from Mongolia, is thought to have been the closest relative ofGallimimus.
As an ornithomimid,Gallimimus would have been a fleet (orcursorial) 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 toratite birds.Gallimimus may have lived in groups, based on the discovery of several specimens preserved in abone bed. Various theories have been proposed regarding the diet ofGallimimus and other ornithomimids. The highly mobile neck may have helped locate small prey on the ground, but it may also have been an opportunisticomnivore. It has also been suggested that it used small columnar structures in its beak forfilter-feeding in water, though these structures may instead have been ridges used for feeding on tough plant material, indicative of aherbivorous diet.Gallimimus is the most commonly found ornithomimosaur in theNemegt Formation, where it lived alongside its relativesAnserimimus andDeinocheirus.Gallimimus was featured in the movieJurassic Park, in a scene that was important to the history ofspecial effects, and in shaping the common conception of dinosaurs as bird-like animals.
Between 1963 and 1965, thePolish Academy of Sciences and theMongolian Academy of Sciences organised the Polish-Mongolian palaeontological expeditions to theGobi Desert of Mongolia. Among the dinosaur remains discovered in sand beds of theNemegt Basin were numerousornithomimids 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 ofGallimimus bullatus) was discovered by palaeontologistZofia 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 andUSSR Academy of Sciences.[1][2][3] 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 theCretaceousperiod.[4][5][6] Some of the skeletons were exhibited in Warsaw in 1968, mounted in tall, semi-erect postures, which was accepted at the time, though more horizontal postures are favoured today.[6]
In 1972, palaeontologistsHalszka Osmólska, Ewa Roniewicz andRinchen Barsbold named the newgenus and speciesGallimimus bullatus, using the largest collected skeleton, specimen IGM 100/11 (from Tsaagan Khushuu, formerly referred to as G.I.No.DPS 100/11 and MPD 100/11), as theholotype. The generic name is derived from theLatingallus, "chicken", and the Greekmimos, "mimic", in reference to the front part of the neck vertebrae which resembled those of theGalliformes. Thespecific name is derived from the Latinbulla, a gold capsule worn byRoman youth around the neck, in reference to the bulbous capsule on the parasphenoid at the base of the dinosaur's skull. Such a feature had not been described from other reptiles at the time, and was considered unusual. The holotype consists of an almost complete skeleton with a distorted snout, incomplete lower jaw, vertebral series, pelvis, as well as some missing hand and foot bones.[1][7]
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.[1][8]
At the time it was named, the fossils ofGallimimus represented the most complete and best preserved ornithomimid material yet discovered, and the genus remains one of the best known members of the group. Ornithomimids were previously known mainly from North America,Archaeornithomimus being the only prior known member from Asia (though without a skull). Since the first discoveries, more specimens have been found by further Mongolian-led international expeditions.[1][8][5][6] Three of theGallimimus skeletons (including the holotype) later became part of a travelling exhibit of Mongolian dinosaur fossils, which toured various countries.[9][10]
Fossil poaching has become a serious problem in Mongolia in the 21st century, and severalGallimimus specimens have been looted. In 2017, Hang-Jae Lee and colleagues reported a fossil trackway discovered in 2009 associated with a clenchedGallimimus foot (specimen MPC-D100F/17). The rest of the skeleton appeared to have been removed previously by poachers, along with several otherGallimimus 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.[11][12] In 2014, a slab with twoGallimimus specimens was repatriated to Mongolia along with other dinosaur skeletons, after having been smuggled to the US.[13]
In 1988, the palaeontologistGregory 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 thenew combinationO. bullatus.[14] In 2010, he instead listed it as "Gallimimus (orStruthiomimus)bullatus", but returned to using only the genus nameGallimimus in 2016.[15][16] The species involved have generally been kept in separate genera by other writers.[17] An ornithomimid vertebra from Japaninformally named "Sanchusaurus" was reported in a 1988 magazine, but was assigned toGallimimus sp. (of uncertain species) by the palaeontologistDong Zhiming and colleagues in 1990.[7] In 2000, the palaeontologistPhilip J. Currie proposed thatAnserimimus, which is only known from one skeleton from Mongolia, was ajunior synonym ofGallimimus, but this was dismissed by Kobayashi and Barsbold, who pointed out several differences between the two. Barsbold noted somemorphological variation among newerGallimimus specimens, though this has never been published. Barsbold informally referred to a nearly complete skeleton (IGM 100/14) as "Gallimimus mongoliensis", but since it differs fromGallimimus in some details, Yoshitsugu Kobayashi and Barsbold proposed in 2006 that it probably belongs to a different genus.[8]
