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Lystrosaurus Empire

The end-Permian mass-extinction was an important event as far as life in the sea goes, but less so for the land. Plants and insects had already evolved into the classic "mesozoic" mode some ten or twenty million years earlier. And the vertebrate transition - represented by the base of the "Lystrosaurus zone" occured not at the base of the Triassic, as usually believed, but one or two million years earlier, perhaps as a result of a drying of the climate that brought about the end of the giant pareiasaurs and big dicynodonts and the gorgonopsian preditors that fed on them.

During this time, the world was still ruled by Therapsids. These had gained ecological dominance in lowland basins during the Middle and Late Permian, and this trend continued in the Early Triassic Lystrosaurid community type, and through to the early Kannemeyeriid-Rhynchosaur-Traversodontid fauna that was to follow. The largest herbivores were squat quadrupedal forms, almost all belonging to a single genus, Lystrosaurus, an animal a little over a meter in length. Although frequenting aquatic waterside and thickly vegetated terrestrial settings, it is likely that these animals could also survive in arid environments. These were accompanied by the lizard like procolophonids, herbivorous Anapsid reptiles with chisel-like teeth for chopping up pant material

Newcomers, who were to supplant the therapsids and dominate the land for the entire Mesozoic era, were the Archosaurs or "ruling reptiles", a group that was to later include dinosaurs, crocodiles, and Pterosaurs (flying reptiles or "pterodactyls"), as well as a number of other forms. The first Archosaurs were terrestrial lizard- (family Prolacertidae) and semi-aquatic crocodile-like (family Proterosuchidae) creatures about 1 to 1 1/2 metres in length.

image courtesy of Mathematical Com

Holdovers from the Permian included the Labyrinthodont amphibians (left), some of which were quite large (upto 2 or 3 metres in length). During this period they experienced something of a rennaisance, and evolved along a number of parallel evolutionary lines.

Apart from some of the labyrinthodonts which, being freshwater forms, were limited to river basins, most of these same animals existed all over the globe. There is a simple geographical reason for this. During the existence of Pangea, especially during the early Triassic, there was not much diversity among the animal life. There being no oceans to bar progress, any species could wander over the entire earth, and if it was successful it could push to extinction other species. There was evolution and ecological replacement, certainly, but it wasn't as it is nowdays, with different animals evolving on different continents. Rather, there was only one continent, across the whole of which ecological succession took place.

Known Distribution

The following map by Anderson and Cruikshank give the known distribution of Lystrosaur age faunas. This refers only to the location of fossil remains. The actual distribution would naturally have been much wider.

some Links and References

J. M. Anderson & A. R. I. Cruikshank, "The Biostratigraphy of the Permian and Triassic, Part 5, a review of the classification and distribution of Permo-Triassic Tetrapods," in Paleontologica Africana, 21, 15-44 (1978)

R.T. Bakker, 1977 "Tetrapod Mass Extinctions - A model of the regulation of speciation rates and immigration by cycles of topographic diversity" in A. Hallam, ed. Patterns of Evolution as illustrated by the Fossil Record, Elsevier Scientific Publishing Company, Amsterdam, Oxford, New York, pp.439-68

Professor Paul Eric Olsen, The Triassic World

Terrestrial Evolutionary Biotas | Pangea | Late Permian period | Triassic period | Early Triassic | Tetrapoda | Permo-Triassic Tetrapods | Temnospondyli | Archosauria | Therapsida

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