Gastrolith

A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In other species the rocks are ingested and pass through the digestive system and are frequently replaced. The grain size depends upon the size of the animal and the gastrolith's role in digestion. Other species use gastroliths as ballast. Particles ranging in size from sand to cobble have been documented.

Gastroliths
Plesiosaur gastroliths from Tropic Shale.

Etymology

Gastrolith comes from the Greek γαστήρ (gastēr), meaning "stomach", and λίθος (lithos), meaning "stone".

Occurrence

Starr Springs Gastroliths Jurassic Utah
Gastroliths from Jurassic strata near Starr Springs, Utah.
Axolotl with Grit XRay
Axolotl seek out and swallow gravel to create gastroliths (as visible in this x-ray of a living animal)

Among living vertebrates, gastroliths are common among crocodiles, alligators, herbivorous birds, seals and sea lions. Domestic fowl require access to grit. Stones swallowed by ostriches can exceed a length of 10 centimetres (3.9 in). Amphibians such as the Axolotl are also known to deliberately ingest rocks that are presumed to be gastroliths.[1][2] Apparent microgastroliths have also been found in frog tadpoles.[3] Ingestion of silt and gravel by tadpoles of various anuran (frog) species has been observed to improve buoyancy control.[4]

Some extinct animals such as sauropod dinosaurs appear to have used stones to grind tough plant matter. A rare example of this is the Early Cretaceous theropod Caudipteryx zoui from northeastern China, which was discovered with a series of small stones, interpreted as gastroliths, in the area of its skeleton that would have corresponded with its abdominal region. Aquatic animals, such as plesiosaurs, may have used them as ballast, to help balance themselves or to decrease their buoyancy, as crocodiles do.[5] While some fossil gastroliths are rounded and polished, many stones in living birds are not polished at all. Gastroliths associated with dinosaur fossils can weigh several kilograms.

Gastroliths in paleontology

History of discovery

In 1906, George Reber Weiland reported the presence of worn and polished quartz pebbles associated with the remains of plesiosaurs and sauropod dinosaurs and interpreted these stones as gastroliths.[6] In 1907, Barnum Brown found gravel in close association with the fossil remains of the duck-billed hadrosaur Claosaurus and interpreted it as gastroliths. Brown was among the first paleontologist to recognize that dinosaurs used gastroliths in their digestive systems to aid in the grinding of food.[7] This interpretation, however, has been regarded as unconvincing by other paleontologists over the years. In 1932, Friedrich von Huene found stones in Late Triassic sediments, in association with the fossil remains of the prosauropod Sellosaurus and interpreted them as gastroliths.[8] In 1934, the Howe Quarry, a fossil location in northwestern Wyoming also yielded dinosaur bones with their associated gastroliths. In 1942, William Lee Stokes recognized the presence of gastroliths in the remains of sauropod dinosaurs recovered from Late Jurassic strata.

Identification

Diplodocinae jmallon
A diplodocid ingesting gastroliths entangled in vegetation it is consuming

Geologists usually require several pieces of evidence before they will accept that a rock was used by a dinosaur to aid its digestion. First, the stone must be unlike the rock found in its geological vicinity. Secondly, it should be rounded and polished, because inside a dinosaur's gizzard any genuine gastrolith would have been acted upon by other stones and fibrous materials in a process similar to the action of a rock tumbler. Lastly, the stone must be found with the fossils of the dinosaur which ingested it. It is this last criterion that causes trouble in identification, as smooth stones found without context can (possibly erroneously in some cases) be dismissed as having been polished by water or wind. Christopher H. Whittle (1988,9) pioneered scanning electron microscope analysis of wear patterns on gastroliths. Wings (2003) found that ostrich gastroliths would be deposited outside the skeleton if the carcass was deposited in an aquatic environment for as little as a few days following death. He concludes that this is likely to hold true for all birds (with the possible exception of moa) due to their air-filled bones which would cause a carcass deposited in water to float for the time it needs to rot sufficiently to allow gastroliths to escape.

