Hadrosaurid
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| Hadrosaurids Fossil range: Late Cretaceous | ||||||||||||||||||
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Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper Jurassic/Lower Cretaceous iguanodontian dinosaurs and had similar body layout. They were ornithischians.
Hadrosaurids are divided into two subfamilies. The lambeosaurines (Lambeosaurinae) have large cranial crests or tubes, and are less bulky. The hadrosaurines (Hadrosaurinae) lack the cranial crests or tubes and are larger.
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[edit] Characteristics
The hadrosaurs are known as the duck-billed dinosaurs due to the similarity of their head to that of modern ducks. In some species, most notably Anatotitan, the whole front of the skull was flat and broadened out to form a beak, ideal for clipping leaves and twigs from the forests of Asia, Europe and North America. However, the back of the mouth contained literally thousands of teeth suitable for grinding food before it was swallowed. Hadrosaurs, like their iguanodontian cousins, had a rudimentary dental specialisation analogous to incisors and molars. This has been hypothesized to have been a crucial factor in the success of this group in the Cretaceous, compared to the sauropods which were still largely dependent on gastroliths for grinding their food.
[edit] Discoveries
Hadrosaurids were the first dinosaur family to be identified in North America, the first traces being found in 1855-1856 with the discovery of fossil teeth. Joseph Leidy examined the teeth, and erected the genera Trachodon and Thespesius (others included Troodon, Deinodon and Palaeoscincus). One species was named Trachodon mirabilis. Now it seems that the teeth genus Trachodon is a mixture of all sorts of cerapod dinosaurs, including ceratopsids. In 1858 the teeth were associated with Leidy's eponymous Hadrosaurus foulkii, named after the fossil hobbyist William Parker Foulke. More and more teeth were found, resulting in even more (now obsolete) genera.
A second duck-bill skeleton was unearthed, and was named Diclonius mirabilis in 1883 by Edward Drinker Cope, which he incorrectly used in favor of Trachodon mirabilis. But Trachodon, together with other poorly typed genera, was used more widely and, when Cope's famous "Diclonius mirabilis" skeleton was mounted at the American Museum of Natural History, it was labeled as "Trachodont dinosaur". The duck-billed dinosaur family was then named Trachodontidae.
A very well-preserved complete hadrosaurid specimen (Edmontosaurus annectens) was recovered in 1908 by the fossil collector Charles Hazelius Sternberg and his three sons, in Converse County, Wyoming. It was known as the "Trachodon mummy". This specimen's skin was almost completely preserved, together with some muscles and was analysed by Henry Osborn in 1912. Sternberg was in Cope's camp during his famous competition to name new species with Othniel Charles Marsh. This discovery was a victory for Cope in the Bone Wars.
Lawrence Lambe erected the genus Edmontosaurus ("lizard from Edmonton") in 1917 from a find in the lower Edmonton Formation (now Horseshoe Canyon Formation), Alberta. Hadrosaurid systematics were a mess until 1942, when Richard Swann Lull and Nelda Wright proposed the genus Anatosaurus. Cope's famous mount at the AMNH became Anatosaurus copei. In 1975, Anatosaurus was moved to Edmontosaurus, because the species were just too similar to the Edmontosaurus type species, E. regalis and because Edmontosaurus was older, it had precedence. The original sample was probably a young Edmontosaurus. One former Anatosaurus species was distinct enough from Edmontosaurus to be placed in a separate genus, named Anatotitan, so in 1990 the AMNH mount was re-labelled Anatotitan copei.
