Saturday, 26 April 2014

Scavenging on the body of a Dicynodont Therapsid in the Late Permian of the Karoo Basin.

Therapsids were a group of Synapsid Amniotes (the group of terrestrial vertebrates that include the modern Mammals which are sometimes, misleadingly, known as ‘Mammal-like Reptiles), that reached great diversity in terrestrial ecosystems throughout Pangea (the ancient supercontinent of the time, which included all the modern continents joined together) in the Permian and Triassic, before being  largely replaced by more successful Archosaur groups, notably the Dinosaurs and Crocodylomprphs. The group is particularly well known from the Karoo Basin of South Africa.

In a paper published in the South African Journal of Science on 29 October 2012, Nicholas Fordyce of the Department of Zoology at the University of Cape Town, Roger Smith of the Iziko South African Museum in Cape Town and Anusuya Chinsamy, also of the Department of Zoology at the University of Cape Town, describe evidence of scavenging on the body of a Dicynodont Therapsid (a group of herbivorous Theraspids which often reached large sizes that had both beaks and tusks, and which may have survived as late as the Cretaceous) from mudrocks of the Tropidostoma Assemblage Zone of the Late Permian Beaufort Group, near Loxton in Northern Cape Province by John Nyaphuli in 1984, and prepared at the Iziko South African Museum in Cape Town by Annelise Crean. It has never been formally described and named, but is affectionately known as ‘Mamafura’.

The partially articulated Dicynodont ‘Mamafura’; the arrow indicates the left femur. Fordyce et al. (2012).

The skeleton of ‘Mamafura’ has articulated foreparts, but the hindquarters are more-or-less totally disarticulated. The bones show a level of weathering that is consistent with about two years spent exposed on the surface prior to complete burial. Sedimentary evidence suggests they originally lay on a semi-arid floodplain, and underwent three or four flood events before being finally buried, during which time some of the smaller bones of the animals feet were lost, either to water transportation or scavenging.

The left tibia of ‘Mamafura’ has two elongate grooves, which are thought to be the result of the actions of a scavenging or predatory animal. There is also a single circular indentation, 18 mm in diameter, on the left femur. 

(b and c) A large spherical puncture on the left femur, and (d) tooth scratch marks on the left tibia of ‘Mamafura’. Fordyce et al. (2012).

A broken canine tooth, 3.5 cm in length, was found with the skeleton. This has distinctive serrations on its lateral margins. Two Therapsid groups present in the fauna of the Karoo basin at the time of ‘Mamafura’ could produce a canine tooth of this size, the Therocephalians and Gorgonopsians, but no known Therocephalian has the sort of serrations seen on the tooth, suggesting that it came from a Gorgonopsian, probably Aelurognathus or possibly Cyonosaurus.

(a) The unidentified canine associated with the Dicynodont skeleton and (b) its serrations. (c) A Cyonosaurus specimen and (d) the 0.2-mm long serrations on the canine of Cyonosaurus and (e) an Aelurognathus specimen. (f) A silicon cast showing details of the serrations on a canine of Aelurognathus. Note the square serrations of (b) and (f) compared to the somewhat more rectangular serrations in (d). Fordyce et al. (2012).

Fordyce et al. suggest that soon after death ‘Mamafura’ was scavenged by a pack of Aelurognathus, acting in a similar way to modern Canids (Dogs). These preferentially attacked the rear and underbelly of the corpse, disarticulating the bones of the hindquarters, but not opening the ribs. Neither Aelurognathus nor Cyonosaurus appears to have been well adapted for durophagy (crushing bones or other hard foods), so it is doubtful that capable of making the marks found on the bones of the left hindlimb of ‘Mamafura’. Fordyce et al. suggest that these marks were either made by some other, unidentified, predator, possibly the animal responsible for the initial kill, or are the result of some other taphonomic process (post-mortem bone modification) that resembles tooth damage.

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