Angonisaurus
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Angonisaurus Temporal range: Anisian 247.2–242 Ma |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | Therapsida |
| Infraorder: | †Dicynodontia |
| Clade: | †Kannemeyeriiformes |
| Genus: |
†Angonisaurus Newton, 1893 |
| Type species | |
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†Angonisaurus cruickshanki Cox and Li, 1983 |
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| Species | |
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Angonisaurus is an extinct genus of kannemeyeriiform dicynodont from the Late Triassic of Africa somewhere between 251 million years ago and 199 million years ago. Only one species, Angonisaurus cruickshanki has been assigned to this genus. This genus is thought to have been widely spread but rare in southern Gondwana. Though few in number, the fossil record of Angonisaurus cruickshanki contains multiple specimens giving it a measurable stratigraphic range. Sexually dimorphic features are found in Angonisaurs which include presence or absence of tusks and difference is size and robustness of the temporal arch and the rostral.
Angonisaurus was discovered in the African Karoo Basin in 1983. Because of the lack of good lithostratigraphic marker beds, biostratigraphy has proven to be the most reliable aid for stratigraphic subdivision of this Lower–Middle Triassic succession. Angonisaurus was found in the present day locations of the towns of Sterkstroom and the Molteno. Within the area, there are three subzones, Angonisaurus are biostratigraphically constrained to the uppermost Cynognathus Assemblage Zone (subzone C).
Angonisaurus was named by its discoverers Cox and Li in 1983. (Angonisaurus, "an" = without, "gon" = angle(d), knee) Angonisaurus has erect hind limbs with forelimbs that bend at the elbow.
Identification was based on a number of characters shared by the South African specimens and the holotype of Angonisaurus cruickshanki, including the broad Occipital bone; robust Squamosal; Interparietal contribution to the skull roof; Postorbitals that do not contact the Squamosals on the skull roof, such that the Parietals form a significant portion of the temporal bar; pineal foramen located within a deep conical depression; wide interorbital bar; and the triangular, tuskless caniniform process. However, there are marked differences between the South African specimens and the Tanzanian Holotype, including the absence of a midline groove that extends along the entire length of the temporal bar, the absence of a dorsal margin of the occiput that overhangs the remainder of the occipital plate, and the more gracile caniniform processes in the South African specimens. Because the type of A. crucikshanki was the only known specimen of Angonisaurus at the time, Hancox and Rubidge (1996 Hancox, P. J. and Rubidge, B. S. 1996. The first specimen of the mid-Triassic Dicynodont Angonisaurus from the Karoo Supergroup of South Africa: implications for the dating and biostratigraphy of the Cynognathus Assemblage Zone, Upper Beaufort Group. South African Journal of Science, 92: 391–392. [Web of Science ®]) expressed uncertainty as to whether these differences reflected a species-level distinction between South African and Tanzanian Angonisaurus, or if they stemmed from intraspecific variation, and they did not offer a species-level identification for BP/1/5530 and BP/1/5531.
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