Saurornithoides

Saurornithoides (/sɔːˌrɔːrnɪˈθɔɪdiːz/ saw-ROR-ni-THOY-deez) is a genus of troodontid maniraptoran dinosaur, which lived during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. The name is derived from the Greek stems saur~ (lizard), ornith~ (bird) and eides (form), referring to its bird-like skull.

Saurornithoides
Temporal range: Late Cretaceous, 75 Ma
Saurornithoides mongoliensis
Holotype skull, AMNH 6516
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Troodontidae
Genus: Saurornithoides
Osborn, 1924
Species:
S. mongoliensis
Binomial name
Saurornithoides mongoliensis
Osborn, 1924
Synonyms
  • Troodon mongoliensis
    Paul, 1988[1]

Description

Saurornithoides foot
Left foot of the type specimen as seen from the inside

Saurornithoides is a member of the troodontids, a group of small, bird-like, gracile maniraptorans. All troodontids have many unique features of the skull, such as closely spaced teeth in the lower jaw, and large numbers of teeth. Troodontids have sickle-claws and raptorial hands, and some of the highest non-avian encephalization quotients, meaning they were behaviourally advanced and had keen senses.[2] Saurornithoides was a rather small troodontid. Though a possible adult, the type specimen has a midline skull length of 189 millimetres, compared to 272 millimetres for Zanabazar junior, itself estimated at 2.3 metres long. It had large eye sockets and stereoscopic vision, allowing for good depth perception. It probably had good vision in light and very good night vision. It had a long, low head, a depressed muzzle, sharp teeth and a relatively large brain. Swift and smart, like its North American cousin Troodon, Saurornithoides probably scoured the Gobi Desert, looking for small mammals or reptiles to eat. Like other troodontids, it had an enlarged retractable claw on the second toe of each foot, that in this case was of moderate size though rather curved.[3]

A revision of the genus in 2009 provided a differential diagnosis, a list of traits in which Saurornithoides differed from certain relevant relatives, especially concentrating on determining its place in the evolutionary tree. That Saurornithoides mongoliensis might be more derived, higher in the tree, than Sinornithoides and Sinusonasus, is indicated by the lack of a fenestra promaxillaris, a small opening at the front side of the snout, and the possession of large denticles on the rear tooth edges as well as the presence of the high number of six sacral vertebrae. That S. mongoliensis might be more basal, lower in the tree, than Zanabazar and Troodon, is shown by the presence of a recessus tympanicus dorsalis, the upper one of three small openings on the side of the braincase, in the inner ear region.[3]

History of discovery

SaurornithoidesSkull
Cast of the skull shown from the right

Originally, only one or possibly two individuals of Saurornithoides were known, closely associated within the same layer of the Djadochta Formation of Mongolia. The fossils were found on 9 July 1923 by a Chinese employee of an American Museum of Natural History expedition, Chih. The material contained a single skull and jaw in association, and vertebrae, a partial pelvis, hindlimb and foot associated nearby. More bones were initially included but later shown to belong to Protoceratops. Henry Fairfield Osborn at first intended to name the animal "Ornithoides", the "bird-like one", and in 1924 mentioned this name in a popular publication but without a description so that it remained an invalid nomen nudum.[4] He then formally described the remains in the same year, finding them to be a new genus and species, which he named Saurornithoides mongoliensis. The generic name was chosen because of the bird-like bones of the taxon, which was thought to represent a megalosaurian, translating as "saurian with bird-like rostrum". Saurornithoides was noted to resemble Velociraptor, although more sluggish according to Osborn. The holotype specimen is AMNH 6516.[5] This specimen was the first troodontid skeleton found, though at the time the connection with Troodon, then known only from its teeth, was not realised.[3]

Saurornithoides teeth
Maxillary teeth

In 1964, another specimen was described from the Late Cretaceous of Mongolia. The first specimen ever collected by a professional Mongolian palaeontologist, it was given the specimen number IGM 100/1. In 1974, it was described by Rinchen Barsbold as a new species, Saurornithoides junior. It was assigned to the genus based on cranial comparisons, as well as the similar provincialism.[6] However, since the description, many more troodontids have been described with cranial material, and as such, a 2009 study on Saurornithoides reassigned this species to its own genus, Zanabazar.[3]

