Ornithomimosauria
| Ornithomimosauria | ||||||||||||
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Skeleton of Struthiomimus |
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| Chalk ( Hauterivium to Maastrichtian ) | ||||||||||||
| 133.9 to 66 million years | ||||||||||||
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| Ornithomimosauria | ||||||||||||
| Barsbold , 1976 |
The ornithomimosauria ("bird imitation lizards") are ratites- like dinosaurs . In English they are also called ostrich dinosaurs (" ostrich dinosaurs ").
The ornithomimosauria were slender, and with two to five meters in length, medium-sized representatives of the theropods . They could probably run very quickly, although like all theropods they were obligatorily biped , that is, only walked on their hind legs. Except for the primitive representatives, they were toothless. What they fed on has not yet been clarified. They lived in the Cretaceous Period around 134 to 66 million years ago, the majority of the fossil finds come from eastern Asia and western North America . Informally, some primeval representatives - Pelecanimimus , Shenzhousaurus , Harpymimus and Garudimimus - can be distinguished from the "higher" ornithomimosaurs, the Ornithomimidae .
features
Skull and teeth
The skull of the ornithomimosauria was relatively small and sat on a long neck. The skull was lightly built, the muzzle was elongated, the eyes very large. The cranial cavity was large and contained a well-developed brain . The roof of the skull was mostly flat, in contrast to other Theropoda there were no crests except in Pelecanimimus . The brain skull and the snout region were pneumatized, i.e. provided with air-filled cavities. The intermaxillary bone (premaxillary) sat at the tip of the upper jaw . This had a long, backward extension that formed the posterior limitation of the nostril. This extension is a systematically significant synapomorphism , a common derived feature. In some representatives such as Garudimimus and Gallimimus , the intermaxillary bone was U-shaped, in others, such as Struthiomimus, it was pointed. Behind it was the flat, low upper jaw bone (maxillary).
As with all Theropoda, the skull had several skull windows . The two temporal windows (the cranial windows of the temple region) were small, while the antorbital window (the cranial window in front of the eye) was enlarged. In addition, there was a maxillary window and sometimes an additional promaxillary window. The nasal bone was elongated, the pair of frontal and parietal bones formed the flat top of the skull.
The lower jaw was slender and elongated, the dental - the front, tooth-bearing part of the lower jaw - was slender and elongated and, viewed from the side, approximately triangular. A find by Ornithomimus revealed the remains of a keratin beak on the upper and lower jaw , which could be tightly sealed.
The more primitive genera of the Ornithomimosauria still had teeth: Pelecanimimus , the most basic representative, had around 220 small teeth in the upper jaw (on the premaxillary and maxillary) and lower jaw. In all other animals the upper jaw was toothless, Shenzhousaurus and Harpymimus still had teeth in the lower jaw, probably around nine to eleven per jaw half. All other ornithomimosaurs were completely toothless. The teeth of the primitive representatives did not show any serration on their teeth, as is typical for Theropoda. The teeth were approximately conical and round in shape.
The brains of these animals should have been relatively large. Skull casts showed that the forebrain (prosencephalon) was enlarged, while the olfactory bulb was small. The sight was - probably well developed, the - also due to the wide-eyed sense of smell is not.
Trunk skeleton and limbs
The spine of the Ornithomimosauria consisted of 10 cervical , 13 thoracic , 6 cross and around 35 caudal vertebrae . As with all representatives of the Tetanurae, the tail was stiffened. This stiffening was achieved on the one hand by the fact that the caudal vertebrae were connected by long bone rods ( zygapophyses ) reaching forwards and backwards and on the other hand by chevron bones (V-shaped appendages on the underside of the caudal vertebrae).