Gallimimus is the largest known member of thefamily Ornithomimidae. The adult holotype (specimen IGM 100/11) was about 6 metres (20 ft) long and 1.9 metres (6.2 ft) tall at the hip; its skull was 330 millimetres (1.08 ft) long and thefemur (thigh bone) was 660 millimetres (2.17 ft). It would have weighed about 400–490 kilograms (880–1,080 lb).[14][15][18][19] In comparison, one juvenile specimen (ZPAL MgD-I/94) was about 2.15 metres (7.1 ft) long, 0.79 metres (2.6 ft) tall at the hip, and weighed about 26–30.2 kilograms (57–67 lb).[14][18] Based on fossils of the relatedOrnithomimus, it is known thatornithomimosaurs ("ostrich dinosaurs") werefeathered, and that the adults bore wing-like structures as evidenced by the presence of quill-knobs on theulna bone of the lower arm, bumps that indicate where feathers would have attached.[20]
.JPG)
The head ofGallimimus 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 thepremaxilla 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 (orU-shaped), whereas it was acute (or V-shaped) in North American ornithomimids. Theorbits (eye sockets) were large and faced sideways, as in other ornithomimids. Thetemporal region at the side of the skull behind the eyes was deep, and theinfratemporal fenestra (the lower opening behind the orbit) was nearly triangular and smaller than that of the relatedStruthiomimus. It had deep muscle scars at the back part of the skull roof, along theparietal bone. Theparasphenoid (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. Theinternal nares (internal openings for the nasal passage) were large and placed far back on thepalate, due to the presence of an extensivesecondary palate, which was common to ornithomimids.[1][17][21][22]
The delicate lower jaw, consisting of thin bones, was slender and shallow at the front, deepening towards the rear. The front of the mandible was shovel-like, resulting in a gap between the tips of the jaws when shut. The shovel-like shape was similar to that of thecommon seagull, and the lower beak may have had a shape similar to that of this bird. The retroarticular process at the back of the jaw (where jaw muscles attached that opened the beak) was well developed and consisted mainly of theangular bone. Thesurangular was the largest bone of the lower jaw, which is usual in theropods. Themandibular fenestra, a sidewards-facing opening in the lower jaw, was elongated and comparatively small. The lower jaw did not have acoronoid process or a supradentary bone, the lack of which is a common feature of beaked theropods (ornithomimosaurs,oviraptorosaurs,therizinosaurs and birds), but unusual among theropods in general.[1][23] The jaws ofGallimimus wereedentulous (toothless), and the front part would have been covered in akeratinous rhamphotheca (horny beak) in life. The beak may have covered a smaller area than in North American relatives, based on the lack of nourishing foramina on the maxilla. The inner side of the beak had small, tightly packed and evenly spaced columnar structures (their exact nature is debated), which were longest at the front and shortening towards the back.[21][23][24]
Gallimimus had 64–66vertebrae in itsspine, fewer than other ornithomimids. The centra (or bodies) of the vertebrae were platycoelous, with a flat front surface and a concave hind surface, except for the first sixcaudal (tail) vertebra—where the hind surface was also flat—and those at the end of the tail—which were amphiplatyan with both surfaces flat. Many of the centra hadforamina (openings which have also been called "pleurocoels"), and were therefore probablypneumatic (with their hollow chambers invaded byair sacs). The neck consisted of 10cervical vertebrae, which were all long and wide, except for theatlas bone (the first vertebra that connects with the back of the skull). The atlas differed from that of other ornithomimids in that the front surface of its intercentrum was slanted downwards towards the back, instead of being concave and facing upwards to support theoccipital condyle. The neck appears to have been proportionally longer in relation to the trunk than in other ornithomimids. The neck was divided into two distinct sections: the cervical vertebrae at the front had centra which were nearly triangular in side view and tapered towards the back, as well as low neural arches and short, broadzygapophyses (theprocesses that articulated between the vertebrae); the cervical vertebrae at the back had spool-like centra which became gradually higher, and long, thin zygapophyses. The pneumatic foramina here were small and oval, and the neural spines projecting outwards from the centra formed long, low and sharp ridges, except for in the hindmost cervical vertebrae.[1][25]
