Ornithomimosauria

Skeleton of Gallimimus

• Europe
• East Asia
• West North America

The Ornithomimosauria ( " bird mimic lizards " ) are a systematic group of dinosaurs within the Theropoda.

Due to some similarities in physique and in the presumed life they are often compared to ratites and in English as " ostrich dinosaurs " ( " ostrich dinosaurs " ) called. There were slim built and animals with two to five meters long, medium-sized representative of the Theropoda. They moved like all dinosaurs of this group biped, that means at the back legs and could probably run very fast. Except for the primitive representatives they were toothless, what they ate, is not understood. They lived in the Cretaceous period, approximately 134-66 million years ago, the majority of the fossil record is native to eastern Asia and western North America. Systematically, they can in some primitive representatives - are classified as well as in the group of Ornithomimidae - Pelecanimimus, Shenzhousaurus, Harpymimus and Garudimimus.

• 2.1 locomotion and social behavior
• 2.2 Dining
• 2.3 Reproduction

• 3.1 palaeobiogeography and period
• 3.2 External systematics
• 3.3 Internal systematics

Features

Skull and teeth

The skull of Ornithomimosauria was relatively small and was sitting on a long neck. The skull was slightly built, the muzzle was elongated, very large eyes. The cranial cavity was large and harbored a well-developed brain. The skullcap was mostly flat, unlike other theropods no cranial crests were present except for Pelecanimimus. The skull and the muzzle region were pneumatized, ie, with air spaces provided. At the tip of the upper jaw the Zwischenkieferbein sat ( premaxilla ). This pointed to a long, reaching to the rear extension which formed the posterior border of the nostril. This extension is a systematically important synapomorphy, a shared derived character. Some representatives as Garudimimus and Gallimimus the Zwischenkieferbein was U-shaped, pointed at others like Struthiomimus. Behind it was the flat, low upper jaw bone ( maxilla ).

The skull had like all theropods multiple skull window. The two pace Ralf Rochester ( the cranial window of the temporal region ) were small, the Antorbitalfenster ( the skull window in front of the eye ), however, increased. In addition, before a Maxillarfenster and sometimes yet another Promaxillarfenster were still present. The nasal bone was elongated, the paired frontal and parietal bones were the flat skull.

The lower jaw was slender and elongated, the dentals - the front, tooth-bearing part of the lower jaw - was slender and elongated and laterally viewed approximately triangular. A Fund of Ornithomimus came in from the upper and lower jaw, the remains of a beak made ​​of keratin recognize which could be sealed.

The urtümlicheren genres of Ornithomimosauria still had teeth: Pelecanimimus, the basalste representatives, contributed about 220 small teeth in the upper jaw ( maxilla and premaxilla on ) and lower jaw. For all other animals of the upper jaw was toothless, and Shenzhousaurus Harpymimus still had teeth in the lower jaw, probably around nine to eleven per half of the jaw. All other Ornithomimosauria were completely toothless. The teeth of the primitive representatives had no serrations on the teeth ( serration ), as it is typical for theropods. The teeth were approximately cone-shaped and had a circular plan.

The brain of these animals may have been relatively large. Casts of skulls revealed that the forebrain ( prosencephalon ) was increased, the olfactory bulb, however small. The sight was - also due to the large eyes - probably well developed sense of smell is not.

Fuselage skeleton and limbs

The spine of the Ornithomimosauria consisted of 10 cervical, 13 thoracic, 6 Cross and about 35 caudal vertebrae. The tail was stiffened as with all representatives of the Tetanurae. These stiffening was achieved on the one hand, that the vertebrae of the tail by long, forward and backward reaching bone rods ( zygapophyses ) and the other by Chevronknochen (V- shaped projections at the base of the caudal vertebrae) were connected.