The shoulder girdle was lightly built, in contrast to most other Theropoda, the fork bone (furcula) was missing . The arms were elongated, the hands were rather large, but lightly built and not adapted to a predatory way of life. The hand consisted of rays ( metacarpal bones and fingers ) I, II and III (counted from the thumb), the first finger consisted of two, the second finger of three and the third finger of four phalanges. Since the first phalanx of the first finger was the longest, all fingers were approximately the same length. A special feature - at least of the more highly developed ornithomimosauria - was that the metacarpus of the first ray, in contrast to most of the other theropods, was almost as long as that of the two other rays. The fingers ended in claws that were rounded on the underside and unsuitable for predatory purposes.
The pool was rather small and light; the iliac bone was elongated and had a downward protrusion at the front end. The pubic bone jutted forward and downward, the rear-facing seat leg was bent at the most representatives to the front to the rear end.
The hind legs were longer than the front legs and, in relation to body size, also longer than most other Theropoda. The lower leg was more than ten percent longer than the thigh, and the tibia and fibula were firmly compressed at the lower end of the leg. The first toe was already shortened in the more primitive representatives as in all Theropoda, in the Ornithomimidae it was completely absent. Toes II, III and IV were symmetrically directed forward, the third (middle) was the longest, the second and fourth were almost the same length. The three protruding toes had claws made of horn (keratin), they were triangular in cross-section and flat on the underside. The metatarsus was narrow and elongated. In the "primitive" representatives the three metatarsal bones were still next to each other, in the Ornithomimidae the upper ends of the second and fourth metatarsal bones touched each other and the upper section of the third metatarsal bone tapered sharply towards the top. This structure of the metatarsus is known as "arctometatarsal" and towards the end of the 20th century had a certain importance for the systematics of the "higher" theropods. The taxon based on this characteristic was called arctometatarsalia . According to current knowledge of the tribal history of the "higher" theropods, this taxon is identical to the ornithomimosauria and the name is therefore no longer used.
Body covering
For a long time there was no evidence from the fossil record about the body covering ( integument ) of the ornithomimosaurs apart from the impressions of a skin ridge on the head and a throat pouch in pelecanimimus . However, the discovery of several feathered dinosaurs since the mid-1990s and phylogenetic studies made it possible that these dinosaurs had feathers.
In October 2012, fossils of a young animal and two adult specimens of ornithomimus were described in an approximately 72 million year old rock layer, which show that the animals had down-like fletching and that the older ones also had longer feathers on their forearms, which their forelegs on the bird's wing gave a similar appearance. The late development of the long forearm fletching suggests that it was possibly used for communication with conspecifics (intraspecific communication), for showing off or offering additional protection for the eggs of breeding animals. The find is the first indication of the formation of wing-like forelimbs in dinosaurs that do not belong to the Maniraptora .
Paleobiology
Locomotion and social behavior
Like all Theropoda, the Ornithomimosauria were toe-walkers (digitigrad) and could only move their legs in the sagittal plane (forwards-backwards) - they were unable to turn their limbs outward, as mammals can. The body was balanced over the pelvis, the spine was kept almost horizontal. In order to still allow a good view to the front, the neck was bent into an S-shape. The stiffened tail stood horizontally backwards. Due to the construction of their rear legs - especially the long lower legs and the modified metatarsal bones - the ornithomimosauria are considered to be fast runners. A comparison of the pelvis and hind legs of these dinosaurs with those of ratites came to the conclusion, based on the reconstructed musculature, that ornithomimosauria achieved the speed but not the maneuverability of today's birds. Other estimates of the maximum speed of these animals are 35 to 60 km / h.
Statements about the social behavior of the ornithomimosauria are difficult, as is the case with all animals known only from fossil finds. Even finds of the remains of several animals in one place ( taphozoenosis ) do not have to indicate a group life, but can also be explained by certain circumstances when the bodies are embedded in the sediment. Most of the finds come from individual animals, but two discoveries suggest an at least temporary group life. From Archaeornithomimus there is a bone bed , in which the remains of several animals were discovered in one place. In the case of remains of Sinornithomimus , the finds suggest a sudden mass extinction of an entire group, which was composed of both young and adult animals. It is not known whether these two genera lived all year round or only seasonally and whether other representatives of the ornithomimosauria also lived in groups.
food
There is no reliable knowledge about the diet of the ornithomimosauria - both for the primeval toothed representatives and for the toothless species. Henry Fairfield Osborn already put forward three hypotheses about the diet of these animals in 1917 : They could have been herbivores whose diet consisted of leaves, fruits or the like, they could have eaten ants or hunted invertebrates living in freshwater .
