Heterodontosauridae
Fossil of Heterodontosaurus Tucki
- Africa, North and South America, Europe and Asia
The Heterodontosauridae ( ' Lizards with different types of teeth " ) are a group of bipedal, herbivorous or omnivorous dinosaurs that lived from the Upper Triassic to Lower Cretaceous. The group is classified within the bird Beck dinosaur ( Ornithischia ), the exact systematic position is controversial. The best-known genus, Heterodontosaurus, dates from the Early Jurassic of South Africa; However, the group is occupied by mostly very fragmentary finds also from North and South America, Europe and Asia. Characteristic and eponymous feature was the Heterodontie, the presence of different types of teeth in the dentition, including both molars and often greatly enlarged " Hauer " with. Heterodontosauriden are among the smallest known bird Beck dinosaurs; for example, measures Fruitadens a length of only 65 to 75 centimeters. The skeleton of the Chinese Tianyulong shows filamentous structures that were interpreted as proto- feathers.
Features
With a maximum body length of one to two meters, the different genres of Heterodontosauridae are considered the smallest known representatives of the bird Beck dinosaur ( Ornithischia ). They were plant or omnivores and moving biped, ie only continue on its hind legs.
Hauptsynapomorphie the group is the presence of differently trained groups of teeth ( Heterodontie ) in their teeth. This feature is for synapsids ( Synapsida ) and their descendants, the mammals, typical; Reptiles show but usually a homodontes teeth with only one tooth type. On the maxilla and in the middle and posterior part of the dentary sat hochkronige provided with protuberances molars, adapted to grind plant food. In the front part of the lower jaw and on the premaxilla in the upper jaw were large fang -like teeth ( " Hauer "). The tusks of the lower jaw intervened in a toothless gap ( diastema ) between the tusks and the front molar teeth of the upper jaw.
For the first time Heterodontosauridae occurred in the phylogeny of bird Beck dinosaur cheeks in appearance. Thus the retention of food in the mouth, and was easier achieve better preparation of the food before the digestion.
In the Chinese Tianyulong described only in 2009 spring-like structures on the skin have been obtained fossil. Proto springs were previously found only in advanced theropods.
System
The position of the Heterodontosauridae within the bird Beck dinosaurs is controversial. Originally, the group was considered to be original bird Beck dinosaurs. Later there was a general consensus to put them as a basal group in the ornithopods. In a recent phylogenetic study, they are compared as a sister taxon almost all others, summarized as taxon Genasauria Ornithischiergruppen. Only Pisanoaurus has a more basal position ..
Cladogram of Butler et al 2008:
Pisanosaurus
Heterodontosauridae
Stegosauria
Ornithopods
Pachycephalosauria
Ceratopia
Genera
Currently, the following genera are considered valid:
- Abrictosaurus
- Echinodon
- Fruitadens
- Heterodontosaurus
- Lycorhinus
- Manidens
- Pegomastax
- Tianyulong