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Heterodontosaurus

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Heterodontosaurus

Heterodontosaurus
Temporal range: Early Jurassic, 199–196 Ma
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Cast of SAM-PK-K1332, University of California Museum of Paleontology
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Clade: Dinosauria
Order: Ornithischia
Family: Heterodontosauridae
Subfamily: Heterodontosaurinae
Genus: Heterodontosaurus
Crompton & Charig, 1962
Species
  • H. tucki Crompton & Charig, 1962 (type)

Heterodontosaurus (meaning "different toothed lizard") is a genus of small herbivorous dinosaur with prominent canine teeth which lived in the Early Jurassic of South Africa. It was similar to a hypsilophodont in shape, and ate plants, despite its canines.[1]

Contents

  • Description 1
    • Dentition 1.1
  • Discovery 2
  • Classification 3
  • References 4
  • Sources 5

Description

Size compared to a human

Heterodontosaurus was a small, fleetfooted ornithischian classified inside the family Heterodontosauridae. The family contains some of the smallest known ornithischians[2] – the North American Fruitadens, for example, reached a length of only 65 to 75 cm.[3] Heterodontosaurus was amongst the largest known members of its family, reaching a length of between 1 to 1.75 m and weighing 1.8[4] or 10 kg.[5] Only the South African Lycorhinus might have been larger.[6][7]

The skull was robustly built and triangular in side view. The front of the jaws where covered by a toothless horny beak. The upper beak was carried by the premaxilla and the lower beak by the predentary, which in ornithischians are the foremost bones of the upper and lower jaw, respectively. The eye openings were proportionally large and almost circular in shape, while the external nostril openings were small. A large spur-like bone, the palpebral, protruded backwards into the eye opening.[8] Below the eye socket, the jugal bone gave rise to a sidewards projecting horn like process. The antorbital fossa, a large depression between the eye and nostril openings, contained two smaller openings.[2] Ventrally, the antorbital fossa was bounded by a prominent bony ridge, to which the animal's fleshy cheek would have been attached. Behind the eye opening, there was the proportionally large lower temporal fenestra, which in Heterodontosaurus was egg-shaped and tilted back. The elliptical upper temporal fenestra was visible only in top view of the skull. The left and right upper temporal fenestrae were separated by a pronounced sagittal crest, which in the living animal would have provided attachment sides for the jaw musculature.[8]

It had a long, narrow pelvis and a pubis which resembled those possessed by more advanced ornithischians.[1][8][9] More unusual was that the hand of Heterodontosaurus had five fingers, two of which seem to be opposable. This configuration allowed Heterodontosaurus to grasp and manipulate food. The bone in the foot and ankle were fused in a manner reminiscent of those in birds.[1][9][10]

Dentition

Restored skull

Another feature is the specialization of teeth which gave rise to the animal's name. Most dinosaurs (and indeed most reptiles) have a single type of tooth in their jaws, while Heterodontosaurus had three. At the front of the jaw beside the beak were small teeth likely used for chopping off leaves and stems.[1][9]

Next in the jaw was a large pair of tusks whose purpose is unknown, but it is speculated that they were used as sexual displays (where the tusks could have been used as weapons by rival males in disputes over mates and territories) or to break open prehistoric termite mounds. The final type of teeth were tall and squared off. This type of teeth was well adapted for chewing. Fleshy cheeks helped keep the food in the mouth while chewing occurred.[1][9] Chewing is relatively common in dinosaurs, but uncommon for other groups of reptiles.[7][11]

This bizarre suite of teeth has led to debate over what heterodontosaurs ate. Some scientists think heterodontosaurs were omnivores who used their differently-shaped teeth to eat both plants and small animals.[1][12]

Discovery

Heterodontosaurus is currently known from specimens of the SAFM (South African Museum) from South Africa.[13] There are two known morphologies of this genus, the second of which is thought by some to represent a different species. The type species, H. tucki, is from the Upper Elliot Formation of the Hettangian age, around 199-196 million years ago.[14]

Classification

Timelapse of the construction of a model of H. tucki

The cladogram below follows the analysis by Butler et al., 2011:[15]

Heterodontosauridae 

Echinodon


Abrictosaurus




NHM RU A100


Heterodontosaurus


Lycorhinus




Fruitadens


Tianyulong




References

  1. ^ a b c d e f Benton, Michael J. (2012). Prehistoric Life. Edinburgh, Scotland: Dorling Kindersley. p. 271.  
  2. ^ a b Weishampel, D. B.; Witmer, L. M. (1990). "Heterodontosauridae". In Weishampel, D. B.; Dodson, P.; Osmólska, H. The Dinosauria. University of California Press. pp. 486–497.  
  3. ^ R.J. Butler, P.M. Galton, L.B. Porro, L.M. Chiappe, D.M. Henderson, G.M. Erickson (2010). "Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America". Proceedings of the Royal Society. Series B: Biological Sciences 277 (1680): 375–381.  
  4. ^ Seebacher, F. (2001). "A new method to calculate allometric length-mass relationships of dinosaurs". Journal of Vertebrate Paleontology 21 (1): 51–60.  
  5. ^ Butler, R. J.; Porro, L. B.; Galton, P. M.; Chiappe, L. M. (2012). Farke, Andrew A, ed. "Anatomy and Cranial Functional Morphology of the Small-Bodied Dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA". PLoS ONE 7 (4): e31556.  
  6. ^ Gow, C. E. (1990). Haughton, 1924 (Dinosauria, Ornithischia)"Lycorhinus angustidens"A tooth-bearing maxilla referable to . Annals of the South African Museum 99 (10): 367–380. 
  7. ^ a b Sereno, P.C. (2012). "Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs". ZooKeys 226: 1–225.  
  8. ^ a b c Norman, D. B.; Crompton, A. W.; Butler, R. J.; Porro, L. B.; Charig, A. J. (2011). "The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: Cranial anatomy, functional morphology, taxonomy, and relationships". Zoological Journal of the Linnean Society: no.  
  9. ^ a b c d "Heterodontosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 37. ISBN 0-7853-0443-6.
  10. ^ https://archive.org/stream/annalsofsouth79197980sout/#page/159/mode/1up
  11. ^ Santa Luca, A. P.; Crompton, A. W.; Charig, A. J. (1976). "A complete skeleton of the Late Triassic ornithischian Heterodontosaurus tucki". Nature 264 (5584): 324.  
  12. ^ Tiny Juvenile Dinosaur Fossil Sheds Light on Evolution of Plant Eaters Newswise, Retrieved on October 23, 2008.
  13. ^ Crompton, A. W.; Charig, A. J. (1962). "A new Ornithischian from the Upper Triassic of South Africa". Nature 196 (4859): 1074.  
  14. ^ Butler, R. J.; Porro, L. B.; Norman, D. B. (2008). "A juvenile skull of the primitive ornithischian dinosaur Heterodontosaurus tuckifrom the 'Stormberg' of southern Africa". Journal of Vertebrate Paleontology 28 (3): 702.  
  15. ^ R. J. Butler, J. Liyong, C. Jun, P. Godefroit (2011). "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". Palaeontology 54 (3): 667–683.  

Sources

  • Ingrid Cranfield, ed. (2000). Dinosaurs and other prehistoric creatures. Salamander Books. pp. 132–135. 
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