Other researchers suspected a predatory way of life, since the animals are counted as part of the theropoda group, which includes mostly carnivorous dinosaurs. They could have eaten small vertebrates or eggs. The shape of the teeth or the toothlessness as well as the delicate structure of the forelimbs speak against a predatory way of life. Another counter-argument is the position of the eyes on the side of the head. This enables a good all-round view, but reduces the area of spatial vision that is important for estimating the distance to the prey. Many other clearly predatory theropods, in contrast, have more forward-facing eyes, as do many other carnivorous animals.
1999 were the dentate at two ornithomimosauria, shenzhousaurus and the toothless Sinornithomimus , Gastrolithen (stomach stones) discovered. The position of the gastroliths within the torso could indicate that the dinosaurs had gizzards , similar to today's herbivorous birds , and swallowed stomach stones to better break up the food. This discovery is an indication that at least these two genera could have been herbivores. The absence of bony inclusions and apatite suggests that they did not eat vertebrates. In other well-preserved fossil finds of ornithomimosauria there is no evidence of gastroliths.
In 2001, Gallimimus discovered a lamellar structure at the tip of both jawbones. This structure could indicate a filtering food intake, that is, it would have worked like a sieve to fish small organisms out of the water. A similar form of ingestion is found in today's birds, such as the shoveler . The small teeth on the tip of the snout of the primitive representatives therefore represent an early stage in the evolution of this filtering apparatus. Gastroliths are not a contradiction to the filtering diet, as some stomach stones were very small and such shapes are also found in today's birds with the same diet. This theory is supported by the fact that ornithomimosauria fossil finds are more common in habitats near lakes or rivers than in extremely dry habitats. At least some of these dinosaurs may have filtered some of their food out of the water, but much about the diet of the ornithomimosauria is still unknown.
Reproduction
The ornithomimosaurs laid eggs like all other dinosaurs, but the findings are sparse. Studies of the pelvic canal showed that these animals were relatively wide, which could indicate that they laid larger and fewer eggs than other dinosaurs. From the Iren-Dabasu formation in the Chinese autonomous region of Inner Mongolia there are fossil eggs that were speculatively assigned to the ornithomimosauria. Otherwise nothing is known about the reproduction or rearing of these animals.
Systematics
Paleobiogeography and Period
The ornithomimosauria are a relatively young group of dinosaurs, they are only known from the Cretaceous period . Probably the oldest and most primeval representative, Pelecanimimus , comes from the Barremian (130 to 126 million years ago) and was found in Spain. Apart from fragmentary remains from the Netherlands and Australia - both of which could come from representatives of this group, but are too sparse for a systematic classification - all finds of these dinosaurs come from eastern Asia and western North America . The other basal genera and some representatives of the Ornithomimidae come from East Asia - Mongolia and China . The North American representatives, Ornithomimus and Struthiomimus , are only documented from the middle Campanian or early Maastrichtian (around 80 to 69 million years ago). These animals must have crossed the later Beringia at least once . It is not known whether the North American taxa form a common lineage or whether multiple migrations have taken place. Like all non-avian dinosaurs, these animals became extinct in mass extinction at the end of the Cretaceous Period. (For discussions of the reasons for this extinction, see Cretaceous-Tertiary Boundary and The Extinction of the Dinosaurs .)