Several other Saurornithoides species were named, though none of these is today seen as valid. In 1928, baron Franz Nopcsa coined Saurornithoides sauvagei.[7] However, this was the result of a printing error: he had planned to name a Teinurosaurus sauvagei.[8] In 1982, Kenneth Carpenter renamed Stenonychosaurus inequalis Sternberg 1932 into Saurornithoides inequalis.[9] Today this is usually seen as a junior synonym of Troodon formosus. In 1991, George Olshevsky renamed Pectinodon asiamericanus Nesov 1985 into Saurornithoides asiamericanus.[10] In 1995 he made it a Troodon asiaamericanus.[11][12] In view of its provenance from the Cenomanian of Uzbekistan, it is usually seen as a different taxon from Saurornithoides. In 2000, Olshevsky renamed Troodon isfarensis Nessov 1995 into Saurornithoides isfarensis.[13] In 2007, this was shown to have been a hadrosaurid fossil.[14]

Classification

Saurornithoides
Holotype skull seen from the right, below, and above

Osborn at first placed Saurornithoides in the Megalosauridae, noticing the resemblance to Velociraptor, named in the same paper.[5] Only in 1974, Barsbold, while describing S. junior, understood the connection with American forms such as Stenonychosaurus and named an encompassing Saurornithoididae.[6] In 1987, Philip John Currie showed that this concept was a junior synonym of Troodontidae, implying that Saurornithoides were a troodontid too.[15]

The cladogram below follows a 2012 analysis by Turner, Makovicky and Norell.[16]

Paraves

Epidexipteryx

Avialae

Deinonychosauria

Dromaeosauridae

Troodontidae

Anchiornis

Xiaotingia

Jinfengopteryginae

IGM 100/1323 (Almas)

IGM 100/1126

Jinfengopteryx

Mei

Sinovenator

Xixiasaurus

IGM 100/44

Byronosaurus

Sinornithoides

Troodon

Saurornithoides

Zanabazar

See also

References

  1. ^ Paul, Gregory Scott (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster. pp. 358, 366–369. ISBN 978-0-671-61946-6.
  2. ^ Lü, Junchang; Xu, Li; Liu, Yongqing; Zhang, Xingliao; Jia, Songhai & Ji, Qiang (2010). "A new troodontid (Theropoda: Troodontidae) from the Late Cretaceous of central China, and the radiation of Asian troodontids" (PDF). Acta Palaeontologica Polonica. 55 (3): 381–388. doi:10.4202/app.2009.0047.
  3. ^ a b c d Norell, Mark A.; Makovicky, Peter J.; Bever, Gabe S.; Balanoff, Amy M.; Clark, James M.; Rinchen Barsbold; Rowe, Timothy (2009). "A Review of the Mongolian Cretaceous Dinosaur Saurornithoides (Troodontidae: Theropoda)". American Museum Novitates. 3654: 63. doi:10.1206/648.1.
  4. ^ Osborn, Harry F. (1924). "The discovery of an unknown continent". Natural History. 24 (2): 133–149.
  5. ^ a b Osborn, Harry F. (1924). "Three new Theropoda, Protoceratops zone, Central Mongolia" (PDF). American Museum Novitates (144): 12.
  6. ^ a b Rinchen Barsbold (1974). "Saurornithoididae, a new family of small theropod dinosaurs from Central Asia and North America" (PDF). Palaeontologia Polonica. 30: 5–22.
  7. ^ Nopcsa, Franz (1928). "The genera of reptiles". Palaeobiologica. 1: 163–188.
  8. ^ Nopcsa, Franz (1929). "Addendum: "The genera of reptiles"". Palaeobiologica. 1: 201.
  9. ^ Carpenter, Kenneth (1982). "Baby dinosaurs from the Late Cretaceous Lance and Hell Creek formations and a description of a new species of theropod". Contributions to Geology, University of Wyoming. 20 (2): 123–134.
  10. ^ Olshevsky, George (1991). A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings. 2.
  11. ^ Olshevsky, George (1995). "The origin and evolution of the tyrannosaurids (part 1)". Kyoryugaku Saizensen. 9: 92–119.
  12. ^ Olshevsky, George (1995). "The origin and evolution of the tyrannosaurids (part 2)". Kyoryugaku Saizensen. 10: 75–99.
  13. ^ Olshevsky, George (2000). An annotated checklist of dinosaur species by continent. Mesozoic Meanderings. 3.
  14. ^ Averianov, Alexander O.; Sues, Hans-Dieter (2007). "A new troodontid (Dinosauria: Theropoda) from the Cenomanian of Uzbekistan, with a review of troodontid records from the territories of the former Soviet Union". Journal of Vertebrate Paleontology. 27 (1): 87–98.
  15. ^ Currie, Philip J. (1987). "Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia)". Journal of Vertebrate Paleontology. 7 (1): 72–81.
  16. ^ Turner, Alan H.; Makovicky, Peter J.; Norell, Mark A. (2012). "A Review of Dromaeosaurid Systematics and Paravian Phylogeny". Bulletin of the American Museum of Natural History. 371: 1. doi:10.1206/748.1.

