Skeleton and life reconstruction of Edmontosaurus regalis
|Upper Cretaceous (late Campanium A and Maastrichtian )|
|approx. 73 to 66 million years|
|Lambe , 1917|
Edmontosaurus is a genus of ornithopod dinosaurs from the group of Hadrosauridae . She lived in the late Upper Cretaceous (late Campan A and Maastricht ) of North America. Edmontosaurus is one of the most common and best known genera of dinosaurs in both the United States and around the world.
The genus Edmontosaurus or its type Edmontosaurus regalis were described in 1917 by the Canadian paleontologist Lawrence Lambe on the basis of two skeletons with skulls that were discovered and collected in 1912 by the brothers George and Levi Sternberg on the Red Deer River in Alberta. The genus is named after the Edmonton Formation, the layers in which the finds were made (today designated as the Horseshoe Canyon Formation of the Edmonton Group). The Edmonton "formation" is again named after the capital of Alberta .
Edmontosaurus is a large hadrosaurid without any noticeable bony skull outgrowths. The length of the skull in adult individuals is more than a meter. With an estimated total length of a maximum of 13 meters and a maximum weight of 4 tons , Edmontosaurus was one of the largest representatives of the hadrosaurids.
The skull of Edmontosaurus has an elongated snout (rostrum) that is widened at the front end, typical of hadrosaurs, like a duck's bill. The "upper beak" is mainly formed by the premaxillary. The front (oral) edge of the premaxillary is "folded back" and forms a kind of bony "lip" ( reflected margin of premaxilla ). The rostrum is also characterized by a very large outer nostril , which is sunk into a hollow ( circumnarial fossa ). The size of the nostril is reminiscent of the pre-orbital window that many dinosaurs and geologically older archosaurs have (see → Triapsid skull ). However, the pre-orbital window, which is predominantly framed by the maxillary and lacrimal, is generally reduced in the “higher” ornithopods. The front half of the jaw is toothless, the rear half is equipped with a battery of up to 300 keeled teeth , of which only about 100 were ever actively used.
Edmontosaurus differs from other combless and hornless hadrosaurids with a large nostril in that the premaxillary lip is particularly pronounced and extends relatively far back on the lateral edges of the "beak". Another unique feature is that the circumnarial fossa is particularly deep in its lower posterior (caudoventral) part. A special characteristic is also a pocket-like hollow of the ventral branch of the postorbital B , which is involved in the posterior border of the eye socket, on the side facing the eye socket (English postorbital pocket ). The part of the prefrontal , which is involved in the border of the eye socket, has a similar pocket, but flatter . In addition, the front is involved in the outline of the eye socket.
The postcranial skeleton differs apart from its size, not significantly different from that of other Hadrosauriden or Iguanodontiden . So are u. a. the front limbs are shorter than the hind limbs and the three (weight-bearing) fingers or toes of the extremities end in hoof-like claws.
In some cases, specimens of Edmontosaurus show the preservation of soft tissues that are not normally passed down in fossil form (see below ). Therefore, a lot is known about the soft tissue anatomy of this genus. On the basis of one of these specimens, a fleshy crest (“ cockscomb ”) could be detected at least in Edmontosaurus regalis . Finds with two-dimensional, shadowy skin preservation show that in Edmontosaurus a segmented dorsal ridge ran along the spine, while other hadrosaurids had a continuous crest. The fingers or front toes could not be seen individually from the outside, but rather embedded in a kind of "flesh-and-skin mitt". This used to be interpreted as webbed feet. Today it is assumed that it is an adaptation that enabled the animal to better distribute its body weight on the ground.
