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Hypsilophodonts (named after the Hypsilophus genus of iguana lizard, literally meaning "high-crested tooth") were small ornithopod dinosaurs, regarded as fast, herbivorous bipeds on the order of 1-2 meters long (3.3-6.6 feet). They are known from Asia, Australia, Europe, North America, and South America, from rocks of Middle Jurassic to late Cretaceous age. The group traditionally has included almost all bipedal bird-hipped dinosaurs other than iguanodonts, and some early phylogenetic analyses analyses found it to be a natural group,[1][2] but recent studies have found that the group is mostly paraphyletic and the taxa within represent a series leading up to Iguanodontia.[3][4][5][6][7][8] Some of these studies have moved some traditional hypsilophodonts out of the Ornithopoda.[9][10] Thus, the only certain member at this time is Hypsilophodon. This area of the dinosaur family tree is complicated by a lack of research.
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Relationships
The following cladogram of hypsilophodont relationships supports the paraphyletic hypotheses; the "natural Hypsilophodontidae" hypothesis has been falling out of favor since the mid-late 1990s.
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This cladogram is based on Norman et al. (2004),[7] the most recent review, with the results of the very similar cladogram from Weishampel et al. (2003)[6] used to clarify the position of Iguanodontia, which was left out of Norman et al. Thescelosaurinae is currently used informally.
The following genera were regarded as valid, but weren't classified:[7]
- Atlascopcosaurus
- Drinker
- "Gongbusaurus" wucaiwanensis (= "Eugongbusaurus")
- Fulgurotherium
- Leaellynasaura
- Notohypsilophodon
- Qantassaurus
- Yandusaurus
- "Proctor Lake hypsilophodont"
Several other genera belong here somewhere, but are very poorly known or outright dubious:[7]
- Laosaurus
- Nanosaurus
- Othnielia (without "Laosaurus" consors)
- Phyllodon
Alternate versions and new data
Several recent studies on the base of Ornithischia, such as Butler (2005),[11] Barrett et al. (2005),[12] Xu et al. (2006),[13] and Butler et al. (2007)[9] have found different arrangements of basal Ornithischia and basal ornithopods that have some bearing on the tree, but each has found different relationships. Given the lack of work on this area since the 1980s, this is not unexpected. One aspect is the reclassification of several genera outside of Ornithopoda, such as Agilisaurus and Othnielosaurus (=Othnielia).[8][10]
Varricchio et al. (2007) found that their new genus, Oryctodromeus, forms a clade with two other genera from Montana, Orodromeus and Zephyrosaurus.[8]
Paleobiology
Hypsilophodonts were small (often 1-2 m [3.28 to 6.56 ft (2.00 m)] long), bipedal, cursorial herbivores.[7] The typical informal comparison has been to gazelles. However, there is evidence that at least some of them made burrows as places to rear their young.[8]
References
- ^ Sues, Hans-Dieter; and Norman, David B. (1990). "Hypsilophodontidae, Tenontosaurus, Dryosauridae", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 1st, Berkeley: University of California Press, 498-509. ISBN 0-520-06727-4.
- ^ Weishampel, David B.; and Heinrich, Ronald E. (1992). "Systematics of Hypsilophodontidae and Basal Iguanodontia (Dinosauria: Ornithopoda)". Historical Biology 6: 159–184. Retrieved on 2007-03-10.
- ^ Scheetz, Rodney D. (1998). "Phylogeny of basal ornithopod dinosaurs and the dissolution of the Hypsilophodontidae". Journal of Vertebrate Paleontology 18 (3, Suppl.): p. 75A.
- ^ Winkler, Dale A.; Murry, Phillip A.; and Jacobs, Louis L. (1998). "The new ornithopod dinosaur from Proctor Lake, Texas, and the deconstruction of the family Hypsilophodontidae". Journal of Vertebrate Paleontology 18 (3, Suppl.): p. 87A.
- ^ Buchholz, Peter W. (2002). "Phylogeny and biogeography of basal Ornithischia", The Mesozoic in Wyoming, Tate 2002. Casper, Wyoming: The Geological Museum, Casper College, 18-34.
- ^ a b Weishampel, David B.; Jianu, Coralia-Maria; Csiki, Z.; and Norman, David B. (2003). "Osteology and phylogeny of Zalmoxes (n.g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania". Journal of Systematic Palaeontology 1 (2): 1–56. doi:.
- ^ a b c d e Norman, David B.; Sues, Hans-Dieter; Witmer, Larry M.; and Coria, Rodolfo A. (2004). "Basal Ornithopoda", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 393-412. ISBN 0-520-24209-2.
- ^ a b c d Varricchio, David J.; Martin, Anthony J.; and Katsura, Yoshihiro (2007). "First trace and body fossil evidence of a burrowing, denning dinosaur". Proceedings of the Royal Society B: Biological Sciences 274: 1361–1368. doi:. Retrieved on 2007-03-22.
- ^ a b Butler, Richard J.; Smith, Roger M.H.; and Norman, David B. (2007). "A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia". Proceedings of the Royal Society B: Biological Sciences 274: 2041. doi:.
- ^ a b Butler, Richard J.; Upchurch, Paul; and Norman, David B. (2008). "The phylogeny of the ornithischian dinosaurs". Journal of Systematic Palaeontology 6 (1): 1–40. doi:.
- ^ Butler, Richard J. (2005). "The "fabrosaurid" ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho". Zoological Journal of the Linnean Society 145 (2): 175–218. doi:.
- ^ Barrett, Paul M.; Butler, Richard J.; and Knoll, Fabian (2005). "Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China". Journal of Vertebrate Paleontology 25 (4): 823–834. doi:.
- ^ Xu X.; Forster, C.A.; Clark, J.M.; and Mo J. (2006). "A basal ceratopsian with transitional features from the Late Jurassic of northwestern China". Proceedings of the Royal Society B: Biological Sciences 273: 2135–2140.