External system
The Ornithomimosauria are classified within the dinosaurs in the Theropoda , to which almost all carnivorous dinosaurs, but also the birds are counted. Within the Theropoda they are considered a relatively basal group of the Coelurosauria , their sister taxon are the Maniraptora . A possible cladogram that shows the systematic position within the dinosaurs looks like this:
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Internal system
The Ornithomimosauria are subdivided into some basic representatives, which still show some original features such as teeth, and the Ornithomimidae . The generic list below largely follows Peter Makovicky and others.
- Ornithomimosauria
In the case of Coelosaurus , the finds are too sparse for a systematic classification.
The internal systematics of the Ornithomimosauria is only well documented with the more primitive representatives. Pelecanimimus is the sister taxon of the other genera and is the only one with teeth in the upper jaw. Shenzhousaurus is Schwestertaxon the remaining ornithomimosauria, as indicated by a straight and not bent to the front and below the seat leg is supported. Harpymimus still has teeth in the lower jaw and so faces the toothless Garudimimus Ornithomimidae clade. The Ornithomimidae have as common synapomorphies the arctometatarsal position of the metatarsal bones (see above) and the loss of the first toe of the foot. The lines of descent within the Ornithomimidae have not been clarified, and cladistic studies do not provide clear results.
History of discovery and research
The first member of the Ornithomimosauria to be discovered was Ornithomimus , which was described by Othniel Charles Marsh in 1890 . Marsh also coined the Ornithomimidae family, which at that time was still monotypical . In 1902, Lawrence Lambe brought the animal, later known as Struthiomimus , to light. Because of the noticeable features such as the toothless beak and the arctometatarsal position of the metatarsals, the Ornithomimidae were one of the first higher dinosaur taxa to be recognized. Henry Fairfield Osborn made the first speculations about paleobiology in 1917. In the 1920s and 1930s, more fossils of these animals were discovered in the United States and Canada, all of which are now incorporated into ornithomimus or struthiomimus . In 1933 the first Asian representative was found with the later Archaeornithomimus . Apart from the enigmatic Deinocheirus , it took until 1972 until Gallimimus, a new genus of this group of animals , was brought to light . In the same year Dale Russell published his paleobiological studies. In 1976 the Mongolian paleontologist Rinchen Barsbold coined the taxon Ornithomimosauria, initially only for the Ornithomimidae, later also for the primitive representatives Garudimimus (1981) and Harpymimus (1984). In 1986 the first cladistic studies were published by Jacques Gauthier , in which he presented the view still held today that the ornithomimosauria are the sister group of the Maniraptora . In 1994 Thomas R. Holtz classified the ornithomimosauria as close relatives of the Troodontidae and Tyrannosauroidea and named the common taxa Bullatosauria and Arctometatarsalia , views that are now discarded. In the same year, Pelecanimimus, the first representative of this group of animals from Europe, was described. Further phylogenetic studies followed, including by Paul Sereno , Kevin Padian and Yoshitsugu Kobayashi . Sereno, for example, still included the Therizinosauroidea and the Alvarezsauridae in the ornithomimosauria, while in 1999 Padian established the definition of the ornithomimosauria that is still valid today as the taxon that includes all descendants of the last common ancestor of Pelecanimimus polyodon and Ornithomimus edmontonicus . Research on these animals continues in the 21st century. In addition to phylogenetic and paleobiological studies, new genera are being described again and again, for example Shenzhousaurus and Sinornithomimus , and the remaining questions, such as nutrition, lead us to expect further investigations.
literature
- Peter J. Makovicky , Yoshitsugu Kobayashi, Philip J. Currie : Ornithomimosauria. In: David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. a. 2004, ISBN 0-520-24209-2 , pp. 137-150.
- David E. Fastovsky , David B. Weishampel: The Evolution and Extinction of the Dinosaurs. 2nd edition. Cambridge University Press, Cambridge u. a. 2005, ISBN 0-521-81172-4 .
Individual evidence
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ u. a. 2010, ISBN 978-0-691-13720-9 , pp. 111-117, online .
