Misplaced Pages

#487512

49-568: The Nugget Sandstone is a Late Triassic to Early Jurassic geologic formation that outcrops in Colorado, Idaho, Wyoming, and Utah, western United States . In Wyoming, it is composed of a lower hematite-stained siltstone and thin-bedded sandstone. The upper part is a salmon-pink and light-gray, fine- to medium-grained cliff-forming sandstone that exhibits massive bedding to large scale cross-beds of dunes. Thickness ranges up to 86.9 m (285 feet). Fossil theropod tracks have been reported from

98-420: A different phylogeny with a monophyletic Rauisuchia. The group may even be something of a " wastebasket taxon ". Determining exact phylogenetic relationships is difficult because of the scrappy nature of a lot of the material. However, further discoveries and studies, such as a study on the braincase of Batrachotomus (2002) and restudies of other forms, such as Erpetosuchus (2002) have shed some light on

147-432: A giant landmass known as Pangea, which covered about a quarter of Earth's surface. Towards the end of the period, continental drift occurred which separated Pangea. At this time, polar ice was not present because of the large differences between the equator and the poles. A single, large landmass similar to Pangea would be expected to have extreme seasons; however, evidence offers contradictions. Evidence suggests that there

196-649: A large number of non-"rauisuchian" taxa as controls. Well-known "rauisuchians" include Ticinosuchus of the Middle Triassic of Switzerland and Northern Italy, Saurosuchus of the Late Triassic (late Carnian ) of Argentina, Prestosuchus of the Middle-Late Triassic (late Ladinian-early Carnian) of Brazil, and Postosuchus of the Late Triassic ( Norian ) of the southwest United States. The first "rauisuchian" known to paleontology

245-574: A modern approach to taxonomy based on clades (nested monophyletic groups of common ancestry). Since the early 2010s, archosaur classification schemes have stabilized on a system where Rauisuchia is rendered an evolutionary grade , or even a wastebin taxon . Crocodylomorphs most likely originated from a rauisuchian ancestor based on a myriad of shared traits, and some "rauisuchians" (such as Postosuchus and Rauisuchus ) appear to be more closely related to crocodylomorphs than to other "rauisuchians" (such as Prestosuchus and Saurosuchus ). As

294-423: A more thorough test of archosaurian relationships published in 2011 by Sterling Nesbitt, "rauisuchians" were found to be paraphyletic, with Poposauroidea at the base of the clade Paracrocodylomorpha , and the rest of the "rauisuchians" forming a grade within the clade Loricata . Nesbitt noted that no previous study of "rauisuchian" relationships had ever included a wide variety of supposed "rauisuchians" as well as

343-553: A natural group remains unresolved. Brusatte et al. (2010) was one of the last studies to find a monophyletic Rauisuchia clade. Below is the cladogram from Brusatte et al. (2010): Arganasuchus Fasolasuchus Stagonosuchus Ticinosuchus Saurosuchus Batrachotomus Prestosuchus Tikisuchus Rauisuchus Postosuchus Teratosaurus Yarasuchus Qianosuchus Arizonasaurus Bromsgroveia Lotosaurus Poposaurus Sillosuchus Effigia Shuvosaurus In

392-479: A pillar-erect hip posture, though exceptions exist for all of these traits. Rauisuchians, as a traditional taxonomic group, were considered distinct from other Triassic archosaur groups such as early dinosaurs, phytosaurs (crocodile-like carnivores), aetosaurs (armored herbivores), and crocodylomorphs (lightly-built crocodilian ancestors). However, more recent studies on archosaur evolution have upended this idea based on phylogenetic analyses and cladistics ,

441-425: A result, Rauisuchia in its traditional usage may be considered paraphyletic : a group which is defined by shared ancestry but also excludes a descendant taxon (in this case, crocodylomorphs). To designate it as an informal group in scientific literature, the name is often enclosed in quotation marks. Several monophyletic groups have been erected to classify "rauisuchians" in a cladistic framework. The closest concept

