Кешік Бор кезеңінің Garudimimus туысы

Ornithomimosaur genus from the Late Cretaceous

Garudimimus (meaning "Garuda mimic") is a genus of ornithomimosaur that lived in Asia during the Late Cretaceous. The genus is known from a single specimen found in 1981 by a Soviet Mongolian paleontological expedition in the Bayan Shireh Formation and formally described in the same year by Rinchen Barsbold; the only species is Garudimimus brevipes. Several interpretations about the anatomical traits of Garudimimus were made in posterior examinations of the specimen, but most of them were criticized during its comprehensive redescription in 2005. Extensive undescribed ornithomimosaur remains at the type locality of Garudimimus may represent additional specimens of the genus. The only known specimen of Garudimimus was a medium sized animal measuring nearly in length and weighing about It was an ornithomimosaur with a mix of basal and derived features; unlike primitive ornithomimosaurs, both upper and lower jaws were toothless, a trait that is often reported in more derived ornithomimids. Garudimimus had relatively short and stocky hindlimbs, robust feet, and a reduced ilia. The foot had four toes with the first one very reduced, whereas ornithomimids were three toed with the first toe lost. The toothless skull has very straight jaws ending in a more rounded snout tip than that of other genera. It was previously thought that this primitive ornithomimosaurian possessed a lacrimal "horn" at the top of the skull, in front of the eye socket. However, the redescription of the only specimen has shown that this structure was simply the distorted left prefrontal bone. Another early interpretation was the metatarsus reconstructed with an arctometatarsalian condition. With the first description in 1981, Garudimimus was identified as a primitive ornithomimosaurian within its own family. However, with the description of new specimens of Deinocheirus in 2014, it was found that the latter was the sister taxon of Garudimimus, grouping within the Deinocheiridae—ornithomimosaurs not adapted for running or agile movements. But this placement has also been found to be unlikely. The pelvic girdle and hindlimbs of Garudimimus show that the musculature of the legs was not as well developed as in the fast running ornithomimids, therefore, indicating poor cursorial capacities. Like other members of Ornithomimosauria, Garudimimus was an omnivore/herbivore with a reduced bite force that was compensated by a horny beak.

In 1981, during a Soviet Mongolian paleontological expedition to the Gobi Desert, a relatively small theropod skeleton was discovered by the team at Bayshi Tsav in the Late Cretaceous Bayan Shireh Formation, Southeastern Mongolia. The remains are catalogued as MPC D 100/13 (Mongolian Palaeontological Center; originally GIN 100/13) and represent a rather complete and articulated skeleton. In the same year this specimen was formally and briefly described by the Mongolian paleontologist Rinchen Barsbold as the holotype of the genus and species Garudimimus brevipes. The generic name, Garudimimus, combines a reference to Garuda which are legendary winged creatures from Mongolian Buddhist mythology and Latin mimus (meaning mimic). The specific name is derived from Latin brevis (meaning short) and pes (meaning foot), referring to the short metatarsus. Barsbold identified Garudimimus as an ornithomimosaurian taxon but noted it was more primitive than ornithomimids and gave it its own family, the Garudimimidae. Barsbold described additional remains of the holotype specimen in 1983, and later in 1990 with Halszka Osmólska. The holotype consist of the skull in its entirety, 8 cervical vertebrae (including the atlas and axis), 9 dorsal vertebrae, 6 sacral vertebrae and 4 caudal vertebrae, some ribs, both ilia, pubes, femora, tibiae, fibulae, and a virtually complete left pes of a sub adult individual. Another interpretation was made also in 1988 by Philip J. Currie and Dale Alan Russell who referred the metatarsus of the holotype to Oviraptor sp. and reconstructed it with an arctometatarsal—a condition where the upper end of the third metatarsal is narrowed between the surrounding metatarsals—structure. In 1992 Thomas R. Holtz followed this interpretation and suggested the metatarsus could have been arctometatarsalian and was just disarticulated as preserved. Supporting an arctometatarsalian condition, Currie and David A. Eberth in 1993 claimed that part of the Archaeornithomimus (an ornithomimosaur from the nearby Iren Dabasu Formation) material belonged to Garudimimus based on the assumed arctometatarsalian condition, presence of the vestigial digit I and the proportions of metatarsals II, III, and IV. They pointed out that the metatarsals are crushed and metatarsal III is set back from the extensor surface of metatarsus. In 1994 Holtz suggested some similarities between the metatarsus of Garudimimus and Chirostenotes. In 1994, Bernardino P. Pérez Moreno with colleagues described the primitive ornithomimosaur Pelecanimimus and identified the presence of a crest in the holotype specimen. They claimed a similar trait in Garudimimus which was represented by a nasal horn. In a comprehensive redescription in 2005 at the hands of Yoshitsugu Kobayashi and Barsbold, numerous of the previous statements were refuted. The supposed orbital horn is actually the disarticulated left prefrontal bone and verified that the metatarsus did not suffer taphonomical (changes during decay and fossilisation) distortion and is non arctometatarsalian. Moreover, Kobayashi previously showed that in addition to actually lacking an arctometatarsalian condition, the metatarsal ratios are different to Archaeornithomimus. Although Garudimimus is solely known from MPC D 100/13, additional specimens may potentially be present among a large bonebed composed of at least five individuals in Bayshi Tsav and several undescribed ornithomimosaurs from other localities in the Bayan Shireh Formation.