- ↑ Darla K. Zelenitsky, François Therrien, Gregory M. Erickson, Christopher L. DeBuhr, Yoshitsugu Kobayashi, David A. Eberth, Frank Hadfield: Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins. In: Science . Vol. 338, No. 6106, 2012, pp. 510-514, doi: 10.1126 / science.1225376 .
- ↑ a b c d Dale A. Russell : Ostrich dinosaurs from the Late Cretaceous of western Canada. In: Canadian Journal of Earth Sciences. Vol. 9, No. 4, 1972, ISSN 0008-4077 , pp. 375-402, doi: 10.1139 / e72-031 .
- ^ Richard A. Thulborn: Speeds and gaits of dinosaurs. In: Palaeogeography, Palaeoclimatology, Palaeoecology. Vol. 38, 1982, ISSN 0031-0182 , pp. 227-256, doi: 10.1016 / 0031-0182 (82) 90005-0 .
- ^ A b Henry Fairfield Osborn : Skeletal adaptations of Ornitholestes, Struthiomimus, Tyrannosaurus. In: Bulletin of the American Museum of Natural History. Vol. 35, Article 43, 1917, ISSN 0003-0090 , pp. 733-771, (PDF; 12.3 MB).
- ↑ Yoshitsugu Kobayashi, Jun-Chang Lu, Zhi-Ming Dong, Rinchen Barsbold , Yoichi Azuma, Yukimitsu Tomida: Palaeobiology: Herbivorous diet in an ornithomimid dinosaur. In: Nature . Vol. 402, No. 6761, 1999, pp. 480-481, doi: 10.1038 / 44999 .
- ^ Mark A. Norell , Peter J. Makovicky, Philip J. Currie : Palaeontology: The beaks of ostrich dinosaurs. In: Nature. Vol. 412, No. 6850, 2001, pp. 873-874, doi: 10.1038 / 35091139 .
- ↑ a b c Peter J. Makovicky, Yoshitsugu Kobayashi, Philip J. Currie: Ornithomimosauria. In: David B. Weishampel, Peter Dodson, Halszka Osmólska (eds.): The Dinosauria . University of California Press, Berkeley CA et al. a. 2004, ISBN 0-520-24209-2 , pp. 137-150.
- ↑ Philip J. Currie, David A. Eberth: Palaeontology, sedimentology and palaeoecology of the Iren Dabasu Formation (Upper Cretaceous), Inner Mongolia, People's Republic of China. In: Cretaceous Research. Vol. 14, No. 2, 1993, ISSN 0195-6671 , pp. 127-144, doi: 10.1006 / cres.1993.1011 .
- ↑ Simplified from: Thomas R. Holtz Jr. , Halszka Osmólska: Saurischia. In: David B. Weishampel, Peter Dodson, Halszka Osmólska (eds.): The Dinosauria . University of California Press, Berkeley CA et al. a. 2004, ISBN 0-520-24209-2 , pp. 22-23.
- ↑ Rebecca K. Hunt and James H. Quinn. 2018. A New Ornithomimosaur from the Lower Cretaceous Trinity Group of Arkansas. Journal of Vertebrate Paleontology. DOI: 10.1080 / 02724634.2017.1421209
- ↑ Jin Liyong, Chen Jun and Pascal Godefroit (2012). A New Basal Ornithomimosaur (Dinosauria: Theropoda) from the Early Cretaceous Yixian Formation, Northeast China. In Godefroit, P. (eds). Bernissart Dinosaurs and Early Cretaceous Terrestrial Ecosystems. Indiana University Press. pp. 467-487.
- ↑ Eric Buffetaut , Varavudh Suteethorn , Haiyan Tong: An early 'ostrich dinosaur' (Theropoda: Ornithomimosauria) from the Early Cretaceous Sao Khua Formation of NE Thailand. In: Eric Buffetaut, Gilles Cuny, Jean Le Loeuff, Varavudh Suteethorn (Eds.): Late Palaeozoic and Mesozoic Ecosystems in SE Asia (= The Geological Society, London. Special Publication. Vol. 315). The Geological Society, London 2009, ISBN 978-1-86239-275-5 , pp. 229-243, doi: 10.1144 / SP315.16 .