490-546: A type of large scale volcanic activity that releases a huge volume of lava in addition to sulfur dioxide and carbon dioxide. The sudden increase in carbon dioxide levels is believed to have enhanced the greenhouse effect , which acidified the oceans and raised average air temperature. As a result of the change in biological conditions in the oceans, 22% of marine families became extinct. In addition, 53% of marine genera and about 76–86% of all species became extinct, which vacated ecological niches; thus, enabling dinosaurs to become

539-463: Is a paraphyletic group of mostly large and carnivorous Triassic archosaurs . Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia , which encompasses all archosaurs more closely related to crocodilians than to birds and other dinosaurs . First named in the 1940s, Rauisuchia was a name exclusive to Triassic archosaurs which were generally large (often 4 to 6 metres (13 to 20 ft)), carnivorous, and quadrupedal with

SECTION 10

#1732791139488

588-590: Is absent in Group Y. "Group Y" is now termed Shuvosauridae . Although not placed within Group Y, Lotosaurus shares many similarities with members of the clade, foremost of which is edentulous , or toothless, jaws. Edentulism is also seen in Shuvosaurus and Effigia , which have beak-like jaws. Nesbitt suggested that the derived characters of Lotosaurus may indicate that it is a transitional form between basal members of Group X and members of Group Y. Below

637-470: Is arid climate as well as proof of strong precipitation. The planet's atmosphere and temperature components were mainly warm and dry, with other seasonal changes in certain ranges. The Middle Triassic was known to have consistent intervals of high levels of humidity. The circulation and movement of these humidity patterns, geographically, are not known however. The major Carnian Pluvial Event stands as one focus point of many studies. Different hypotheses of

686-525: Is associated with this impact. The Rhaetian Age was the final age of the Late Triassic, following the Norian Age, and it included the last major disruption of life until the end-Cretaceous mass extinction . This age of the Triassic is known for its extinction of marine reptiles , such as nothosaurs and shastasaurs with the ichthyosaurs , similar to today's dolphin . This age was concluded with

735-476: Is described as semiarid. Semiarid is characterized by light rainfall, having up to 10–20 inches of precipitation a year. The epoch had a fluctuating, warm climate in which it was occasionally marked by instances of powerful heat. Different basins in certain areas of Europe provided evidence of the emergence of the "Middle Carnian Pluvial Event." For example, the Western Tethys and German Basin was defined by

784-423: Is diagnosed by the presence of four or more sacral vertebrae with fully fused neural arches , which is also seen in theropod dinosaurs (a case of evolutionary convergence ). In addition, the cervical vertebrae that make up the neck are strongly amphicoelus , meaning that they are concave at both ends. The fourth trochanter , a ridge of bone on the femur for muscle attachment seen in nearly all archosaurs,

833-636: Is neither the earliest-branching archosaur nor "rauisuchian" despite its early age, and its presence in the Early Triassic suggests that other archosaur fossils are simply undiscovered from that time. The last known "rauisuchians", excluding their descendants the crocodylomorphs, are from the latter part of the Late Triassic. The shuvosaurid Effigia , from the "siltstone member" of the Chinle Formation in New Mexico , may be as young as

882-586: Is set at the first appearance of an ammonite, Daxatina canadensis . In the 1990s, conodonts became increasingly important in the Triassic timescale, and the base of the Rhaetian is now set at the first appearance of a conodont, Misikella posthernsteini . As of 2010 , the base of the Norian has not yet been established, but will likely be based on conodonts. The late Triassic is also divided into land-vertebrate faunachrons . These are, from oldest to youngest,

931-599: Is the cladogram from Nesbitt (2007): Postosuchus Rauisuchus Arizonasaurus Lotosaurus Sillosuchus Shuvosaurus Effigia In their phylogenetic study of archosaurs, Brusatte et al. (2010) found only weak support for Rauisuchia as a monophyletic grouping. As a result of their analysis, two clades were found to be within Rauisuchia, which they named Rauisuchoidea and Poposauroidea. Rauisuchoidea included Rauisuchidae and Prestosuchidae, as well as several basal taxa that were once assigned to