Gastroliths can be distinguished from stream- or beach-rounded rocks by several criteria: gastroliths are highly polished on the higher surfaces, with little or no polish in depressions or crevices, often strongly resembling the surface of worn animal teeth. Stream- or beach-worn rocks, particularly in a high-impact environment, show less polishing on higher surfaces, often with many small pits or cracks on these higher surfaces. Finally, highly polished gastroliths often show long microscopic rilles, presumably caused by contact with stomach acid. Since most gastroliths were scattered when the animal died and many entered a stream or beach environment, some gastroliths show a mixture of these wear features. Others were undoubtedly swallowed by other dinosaurs and highly polished gastroliths may have been swallowed repeatedly.

None of the gastroliths examined in a 2001 study of Cedarosaurus gastroliths had the "soapy" texture popularly used to distinguish gastroliths from other types of clast.[9] The researchers dismissed using a soapy texture to identify gastroliths as "unreliable".[9] Gastroliths tended to be universally dull, although the colors represented were varied including black, dark brown, purplish red and grey-blue.[9] Reflectance values greater than 50% are very diagnostic for identifying gastroliths.[9] Clasts from beaches and streams tended to have reflectance values of less than 35%.[10] Less than ten percent of beach clasts have reflectance values lying between 50 and 80%.[11]

Psittacosaurus stomach stones
Psittacosaurus fossil with gastroliths in its stomach region, American Museum of Natural History

The American Museum of Natural History Photograph # 311488 demonstrates an articulated skeleton of a Psittacosaurus mongoliensis, from the Ondai Sair Formation, Lower Cretaceous Period of Mongolia, showing a collection of about 40 gastroliths inside the rib cage, about midway between shoulder and pelvis.

Geologic distribution

Jurassic

Gastroliths have sometimes been called Morrison stones because they are often found in the Morrison Formation (named after the town of Morrison, west of Denver, Colorado), a late Jurassic formation roughly 150 million years old. Some gastroliths are made of petrified wood. Most known instances of preserved sauropod gastroliths are from Jurassic animals.[12]

Cretaceous

The Early Cretaceous Cedar Mountain Formation of Central Utah is full of highly polished red and black cherts, which may partly represent gastroliths. The cherts may themselves contain fossils of ancient animals, such as corals. These stones do not appear to be associated with stream deposits and are rarely more than fist-sized, which is consistent with the idea that they are gastroliths.

Sauropod gastroliths

Most known instances of preserved sauropod gastroliths are from Jurassic animals.[12] The largest known gastroliths found in association with sauropod skeletons are approximately 10 centimeters in length.[13]

Cedarosaurus weiskopfae

In 2001 Frank Sanders, Kim Manley, and Kenneth Carpenter published a study on 115 gastroliths discovered in association with a Cedarosaurus specimen.[14] The stones were identified as gastroliths on the basis of their tight spatial distribution, partial matrix support, and an edge-on orientation indicative of their being deposited while the carcass still had soft tissue.[14] Their high surface reflectance values are consistent with other known dinosaur gastroliths.[14] Nearly all of the Cedarosaurus gastroliths were found within a .06 m volume of space in the gut region of the skeleton.[15]

The total mass of the gastroliths themselves was 7 kilograms (15 lb).[16] Most were less than 10 millilitres (0.35 imp fl oz; 0.34 US fl oz) in volume.[17] The least massive clast was .1 grams (0.0035 oz) and the most was 715 grams (25.2 oz), with most of them being toward the smaller end of that range.[17] The clasts tended to be close to spherical in shape, although the largest specimens were also the most irregular.[17] The largest gastroliths contributed the most to the total surface area of the set.[18] Some gastroliths were so large and irregularly shaped that they may have been difficult to swallow.[18] The gastroliths were mostly composed of chert, with some sandstone, siltstone, and quartzite clasts also included.[9]

Since some of the most irregular gastroliths are also the largest, it is unlikely that they were ingested by accident.[18] Cedarosaurus may have found irregular clasts to be attractive potential gastroliths or was not selective about shape.[18] The clasts were generally of dull coloration, suggesting that color was not a major factor for the sauropod's decision making.[14] The high surface area to volume ratio of the largest clasts suggests that the gastroliths may have broken down ingested plant material by grinding or crushing it[11] The sandstone clasts tended to be fragile and some broke in the process of collection.[9] The sandstone gastroliths may have been rendered fragile after deposition by loss of cement caused by the external chemical environment.[19] If the clasts had been that fragile while the animal was alive, they probably rolled and tumbled in the digestive tract.[11] If they were more robust, they could have served as part of a ball-mill system.[11]