Sources

  • Fantastic Facts About Dinosaurs. ISBN 0-7525-3166-2.
  • Lessem, Don (2003). Dinosaurs A to Z. p. 170. ISBN 0-439-16591-1.
1922 in archaeology

The year 1922 in archaeology involved some significant events.

1924 in paleontology

Paleontology or palaeontology (from Greek: paleo, "ancient"; ontos, "being"; and logos, "knowledge") is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1924.

Borogovia

Borogovia is a troodontid theropod dinosaur genus which lived during the Late Cretaceous Period, in what is now Mongolia.

In 1971, a Polish-Mongolian expedition discovered the remains of a small theropod at the Altan Ula IV site, in the Nemegt Basin of Ömnögovĭ province. In 1982, the find was reported by Halszka Osmólska and considered by her to be a possible specimen of Saurornithoides. Later she concluded that it represented a species new to science.

In 1987, Osmólska named and described the type species Borogovia gracilicrus. The generic name is derived from the fantasy creatures known as 'borogoves' in the Lewis Carroll poem "Jabberwocky", in his Alice's Adventures in Wonderland. The specific name is a combination of Latin gracilis, "lightly built", and crus, "shin", in reference to the elegant build of the lower leg.The holotype specimen, ZPAL MgD-I/174, was found in the Nemegt Formation, dating from the early Maastrichtian. It consists of two lower legs of a single individual, including fragments of both tibiotarsi, the undersides of both metatarsi and the second, third and fourth toes of each foot.The tibiotarsi have an estimated length of twenty-eight centimetres. Borogovia is about two meters (6 feet) long, weighing some twenty kilograms (forty-five pounds). The tibiotarsus is very elongated. The third toe is narrow. The second phalanx of the second toe is short. The claw of the second toe is short and relatively flat. Osmólska claimed that the second toe could not be hyperextended, and suggested that it had regained a weight-bearing function, compensating for the weakness of the third toe.Borogovia was assigned by Osmólska to the Troodontidae in 1987.

Campanian

The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch (or, in chronostratigraphy: the fifth of six stages in the Upper Cretaceous series). The Campanian spans the time from 83.6 ± 0.7 Ma to 72.1 ± 0.6 Ma (million years ago). It is preceded by the Santonian and it is followed by the Maastrichtian.The Campanian was an age when a worldwide sea level rise drowned many coastal areas. The morphology of some of these areas has been preserved as an unconformity beneath a cover of marine sedimentary rocks.