980-438: Is the clade Paracrocodylomorpha , which includes most "rauisuchian" taxa and their crocodylomorph descendants. Paracrocodylomorpha is divided into two branches: Poposauroidea , which includes a variety of strange "rauisuchians" (some of which were bipedal and/or herbivorous) and Loricata , which includes most typical "rauisuchians" and crocodylomorphs. "Rauisuchians" had an erect gait with their legs oriented vertically beneath

1029-608: The Berdyankian , Otischalkian , Adamanian , Revueltian and Apachean . Following the Permian–Triassic extinction event , surviving organisms diversified. On land, archosauriforms , most notably the dinosaurs became an important faunal component in the Late Triassic. Likewise, bony fishes diversified in aquatic environments, most notably the Neopterygii , to which nearly all extant species of fish belong. Among

SECTION 20

#1732791139488

1078-567: The Olenekian of Russia) that are too primitive and/or poorly known to fit in any of these groups. There has been considerable suggestion that the group as currently defined is paraphyletic , representing a number of related lineages independently evolving and filling the same ecological niche of medium to top terrestrial predator. For example, Parrish (1993) and Juul (1994) considered poposaurid rauisuchians to be more closely related to Crocodilia than to prestosuchids. Nesbitt (2003) presented

1127-668: The Rhaetian , the last stage of the Triassic. Effigia was recovered from the Coelophysis Quarry of Ghost Ranch . The same site also preserves a large undescribed archosaur, CM 73372, which seemingly represents a transitional form between "rauisuchians" and crocodylomorphs. Indeterminate large paracrocodylomorph material from the Lower Elliot Formation of South Africa may be even younger, late Rhaetian or possibly even lowermost Jurassic. The following

1176-520: The geologic time scale , the Late Triassic is usually divided into the Carnian, Norian, and Rhaetian ages, and the corresponding rocks are referred to as the Carnian, Norian, and Rhaetian stages. Triassic chronostratigraphy was originally based on ammonite fossils, beginning with the work of Edmund von Mojsisovics in the 1860s. The base of the Late Triassic (which is also the base of the Carnian)

1225-539: The pelvis , including fully fused sacral vertebrae and a long, thin crest on the ilium called the supra- acetabular crest. Additionally, many members of Group X have smooth frontal and nasal bones , which make up the upper portion of the rostrum . In other "rauisuchians" and many other crurotarsans, this area has bumps and ridges. "Group X" is now termed Poposauroidea . Nesbitt later erected another clade, "Group Y", in 2007. Group Y falls within Group X to include Sillosuchus , Shuvosaurus , and Effigia . Group Y

1274-634: The Late Triassic Epoch did not prove to be as destructive as the preceding Permian Period, which took place approximately 50 million years earlier and destroyed about 70% of land species, 57% of insect families as well as 95% of marine life , it resulted in great decreases in population sizes of many living organism populations. The environment of the Late Triassic had negative effects on the conodonts and ammonoid groups. These groups once served as vital index fossils , which made it possible to identify feasible life span to multiple strata of

1323-503: The Triassic strata. These groups were severely affected during the epoch, and conodonts became extinct soon after (in the earliest Jurassic). Despite the large populations that withered away with the coming of the Late Triassic, many families, such as the pterosaurs , crocodiles , mammals and fish were very minimally affected. However, such families as the bivalves, gastropods , marine reptiles and brachiopods were greatly affected and many species became extinct during this time. Most of

1372-545: The Triassic. The end of the Triassic also brought about the decline of corals and reef builders during what is called a "reef gap". The changes in sea levels brought this decline upon corals, particularly the calcisponges and scleractinian corals. However, some corals would make a resurgence during the Jurassic Period. 17 brachiopod species were also wiped out by the end of the Triassic. Furthermore, conulariids became extinct. Rauisuchians " Rauisuchia "

1421-542: The Triassic. Along with many other large archosaurs, the group died out in the Triassic-Jurassic extinction event (barring crocodylomorphs, which survive to the present in the form of crocodilians). After their extinction, theropod dinosaurs were able to emerge as the sole large terrestrial predators, though there is still some debate over how the extinction influenced dinosaur evolution. The footprints of meat-eating dinosaurs may have suddenly increased in size at

