Abrictosaurus
'' Abrictosaurus ''
| Abrictosaurus | ||||||||||
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Artistic live image of Abrictosaurus |
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| Temporal occurrence | ||||||||||
| Lower Jurassic ( Hettangian to Sinemurian ) | ||||||||||
| 201.3 to 190.8 million years | ||||||||||
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| Scientific name | ||||||||||
| Abrictosaurus | ||||||||||
| Hopson , 1975 | ||||||||||
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Abrictosaurus is a genus of bird basin dinosaurs from the group of Heterodontosauridae thatlived in Africaduring the Lower Jurassic ( Hettangium or Sinemurium ). It was a small, two-legged walking ( bipeden ) herbivore.
Abrictosaurus was described on the basis of a fragmentary skull and skeleton that originated from the Lower Elliot Formation of Lesotho . Another, fragmentary skull from South Africa has also been assigned to Abrictosaurus , although this assignment has recently been questioned. The only species is Abrictosaurus consors .
features
Abrictosaurus is estimated to be around 1.2 meters long. It was an original (basal) representative of the Heterodontosauridae. Representatives of this group such as Heterodontosaurus show a pronounced heterodontia : In the front area of the snout there was a pair of long canines ( called caniniforms ) in the lower jaw (dentals) and in the intermaxillary bone in front of the upper jaw (premaxillary). These elongated teeth were separated from the molars by a gap. In the intermaxillary bone there were two more, smaller teeth in front of the elongated canine. Teeth were missing in the area of the tip of the snout, instead a thin beak (Rhamphoteka) was probably formed.
Abrictosaurus had 12 teeth in the upper jaw (maxilla) on each half of the jaw, while there were 13 to 14 teeth in the lower jaw (dentals). In comparison with the genera Lycorhinus and Heterodontosaurus , the molars were further apart and did not form a continuous chewing surface. In addition, the crowns were lower.
The holotype specimen of Abrictosaurus lacks the elongated canine in both the upper and lower jaw. The second find meanwhile shows the long canine teeth known from Heterodontosaurus . Thulborn (1974) suspects that the specimen without elongated canines was a female ( sexual dimorphism ). Sereno (1986) suggests, however, that the absence of the elongated canine is characteristic of the genus Abrictosaurus and that it is a basic (original) feature. Weishampel and Witmer (1990) speculate that the specimen without long canine teeth was a young animal ( ontogenetic variation ), while Norman and colleagues (2004) point out the possibility that the long canine teeth may have been temporarily missing due to the periodic change of teeth . Butler and colleagues (2008) state that the specimen with elongated canines may actually represent a genus in its own right, and that the absence of elongated canines is a genus-specific feature of Abrictosaurus , as already suggested by Sereno (1986).
Systematics
As a basic representative, Abrictosaurus is mostly classified at the base of the Heterodontosauridae and was less derived than, for example, Heterodontosaurus . Sereno (1986) suspects that it is the sister taxon of all other, more advanced heterodontosaurids.
Butler and colleagues (2008) come to the conclusion that the fragmentary skull from South Africa (specimen number BMNH A100, formerly UCL A100) cannot be assigned to this genus. As these researchers note, Hopson's (1975) initial assignment of this skull to Abrictosaurus was based solely on the general similarity of the skulls and not on individual, common features.
The following is a current classification according to Butler and colleagues, 2011:
| Heterodontosauridae |
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Research history and naming
The holotype specimen (specimen number UCL B54) consists of a fragmentary skull and comes from the Lower Elliot Formation of Lesotho . Initially Thulborn (1974) described this skull and a fragmentary skeleton as a new species of the genus Lycorhinus ( Lycorhinus consors ). A year later, Hopson (1975) described this material, along with another fragmentary skull from South Africa , as a new genus - Abrictosaurus .
Hopson chose the name Abrictosaurus ( Gr. Abriktos - "awake", sauros - "lizard"), which means something like "awake lizard", to contradict Thulborn's hypothesis that heterodontosaurids would have kept the type of summer sleep during the dry season. Thulborn derived this assumption from the tooth change pattern he reconstructed.
Individual evidence
- ^ Gregory S. Paul : The Princeton Field Guide To Dinosaurs. Princeton University Press, Princeton NJ 2010, ISBN 978-0-691-13720-9 , p. 240, online .
- ^ A b c Richard J. Butler, Paul Upchurch , David B. Norman : The phylogeny of the ornithischian dinosaurs. In: Journal of Systematic Palaeontology. Vol. 6, No. 1, 2008, ISSN 1477-2019 , pp. 1-40, doi : 10.1017 / S1477201907002271 .
- ↑ Thomas R. Holtz Jr .: Supplementary Information. to: Thomas R. Holtz Jr .: Dinosaurs. The most complete, up-to-date Encyclopedia for Dinosaur Lovers of all ages. Random House, New York NY 2007, ISBN 978-0-375-82419-7 , online (PDF; 184.08 kB) .
- ↑ a b David B. Weishampel , Lawrence M. Witmer : Heterodontosauridae. In: David B. Weishampel, Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . University of California Press, Berkeley CA et al. 1990, ISBN 0-520-06726-6 , pp. 286-297.
- ^ A b David B. Norman , Hans-Dieter Sues , Lawrence M. Witmer, Rodolfo A. Coria : Basal Ornithopoda. In: David B. Weishampel, Peter Dodson, Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 393-412.
- ^ A b c Paul C. Sereno : Phylogeny of the bird-hipped dinosaurs (Order Ornithischia). In: National Geographic Research. Vol. 2, No. 2, 1986, ISSN 8755-724X , pp. 234-256.
- ^ A b Donald F. Glut : Dinosaurs. The Encyclopedia. McFarland, Jefferson NC et al. 1997, ISBN 0-89950-917-7 .
- ↑ a b Richard J. Butler, Jin Liyong, Chen Jun, Pascal Godefroit: The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian – Cenomanian) of Jilin Province, north-eastern China. In: Palaeontology. Vol. 54, No. 3, 2011, ISSN 0031-0239 , pp. 667-683, doi : 10.1111 / j.1475-4983.2011.01046.x .
- ^ Richard A. Thulborn: A new heterodontosaurid dinosaur (Reptilia: Ornithischia) from the Upper Triassic Red Beds of Lesotho. In: Zoological Journal of the Linnean Society. Vol. 55, No. 2, 1974, ISSN 0024-4082 , pp. 151-175, doi : 10.1111 / j.1096-3642.1974.tb01591.x .
- ↑ James A. Hopson: On the generic separation of the ornithischian dinosaurs lycorhinus and heterodontosaurus from the stormberg series upper triassic of south africa. In: South African Journal of Science. Vol. 71, No. 10, 1975, ISSN 0038-2353 , pp. 302-305.
- ↑ Dinosauria Translation and Pronunciation Guide A . ( online ( memento of July 20, 2011 in the Internet Archive ) [accessed on August 30, 2014]). Dinosauria Translation and Pronunciation Guide A ( Memento of the original from August 18, 2010 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
