Hypsilophodont
Atlascopcosaurus, live reconstruction
- Worldwide
The Hypsilophodontidae were small ornithopod dinosaurs. Their fossils have been found almost in Middle Jurassic to Upper Cretaceous sediments worldwide.
Genera of Hypsilophodontidae how Leaellynasaura and Qantassaurus, provide more than half of the found in southeastern Australia " Polar Dinosaurs". The reference in the present state of Victoria was in the Lower Cretaceous, 115-105 million years ago, near the Antarctic Circle and has a much colder climate with annual average temperatures have been just below freezing.
Features
They were built quite primitive and resembled the Heterodontosaurinen, but they were the first dinosaur, which had the ability to chew food plants. Later, this ability was even better pronounced in Iguanodontiden and Hadrosauriern. In addition, the Ceratopsiden should have possessed higher Kaufähigkeiten. The molars had increases ( Hypsilophodontiden = dt ' teeth with increases " ) and should probably cut better the food while chewing. The skull did not have the enlarged canines of Heterodontosauridae and the skull midline was narrower. In the ventral view can be seen that the cheek regions were extended by the wide lower jaw outside of the tooth rows. Requirements for chewing at Hypsilophodontiden were good together matching upper and lower rows of teeth by the development of secondary occlusal surfaces. In addition, the skull was particularly moving.
Earlier views that Hypsilophodonten were arboreal and that's clutching the feet branches discarded because the foot had no grip function, but it is here a typical " walking foot " with claws. The tail end was ossified and was probably used for balance, similar to the dromaeosaurid Deinonychus. The whole Gliedmaßenbau, but especially the long shin and foot, resembling a gazelle. They were probably quite nimble animals and were up to five meters long, the smaller species reaching up to two meters.
System
Outer systematics
Earlier theories claimed that the Hypsilophodontidae was a sister taxon of Iguanodontia. However, modern analysis proved that the Hypsilophodontidae is paraphyletic, with some authors still classify as, for example, Michael J. Benton, this taxon as the sister group of the Iguanodontidae and Hadrosauridae.
Cladogram according to Benton ( 2007):
Heterodontosauridae
Hypsilophodontidae
Iguanodontidae
The following cladogram ( Boyd et al. 2009) shows the Hypsilophodontidae paraphyletic. The Hypsilophodontidae would all taxa of Agilisaurus or Hexinlusaurus to Hypsilophodon or Gasparinisaura in this case.
Agilisaurus
Hexinlusaurus
Zephyrosaurus
Hypsilophodon
Gasparinisaura
Other ornithopods
Genera
- Agilisaurus
- Alocodon
- Anabisetia
- Atlascopcosaurus
- Bugenasaura
- Drinker
- Fulgurotherium
- Gasparinisaura
- Hypsilophodon
- Jeholosaurus
- Leaellynasaura
- Notohypsilophodon
- Orodromeus
- Oryctodromeus
- Othnielia
- Parksosaurus
- Thescelosaurus
- Yandusaurus
- Zephyrosaurus
Swell
- Reinhard Rieger and Wilfried West Heath (ed.): Systematic Zoology Part 2: vertebral or cranial Animals, Gustav Fischer Verlag, Stuttgart, Jena 6 New York 2003, ISBN 3-8274-0900-4.
- Michael J. Benton: vertebrate paleontology. 2007, ISBN 3-89937-072-4, p 222