1470-443: The body rather than sprawling outward. This type of gait is also seen in dinosaurs, but evolved independently in the two groups. In dinosaurs, the hip socket faces outward and the femur (thigh bone) connects to the side of the hip; while in rauisuchians, the hip socket faces downward to form a shelf of bone under which the femur connects. This has been referred to as the pillar-erect posture. "Rauisuchians" lived throughout most of

1519-537: The description of Ticinosuchus in the 1960s. The oldest known "rauisuchians", in terms of geological age, are probably from the end of the Early Triassic (late Olenekian ). Most of these early fossils are fragmentary and dubious remains from Russia, but some are better-described and constrained, such as Xilousuchus , a ctenosauriscid from the Heshanggou Formation of China. Xilousuchus

Nugget Sandstone - Misplaced Pages Continue

1568-461: The dinosaurs gradually began to displace. The emergence of the first dinosaurs came at about the same time as the Carnian pluvial episode , at 234 to 232 Ma. This was a humid interval in the generally arid Triassic. It was marked by high extinction rates in marine organisms, but may have opened niches for the radiation of the dinosaurs. The Norian is the second age of the Late Triassic, covering

1617-524: The disappearance of many species that removed types of plankton from the ocean, as well as some organisms known for reef -building, and the pelagic conodonts . In addition to these species that became extinct, the straight-shelled nautiloids , placodonts , bivalves , and many types of reptile did not survive through this age. During the beginning of the Triassic Period, the Earth consisted of

1666-465: The dominant presence in the Jurassic Period. While the majority of the scientists agree that volcanic activity was the main cause of the extinction, other theories suggest the extinction was triggered by the impact of an asteroid, climate change, or rising sea levels . The impacts that the Late Triassic had on surrounding environments and organisms were wildfire destruction of habitats and prevention of photosynthesis. Climatic cooling also occurred due to

1715-519: The events occurrence include eruptions, monsoonal effects, and changes caused by plate tectonics. Continental deposits also support certain ideas relative to the Triassic Period. Sediments that include red beds, which are sandstones and shales of color, may suggest seasonal precipitation. Rocks also included dinosaur tracks, mudcracks, and fossils of crustaceans and fish, which provide climate evidence, since animals and plants can only live during periods of which they can survive through. The Late Triassic

1764-588: The evidence suggests the increase of volcanic activity was the main cause of the extinction. As a result of the rifting of the super continent Pangea , there was an increase in widespread volcanic activity which released large amounts of carbon dioxide. At the end of the Triassic Period, massive eruptions occurred along the rift zone , known as the Central Atlantic Magmatic Province , for about 500,000 years. These intense eruptions were classified as flood basalt eruptions, which are

1813-524: The evolutionary relationships of this poorly known group. Despite its inclusion as an informal grouping in numerous phylogenetic studies, "Rauisuchia" has never received a formal definition. Most analyses in the past decade have found "Rauisuchia" to be a paraphyletic grouping, including all studies with a large sample size. Those that found the possibility that it was a natural group produced only weak support for this hypothesis. In his large 2011 analysis of archosaurian relationships, Nesbitt recommended that

1862-399: The families, including Fasolasuchus and Ticinosuchus . Poposauroidea included poposaurids and ctenosauriscids, but the phylogeny had a large polytomy of genera in both groups that was difficult to resolve, which included Arizonasaurus , Poposaurus , and Sillosuchus . However, the characters linking these two groups were weak, and the question as to whether or not "Rauisuchia" forms

1911-425: The formation. Intermediate theropod, sphenosuchian, drepanosaurid and sphenodontian remains are known. Late Triassic Many of the first dinosaurs evolved during the Late Triassic, including Plateosaurus , Coelophysis , Herrerasaurus , and Eoraptor . The Triassic–Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth. The Triassic