The back ofGallimimus had 13dorsal 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 shallowfossae (depressions), and the neural spines were prominent being somewhat triangular or rectangular in shape. Thesacrum (fused vertebrae between the pelvic bones) consisted of fivesacral 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 theiliac 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 boreribs except for the atlas and the last dorsal vertebra.[1][25]
Thescapula (shoulder blade) was short and curved, thin at the front end, and thick at the back. It was connected relatively weakly with thecoracoid, which was large and deep from top to bottom. Overall, the forelimbs did not differ much from those of other ornithomimids, all of which were comparatively weak. Thehumerus (upper arm bone), which had a near circular cross-section, was long and twisted. The deltopectoral crest on the upper front part of the humerus was comparatively small, and therefore provided little surface for attachment of upper arm muscles. The ulna was slender, long and weakly curved, with a nearly triangular shaft. Theolecranon (the projection from the elbow) was prominent in adults, but not well developed in juveniles. Theradius (the other bone in the lower arm) was long and slender with a more expanded upper end compared to the lower. Themanus (hand) was proportionally short compared to those of other ornithomimosaurs, having the smallest manus to humerus length ratio of any member of the group, but was otherwise similar in structure. It had three fingers, which were similarly developed; the first (the "thumb") was the strongest, the third was the weakest and the second was the longest. Theunguals (claw bones) were strong, somewhat curved (that of the first finger was most curved) and compressed sideways with a deep groove on each side. The unguals were similarly developed, though the third was slightly smaller.[1][8][17]
Thepubis (pubic bone) was long and slender, ending in a pubic boot which expanded to the front and back, a general feature of ornithomimosaurs. The hind limbs differed little from those of other ornithomimids, and were proportionally longer than in other theropods. The femur was nearly straight, long and slender, with a sideways flattened shaft. Thetibia was straight, long, with two well developedcondyles (rounded end of a bone) on the upper end and a flattened lower end. Thefibula of the lower leg was flat, thin and broad at the upper end narrowing towards the lower end. The lower half of the thirdmetatarsal was broad when viewed end on, partly covering the adjoining two metatarsals to each side, but narrowed abruptly at mid-length, wedging between those bones and disappearing (anarctometatarsalian foot structure). The third toe was proportionally shorter in relation to the limb than in other ornithomimids. As in other ornithomimids, the foot had nohallux (or dewclaw, the first toe of most other theropods). The unguals of the toes were flat on their lower sides; the outer two declined slightly outwards from their digits.[1][17]
Osmólska and colleagues assignedGallimimus to the family Ornithomimidae in 1972, with the North AmericanStruthiomimus as the closest relative, while lamenting the fact that comparison betweentaxa was difficult because other ornithomimids known at the time were either poorly preserved or inadequately described.[1] In 1975, Kielan-Jaworowska stated that though many dinosaurs from Asia were placed in the same families as North American relatives, this category of classification tended to be more inclusive than was used for modern birds. She highlighted that whileGallimimus had a rounded beak (similar to a goose or duck), North American ornithomimids had pointed beaks, a difference that would otherwise lead taxonomists to place modern birds in different families.[5] In 1976, Barsbold placed Ornithomimidae in the new group Ornithomimosauria. In 2003, Kobayashi and Jun-Chang Lü found thatAnserimimus was thesister taxon toGallimimus, both forming aderived (or "advanced")clade with North American genera, which was confirmed by Kobayashi and Barsbold in 2006.[8][21]
The followingcladogram shows the placement ofGallimimus among Ornithomimidae according to the palaeontontologist Bradley McFeeters and colleagues, 2016:[26]
| Ornithomimidae |