Migration

Paleontologists are researching new methods of identifying gastroliths that have been found disassociated from animal remains, because of the important information they can provide. If the validity of such gastroliths can be verified, it may be possible to trace gastrolithic rocks back to their original sources. This may provide important information on how dinosaurs migrated. Because the number of suspected gastroliths is large, they could provide significant new insights into the lives and behaviour of dinosaurs.

See also

Footnotes

  1. ^ Kulbisky et al The axolotl as an animal model for the comparison of 3-D ultrasound with plain film radiography rrr in Medicine and Biology, July 1999 Volume 25, Issue 6, Pages 969–975
  2. ^ Wings, O A review of gastrolith function with implications for fossil vertebrates and a revised classification Acta Palaeontologica Polonica 52 (1): 1–16
  3. ^ Wickramasinghe, DD et al Ontogenetic changes in diet and intestinal morphology in semi-terrestrial tadpoles of Nannophrys ceylonensis (Dicroglossidae) Copeia, Vol2007, Iss 4 (Dec 2007)
  4. ^ Rondeau, et al Larval Anurans Adjust Buoyancy in Response to Substrate Ingestion Copeia: February 2005, Vol. 2005, No. 1, pp. 188-195.
  5. ^ Darby and Ojakangas (1980).
  6. ^ Wieland, G. R., 1906, Dinosaurian gastroliths: Science, v. 23, p. 819-821.
  7. ^ Brown, B. 1907. Gastroliths. Science 25(636): 392.
  8. ^ Huene, F. von. 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien für Geologie und Paläontologie (1) 4: 1–361.
  9. ^ a b c d e f "Description," Sanders et al. (2001). Page 176.
  10. ^ "Description," Sanders et al. (2001). Pp. 176-177.
  11. ^ a b c d "Description," Sanders et al. (2001). Page 177.
  12. ^ a b "Occurrence of Gastroliths in Mesozoic Taxa," Sanders et al. (2001). Page 168.
  13. ^ Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. ISBN 1-4051-3413-5.</
  14. ^ a b c d "Abstract," Sanders et al. (2001). Page 166.
  15. ^ "Occurrence in Cedarosaurus," Sanders et al. (2001). Page 169.
  16. ^ "Table 12.2," Sanders et al. (2001). Page 171.
  17. ^ a b c "Description," Sanders et al. (2001). Page 172.
  18. ^ a b c d "Description," Sanders et al. (2001). Page 174.
  19. ^ "Conclusion," Sanders et al. (2001). Page 177.

References

  • Darby, D.G. and Ojakangas, J. (1980). Gastroliths from an Upper Cretaceous Plesiosaur. Journal of Paleontology 54:3
  • Whittle, C. (1989). On the Origins of Gastroliths: Determining the Weathering Environment of Rounded and Polished Stones by Scanning Electron Microscope Analysis. Geological Society of America Bulletin 51:5.
  • Whittle, C. (1988). On the Origins of Gastroliths. Journal of Vertebrate Paleontology, Supplement to 3:28.
  • Wings, Oliver (2003): Observations on the Release of Gastroliths from Ostrich Chick Carcasses in Terrestrial and Aquatic Environments. Journal of Taphonomy 1(2): 97-103. PDF fulltext
  • Wings, Oliver (2004): Identification, distribution, and function of gastroliths in dinosaurs and extant birds with emphasis on ostriches (Struthio camelus). Ph.D. Thesis, The University of Bonn, Bonn, Germany, 187 pp. URN: urn:nbn:de:hbz:5N-04626 PDF fulltext
  • Wings, Oliver (2007): A review of gastrolith function with implications for fossil vertebrates and a revised classification. Acta Palaeontologica Polonica 52(1): 1-16. PDF fulltext
  • Wings, Oliver & Sander, P.M. (2007): No gastric mill in sauropod dinosaurs: new evidence from analysis of gastrolith mass and function in ostriches. Proc. R. Soc. B 274(1610): 635–640. doi:10.1098/rspb.2006.3763 PMID 17254987 PDF fulltext
  • Stokes, W. L. 1987. Dinosaur gastroliths revisited. Journal of Paleontology 61: 1242–1246.
Axolotl