Some paleontologists found a hadrosaurid leg bone in Paleocene rocks, but it was probably reworked from a Cretaceous source.[1]
One of the most complete fossilized specimens was found in 1999 in Hell Creek Formation of North Dakota and now is nicknamed "Dakota". The hadrosaur fossil is so well preserved that scientists have been able to calculate its muscle mass and learn that it was more muscular than thought, probably giving it the ability to outrun predators such as T. rex. Unlike the collections of bones found in museums, this mummified hadrosaur fossil comes complete with skin (not merely skin impressions), ligaments, tendons and possibly some internal organs. It is being analyzed in the world's largest CT scanner, operated by the Boeing Co.[2] The machine usually is used for detecting flaws in space shuttle engines and other large objects, but previously none as large as this. Researchers hope the technology will help them learn more about the fossilized insides of the creature. They also found a gap of about a centimeter between each vertebra, indicating there may have been a disk or other material between them, allowing more flexibility and meaning the animal was actually longer than what is shown in a museum.[3]
[edit] Systematics
<imagemap> Image:Hadrosaur-tree-v4.jpg|400px|thumb|Family tree of the Hadrosauroidea. Representative genera of each tribe are shown to scale. poly 1498 862 441 856 6 168 3 9 1943 18 1901 420 Shantungosaurus poly 1967 498 1639 919 2030 1360 2940 1348 3126 1138 3384 759 3381 558 3375 567 Charonosaurus poly 1258 1120 1093 1303 150 1294 159 1084 570 898 871 877 1105 907 1108 916 Brachylophosaurus poly 12 1348 126 1778 336 1916 1192 1898 1096 1718 1156 1633 1243 1615 1264 1507 1111 1372 777 1330 780 1333 Saurolophus poly 1345 2291 1243 2468 714 2459 483 2360 480 2252 681 2156 1033 2138 1261 2195 Telmatosaurus poly 1204 2541 672 2562 543 2781 576 2874 1462 2865 1435 2757 1540 2616 1414 2568 Probactrosaurus poly 3261 1354 2183 1384 2108 1666 2225 1763 2279 1976 2742 1970 3123 1973 Hypacrosaurus poly 3030 2000 2853 1982 2288 2003 2147 2081 2138 2225 2255 2384 2769 2378 2991 2228 2991 2231 2991 2222 Amurosaurus poly 1892 2772 2036 2706 1784 2348 1648 2432 Hadrosauridae poly 1775 2312 1651 2303 1787 1862 1880 1907 Lambeosaurinae poly 1772 1678 1883 1657 1838 1447 1931 1327 1871 1252 1751 1444 Parasaurolophini poly 1838 1838 1904 1913 2039 1853 2213 1856 2219 1772 2003 1769 2003 1772 2006 1772 2009 1772 2012 1772 Corythosaurini poly 1546 1844 1378 1871 1516 2279 1624 2186 Hadrosaurinae poly 1159 1657 1123 1727 1369 1859 1435 1808 1300 1706 Saurolophini poly 1468 1375 1414 1441 1171 1276 1219 1204 Maiasaurini poly 1471 1231 1564 1207 1483 1012 1378 853 1318 910 1426 1075 Edmontosaurini rect 2360 2607 3099 2763 Meter
desc bottom-left </imagemap>
[edit] Taxonomy
The family Hadrosauridae was first used by Edward Drinker Cope in 1869. Since its creation, a major division has been recognized in the group, between the (generally crested) subfamily Lambeosaurinae and (generally crestless) subfamily Hadrosaurinae. Phylogenetic analysis has increased the resolution of hadrosaurid relationships considerably (see Phylogeny below), leading to the widespread usage of tribes (a taxonomic unit below subfamily) to describe the finer relationships within each group of hadrosaurids. However, hadrosaurid tribes commonly recognized in online sources have not yet been formally defined or seen wide use in the literature. Several were briefly mentioned but not named as such in the first edition of The Dinosauria, under informal names. In this 1990 reference, "gryposaurs" included Aralosaurus, Gryposaurus, Hadrosaurus, and Kritosaurus; "brachylophosaurs" included Brachylophosaurus and Maiasaura; "saurolophs" included Lophorhothon, Prosaurolophus, and Saurolophus; and "edmontosaurs" included Anatotitan, Edmontosaurus, and Shantungosaurus.[4]
Lambeosaurines have also been split into Parasaurolophini (Parasaurolophus) and Corythosaurini (Corythosaurus, Hypacrosaurus, and Lambeosaurus).[5] Corythosaurini and Parasaurolophini as terms entered the formal literature in Evans and Reisz's 2007 redescription of Lambeosaurus magnicristatus. Corythosaurini is defined as all taxa more closely related Corythosaurus casuarius than to Parasaurolophus walkeri, and Parasaurolophini as all those taxa closer to P. walkeri than to C. casuarius. In this study, Charonosaurus and Parasaurolophus are parasaurolophins, and Corythosaurus, Hypacrosaurus, Lambeosaurus, Nipponosaurus, and Olorotitan are corythosaurins.[6]
The following taxonomy includes dinosaurs currently referred to the Hadrosauridae and its subfamilies. Hadrosaurids that were accepted as valid but were not placed in a cladogram at the time of the 2004 review in The Dinosauria,[7] or, in the case of lambeosaurines, the 2007 redescription of Lambeosaurus magnicristatus,[6] are included at the highest level to which they were placed (either then, or in their description if they postdate the papers used here).