Way of life
|Skeletal reconstruction of an Edmontosaurus annectens individual from the Hell Creek Formation of Montana in the Denver Museum of Nature and Science. The incomplete spinous process of one of the anterior caudal vertebrae (see marking) is interpreted as the result of a successfully warded off attack by a large theropod, probably Tyrannosaurus rex .|
Edmontosaurus might have had a similar way of life as it is assumed for other hadrosaurids. The tooth batteries show large chewing surfaces created by wear and tear and represent a convergent development to the flat molars of today's herbivorous mammals. They show that the food was chewed up by intensive chewing . C The food consisted of taller ground vegetation as well as leaves and needles from bushes and the lowest areas of the tree canopy. All Edmontosaurus finds come from sediments that, according to their special training ( facies ), were deposited in heavily forested areas of coastal lowlands or river deltas that are relatively close to the sea . D It cannot be ruled out that this indicates a lifestyle that is closely related to water.
As for most ornithopods , a predominant locomotion on four legs ( Quadrupedie ) is assumed for Edmontosaurus . Two-legged locomotion ( bipedia ) probably only took place in the event of an escape. The main predators of Edmontosaurus are large tyrannosaurids : Albertosaurus for the representatives in the late Campan and early Maastricht, Tyrannosaurus for the representatives in the late Maastricht.
With its comb- and hornless skull, the very broad beak and the large outer nostril, Edmontosaurus is a typical representative of the Hadrosaurinae, a subfamily that is traditionally kept within the Hadrosauridae family and is contrasted with the comb- or horn-bearing Lambeosaurinae . E.
Although Edward Lambe's naming of the genus Edmontosaurus in 1917 was still in a relatively early phase of North American dinosaur research, representatives of this genus - according to today's concept - were discovered as early as the late 19th century and described or mentioned under other names. The earliest documented find with taxonomic relevance is a skeleton from the "Laramie layers of Dakota" (today Hell Creek Formation ), which is described in detail by Edward Drinker Cope in 1883 F under the name Diclonius mirabilis . He actually assigns this material to the species Trachodon mirabilis described by Joseph Leidy in 1856 , but uses the generic name Diclonius G coined by him in 1876 on the assumption that Leidy had discarded the name Trachodon in the meantime. In 1892 Othniel Marsh published the description of a hadrosaurid from the "Laramie layers" of Wyoming (today Lance formation ), which he calls Claosaurus annectens . The genus Claosaurus had been built by himself two years earlier on the basis of a skeleton from the " Pteranodon layers" (today Smoky Hill Subformation, Upper Coniac to Lower Campan) of the Niobrara Formation of Kansas , which he built in 1872 under the Name " Hadrosaurus agilis " had described. In a revision of the previously known "trachodontids" (i.e. hadrosaurids) of North America, John Bell Hatcher noted in 1901 due to the relatively large geographical and stratigraphic distance between the "Pteranodon layers" of Kansas and the "Laramie layers" of Wyoming and South Dakota the species Claosaurus annectens in Leidy's genus Trachodon . He does the same with Cope's “ Diclonius mirabilis ”. In 1913, four years before Edmontosaurus regalis was first described , Lambe published an article on the fore-extremity of a hadrosaurid from the same area in which the type material of E. regalis was also collected. A comparison of the teeth leads Lambe - with reservations - to assign this find to the species Trachodon marginatus, which he described in 1902 . Eleven years later, Charles Whitney Gilmore describes a new species based on the same specimen under the name Thespesius edmontoni , the genus Thespesius being established by Leidy as early as 1856. In 1926 Charles M. Sternberg , the brother of the two discoverers of the type material of E. regalis , described the youngest type material of an “Edmontosaur” under the name Thespesius saskatchewanensis from the “Lance Formation” (today Frenchman Formation) of Saskatchewan .
In a comprehensive revision of the North American hadrosaurids, published in 1942 by Richard Swann Lull and Nelda E. Wright, five species of the Hadrosaurinae are placed in the specially established genus Anatosaurus , including Claosaurus annectens as a type and Thespesius edmontoni and Thespesius saskatchewanensis . They also assign Cope's “ Diclonius mirabilis ” to Anatosaurus . However, based on the relatively large stratigraphic distance between Leidy's original finds of Trachodon mirabilis (“ Judith River formation ”) and the material described by Cope from the “Laramie layers”, the two are not the same species can act. Consequently, they found the new species Anatosaurus copei on Cope's "Laramie" material . Edmontosaurus remains monotypical for the time being .