The axolotl (, from Classical Nahuatl: āxōlōtl [aːˈʃoːloːtɬ] (listen); plural axolotls or rarely axolomeh), Ambystoma mexicanum, also known as the Mexican walking fish, is a neotenic salamander related to the tiger salamander. Although the axolotl is colloquially known as a "walking fish", it is not a fish, but an amphibian. The species was originally found in several lakes, such as Lake Xochimilco underlying Mexico City. Axolotls are unusual among amphibians in that they reach adulthood without undergoing metamorphosis. Instead of developing lungs and taking to the land, adults remain aquatic and gilled.

Axolotls should not be confused with waterdogs, the larval stage of the closely related tiger salamanders (A. tigrinum and A. mavortium), which are widespread in much of North America and occasionally become neotenic. Neither should they be confused with mudpuppies (Necturus spp.), fully aquatic salamanders that are not closely related to the axolotl but bear a superficial resemblance.As of 2010, wild axolotls were near extinction due to urbanization in Mexico City and consequent water pollution, as well as the introduction of invasive species such as tilapia and perch. They are currently listed by CITES as an endangered species and by IUCN as critically endangered in the wild, with a decreasing population. Axolotls are used extensively in scientific research due to their ability to regenerate limbs. Axolotls were also sold as food in Mexican markets and were a staple in the Aztec diet.Surveys in 1998, 2003, and 2008 found 6,000, 1,000, and 100 axolotls per square kilometer in its Lake Xochimilco habitat, respectively. A four-month-long search in 2013, however, turned up no surviving individuals in the wild. Just a month later, two wild ones were spotted in a network of canals leading from Xochimilco. The city is currently working on conserving axolotls by building "axolotl shelters" and conserving remaining and potential habitats for the salamanders.

Bohaiornithidae

Bohaiornithidae is a group of early predatory enantiornitheans from the early Cretaceous Period of China. All known specimens come from the Jiufotang Formation and Yixian Formation, dating to the early Aptian age, 125-120 million years ago. Bohaiornithidae was first coined as a family of enantiornithean birds by Wang and colleagues in 2014. They defined it as the natural group formed by all descendants of the common ancestor of the type species, Bohaiornis guoi, and Shenqiornis mengi.

Camarasaurus

Camarasaurus ( KAM-ər-ə-SAWR-əs) was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America. Its fossil remains have been found in the Morrison Formation of Colorado and Utah, dating to the Late Jurassic epoch (Kimmeridgian to Tithonian stages), between 155 and 145 million years ago.

Camarasaurus presented a distinctive cranial profile of a blunt snout and an arched skull that was remarkably square. It likely travelled in herds, or at least in family groups.

The name means "chambered lizard", referring to the hollow chambers in its vertebrae (Greek καμαρα/kamara meaning "vaulted chamber", or anything with an arched cover, and σαυρος/sauros meaning "lizard").

Coprolite

A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name is derived from the Greek words κόπρος (kopros, meaning "dung") and λίθος (lithos, meaning "stone"). They were first described by William Buckland in 1829. Prior to this they were known as "fossil fir cones" and "bezoar stones". They serve a valuable purpose in paleontology because they provide direct evidence of the predation and diet of extinct organisms. Coprolites may range in size from a few millimetres to over 60 centimetres.

Coprolites, distinct from paleofaeces, are fossilized animal dung. Like other fossils, coprolites have had much of their original composition replaced by mineral deposits such as silicates and calcium carbonates. Paleofaeces, on the other hand, retain much of their original organic composition and can be reconstituted to determine their original chemical properties, though in practice the term coprolite is also used for ancient human faecal material in archaeological contexts.