1960-417: The genus Rauisuchus , which was named after fossil collector Dr. Wilhelm Rau . The name Rauisuchus means Wilhelm Rau's crocodile. "Rauisuchians" were originally thought to be related to erythrosuchids , but it is now known that they are pseudosuchians . Three families have historically been recognised: Prestosuchidae , Rauisuchidae , and Poposauridae , as well as a number of forms (e.g. those from

2009-527: The neopterygians, stem-group teleosts and the now extinct Pycnodontiformes became more abundant in the Late Triassic. The Carnian is the first age of the Late Triassic, covering the time interval from 237 to 227 million years ago. The earliest true dinosaurs likely appeared during the Carnian and rapidly diversified. They emerged in a world dominated by crurotarsan archosaurs (ancestors of crocodiles ), predatory phytosaurs , herbivorous armored aetosaurs , and giant carnivorous rauisuchians , which

Nugget Sandstone - Misplaced Pages Continue

2058-514: The satisfactory clarification of facts and common conceptions on the Late Triassic. Conclusions summarized that the correlation of these sediments led to the modified version of the new map of Central Eastern Pangea, as well as that the sediment's relation to the "Carnian Pluvial Event" is greater than expected. The extinction event that began during the Late Triassic resulted in the disappearance of about 76% of all terrestrial and marine life species, as well as almost 20% of taxonomic families. Although

2107-482: The soot in the atmosphere. Studies also show that 103 families of marine invertebrates became extinct at the end of the Triassic, but another 175 families lived on into the Jurassic. Marine and extant species were hit fairly hard by extinctions during this epoch. Almost 20% of 300 extant families became extinct; bivalves, cephalopods, and brachiopods suffered greatly. 92% of bivalves were wiped out episodically throughout

2156-487: The start of the Jurassic , when rauisuchians were absent. However, the apparent increase in dinosaur footprint size has instead been argued to be a result of increasing abundance of large theropods, rather than an abrupt acquisition of large size. Some "rauisuchians" may have existed in the very early Jurassic based on bone fragments from South Africa, but this identification is tentative. The name "Rauisuchia" comes from

2205-432: The term "Rauisuchia" be abandoned. In a study of the ctenosauriscid Arizonasaurus , paleontologist Sterling Nesbitt defined a clade of rauisuchians called "Group X". This group includes Arizonasuchus , Lotosaurus , Sillosuchus , Shuvosaurus , and Effigia . One distinguishing feature of Group X is their lack of osteoderms, which are common among many other crurotarsans . Many more features are found in

2254-502: The theory of a middle Carnian wet climate phase. This event stands as the most distinctive climate change within the Triassic Period. Propositions for its cause include: Theories and concepts are supported universally, due to extensive areal proof of Carnian siliciclastic sediments. The physical positions as well as comparisons of that location to surrounding sediments and layers stood as basis for recording data. Multiple resourced and recurring patterns in results of evaluations allowed for

2303-525: The time interval from about 227 to 208.5 million years ago. During this age, herbiverous sauropodomorphs diversified and began to displace the large herbivorous therapsids , perhaps because they were better able to adapt to the increasingly arid climate. However crurotarsans continued to occupy more ecological niches than dinosaurs. In the oceans, neopterygian fish proliferated at the expense of ceratitid ammonites. The Manicouagan impact event occurred 214 million years ago. However, no extinction event

2352-514: Was Teratosaurus , a German genus from the Late Triassic (Norian) of Germany. However, Teratosaurus was considered an early theropod dinosaur for much of its history, before it was demonstrated to be non-dinosaurian in the 1980s. The concept of "rauisuchians" as a distinct group of reptiles distantly related to crocodiles was recognized by discoveries in Brazil in the 1940s (particularly Prestosuchus and Rauisuchus ) and emphasized further by

2401-405: Was named in 1834 by Friedrich von Alberti , after a succession of three distinct rock layers (Greek triás meaning 'triad') that are widespread in southern Germany : the lower Buntsandstein (colourful sandstone ) , the middle Muschelkalk (shell-bearing limestone) and the upper Keuper (coloured clay). The Late Triassic Series corresponds approximately to the middle and upper Keuper. On

#487512