Flaming Cliffs

The Flaming Cliffs site, also known as Bayanzag, sometimes Bain-Dzak, (Mongolian: Баянзаг rich in saxaul), with the alternative Mongolian name of Mongolian: Улаан Эрэг (red cliffs), is a region of the Gobi Desert in the Ömnögovi Province of Mongolia, in which important fossil finds have been made. It was given this name by American paleontologist Roy Chapman Andrews, who visited in the 1920s. The area is most famous for yielding the first discovery of dinosaur eggs. Other finds in the area include specimens of Velociraptor and eutherian mammals. It is illegal to remove fossils from the area without appropriate permits.The nickname refers to the red or orange color of the sandstone cliffs (especially at a sunset),.

Gobivenator

Gobivenator is an extinct genus of troodontid theropod dinosaur known from the late Campanian Djadokhta Formation of central Gobi Desert, Mongolia. It contains a single species, Gobivenator mongoliensis. G. mongoliensis is known from a single individual, which represents the most complete specimen of a Late Cretaceous troodontid currently known.

Halszkaraptorinae

Halszkaraptorinae is a basal ("primitive") subfamily of Dromaeosauridae that includes the enigmatic genera Halszkaraptor, Mahakala, and Hulsanpes. A comparison of the fossils of Halszkaraptor with the bones of extant crocodilians and aquatic birds revealed evidence of a semiaquatic lifestyle. The group is named after Polish paleontologist Halszka Osmólska.

Last Day of the Dinosaurs

Last Day of the Dinosaurs is a 2010 Discovery Channel television documentary about the extinction of the dinosaurs. It portrays the Alvarez hypothesis as the cause of extinction. The documentary was released on August 28, 2010 and narrated by Bill Mondy.

Pectinodon

Pectinodon is a genus of dinosaurs from the Late Cretaceous period (66 mya). It currently contains a single valid species, Pectinodon bakkeri (sometimes classified as Troodon bakkeri), known mainly from teeth, as well as fragments of juvenile skeletons and eggshells.In 1982, Kenneth Carpenter named a number of theropod teeth from the late Maastrichtian Lance Formation of Wyoming as the type species Pectinodon bakkeri. The generic name is derived from Latin pecten, "comb", and Greek ὀδών, odon, "tooth", in reference to the comb-like serrations on the rear edge of the teeth. The specific name honours Robert Thomas Bakker.The holotype, UCM 38445, consists of a 6.2 mm long tooth. The paratypes include other teeth, a front dentary and a lower braincase.In 1985 Lev Nesov named a second species, Pectinodon asiamericanus, based on specimen CCMGE 49/12176, a tooth from the Khodzhakul Formation of Uzbekistan dating from the Cenomanian. This is today often considered a nomen dubium.While historically considered synonymous with Troodon or more specifically the species Troodon formosus, Philip Currie and colleagues (1990) noted that the P. bakkeri fossils from the Hell Creek Formation and Lance Formation might belong to different species. In 1991, George Olshevsky assigned the Lance formation fossils to the species Troodon bakkeri. In 2011, Zanno and colleagues reviewed the convoluted history of troodontid classification in Late Cretaceous North America. They followed Longrich (2008) in treating Pectinodon bakkeri as a valid genus, and noted that it is likely the numerous Late Cretaceous specimens currently assigned to Troodon formosus almost certainly represent numerous new species, but that a more thorough review of the specimens is required.In 2013 Currie and Derek Larson concluded that Pectinodon bakkeri was valid and its teeth could be found both in the Lance Formation and the coeval Hell Creek Formation. Some teeth from the older Campanian Dinosaur Park Formation could not be statistically differentiated from them, likely due to an insufficiently large sample, and were referred to a cf. Pectinodon.

Philovenator

Philovenator (literally meaning "love hunter") is an extinct genus of troodontid paravian dinosaurs from the Wulansuhai Formation (dated to the Campanian age, sometime between 75 and 71 million years ago) of Inner Mongolia, China. Its specific name honors Phillip J. Currie.