The shoulder girdle was slightly built, as opposed to most other theropods lacked the wishbone ( furcula ). The arms were extended, built hands rather large, but light and not adapted to a predatory lifestyle. The hand consisted of the rays ( metacarpals and fingers) I, II and III ( counted from the thumb ago), the first finger was made up of two, the second finger of three and the third finger of four phalanges ( phalanges ) together. Since the first phalanx of the first finger was the longest, all fingers were approximately equal in length. A special feature - at least in the more developed Ornithomimosauria - was that the metacarpal bone ( metacarpal ) was the first beam in contrast to most other theropods approximately the same length as the other two beams. The fingers ended in claws that were rounded at the bottom and for predatory purposes unsuitable.

The pool was rather small and slightly built; the ilium was elongated and was at the front end a downwardly extending extension. The pubic bone jutted forward and down, the rear-facing seat leg was bent at the rear end of most representatives to the front.

The hind legs were longer than the front legs and in relation to body size is also longer than in most other theropods. The lower leg was by more than ten percent longer than the femur, tibia and fibula were firmly compressed at the lower end of the leg. The first toe was already reduced at the urtümlicheren representatives like all theropods, at the Ornithomimidae it was totally absent. The digits II, III and IV were focused symmetrically to the front, and the third (middle ) is the longest, the second and fourth approximately the same length. The three forwardly projecting toe bore mouth horn ( keratin), they were triangular and flat at the bottom in cross section. The midfoot was narrow and elongated. In the primitive representatives of the three metatarsal bones were still side by side, the second and fourth metatarsal bone in contact with the Ornithomimidae and pushed the third back so this was visible from the front, only the lower part of the midfoot. This position is referred to as " arctometatarsal " and was formerly used for the systematic classification - so some Dinosauriertaxa were combined with similar construction of the foot as Arctometatarsalia.

Body covering

About the body covering (tegument ) of the Ornithomimosauria it gabT long time from the fossil record except the impressions of a ridge skin on the head and a throat sac at Pelecanimimus no evidence. The discovery of several feathered dinosaurs since the mid -1990s and the phylogenetic studies, it did appear, however, conceivable that these dinosaurs had feathers.

In October 2012 Fossils of a bullock and two adult specimens of Ornithomimus were described in an approximately 72 million year old rock layer, showing that the animals had a downy plumage and the elderly in addition to the fore-arms longer springs possessed that their forelimbs a bird wing like appearance gave. The late development of the long Vorderarmbefiederung suggests that they may communicate with conspecifics ( intraspecific communication ), the display behavior served or the eggs of breeding animals offered additional protection. The find is the first evidence for the formation wing-like forelimbs at dinosaurs are not part of the Maniraptora.

Paleobiology

Locomotion and social behavior

Like all theropods were the Ornithomimosauria digitigrade ( digitigrad ) and were able to move their legs only in the sagittal plane (forward-backward ) - them has not been possible to rotate the limb outwards as it can about mammals. The body was balanced over the pelvis, the spine was kept approximately horizontal. In order to still allow a clear view to the front of the neck was an S-shaped bend. The stiffened cock stood horizontally to the rear. Due to the construction of their hind legs - especially the long leg and the modified metatarsal bone - are the Ornithomimosauria as fast runners. A comparison of the pelvis and hind legs, this dinosaur with those of ratites came to the conclusion that Ornithomimosauria the speed, but not reached the maneuverability of modern birds due to the reconstructed muscles. Other estimates of the speed of these animals amounted to 35 to 60 km / h

Statements about the social behavior of Ornithomimosauria are difficult, as with all known only by fossil finds animals. Even seen from the remains of several animals in one place ( Taphozönose ) do not indicate a group life, but can be explained in the sediment by certain circumstances when embedding the body. Most evidence comes from individual animals, two discoveries speak but for an at least temporary group life. From Archaeornithomimus there is a bone bed ( " bone stock " ), in which the remains of several animals were discovered in one place. With remnants of Sinornithomimus the findings suggest a sudden mass extinction of a whole group, which was composed of both young animals and from adult animals. Whether these two classes all year round or only seasonally and whether other representatives of Ornithomimosauria lived in groups is not known.

