Re: LYSTROSAURUS (long) (was Re: Mammal - Like - Reptiles)

[Greg Popwell <torvo@bellsouth.net>]

Pieter.Depuydt@rug.ac.be wrote:

> The following contains no information about dinosaurs, but about one
> of the icons of vertebrate paleontology, the well-loved Lystrosaurus.
> Since there have been some questions about this animal, I thought it
> would be appropriate to mention some recent studies which
> questioned some well-established ideas and gave new insights in
> the ecology of  Lystrosaurus and the end-Permian extinction
> event.
>
> The generic name Lystrosaurus was proposed by Cope in 1870, although
> the holotype skull was described more than ten years earlier by Owen.
> Lystrosaurus remains have been found in abundant numbers in the South
> African Karoo, on Antarctica, India, China, and Russia, thus
> providing one of the strongest arguments for Wegener's theory of
> continental drift, as Jonatan Woolf already mentioned.
> More than 20 species have been described in the course of the years,
> but taxonomic revisions (by Cosgriff, by King and Grine) have
> steadily reduced the number of valid species to 6 and maybe even to
> 2.
> The classical view of Lystrosaurus, and the way it has been
> reconstructed in countless popular books, is that of a
> hippopotamus-like amphibious or even fully aquatic animal; the
> pecular skull morphology with the long downturned snout and the
> highly placed nasal openings have traditionally been interpreted
> as adaptations to feeding below the water table. However, King and
> Cluver have argued that the skull and jaw features more likely were
> modifications to increase the orthal bite force (opposite to the more
> longitudinal jaw movement in earlier dicynodonts) and hence were
> adaptations to a tougher and more fibrous diet, which is also
> illustrated by the presence of some polished surface on the tusks of
> some specimens. The sacrum was well developed and the hind limbs
> operated in a more semi-erect fashion, also pointing towards a more
> terrestrial way of living. And finally, sedimentologic study and
> taphonomic study of  the Lystrosaurus environment  by R. Smith of
> the South African Museum has revealed that Lystrosaurus lived and
> died on a rather dry floodplain (in contrast with the wet floodplain
> habitat of the earlier Dicynodon fauna).
> Lystrosaurus traditionally has been used as a stratigraphic marker, a
> guide fossil which identifies the strata in which it occurs as
> earliest Triassic. However, a Lystrosaurus specimen has recently been
> identified by King in a fossil assemblage which is otherwise
> typically Latest Permian, coming from the Madumabisa sandstone of
> Zambia. In the South African Karoo, a transitional zone has been
> identified between typically Latest Permian and Early Triassic
> sediments, in which Lystrosaurus occurs together with the typical
> Permian dicynodont Dicynodon. A similar transitional assemblage has
> been identified in China, where small Lystrosaurus specimens occur
> together with the Permian dicynodont Jimusuaria.
> Based on all this, a picture emerges of a gradually changing
> environment in the Karoo in the Latest Permian and Earliest Triassic,
> with aridification of the climate, and the Permian wetland horsetail
> habitat, with its Dicynodon fauna, giving slowly way to a more dry
> floodplain, dominated by Lystrosaurus, well adapted to drought and
> feeding on a more sparse and resistant vegetation.
>
> references:
>
> R.M.H. Smith 1995: Changing fluvial environments across the
> Permian-Triassic boundary in the Karoo Basin, South Africa and
> possible causes of tetrapod extinctions.
> Palaeogeography, Palaeoclimatology, Palaeoecology 117, 81-104.
>
> G.M. King 1992: Species longevity and generic divesity in dicynodont
> mammal-like reptiles.
> Palaeogeography, Palaeoclimatology, Palaeoecology 102, 321-332.
>
> G.M. King 1991: The aquatic Lystrosaurus: a palaeontological myth.
> Historical Biology 4, 285-321.
>
> G.M. King 1997: The dicynodont Lystrosaurus from the Upper Permian of
> Zambia: evolutionary and stratigraphic implications.
> Palaeontology 40 (1), 149-156.
>
> Pieter Depuydt

 That's the most information I've ever seen on Lystrosaurus. I don't have
access to the journals that you referenced. Feel free to post more
detailed info on other "mammal-like reptiles".