The early 20th century saw such a boom in hadrosaur discoveries and research that paleontologists' knowledge of these dinosaurs "increased by virtually an order of magnitude" according to a 2004 review by Horner, Weishampel, and Forster. This period is known as the great North American Dinosaur rush because of the research and excavation efforts of paleontologists like Brown, Gilmore, Lambe, Parks, and the Sternbergs. Major discoveries included the variety of cranial ornamentation among hadrosaurs as scientist came to characterize uncrested, solid crested, and hollow crested species.[2] Notable new taxa included Saurolophus, Corythosaurus, Edmontosaurus, and Lambeosaurus.[3] In 1942Richard Swann Lull and Wright published what Horner, Weishampel, and Forster characterized as the "first important synthesis of hadrosaurid anatomy and phylogeny".[2]
More recent discoveries include gigantic hadrosaurs like Shantungosaurus giganteus from China.[4] At 15 meters in length and nearly 16 metric tons in weight it is the largest known hadrosaur and is known from a nearly complete skeleton.[5]
Hadrosaur research has continued to remain active even into the new millennium. In 2000, Horner and others found that hatchling Maiasaura grew to adult body sizes at a rate more like a mammal's than a reptile. That same year, Case and others reported the discovery of hadrosaur bones in Vega Island, Antarctica. After decades of such dedicated research, hadrosaurs have become one of the best understood group of dinosaurs.[2]
Joseph Leidy described the new genus and species Thespesius occidentalis. He also described the new genus and species Trachodon mirabilis.[1] Although both species were based on poorly preserved material, this paper was the first to be published on hadrosaurid dinosaurs.
Leidy collaborated with artist Benjamin Waterhouse Hawkins to mount Hadrosaurus foulkii for the Academy of Natural Sciences of Philadelphia. This became both the first mounted dinosaur skeleton ever mounted for public display and also one of the most popular exhibits in the history of the academy. Estimates have the Hadrosaurus exhibit as increasing the number of visitors by up to 50%.[8]
Cutler excavated a juvenile Gryposaurus now catalogued by the Canadian Museum of Nature as CMN 8784. The site of the excavation has since been designated "quarry 252".[13]
Winter: Cutler partly prepared the young Gryposaurus specimen, possibly in Calgary while working on dinosaurs for Euston Sisely.[13]
Charles H. Sternberg's crew excavated a Corythosaurus from quarry 243 in Dinosaur Provincial Park, Alberta, Canada. The specimen would later be displayed at the Calgary Zoo.[14]
Matthew observed that fossils of hadrosaur eggs and hatchlings were absent in coastal areas and suggested that hadrosaurs may have preferred nesting grounds further inland. He believed that these inland nesting grounds were actually where hadrosaurs first evolved and therefore to breed, hadrosaurs retraced their ancestors route back to their place of origin. After hatching, the young hadrosaurs would spend some time inland maturing before migrating out to more coastal areas.[15]
Abel argued that the plant material Krausel argues was the fossilized remains of the gut contents of an Edmontosaurus annectens was actually deposited by flowing water.[7]
Ostrom supported Krausel's 1922 claim that fossil plant material found associated with an Edmontosaurus annectens mummy was actually its gut contents.[7]
Russel and Chamney studied distribution of hadrosaur in Maastrichtian North America. The concluded that Edmontosaurus regalis lived near the coasts while Hypacrosaurus altispinus and Saurolophus osborni lived slightly more inland.[15]
Galton argued that the anatomy of the hadrosaur pelvis was more consistent with a horizontal posture like that seen in modern flightless birds than with the "kangaroo" posture they were often reconstructed in.[7]
Brett-Surman was unable to determine where hadrosaurs first evolved.[15]
Horner and Makela described the new genus and species Maiasaura peeblesorum.[6] They argued that hadrosaurs cared for their young for an extended period after hatching.[16]
Horner argued that hadrosaur fossils found in marine deposited were simply the preserved remains of individuals that had washed out to sea from a terrestrial place of origin.[7]
Carpenter disputed the idea that hadrosaurs only nested in upland environments, instead arguing that fossil hadrosaur eggs and hatchlings were only absent from coastal deposits because the chemistry of the ancient soils were simply too acidic to preserve them.[7]
Thulborn argued that hadrosaurs may have been able to run at speeds of up to 14–20 km/h for sustained periods.[7]
Milner and Norman argued that hadrosaurs evolved in Asia.[15]
Horner observed that fossil eggs and hadrosaur hatchlings were common in sediments deposited in the upper regions of what were once coastal plains.[15]
Weishampel described hadrosaur chewing and cranial kinetics.[7]
Norman described hadrosaur chewing and cranial kinetics.[7]
Weishampel argued that hadrosaurs fed mainly on vegetation of 2 m in height or less but had a maximum browsing height of 4 m.[7]
Horner observed that fossil eggs and hadrosaur hatchlings were common in sediments deposited in the upper regions of what were once coastal plains.[15]
Farlow argued that their highly developed chewing abilities and large gut volumes meant hadrosaurs werehighly adapted to feeding on nutrient poor, fibrous vegetation.[7]
Brett-Surman described the new genus Anatotitan for Anatosaurus copei.