After Lull and Wright (1942) established a relatively strong similarity between the Anatosaurus species and Edmontosaurus regalis , the Soviet paleontologist Anatoli Konstantinowitsch Roshdestwenski went one step further in 1968 in a review of Kazakh hadrosaurids and declared Anatosaurus to be a younger synonym for Edmontosaurus .
In a revision of the Hadrosauridae in 1989, Michael Brett-Surman agrees with Roshdestwenski's synonymization and also reduces the number of Edmontosaurus species to one: E. annectens . He only differentiates between two differently sized morphotypes (regalis and annectens, with regalis as the larger), which in his opinion could be an expression of a sexual dimorphism . For " Anatosaurus " COPEI built it but the new genus Anatotitan , which he called "the pinnacle of evolution of Hadrosaurinae" H respectively. Furthermore, the genera Thespesius and Trachodon are declared to be nomina dubia , a view that is now generally accepted.
In the chapters on the hadrosaurids of the two editions of the compendium The Dinosauria , the synonymy between Anatosaurus and Edmontosaurus is confirmed. However, three Edmontosaurus species are distinguished: Edmontosaurus regalis , E. annectens (including “ Thespesius edmontoni ”) and E. saskatchewanensis . In the first edition (1990) Anatotitan copei is listed as an independent taxon, but in the second edition (2004) it is used as a synonym for E. annectens .
In 2011, Nicolás Campione and David Evans finally found, as a result of a morphometric analysis, that only two Edmontosaurus species can be distinguished in the late Upper Cretaceous North America : Edmontosaurus regalis and E. annectens . “ Anatotitan copei ” is therefore within the variation spectrum of E. annectens and represents the oldest and largest individuals of this species. In addition, “ Thespesius edmontoni ” lies within the variation spectrum of E. regalis and is therefore not a synonym for E. annectens , as postulated by other authors.
Remains of a Hadrosaurid from the Liscomb Bonebed (late Campan / early Maastricht) of the Prince Creek Formation in northern Alaska, initially known as Edmontosaurus sp. were classified as the new genus and species Ugrunaaluk kuukpikensis were described in 2015 , with other authors sticking to the original classification.
According to the latest revision, the genus Edmontosaurus contains two species:
Edmontosaurus regalis Lambe , 1917 (generotype), late Campan A from Alberta
- syn. Thespesius edmontoni Gilmore , 1924
- syn. Anatosaurus edmontoni ( Gilmore , 1924)
- syn. Anatosaurus edmontonensis ( Gilmore , 1924)
Edmontosaurus annectens ( Marsh , 1892), Maastricht from Montana , North Dakota , South Dakota , Wyoming , Alberta and Saskatchewan
- syn. Claosaurus annectens Marsh , 1892
- syn. Trachodon annectens ( Marsh , 1892)
- syn. Anatosaurus annectens ( Marsh , 1892)
- syn. Thespesius saskatchewanensis C. M. Sternberg , 1926
- syn. Anatosaurus saskatchewanensis ( CM Sternberg , 1926)
- syn. Edmontosaurus saskatchewanensis ( CM Sternberg , 1926)
- syn. " Diclonius mirabilis " sensu Cope , 1883
- syn. Anatosaurus copei Lull & Wright , 1942
- syn. Anatotitan copei ( Lull & Wright , 1942)
E. regalis is particularly characterized by a particularly wide, “swollen” -looking premaxillary lip (cf. characteristics of the genus ) and an anterior part of the nasal that extends downwards (ventrad). Furthermore, the front part of the snout, between the tip of the snout and the front end of the nostril, is shorter than that of E. annectens . Also, unlike in E. annectens , the rear upper (caudodorsal) part of the circumnarial fossa is particularly pronounced and protrudes upwards (dorsad) beyond the back of the snout. Another specialty of E. regalis is the more pronounced "postorbital pocket", with a horizontal, cornice-like contact surface of the dorsal branch of the Jugale for the ventral branch of the postorbital.