Food

About the diet of Ornithomimosauria there is no sound data - both for the primitive toothed as representatives for the toothless species. Even Henry Fairfield Osborn introduced in 1917 three hypotheses about the diet of these animals: they could have been herbivores that fed on leaves, fruits or the like, they could have eaten ants or they could have the freshwater invertebrates hunted.

Other researchers suspected a predatory lifestyle, because the animals are counted in the group of theropods, which mostly comprises carnivorous dinosaurs. You could therefore have consumed small vertebrates or even eggs. However, the shape of the teeth or the absence of teeth as well as the delicate construction of the forelimbs speaks against a predatory lifestyle. Another counter-argument is the position of the eye side of the head. This allows a good all-round view, but reduces the area of spatial vision, which is important for the range estimate to prey. Many others, clearly predatory theropods, by contrast, have more eyes looking forward, as well as many other carnivorous animals.

1999 at two Ornithomimosauria, the dentate Shenzhousaurus and the toothless Sinornithomimus, gastroliths (stomach stones) discovered. The position of gastroliths within the hull may suggest that the dinosaurs have similar today herbivorous birds possessed a gizzard and stomach swallowed stones for better crushing the food. This discovery is an indication that at least these two genera may have been herbivores. The absence of bony inclusions of apatite and suggests that they have not eaten vertebrates. For other well-preserved fossils of Ornithomimosauria however, there is no evidence of gastroliths.

2001 Gallimimus a lamellar structure was discovered at the top of both jawbones. This structure could indicate a filtering food intake, that is, they would like a sieve works to fish small organisms from the water. A similar form of dietary intake is also found in modern birds, such as the Shoveler. The small teeth at the tip of the snout of the primitive representatives thus represent an early stage in the evolution of this filtering apparatus dar. Gastrolithen do not contradict the filtered diet, as some stomach stones were very small and there are also such forms in modern birds with the same diet. For this theory is the fact that fossils of Ornithomimosauria in habitats near lakes or rivers are more common than in very dry habitats. At least some of these dinosaurs might have filtered a portion of their food from the water, but much in the diet of Ornithomimosauria is still unknown.

Reproduction

The Ornithomimosauria have placed as any other dinosaur eggs, but the finds are sparse. Studies of the pelvic canal showed that this was relatively wide in these animals, which could indicate that they have larger and fewer eggs laid than other dinosaurs. From the Irish - Dabasu formation in the Chinese province of Inner Mongolia, there are fossil eggs that have been speculatively attributed to the Ornithomimosauria. Otherwise, on the propagation or rearing young of these animals not known.

System

Palaeobiogeography and period

The Ornithomimosauria are a geologically relatively young group of dinosaurs, they are only known from the Cretaceous period. Probably the oldest and most primitive representatives, Pelecanimimus, dates from the Barremian (before 130-126 million years ago) and was found in Spain. Apart from fragmentary remains from the Netherlands and Australia - both of which could come from members of this group, but are too sparse for a systematic mapping - come all this dinosaur finds from eastern Asia and western North America. From East Asia - Mongolia and China - come here the other basal genera and some representatives of the Ornithomimidae. The North American representatives, Ornithomimus and Struthiomimus are only occupied from the middle Campanian or early Maastrichtian ( million years ago, around 80 to 69). At least once these animals must therefore have crossed the Beringia later. Whether the North American taxa form a common lineage or whether multiple migrations have taken place, is not known. Like all non-avian dinosaurs are extinct these animals during mass extinction at the end of the Cretaceous period. ( For discussion of the reasons for this extinction see Cretaceous-Tertiary boundary and the extinction of the dinosaurs. )

Outer systematics

The Ornithomimosauria be classified within the dinosaurs in the theropods, which includes almost all carnivorous dinosaurs, but also the birds are counted. Within the theropods they are considered relatively basal group of Coelurosauria, their sister taxon, the Maniraptora. A possible cladogram showing the systematic position within the dinosaur looks like this:

Ceratosauria

Spinosauroidea

Carnosauria

Compsognathidae

Tyrannosauroidea

Ornithomimosauria

Maniraptora

Inside systematics

The Ornithomimosauria be divided into several basal representatives who still show some original features such as teeth, and the Ornithomimidae. The following species list follows Peter Makovicky and others.