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Ornithomimosaurs belonged to the cladeManiraptoriformes ofcoelurosaurian theropods, which also includes modern birds. Early ornithomimosaurs had teeth, which were lost in more derived members of the group.[27] 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 mostbasal (or "primitive") taxa, although they acknowledged that the presence of the basalPelecanimimus in Europe presents a complication in classification. The group must have dispersed once or twice from Asia to North America acrossBeringia 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 theTurgai Strait.[17]
In 1994, the palaeontologistThomas R. Holtz grouped ornithomimosaurs andtroodontids in a clade, based on shared features such as the presence of a bulbous capsule on the parasphenoid. He named the clade Bullatosauria, based on the specific name ofGallimimus bullatus, which was also in reference to the capsule.[28] 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.[29][30]
The cervical vertebrae ofGallimimus indicate that it held its neck obliquely, declining upwards at an angle of 35 degrees. Osmólska and colleagues found that the hands ofGallimimus were notprehensile (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 ornithomimosaurDeinocheirus. They agreed with the interpretations of ornithomimid biology by palaeontologistDale Russell from earlier in 1972, including that they would have been very fleet (orcursorial) 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 modernratite birds. Since their predators may have hadcolour vision, he suggested it would have influenced their colouration, perhaps resulting incamouflage.[1][31] In 1982, palaeontologistRichard A. Thulborn estimated thatGallimimus could have run at speeds of 42–56 km/h (29–34 mph). He found that ornithimimids 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.[32]
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, theirbinocular 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.[14] In 2015, Akinobu Watanabe and colleagues found that together withDeinocheirus andArchaeornithomimus,Gallimimus had the most pneumatised skeleton among ornithomimosaurs. Pneumatisation is thought to be advantageous for flight in modern birds, but its function in non-avian dinosaurs is not known with certainty. It has been proposed that pneumatisation was used to reduce the mass of large bones, that it was related to highmetabolism, balance during locomotion, or used forthermoregulation.[25]
In 2017, Lee and colleagues suggested various possibletaphonomic circumstances (changes during decay and fossilisation) to explain how theGallimimus foot discovered in 2009 was associated with a trackway. The trackway is preserved insandstone while the foot is preserved inmudstone, extending 20 centimetres (7.9 in) below the layer with the tracks. It is possible the fossil represents an animal that died in its tracks, but the depth of the foot in the mud may be too shallow for it to have become mired. It may also have been killed by a flood, after which it was buried in a pond. However, the layers of mud and sand do not indicate flooding but probably a dry environment, and the disruptedsediments around the fossil indicate the animal was alive when it came to the area. The authors thus suggested that the tracks had been made over an extended amount of time and period of drying, and that probably none of them were produced by the individual that owned the foot. The animal may have walked across the floor of a pond, breaking through the sediment layer with the tracks while it was soaked from rain or contained water. The animal may have died in this position from thirst, hunger, or another reason, and mud then deposited on the sand, thereby covering and preserving the tracks and the carcass. The foot may have become clenched and disarticulated as it decomposed, which made thetendons flex, and was later stepped on by heavy dinosaurs. The area may have been a singlebone bed (based on the possible number of poached specimens) representing aGallimimus mass mortality, perhaps due to a drought or famine. The fact that the animals seem to have died at the same time (the empty excavation pits were stratigraphically identical) may indicate thatGallimimus wasgregarious (lived in groups), which has also been suggested for other ornithomimids.[12]
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Osmólska and colleagues pointed out that the front part of the neck ofGallimimus 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 ofGallimimus 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 ofinsectivorous birds. Osmólska and colleagues suggested thatGallimimus was capable ofcranial 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.[1] The hands ofGallimimus may have been weaker than for example those ofStruthiomimus, which may instead have used its hands for hooking and gripping, according to a 1985 article by palaeontologists Elizabeth L. Nicholls and Anthony P. Russell.[33]