Edmontosaurus is one of the few dinosaurs from which not only bones are known, but also to a large extent fossilized soft tissues, up to more or less completely and three-dimensionally preserved individuals. The latter form of conservation is commonly referred to as “mummy”, but unlike real mummies, it is not really a matter of preserved organic material. In some of the “mummies” the soft tissue has been replaced by sediment. The sediment that surrounded the buried dead dinosaur, preferably fine-grain sand , initially formed the surface of the skin as a negative imprint. The metabolic activity of decomposing bacteria or the resulting mineralization stabilized this sediment in the immediate vicinity of the decaying carcass. The increasingly crumbling carcass could leave a cavity in the sand that had solidified in this way. Subsequently, loose sand penetrated this cavity and filled it in, including the skin marks in its walls. In other "mummies" the soft tissue itself has apparently been mineralized down to the cellular level.
The type specimen of “ Diclonius mirabilis ” is said to have shown large areas of “skin impressions”, which, however, were destroyed during the excavation work. A relatively complete "mummy" of Edmontosaurus was first recovered from the Lance Formation in Wyoming in 1908. Henry Fairfield Osborn published a detailed description of this so-called Trachodon mummy in 1912 . As early as 1910, a second "mummy" was excavated in Wyoming and then acquired by the Senckenberg Natural Research Society . She is still part of the exhibition in her museum in Frankfurt am Main (see → Edmontosaurus mummy in the Senckenberg Nature Museum ).
In 1999, an almost completely preserved "mummy" was discovered in the Hell Creek Formation in the Badlands in the southwest of North Dakota , which probably belongs to a member of the genus Edmontosaurus (classified in the first scientific publication as cf. Edmontosaurus sp. ), and baptized “Dakota”. It is one of the most fully preserved dinosaur finds ever. The analysis of the unique find by means of computed tomography led to preliminary new findings regarding the muscle mass and the calculation of the length of dinosaurs in general and gave rise to new hypotheses about skin texture and color.
Although it is relatively incomplete and only consists of an incomplete head, a neck and a small back, a mummy from the Wapiti formation (late Campan / early Maastricht) of Alberta, which is assigned to the species Edmontosaurus regalis , caused quite a stir : The upper rear skull-roof has a dome-like structure, which is interpreted as the remnant of a fleshy crest, roughly comparable to a cockscomb . It is the first such evidence of a non-avian dinosaur. Head appendages in hadrosaurids have been known for a long time, especially and in considerable size among representatives of the lambeosaurinae , but these are all bony cranial outgrowths.
- A.With regard to the stratigraphic position of the oldest finds or rather their horizons, especially the lower Horseshoe Canyon Formation , there are different information in the literature. In more recent work, the lower Horseshoe Canyon formation is often placed in the youngest Campan, with the editors drawing the Campan-Maastricht boundary at 70.6 mya . Accordingly, the geologically oldest finds of Edmontosaurus also fell in the campan. According to the current international time scale, however, the limit is 72.1 mya and thus the Horseshoe Canyon formation is almost entirely in Maastricht.
- C.For an animation of the reconstructed chewing movement of Edmontosaurus - exemplarily for all hadrosaurids - see Rybczynski et al. (2008).
- E. For a detailed consideration of the taxonomic history and the various structural concepts of the Hadrosauridae in pre-cladistic and cladistic times see Prieto-Marquez (2008).
- F.In fact, as early as 1871 and 1874, Cope named the species Trachodon atavus from New Jersey and Agathaumas milo from Colorado, which were identified by Weishampel & Horner (1990) and Horner et al. (2004) are listed as synonyms of Edmontosaurus regalis , but these are very incomplete, little-known pieces.
- H "The epitome of hadrosaurine evolution"
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