• Ornithomimosauria Pelecanimimus
• Shenzhousaurus
• Kinnareemimus
• Harpymimus
• Beishanlong
• Garudimimus
• Ornithomimidae Anserimimus
• Archaeornithomimus
• Gallimimus
• Ornithomimus (including Dromiceiomimus )
• Qiupalong
• Sinornithomimus
• Struthiomimus

• Deinocheirus
• Coelosaurus
• Timimus

From Deinocheirus only two very large arms are obtained, which agree in some respects with the Ornithomimosauria of Coelosaurus and Timimus only individual limb bones and vertebrae. In all cases the findings are too sparse for a systematic mapping.

The internal classification of Ornithomimosauria is well documented only in the urtümlicheren representatives. Pelecanimimus regarded as sister taxon of the remaining genera and has still the only teeth in the upper jaw. Shenzhousaurus is sister taxon of the remaining Ornithomimosauria, which is underpinned by a straight and not forward and downward curved ischium. Harpymimus still has teeth in the lower jaw and is thus the toothless Garudimimus - Ornithomimidae clade opposite. The Ornithomimidae have as a common synapomorphies arctometatarsale the position of the metatarsal bone ( see above) and the loss of the first toe of the foot. The lineages within the Ornithomimidae are not clarified, cladistic studies provide inconclusive results.

Discovery and exploration history

The first representative of Ornithomimosauria that was discovered was Ornithomimus, which was described in 1890 by Othniel Charles Marsh. Marsh also coined at the same time the family Ornithomimidae, which was then still monotypic. Lawrence Lambe in 1902 brought the later designated as Struthiomimus animal to light. Due to the salient features such as the toothless beak and the arctometatarsalen position of the metatarsals the Ornithomimidae one of the first higher Dinosauriertaxa recognized were. First conjectures about the Paleobiology Henry Fairfield Osborn presented in 1917. In the 1920s and 1930s, more fossils were discovered from these animals in the United States and Canada, that were all incorporated into Ornithomimus or Struthiomimus. 1933 with the later Archaeornithomimus the first Asian team found. Apart from the enigmatic Deinocheirus it took then until 1972, with Gallimimus to a new genus of this group of animals was brought to light. In the same year Dale Russell published his paleontologic studies. 1976 coined the Mongolian paleontologist Rinchen bars Bold taxon Ornithomimosauria, initially only for the Ornithomimidae, later also for the primitive representatives Garudimimus (1981) and Harpymimus (1984). In 1986, the first cladistic studies by Jacques Gauthier were published in which he presented the view still represented, the Ornithomimosauria are the sister group of the Maniraptora. 1994 Thomas R. Holtz classified the Ornithomimosauria as close relatives of the Troodontidae and Tyrannosauroidea and called the common taxa Bullatosauria and Arctometatarsalia, perspectives that are discarded today. In the same year described with Pelecanimimus the first indigenous European representatives of this group of animals. It was followed by further phylogenetic studies, including by Paul Sereno, Kevin Padian and Yoshitsugu Kobayashi. Sereno concluded, for example, nor the Therizinosauroidea and Alvarezsauridae in the Ornithomimosauria a while Padian 1999 still valid definition of Ornithomimosauria aufstellte as the taxon polyodon all descendants of the last common ancestor of Pelecanimimus and Ornithomimus edmontonicus covers. In the 21st century, the research continues on these animals. In addition to phylogenetic and paleobiological studies are also repeatedly described new genera, for example Shenzhousaurus and Sinornithomimus, and the outstanding issues, such as nutrition, can be expected to further investigation.