- Family Hadrosauridae
- Telmatosaurus
- Subfamily Hadrosaurinae
- Brachylophosaurus
- Edmontosaurus (including Anatotitan in Horner et al., 2004[7])
- Gryposaurus
- "Kritosaurus" australis
- Lophorhothon
- Maiasaura
- Naashoibitosaurus
- Prosaurolophus
- Saurolophus
- Unclassified hadrosaurines
- Subfamily Lambeosaurinae
- Hadrosaurids of uncertain placement (incertae sedis)
- Dubious hadrosaurids
[edit] Phylogeny
Hadrosauridae was first defined as a clade, by Forster in a 1997 abstract, as simply "Labeosaurinae plus Hadrosaurinae and their most recent common ancestor." In 1998, Paul Sereno defined the clade Hadrosauridae as the most inclusive possible group containing Saurolophus (a well-known hadrosaurine) and Parasaurolophus (a well-known lambeosaurine), later emending the definition to include Hadrosaurus, the type genus of the family, which ICZN rules state must be included, despite its status as a nomen dubium. According to some studies,[attribution needed] Sereno's definition would place a few other well-known hadrosaurs (such as Telmatosaurus and Bactrosaurus) outside the family, which led Horner et al. (2004) to define the family to include Telmatosaurus by default.
The following cladogram is after the 2004 review by Jack Horner, David B. Weishampel, and Catherine Forster, in the second edition of The Dinosauria.[7]
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[edit] Lambeosaurinae cladogram
The following cladogram is after the 2007 redescription of Lambeosaurus magnicristatus (Evans and Reisz, 2007):[6]
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[edit] References
- ^ Fassett, J, Zielinski, R.A., and Budahn, J.R. (2002). Dinosaurs that did not die; evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico. In: Koeberl, C., and MacLeod, K. (eds.). Catastrophic events and mass extinctions: impacts and beyond. Special Paper - Geological Society of America 356:307-336.
- ^ (Reuters News) "Mummified dinosaur reveals surprises: scientists" 3 December 2007.
- ^ SCHMID, RANDOLPH. "'Mummified Dinosaur May Have Outrun T Rex", Associated Press, Dec 3, 5:52 PM EST. Retrieved on 2007-12-03.
- ^ Weishampel, David B.; and Horner, Jack R. (1990). "Hadrosauridae", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 1st, Berkeley: University of California Press, 534-561. ISBN 0-520-06727-4.
- ^ Glut, Donald F. (1997). Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co, 69. ISBN 0-89950-917-7.
- ^ a b c Evans, David C.; and Reisz, Robert R. (2007). "Anatomy and relationships of Lambeosaurus magnicristatus, a crested hadrosaurid dinosaur (Ornithischia) from the Dinosaur Park Formation, Alberta". Journal of Vertebrate Paleontology 27 (2): 373-393.
- ^ a b c Horner, John R.; Weishampel, David B.; and Forster, Catherine A (2004). "Hadrosauridae", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 438-463. ISBN 0-520-24209-2.
- ^ Gates, Terry A.; Sampson, Scott D.; Delgado de Jesús, Carlos R.; Zanno, Lindsay E.; Eberth, David; Hernandez-Rivera, René; Aguillón Martínez, Martha C.; and Kirkland, James I. (2007). "Velafrons coahuilensis, a new lambeosaurine hadrosaurid (Dinosauria: Ornithopoda) from the Late Campanian Cerro del Pueblo Formation, Coahuila, Mexico". Journal of Vertebrate Paleontology 27 (4): 917-930.
[edit] External links
| Dinosaurs Portal |
- UCMP Tree of Life
- Trachodonde:Hadrosaurier
es:Hadrosauridae fr:Hadrosauridae it:Hadrosauridae he:הדרוזאוריים lt:Ančiasnapiai dinozaurai hu:Hadrosauridae nl:Hadrosauridae ja:ハドロサウルス科 pl:Hadrozaury pt:Hadrossaurídeos sv:Hadrosaurider zh:鴨嘴龍科