- ↑ Choiniere, JN; Forster, CA; De Klerk, WJ (2012). New information on Nqwebasaurus thwazi, a coelurosaurian theropod from the Early Cretaceous (Hauteriverian?) Kirkwood Formation in South Africa. Journal of African Earth Sciences. doi: 10.1016 / j.jafrearsci.2012.05.005
- ↑ a b R. Allain, R. Vullo, J. Le loeuff & J.-F. Tournepiche (2014) European ornithomimosaurs (Dinosauria, Theropoda): an undetected record. Geologica Acta 12 (2) June 2014.
- ↑ Yuong-Nam Lee, Rinchen Barsbold, Philip J. Currie, Yoshitsugu Kobayashi, Hang-Jae Lee, Pascal Godefroit, François Escuillié and Tsogtbaatar Chinzorig. 2014. Resolving the Long-standing Enigmas of A Giant Oornithomimosaur Deinocheirus mirificus. Nature . October 2014, doi: 10.1038 / nature13874
- ↑ Peter J. Makovicky, Daqing Li, Ke-Qin Gao, Matthew Lewin, Gregory M. Erickson, Mark A. Norell: A giant ornithomimosaur from the Early Cretaceous of China. In: Proceedings of the Royal Society. Series B: Biological Sciences. Vol. 277, No. 1679, 2010, ISSN 0080-4649 , pp. 191-198, doi: 10.1098 / rspb.2009.0236 .
- ↑ Claudia Inés Serrano-Brañas, Belinda Espinosa-Chávez, S. Augusta Maccracken, Cirene Gutiérrez-Blando, Claudio de León-Dávila: Paraxenisaurus normalensis, a large deinocheirid ornithomimosaur from the Cerro del Pueblo Formation (Upper Cretaceous), Mexico . Coahuila . In: Journal of South American Earth Sciences . April 24, 2020, ISSN 0895-9811 , p. 102610 , doi : 10.1016 / j.jsames.2020.102610 ( sciencedirect.com [accessed April 27, 2020]).
- ↑ Li Xu, Yoshitsugu Kobayashi, Junchang Lü, Yuong-Nam Lee, Yongqing Liu, Kohei Tanaka, Xingliao Zhang, Songhai Jia, Jiming Zhang: A new ornithomimid dinosaur with North American affinities from the Late Cretaceous Qiupa Formation in Henan Province of China. In: Cretaceous Research. Vol. 32, No. 2, 2011, pp. 213-222, doi: 10.1016 / j.cretres.2010.12.004 .
- ↑ Bradley McFeeters, Michael J. Ryan, Claudia Schröder-Adams and Thomas M. Cullen: A new ornithomimid theropod from the Dinosaur Park Formation of Alberta, Canada. In: Journal of Vertebrate Paleontology. 2016, p. E1221415, doi: 10.1080 / 02724634.2016.1221415 .
- ↑ Thomas R. Holtz Jr .: The phylogenetic position of the Tyrannosauridae: implications for theropod systematics. In: Journal of Paleontology. Vol. 68, No. 5, 1994, pp. 1100-1117.
- ^ Paul C. Sereno : A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria. In: New Yearbook for Geology and Paleontology. Treatises. Vol. 210, No. 1, 1998, ISSN 0077-7749 , pp. 41-83.
- ↑ Kevin Padian , John R. Hutchinson, Thomas R. Holtz Jr .: Phylogenetic definitions and nomenclature of the major taxonomic categories of the carnivorous Dinosauria (Theropoda). ( Memento of March 3, 2012 in the Internet Archive ) In: Journal of Vertebrate Paleontology. Vol. 19, No. 1, 1999, ISSN 0272-4634 , pp. 69-80, doi: 10.1080 / 02724634.1999.10011123 .