Garudimimus (based on the holotype specimen) is estimated to have been around weighing approximately Several unfused vertebrae indicates that the holotype was likely a still growing sub adult animal.

Limb proportions, pedal unguals morphology and the extension of the ilium of Garudimimus suggest that it was not adapted for speed as in the more cursorial ornithomimids, which are characterized by powerful thighs and straight unguals. However, this analysis was criticized in the same year by Hall and colleagues arguing against the methods employed by Schmitz and Motani in that there is a considerable degree of similarities on scleral anatomy between diurnal, cathemeral and nocturnal animals. Moreover, soft tissues like the cornea are essential in figuring out how much light can enter the eye, which is clearly absent in fossil specimens. Schmitz and Motani made a response to this comment affirming their research and methodology properly categorized extinct dinosaur behaviors based on extant species. They cited the exterior border of the scleral ring as a reliable source when reconstructing visual capabilities.

In 2019, Graham M. Hughes and John A. Finarelli analyzed the olfactory bulb ratio in modern birds and preserved skulls of several extinct dinosaur species to predict how many genes would have been involved in the olfactory strength of these extinct species. Their analysis found that most ornithomimosaurs had relatively weak senses of smell; Garudimimus had roughly 417 genes encoding its olfactory receptors and an olfactory bulb ratio of 28.8, indicating a poorly developed sense of smell. Given that these values were more pronounced in larger dinosaur species, such as tyrannosaurids, Hughes and Finarelli pointed out that as dinosaurian lineages became larger, the size of the olfactory bulb also increased, which may suggest olfaction as the dominant sensory modality in non avian dinosaurs.

Kobayashi and Barsbold stated in 2005 that the absence of dentition on the lower jaw and the recurved shape of the same indicates that Garudimimus was fairly more similar to ornithomimids when consuming food than to other primitive ornithomimosaurs. Like ornithomimids, the anterior parts of the upper and lower jaws of Garudimimus were both covered by a beak and may have been used for plucking food. In addition, the sharp edges on the middle portions of the jaws helped for cutting food. During the same year, Ali Nabavizadeh studied the jaw musculature in herbivorous dinosaurs and concluded that some were primarily orthal feeders—moving their jaws up and down—including theropods, sauropodomorphs, primitive ornithischians, and some stegosaurs. Nabavizadeh noted that ornithomimosaurs were orthal feeders and raised their jaws isognathously whereby the upper and lower teeth of each side occluded (contacted each other) at once. Deinocheirus and Garudimimus have unique attachment sites for the muscles that open and close the jaws, which are composed by a downwards expanded, triangular adductor musculature complex attaching to a forwards expanding surangular bone. This, working together with a flared jugal flange, allows more cavity for the adductor muscle. With such elongate snout, the bite forces of both deinocheirids were low with reduced mechanical advantage, however, if this muscle extended farther forwards then this would have added strength to the temporal muscle.

The known remains of Garudimimus were unearthed from the Late Cretaceous Bayan Shireh Formation at the Bayshi Tsav locality. Bayshi Tsav itself, is interpreted to have been deposited under fluvial environments. Using calcite U–Pb measurements, the age of the Bayan Shireh Formation has been dated from about 95.9 ± 6.0 million to 89.6 ± 4.0 million years ago during the Cenomanian Santonian stages. Numerous scale like cross stratifications at the Baynshire locality are indicators of large meanders, and the vast majority of these water bodies may have drained the eastern part of the Gobi Desert. Based on the similar fossil assemblages, a correlation between the Bayan Shireh and Iren Dabasu formations has been proposed by numerous authors. Furthermore, the Iren Dabasu Formation has been dated about 95.8 ± 6.2 million years ago. Garudimimus shared its habitat with multiple dinosaurian fauna, such as the herbivorous ornithischians Gobihadros, Graciliceratops and Talarurus. Other theropods are represented by the predator of medium sized prey Achillobator, and the therizinosaurids Erlikosaurus and Segnosaurus. Erketu may have been the tallest herbivore within the fauna. Several species were separated by niche differentiation, such as Erlikosaurus and the large Segnosaurus, Though Garudimimus is currently the only ornithomimosaur taxon named, the Bayan Shireh Formation has produced locally abundant ornithomimosaurs at Bayshi Tsav.