Dinheirosaurus

Dinheirosaurus is a genus of diplodocid sauropod dinosaur that is known from fossils uncovered in modern-day Portugal. It may represent a species of Supersaurus. The only species is Dinheirosaurus lourinhanensis, first described by José Bonaparte and Octávio Mateus in 1999 for vertebrae and some other material from the Lourinhã Formation. Although the precise age of the formation is not known, it can be dated around the early Tithonian of the Late Jurassic.

The known material includes two cervical vertebrae, nine dorsal vertebrae, a few ribs, a fragment of a pubis, and many gastroliths. Of the material, only the vertebrae are diagnostic, with the ribs and pubis being too fragmentary or general to distinguish Dinheirosaurus. This material was first described as in the genus Lourinhasaurus, but differences were noticed and in 1999 Bonaparte and Mateus redescribed the material under the new binomial Dinheirosaurus lourinhanensis. Another specimen, ML 418, thought to be Dinheirosaurus, is now known to be from another Portuguese diplodocid. This means that Dinheirosaurus lived alongside many theropods, sauropods, thyreophorans and ornithopods, as well as at least one other diplodocid.

Dinheirosaurus is a diplodocid, a relative of Apatosaurus, Diplodocus, Barosaurus, Supersaurus, and Tornieria. Among those, the closest relative to Dinheirosaurus is Supersaurus.

Dropstone

Dropstones are isolated fragments of rock found within finer-grained water-deposited sedimentary rocks. They range in size from small pebbles to boulders. The critical distinguishing feature is that there is evidence that they were not transported by normal water currents, but rather dropped in vertically through the water column.

Elasmosaurus

Elasmosaurus (;) is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, about 80.5 million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, and was sent to the American paleontologist Edward Drinker Cope, who named it E. platyurus in 1868. The generic name means "thin-plate reptile", and the specific name means "flat-tailed". Cope originally reconstructed the skeleton of Elasmosaurus with the skull at the end of the tail, an error which was made light of by the paleontologist Othniel Charles Marsh, and became part of their "Bone Wars" rivalry. Only one incomplete Elasmosaurus skeleton is definitely known, consisting of a fragmentary skull, the spine, and the pectoral and pelvic girdles, and a single species is recognized today; other species are now considered invalid or have been moved to other genera.

Measuring 10.3 meters (34 ft) long, Elasmosaurus would have had a streamlined body with paddle-like limbs, a short tail, a small head, and an extremely long neck. The neck alone was around 7.1 meters (23 ft) long. Along with its relative Albertonectes, it was one of the longest-necked animals to have lived, with the largest number of neck vertebrae known, 72. The skull would have been slender and triangular, with large, fang-like teeth at the front, and smaller teeth towards the back. It had six teeth in each premaxilla of the upper jaw, and may have had 14 teeth in the maxilla and 19 in the dentary of the lower jaw. Most of the neck vertebrae were compressed sideways, and bore a longitudinal crest or keel along the sides.

The family Elasmosauridae was based on the genus Elasmosaurus, the first recognized member of this group of long-necked plesiosaurs. Elasmosaurids were well adapted for aquatic life, and used their flippers for swimming. Contrary to earlier depictions, their necks were not very flexible, and could not be held high above the water surface. It is unknown what their long necks were used for, but they may have had a function in feeding. Elasmosaurids probably ate small fish and marine invertebrates, seizing them with their long teeth, and may have used gastroliths (stomach stones) to help digest their food. Elasmosaurus is known from the Pierre Shale formation, which represents marine deposits from the Western Interior Seaway.

Enterolith

An enterolith is a mineral concretion or calculus formed anywhere in the gastrointestinal system. Enteroliths are uncommon and usually incidental findings but, once found, they require at a minimum watchful waiting. If there is evidence of complications, they must be removed.

An enterolith may form around a nidus, a small foreign object such as a seed, pebble, or piece of twine that serves as an irritant. In this respect, an enterolith forms by a process similar to the creation of a pearl.

An enterolith is not to be confused with a gastrolith, which helps digestion.

Gastro-

Gastro- is a common English-language prefix derived from the ancient Greek γαστήρ gastēr ("stomach").