Polyodontosaurus

Polyodontosaurus is a potentially dubious genus of troodontid dinosaur named in 1932 by Gilmore for a left dentary from the Dinosaur Park Formation. It had been considered a synonym of Stenonychosaurus or Troodon for a significant time, before being declared a nomen dubium.

Sinovenator

Sinovenator (meaning "Chinese hunter") is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period.

Teinurosaurus

Teinurosaurus (meaning "extended tail lizard") is a genus of carnivorous theropod dinosaur. Teinurosaurus lived during the Late Jurassic in what is now Portugal. Only a single caudal vertebra (now destroyed) has ever been discovered, and the genus is usually considered a nomen dubium. The type species is Teinurosaurus sauvagei.

In 1897 French paleontologist Henri-Émile Sauvage referred a tail vertebra from the Kimmeridgian of Portugal, present in the collection of the Musée Géologique du Boulonnais at Boulogne-sur-Mer in France, to Iguanodon prestwichii (now Cumnoria prestwichii), a herbivorous iguanodont.In 1928 Baron Franz Nopcsa recognised the fossil to be the vertebra of a theropod instead. He decided to name it as the genus Teinurosaurus. The name is derived from Greek teinein, "to stretch", and oura, "tail", referring to the elongated form. However, by a mistake of the printer, the footnote in which the new name was mentioned was not placed at the end of the section referring to the fossil but adjacent to a citation of Saurornithoides Osborn 1924, giving the false impression Nopcsa intended to rename the latter genus. After having discovered the typographical error, Nopcsa in 1929 added an addendum to the article, correcting the mistake.In 1932 German paleontologist Friedrich von Huene again named the fossil, giving it the species name Caudocoelus sauvagei. "Caudocoelus" means "hollow tail" in Latin. The specific epithet honours Sauvage. The name Teinurosaurus was largely forgotten or not even understood to be a synonym of Caudocoelus, until in 1969 John Ostrom revealed its priority. Ostrom also pointed out that Nopcsa had not provided a specific name. In 1978 George Olshevsky was the first to combine the two names, making Teinurosaurus sauvagei (von Huene 1932) Olshevsky 1978 vide Nopcsa 1928 emend. 1929 a valid species name.The holotype, once having the inventory number MGB 500 but later lost, was a distal caudal vertebra, 152 millimetres long. The species was by von Huene considered a member of the Coeluridae but is now generally seen as a nomen dubium, Neotheropoda incertae sedis.

Timeline of troodontid research

This timeline of troodontid research is a chronological listing of events in the history of paleontology focused on the troodontids, a group of bird-like theropod dinosaurs including animals like Troodon. Troodontid remains were among the first dinosaur fossils to be reported from North America after paleontologists began performing research on the continent, specifically the genus Troodon itself. Since the type specimen of this genus was only a tooth and Troodon teeth are unusually similar to those of the unrelated thick-headed pachycephalosaurs, Troodon and its relatives would be embroiled in taxonomic confusion for over a century. Troodon was finally recognized as distinct from the pachycephalosaurs by Phil Currie in 1987. By that time many other species now recognized as troodontid had been discovered but had been classified in the family Saurornithoididae. Since these families were the same but the Troodontidae named first, it carries scientific legitimacy.Many milestones of troodontid research occurred between the description of Troodon and the resolution of their confusion with pachycephalosaurs. The family itself was named by Charles Whitney Gilmore in 1924. That same year Henry Fairfield Osborn named the genus Saurornithoides. In the 1960s and 1970s researchers like Russell and Hopson observed that troodontids had very large brains for their body size. Both attributed this enlargement of the brain to a need for processing the animal's especially sharp senses. Also in the 1970s, Barsbold described the new species Saurornithoides (now Zanabazar) junior and named the family Saurornithoidae, but as noted this was just a junior synonym of the Troodontidae in the first place.In the 1980s Gauthier classed them with the dromaeosaurids in the Deinonychosauria. That same decade Jack Horner reported the discovery of Troodon nests in Montana. Interest in the life history of Troodon continued in the 1990s with a study of its growth rates based on histological sections of fossils taken from a bonebed in Montana and the apparent pairing of eggs in Troodon nests. This decade also saw the first potential report of European troodontid remains, although this claim has been controversial. A single mysterious tooth from the Late Jurassic Morrison Formation of the United States was described as the oldest known troodontid remains, although this has also been controversial. In the 2000s, several new kinds of troodontid were named, like Byronosaurus and Sinovenator.