In 1988 Paul disagreed that ornithomimids wereomnivores that ate small animals and eggs as well as plants, as had previously been suggested. He pointed out that ostriches and emus are mainlygrazers andbrowsers, and that the skulls of ornithomimids were most similar to those of the extinctmoas, 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.[14] PalaeontologistJørn Hurum suggested in 2001 that due to its similar jaw structure,Gallimimus may have had an opportunistic, omnivorous diet like seagulls. He also observed that the tightintramandibular joint would prevent any movement between the front and rear portions of the lower jaw.[23]
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In 2001, palaeontologistsMark A. Norell, Makovicky, and Currie reported aGallimimus skull (IGM 100/1133) and anOrnithomimus skull that preserved soft tissue structures on the beak. The inner side of theGallimimus beak had columnar structures that the authors found similar to thelamellae in the beaks ofanseriform 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 theNorthern shoveller, which feeds on plants, molluscs,ostracods, andforaminiferans, to be the modern anseriform with structures most similar in anatomy to those ofGallimimus. The authors noted that ornithomimids probably did not use their beaks to prey on large animals and were abundant inmesic environments, while rarer in more arid environments, suggesting that they may have depended on aquatic food sources.[24] Makovicky, Kobayashi, and Currie pointed out that if this interpretation is correct,Gallimimus would have been one of the largest known terrestrial filter feeders.[17]
In 2005, palaeontologist Paul Barrett pointed out that the lamella-like structures ofGallimimus did not appear to have been flexible bristles like those of filter-feeding birds (as there is no indication of these structures overlapping or being collapsed), but were instead more akin to the thin, regularly spaced vertical ridges in the beaks of turtles andhadrosaurid dinosaurs. In these animals, such ridges are thought to be associated with herbivorous diets, used to crop tough vegetation. Barrett suggested that the ridges in the beak ofGallimimus represented a natural cast of the internal surface of the beak, indicating that the animal was a herbivore that fed on material high in fibre. The discovery of manygastroliths (gizzard stones) in some ornithomimids indicate the presence of a gastric mill, and therefore point towards a herbivorous diet, as these are used to grind food of animals that lack the necessary chewing apparatus. Barrett also calculated that a 440 kilograms (970 lb)Gallimimus would have needed between 0.07 and 3.34 kilograms (0.15 and 7.36 lb) of food per day, depending on whether it had anendothermic or anectothermic ("warm" or "cold"-blooded) metabolism, an intake which he found to be unfeasible if it was a filter feeder. He also found that ornithomimids were abundant not only in formations that represented mesic environments, but also in arid environments where there would be insufficient water to sustain a diet based on filter-feeding.[22] 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.[34]
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, andcaenagnathids, were found to be in the former category. These researchers suggested that ornithomimid ornithomimosaurians such asGallimimus 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.[35]
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 moderncrocodiles. 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.[1][23] In 2012, palaeontologist Darla K. Zelenitsky and colleagues concluded that, since adult ornithomimosaurs had wing-like structures on their arms whereas juveniles did not (as evidenced by specimens ofOrnithomimus), these structures were originallysecondary sexual characteristics, which could have been used for reproductive behaviour such ascourtship,display, and brooding.[20]
A 1987 study by the biologists Roman Pawlicki and P. Bolechała showed age-related differences in the content ofcalcium andphosphorus (important components in the formation of bone) ofGallimimus specimens. They found that the ratio was highest in young to middle aged animals, decreasing with age.[36] 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.[37] A study of the bonehistology of various dinosaurs in 2000, by biologists John M. Rensberger and Mahito Watabe, revealed that thecanaliculi (channels which connect bone cells) andcollagen fibre bundles ofGallimimus and other ornithomimids were more akin to those in birds than mammals, unlike those ofornithischian dinosaurs, which were more similar to mammals. These differences may have been related to the process and rate at which bone formed.[38]