Gaviiformes

Gaviiformes is an order of aquatic birds containing the loons or divers and their closest extinct relatives. Modern gaviiformes are found in many parts of North America and northern Eurasia (Europe, Asia and debatably Africa), though prehistoric species were more widespread.

Loon

The loons (North America) or divers (United Kingdom / Ireland) are a group of aquatic birds found in many parts of North America and northern Eurasia. All living species of loons are members of the genus Gavia, family Gaviidae and order Gaviiformes.

Macronaria

Macronaria is a clade of the "suborder" (more likely an unranked clade than a suborder) Sauropodomorpha. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence macro- meaning large, and –naria meaning nose). Fossil evidence suggests that macronarian dinosaurs lived from the Late Jurassic (Kimmeridgian) through the Late Cretaceous (Maastrichtian). Macronarians have been found globally, including discoveries in Argentina, the United States, Portugal, China, and Tanzania. Like other sauropods, they are known to have inhabited primarily terrestrial areas, and little evidence exists to suggest that they spent much time in coastal environments. Macronarians are diagnosed through their distinct characters on their skulls, as well as appendicular and vertebral characters. Macronaria is composed of several subclades and families notably including Camarasauridae and Titanosauriformes, among several others. Titanosauriforms are particularly well known for being some of the largest terrestrial animals to ever exist.

Macronaria was described by Wilson and Sereno who proposed the new subdivisions among the clade Neosauropoda. Previously, this clade was thought to have Brachiosaurus and Camarasauridae forming one sister group, and Titanosauroidea and Diplodocoidea forming another. This proposed shift with Macronaria placed Diplodocoidea as an outgroup to the new clade Macronaria, under which all other neosauropods would fall.

Physiology of dinosaurs

Overall, dinosaurs are reptiles. However preliminary note: In this article "dinosaur" means "non-avian dinosaur," since birds are a monophyletic taxon within the clade Dinosauria and most experts regard birds as dinosaurs.The physiology of dinosaurs has historically been a controversial subject, particularly their thermoregulation. Recently, many new lines of evidence have been brought to bear on dinosaur physiology generally, including not only metabolic systems and thermoregulation, but on respiratory and cardiovascular systems as well.

During the early years of dinosaur paleontology, it was widely considered that they were sluggish, cumbersome, and sprawling cold-blooded lizards. However, with the discovery of much more complete skeletons in western United States, starting in the 1870s, scientists could make more informed interpretations of dinosaur biology and physiology. Edward Drinker Cope, opponent of Othniel Charles Marsh in the Bone Wars, propounded at least some dinosaurs as active and agile, as seen in the painting of two fighting "Laelaps" produced under his direction by Charles R. Knight.In parallel, the development of Darwinian evolution, and the discoveries of Archaeopteryx and Compsognathus, led Thomas Henry Huxley to propose that dinosaurs were closely related to birds. Despite these considerations, the image of dinosaurs as large reptiles had already taken root, and most aspects of their paleobiology were interpreted as being typically reptilian for the first half of the twentieth century. Beginning in the 1960s and with the advent of the Dinosaur Renaissance, views of dinosaurs and their physiology have changed dramatically, including the discovery of feathered dinosaurs in Early Cretaceous age deposits in China, indicating that birds evolved from highly agile maniraptoran dinosaurs.

Plateosaurus

Plateosaurus (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Europe and Greenland, North America. Plateosaurus is a basal (early) sauropodomorph dinosaur, a so-called "prosauropod". As of 2011, two species are recognised: the type species P. engelhardti from the late Norian and Rhaetian, and the slightly earlier P. gracilis from the lower Norian. However, others have been assigned in the past, and there is no broad consensus on the species taxonomy of plateosaurid dinosaurs. Similarly, there are a plethora of synonyms (invalid duplicate names) at the genus level.

Discovered in 1834 by Johann Friedrich Engelhardt and described three years later by Hermann von Meyer, Plateosaurus was the fifth named dinosaur genus that is still considered valid. Although it had been described before Richard Owen formally named Dinosauria in 1842, it was not one of the three genera used by Owen to define the group, because at the time, it was poorly known and difficult to identify as a dinosaur. It is now among the dinosaurs best known to science: over 100 skeletons have been found, some of them nearly complete. The abundance of its fossils in Swabia, Germany, has led to the nickname Schwäbischer Lindwurm (Swabian lindworm).