Troodon

Troodon ( TROH-ə-don; Troödon in older sources) is a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Cretaceous period (about 77 mya). It includes at least one species, Troodon formosus, known from Montana. Discovered in October 1855, T. formosus was among the first dinosaurs found in North America, although it was thought to be a lizard until 1877. Several well-known troodontid specimens from the Dinosaur Park Formation in Alberta were once believed to be members of this genus. However, recent analyses in 2017 have found the genus to be undiagnostic and referred some of these specimens to the genus Stenonychosaurus (long believed to be synonymous with Troodon) and others to the newly created genus Latenivenatrix.

The genus name is Greek for "wounding tooth", referring to the teeth, which were different from those of most other theropods known at the time of their discovery. The teeth bear prominent, apically oriented serrations. These "wounding" serrations, however, are morphometrically more similar to those of herbivorous reptiles, and suggest a possibly omnivorous diet.

Troodontidae

Troodontidae is a family of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and scrappy and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens (including specimens which preserve feathers, eggs, embryos, and complete juveniles), have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.

Troodontinae

Troodontinae is a subfamily of troodontid dinosaurs. The subfamily was first used in 2017 for the group of troodontids descended from the last common ancestor of Gobivenator mongoliensis and Zanabazar junior.

Urbacodon

Urbacodon ("URBAC tooth") is a genus of troodontid dinosaur, a type of small carnivore. It lived in Uzbekistan during the early Late Cretaceous Period, about 95 million years ago.

On 9 September 2004, a lower jaw of a small theropod was uncovered by Anton Sergeevich Rezwiy near Itemir in the IT-01 quarry.The type species, Urbacodon itemirensis, was named by Alexandr Averianov and Hans-Dieter Sues in 2007. The first part of the generic name Urbacodon is an acronym, honouring the Uzbek, Russian, British, American and Canadian scientists who participated in its discovery. This acronym was combined with a Greek ὀδών, odon, "tooth". The specific name refers to the provenance from Itemir.The name was based on the holotype ZIN PH 944/16, a single left dentary with preserved replacement teeth from the Cenomanian Dzharakuduk Formation. Averianov and Sues also identified teeth and other material, earlier described by Lev Nesov, as a Urbacodon sp. from the nearby Turonian Bissekty Formation.The holotype dentary of U. itemirensis is 79.2 millimetres long (3.12 in) and has 32 tooth positions. It is rather straight in top view. The teeth are closely packed but between the front twenty-four teeth and the rear eight teeth, a distinctive gap is present, a diastema. This is a unique trait but was not formally designated as an autapomorphy because it might be the result of individual variation. Urbacodon resembles Byronosaurus and Mei but differs from most other Troodontidae in that its teeth lack serrations. Urbacodon is distinguished from Byronosaurus by a less vascularized lateral dentary groove and more bulbous anterior tooth crowns, and from Mei by considerably larger size.Averianov and Sues viewed Urbacodon as more plesiomorphic than Troodon and Saurornithoides in having a straight dentary with fewer teeth, but did not attempt to place it on a cladogram. In 2010, a cladistic analysis showed it as a close relative of Byronosaurus and Xixiasaurus.

Zanabazar junior

Zanabazar is an extinct genus of troodontid theropod dinosaur from the Late Cretaceous of Mongolia. The genus was originally named by Rinchen Barsbold as a species of Saurornithoides, S. junior. In 2009 it was reclassified as its own genus, named after the first spiritual figurehead of Tibetan buddhism, Zanabazar. The holotype, GIN 100–1, includes a skull, vertebrae, and right hindlimb. Zanabazar was one of the most derived troodontids, and the second largest after Troodon.

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