Gallimimus is known from theNemegt Formation in the Gobi Desert of southern Mongolia. Thisgeologic formation has never beendated radiometrically, but thefauna present in the fossil record indicate it was probably deposited during the earlyMaastrichtian stage, at the end of theLate Cretaceous about 70 million years ago.[39][40][41] The sediments of theGallimimustype locality Tsaagan Khushuu consist ofsilts,siltstones, mudstones, sands, as well as less frequent thin beds of sandstones.[3] The rockfacies of the Nemegt Formation suggest the presence of river channels, mudflats, shallow lakes andfloodplains in an environment similar to theOkavango Delta of present-dayBotswana.[42] Large river channels and soil deposits are evidence of a significantly more humid climate than those found in the olderBarun Goyot andDjadochta formations, althoughcaliche deposits indicate that periodic droughts occurred.[43] Fossil bones from the Nemegt Basin, including ofGallimimus, are moreradioactive than fossils from surrounding areas, possibly becauseuranium accumulated in the bones, transported there by percolating ground water.[6][44]
The Nemegt rivers, whereGallimimus lived, were home to a wide array of organisms. Occasionalmollusc fossils, as well as a variety of other aquatic animals like fish, turtles,[39] andcrocodylomorphs, includingShamosuchus, have been discovered in this region.[45]Mammal fossils are rare in the Nemegt Formation, but many birds, including theenantiornithineGurilynia, thehesperornithiformJudinornis, as well asTeviornis, a possible anseriform, have been found. Herbivorous dinosaurs discovered in the Nemegt Formation includeankylosaurids such asTarchia, thepachycephalosaurianPrenocephale, large hadrosaurids such asSaurolophus andBarsboldia, and sauropods such asNemegtosaurus andOpisthocoelicaudia.[39][46] Predatory theropods that lived alongsideGallimimus includetyrannosauroids such asTarbosaurus,Alioramus andBagaraatan, and troodontids such asBorogovia,Tochisaurus andZanabazar. Herbivorous or omnivorous theropods include therizinosaurs, such asTherizinosaurus, as well as oviraptorosaurians, such asElmisaurus,Nemegtomaia, andRinchenia.[47] Other ornithomimosaurs, includingAnserimimus andDeinocheirus, are also found, butGallimimus is the most common member of the group in the Nemegt.[8]
Gallimimus was featured in the 1993 movieJurassic Park by directorSteven Spielberg; a similar scene in the original1990 novel instead featured hadrosaurs. Spielberg had wanted astampede sequence with animal herds in the movie, but did not know how to achieve it, and it was initially going to be visualised throughstop-motion animation. At the time, there was little faith in creating animals throughcomputer animation, but thevisual effects companyIndustrial Light and Magic was given a go-ahead by the movie's producers to explore possibilities. ILM created aGallimimus skeleton in the computer and animated a test showing a herd of running skeletons, and later aTyrannosaurus chasing a fully renderedGallimimus herd. 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.[48][49] TheGallimimus were animated by tracing frames from footage of ostriches, and footage of herdinggazelles was also referenced.[50] Kielan-Jaworowska, who discovered the holotype specimen, called it a "beautiful scene".[6] The movie's dinosaurs were one of the most widely publicised applications ofcomputer-generated imagery in film, and were considered more lifelike than what had been previously accomplished withspecial effects.[51]
Emphasising the bird-like flocking behaviour of theGallimimus herd was a point inJurassic Park's 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 smallerGallimimus were shown in the middle of the group, as though they were being protected.[48] During the scene, the palaeontologistAlan Grant says that the herd moves with "uniform direction changes, just like a flock of birds evading a predator" as he watches the movements of the fast, gracefulGallimimus. This contrasted with how dinosaurs were traditionally depicted in mass media as lumbering, tail-dragging animals, and the movie helped change the common perception of dinosaurs. This and other scenes reflected then-recent theories ofbird evolution encouraged by the movie's scientific advisor, the palaeontologistJohn R. Horner, ideas which were still contentious at the time.[52][53][54] 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.[52][55]
It has been claimed that theLark Quarry tracks (one of the world's largest concentrations of dinosaur tracks) inQueensland, Australia, served as inspiration and "scientific underpinning" for theGallimimus stampede scene inJurassic 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 toMuttaburrasaurus), and a consultant toJurassic Park has denied the tracks served as inspiration for the movie.[56][57][58]
Media related toGallimimus at Wikimedia Commons
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