Plateosaurus was a bipedal herbivore with a small skull on a long, flexible neck, sharp but plump plant-crushing teeth, powerful hind limbs, short but muscular arms and grasping hands with large claws on three fingers, possibly used for defence and feeding. Unusually for a dinosaur, Plateosaurus showed strong developmental plasticity: instead of having a fairly uniform adult size, fully grown individuals were between 4.8 and 10 metres (16 and 33 ft) long and weighed between 600 and 4,000 kilograms (1,300 and 8,800 lb). Commonly, the animals lived for at least 12 to 20 years, but the maximum life span is not known.

Despite the great quantity and excellent quality of the fossil material, Plateosaurus was for a long time one of the most misunderstood dinosaurs. Some researchers proposed theories that were later shown to conflict with geological and palaeontological evidence, but have become the paradigm of public opinion. Since 1980 the taxonomy (relationships), taphonomy (how the animals became embedded and fossilised), biomechanics (how their skeletons worked), and palaeobiology (life circumstances) of Plateosaurus have been re-studied in detail, altering the interpretation of the animal's biology, posture and behaviour.

Rangle

For other spellings, see Wrangle (disambiguation), Wrangel (disambiguation), or Rangel (disambiguation).In falconry, rangle is a term used for small stones which are fed to hawks to aid in digestion. These stones, which are generally slightly larger than peas, are used less often now than they were historically.

Regurgitalith

Regurgitaliths are the fossilized remains of stomach contents that have been regurgitated by an animal. They are trace fossils and can be subdivided into ichnotaxa. Regurgitaliths might provide useful information on the diet of the animal, but are difficult to relate to any particular species.

Reptile

Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of modern amphibians, is called herpetology.

Because some reptiles are more closely related to birds than they are to other reptiles (e.g., crocodiles are more closely related to birds than they are to lizards), the traditional groups of "reptiles" listed above do not together constitute a monophyletic grouping or clade (consisting of all descendants of a common ancestor). For this reason, many modern scientists prefer to consider the birds part of Reptilia as well, thereby making Reptilia a monophyletic class, including all living Diapsids.The earliest known proto-reptiles originated around 312 million years ago during the Carboniferous period, having evolved from advanced reptiliomorph tetrapods that became increasingly adapted to life on dry land. Some early examples include the lizard-like Hylonomus and Casineria. In addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the Cretaceous–Paleogene extinction event wiped out the pterosaurs, plesiosaurs, ornithischians, and sauropods, as well as many species of theropods, including troodontids, dromaeosaurids, tyrannosaurids, and abelisaurids, along with many Crocodyliformes, and squamates (e.g. mosasaurids).

Modern non-avian reptiles inhabit all the continents except Antarctica, although some birds are found on the periphery of Antarctica. Several living subgroups are recognized: Testudines (turtles and tortoises), 350 species; Rhynchocephalia (tuatara from New Zealand), 1 species; Squamata (lizards, snakes, and worm lizards), over 10,200 species; Crocodilia (crocodiles, gavials, caimans, and alligators), 24 species; and Aves (birds), approximately 10,000 species.Reptiles are tetrapod vertebrates, creatures that either have four limbs or, like snakes, are descended from four-limbed ancestors. Unlike amphibians, reptiles do not have an aquatic larval stage. Most reptiles are oviparous, although several species of squamates are viviparous, as were some extinct aquatic clades – the fetus develops within the mother, contained in a placenta rather than an eggshell. As amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings. Extant reptiles range in size from a tiny gecko, Sphaerodactylus ariasae, which can grow up to 17 mm (0.7 in) to the saltwater crocodile, Crocodylus porosus, which can reach 6 m (19.7 ft) in length and weigh over 1,000 kg (2,200 lb).

Sinornithomimus

Sinornithomimus is a genus of ornithomimid theropod dinosaur found in 1997, in the early Late Cretaceous strata of the Ulansuhai Formation located at Alshanzuo Banner, Inner Mongolia Autonomous Region, Northern China.

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