Hypsilophodont

Taxobox
name = Hypsilophodonts
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Cerapoda
infraordo = Ornithopoda
familia = Hypsilophodontidae
familia_authority = Dollo, 1882
subdivision_ranks = Genera
subdivision = See text.

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,cite book |last=Sues |first=Hans-Dieter |coauthors=and Norman, David B. |editor= Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=1st |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0-520-06727-4 |pages=498-509 |chapter=Hypsilophodontidae, "Tenontosaurus", Dryosauridae] cite journal |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=and Heinrich, Ronald E. |year=1992 |title=Systematics of Hypsilophodontidae and Basal Iguanodontia (Dinosauria: Ornithopoda) |journal=Historical Biology |volume=6 |pages=159–184 |url=http://www.tandf.co.uk/journals/pdf/ghbi_06_01_01.pdf |accessdate=2007-03-10 ] but recent studies have found that the group is mostly paraphyletic and the taxa within represent a series leading up to Iguanodontia.cite journal |last=Scheetz |first=Rodney D. |year=1998 |title=Phylogeny of basal ornithopod dinosaurs and the dissolution of the Hypsilophodontidae |journal=Journal of Vertebrate Paleontology |volume=18 |issue=3, Suppl. |pages=p. 75A ] cite journal |last=Winkler |first=Dale A. |coauthors=Murry, Phillip A.; and Jacobs, Louis L. |year=1998 |title=The new ornithopod dinosaur from Proctor Lake, Texas, and the deconstruction of the family Hypsilophodontidae |journal=Journal of Vertebrate Paleontology |volume=18 |issue=3, Suppl. |pages=p. 87A ] cite book |last=Buchholz |first=Peter W. |title=The Mesozoic in Wyoming, Tate 2002 |year=2002 |publisher=The Geological Museum, Casper College |location=Casper, Wyoming |pages=18-34 |chapter=Phylogeny and biogeography of basal Ornithischia] cite journal |last=Weishampel |first= David B. |authorlink=David B. Weishampel |coauthors=Jianu, Coralia-Maria; Csiki, Z.; and Norman, David B. |year=2003 |title=Osteology and phylogeny of "Zalmoxes" (n.g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania |journal=Journal of Systematic Palaeontology |volume=1 |issue=2 |pages=1–56 |doi=10.1017/S1477201903001032 ] cite book |last=Norman |first=David B. |authorlink=David B. Norman |coauthors=Sues, Hans-Dieter; Witmer, Larry M.; and Coria, Rodolfo A. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=393-412 |chapter=Basal Ornithopoda] cite journal |last=Varricchio |first=David J. |coauthors=Martin, Anthony J.; and Katsura, Yoshihiro |year=2007 |title=First trace and body fossil evidence of a burrowing, denning dinosaur |journal=Proceedings of the Royal Society B: Biological Sciences |volume=274 |pages=1361–1368 |doi=10.1098/rspb.2006.0443 |url=http://journals.royalsociety.org/content/uj1k12wh01587821/fulltext.pdf |accessdate=2007-03-22 ] Some of these studies have moved some traditional hypsilophodonts out of the Ornithopoda.cite journal |last=Butler |first=Richard J. |coauthors=Smith, Roger M.H.; and Norman, David B. |title=A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia |journal=Proceedings of the Royal Society B: Biological Sciences |year=2007 |doi= 10.1098/rspb.2007.0367 |volume=274 |pages=2041] cite journal |last=Butler |first=Richard J. |coauthors=Upchurch, Paul; and Norman, David B. |title=The phylogeny of the ornithischian dinosaurs|journal=Journal of Systematic Palaeontology |volume=6 |issue=1 |year=2008 |pages=1–40 |doi=10.1017/S1477201907002271] Thus, the only certain member at this time is "Hypsilophodon". This area of the dinosaur family tree is complicated by a lack of research.

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.

clade| style=font-size:100%;line-height:80%
label1=Euornithopoda
1=clade
1="Orodromeus"
2="Othnielosaurus"
label3=unnamed
3=clade
label1=unnamed
1=clade
1="Gasparinisaura"
2="Hypsilophodon"
3="Zephyrosaurus"
label2=unnamed
2=clade
label1=unnamed
1=clade
1=?"Bugenasaura"
2="Parksosaurus"
3="Thescelosaurus"
2=Iguanodontia This cladogram is based on Norman "et al." (2004), the most recent review, with the results of the very similar cladogram from Weishampel "et al." (2003)cite journal |last=Weishampel |first= David B. |authorlink=David B. Weishampel |coauthors=Jianu, Coralia-Maria; Csiki, Z.; and Norman, David B. |year=2003 |title=Osteology and phylogeny of "Zalmoxes" (n.g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania |journal=Journal of Systematic Palaeontology |volume=1 |issue=2 |pages=1–56 |doi=10.1017/S1477201903001032 ] 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:
*"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:
*"Laosaurus"
*"Nanosaurus"
*"Othnielia" (without "Laosaurus" "consors")
*"Phyllodon"

Alternate versions and new data

Several recent studies on the base of Ornithischia, such as Butler (2005),cite journal |last=Butler |first=Richard J. |year=2005 |title=The "fabrosaurid" ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho |journal=Zoological Journal of the Linnean Society |volume=145 |issue=2 |pages=175–218 |doi=10.1111/j.1096-3642.2005.00182.x ] Barrett "et al." (2005),cite journal |last=Barrett |first=Paul M. |coauthors=Butler, Richard J.; and Knoll, Fabian |year=2005 |title=Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China |journal=Journal of Vertebrate Paleontology |volume=25 |issue=4 |pages=823–834 |doi=10.1671/0272-4634(2005)025 [0823:SODFTM] 2.0.CO;2 ] Xu "et al." (2006),cite journal |last=Xu X. |coauthors=Forster, C.A.; Clark, J.M.; and Mo J. |year=2006 |title=A basal ceratopsian with transitional features from the Late Jurassic of northwestern China |journal=Proceedings of the Royal Society B: Biological Sciences |volume=273 |pages=2135–2140 |doi= ] and Butler "et al." (2007) 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").cite journal |last=Varricchio |first=David J. |coauthors=Martin, Anthony J.; and Katsura, Yoshihiro |year=2007 |title=First trace and body fossil evidence of a burrowing, denning dinosaur |journal=Proceedings of the Royal Society B: Biological Sciences |volume=online preprint |doi=10.1098/rspb.2006.0443 |pages=1361]

Varricchio "et al." (2007) found that their new genus, "Oryctodromeus", forms a clade with two other genera from Montana, "Orodromeus" and "Zephyrosaurus".

Paleobiology

Hypsilophodonts were small (often 1-2 m [3.28 to convert|6.56|ft|m|abbr=on] long), bipedal, cursorial herbivores. 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.

References