Horner argued that the hadrosaurids were not a natural group, and instead that the two major groups of hadrosaurs, the generally uncrested hadrosaurines and the crested lambeosaurs had separate origins within the Iguanodontia. Horner thought that the uncrested hadrosaurs were descended from a relative of Iguanodon, while the crested lambeosaurs were descended from a relative of Ouranosaurus. However, this proposal would find no support in any subsequent research publication.[10]
Weishampel and Horner found the Hadrosauridae to be a natural group after all.[10] They also found cladistic support for the traditional division of Hadrosauridae into the subfamilies Hadrosaurinae and Lambeosaurinae.[10]
Weishampel reported the presence of hadrosaurs on the Antarctic peninsula.[15][clarification needed]
Weishampel, Norman, and Griogescu named the clade Euhadrosauria.[11]
Weishampel and others proposed a node-based definition for the Hadrosauridae: the descendants of the most recent common ancestor shared by Telmatosaurus and Parasaurolophus.[17] They found the hadrosaurs to be a natural group, contrary to Horner's 1990 arguments that the hadrosaur subfamilies were descended from different kinds of iguanodont.[10] They also found cladistic support for the traditional division of Hadrosauridae into the subfamilies Hadrosaurinae and Lambeosaurinae.[10]
Clouse and Horner reported the presence of hadrosaur egg, embryo and hatchling fossils from the Judith River Formation of Montana. Since these sediments were deposited in a low-lying coastal plain, the researchers' discovery contradicted previous hypotheses that hadrosaurs either didn't nest in lowland areas or that local ancient soil was too acidic to preserve them.[7]
Chin and Gill described Maiasaura peeblesorumcoprolites from an ancient nesting ground of that species. The coprolites were "blocky", irregularly-shaped masses that preserved plant fragments. The researchers identified it as feces because the masses contained fossilized dung beetle burrows. The plant material suggested a diet consisting mainly of conifer stems.[7]
Forster found the hadrosaurs to be a natural group, contrary to Horner's 1990 arguments that the hadrosaur subfamilies were descended from different kinds of iguanodont.[10] They also found cladistic support for the traditional division of Hadrosauridae into the subfamilies Hadrosaurinae and Lambeosaurinae.[10] She preferred to define the Hadrosauridae as the most recent common ancestor of the hadrosaurines and lambeosaurines and all of its descendants. Unlike the definition used by Weishampel and others in 1993, this definition excluded Telmatosaurus.[18]
Sereno found the hadrosaurs to be a natural group, contrary to Horner's 1990 arguments that the hadrosaur subfamilies were descended from different kinds of iguanodont.[10]
Case and others reported the presence of hadrosaurs on the Antarctica peninsula.[2] The remains studied were found on Vega Island and represent the southernmost known hadrosaur fossils. When the animals were still alive, this site was probably at a latitude of about 65 degrees South.[15]
Horner and others studied the histology of Maiasaura peeblesorum bones. They found that Maiasaura only took 8–10 years to reach adult body size. A 7 metres (23 ft) adult Maiasaura could have an adult body mass of over 2,000 kilograms (4,400 lb) despite hatching at a length of about half a meter and with a body mass of less than a kilogram. This disparity implies a rate or growth similar to those found in modern mammals.[7]
A study on the nature of the fluvial systems of Laramidia during the Late Cretaceous, as indicated by data from vertebrate and invertebrate fossils from the Kaiparowits Formation of southern Utah, and on the behavior of hadrosaurid dinosaurs over these landscapes, will be published by Crystal et al. (2019).[64]
A study on the osteology and phylogenetic relationships of "Tanius laiyangensis" is published by Zhang et al. (2019).[65]
A study on the bone histology of tibiae of Maiasaura peeblesorum, focusing on the composition, frequency and cortical extent of localized vascular changes, is published by Woodward (2019).[66]
^Lund, E.K. and Gates, T.A. (2006). "A historical and biogeographical examination of hadrosaurian dinosaurs." pp. 263 in Lucas, S.G. and Sullivan, R.M. (eds.), Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35.
^Prieto-Márquez, Albert; Fondevilla, Víctor; Sellés, Albert G.; Wagner, Jonathan R.; Galobart; Àngel (2019). "Adynomosaurus arcanus, a new lambeosaurine dinosaur from the Late Cretaceous Ibero-Armorican Island of the European Archipelago". Cretaceous Research. 96: 19–37. Bibcode:2019CrRes..96...19P. doi:10.1016/j.cretres.2018.12.002. S2CID134582286.
^Victoria F. Crystal; Erica S.J. Evans; Henry Fricke; Ian M. Miller; Joseph J.W. Sertich (2019). "Late Cretaceous fluvial hydrology and dinosaur behavior in southern Utah, USA: Insights from stable isotopes of biogenic carbonate". Palaeogeography, Palaeoclimatology, Palaeoecology. 516: 152–165. Bibcode:2019PPP...516..152C. doi:10.1016/j.palaeo.2018.11.022. S2CID135118646.
^Eamon T. Drysdale; François Therrien; Darla K. Zelenitsky; David B. Weishampel; David C. Evans (2018). "Description of juvenile specimens of Prosaurolophus maximus (Hadrosauridae: Saurolophinae) from the Upper Cretaceous Bearpaw Formation of southern Alberta, Canada, reveals ontogenetic changes in crest morphology". Journal of Vertebrate Paleontology. 38 (6): e1547310. Bibcode:2018JVPal..38E7310D. doi:10.1080/02724634.2018.1547310. S2CID109440173.
Bell, P. R.; Brink, K. S. (2013). "Kazaklambia convincens comb. nov., a primitive juvenile lambeosaurine from the Santonian of Kazakhstan". Cretaceous Research. 45: 265–274. Bibcode:2013CrRes..45..265B. doi:10.1016/j.cretres.2013.05.003.
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