| Palaeos: Mesozoic | |
Early Triassic |
| Triassic PERIOD | Induan - 2 |
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 illustration © from Steyer 2002
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| The Temnospondyl Labyrinthodont amphibians were characteristic animals of this time. During the Triassic period these creatures experienced something of a rennaisance, and evolved along a number of parallel evolutionary lines. The great majority were semi-aquatic. Illustrated here is a juvenile Wantzosaurus elongatus (the scale bar is 4 cm), a member of the Trematosauridae and cousin (although belonging to a different subfamily) of the Lootsbergian index fossil Luzocephalus illustrated above. These animals were fresh-water and occasionally esturine and marine fish-eaters, with long crocodile or gharial-like snouts. As the adolescent Wantzosaurus shown here matures, its snout will become proportionally longer and thiner, although the rest of the head and body will not increase much. |
 lllustration above © 2001 Vince R Ward - Prehistoric Pages
illustration below right after Colbert and Kitching 1975 |
 Procolophon trigoniceps Owen 1876 known from the Lystrosaurus zone, Beaufort Beds of South Africa and the equivalent Fremouw Formation of Antarctica (during the Triassic these two regions were quite close together) was a stout lizard-like herbivore with chisel-like teeth and a triangular-shaped skull. The whole animal reaxched about 30 cm in length. These little animals were actually cousins of the giant pareiasaurs of the middle and late Permian. Both belong to the clade "Parareptilia", which was a major group of Permian reptiles characterised by primitive skulls without any temporal openinings for musclke attachment. It was originally thought that the turtles (chelonida) evolved from Procolophon-like ancestor, but this is no longer considered the case.
During the early Triassic the Procolophonidae were extremely diverse and widespread, and they remained an important part of terrestrial ecosystems right until the end of the Triassic. Unlike Theraspids, they preferred dry arid conditions Olsen et al. Were one to envisage a plump desert lizard that eats plants rather than insects, that would give a good picture of what Procolophon and its cousins were like. |
 lllustration of skeleton (top) © David Peters; life restoration (bottom) © 2001 Vince R Ward - Prehistoric Pages
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Prolacerta broomi (Family Prolacertidae) was a medum-sized reptile, about a meter in length, whose fossil remains are known from the Lystrosaurus assemblage zone of South Africa and the Fremouw Formation of Antarctica. In habits and appearance it was probably very similar to a large lizard, apart from the enlrged hind legs, and doubtless filled the same ecological role in early Triassic Pangean ecosystems. But it was actually an early representative of the order Prolacertiformes; primitive members of the Archosauromorpha, the clan of "ruling reptiles" and their relatives. As medium-sized lizard-like forms with long hind legs for quick bipedal bursts of speed, the Prolacertiformes are little different in superficial appearance to the mostly Permian Younginiformes, and indeed both groups were for some time included under the (now no longer considered valid) Order Eosuchia. Details in osteology indicate however their relationships to the archosaurs
 Prolacerta broomi - artwork and some comments by Daniel Bensen. |
 illustration by Steve Kirk - Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals
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Proterosuchus fergusi from the Lystrosaurus zone, Beaufort Beds, of South Africa, was a primitive Archosauriforme, upto 1.5 metres in length, that lived a semi-aquatic, crocodile-like existence in a flood-plain pond environment, preying upon fish and labyrinthodont amphibians. Despite the superficial resemblence, Proterosuchus was actually rather more primitive then any crocodile, being a very early member of the (paraphyletic grade - not considered valid in cladistic phylogentics) group of reptiles called Thecodontia, the stem "ruling reptile" (archosaur) group from which all other forms developed. It was thus very close to the ancestry of all higher reptiles (Archosaurs) - crocodiles, dinosaurs, pterodactyls, birds, and a host of other types, all ultimately descended from this one type (or at least a creature very similiar to it).
The taxonomy of this animal is rather confusing, owing to a large amount of material that has been given different names. Chasmatosaurus vanhoepeni (= Proterosuchus vanhoepeni), Chasmatosaurus alexandri, and Elaphrosuchus rubidgei, from the same locality, are now considered synonyms. [Welman 1998]. Similar but distinct species are known from Russia (Chasmatosuchus rossicus and related forms, all poorly known), China (Proterosuchus yuani), India (Proterosuchus sp.), and Australia (Tasmaniosaurus triassicus). [Lucas 1998; Early Triassic World - Vertebrates]. It seems that these animals had a worldwide distribution during the period from the Early Induan (if not Latest Permian) to Early Olenekian. All are members of the Family Proterosuchidae, which were apparently the only thecodonts of this time. Their extinction was probably due to competition from the larger and apparently also semi-aquatic Erythrosuchidae. |
 illustration © Seiji Yamamoto
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| The herbivorous Lystrosaurus, a member of the dicynodont tribe, was the most ubiquitous and widespread animal during the earliest Triassic. They were squat quadrupedal forms, a little over a meter in length. Although originally thought to be semi-aquatic ( a sort of miniature reptilian
hippopotomus), study of functional morphology [King and Cluver 1991]
indicates that Lystrosaurus was fully terrestrial and capable of burrowing; this is supported by paleoenvironmental observations [Retallack and Hammer 1996]. So, lthough frequenting aquatic waterside and thickly vegetated terrestrial settings, it is most likely that these animals could also survive in arid environments, and their association with river sediments is more an artifact of preservation (since these were the conditions animals were most likely to be preserved
Lystrosaurus gives its name to the Upper Beaufort Lystrosaurus assemblage zone (In the Karoo of South Africa). The Lystrosaurus assemblage zone fauna developed in a warm temperate lowland with seasonal floods in lacustrine fluvial environments. The basinal flora comprised mixed Glossopteris (tree-like, not illustrated here) and Dicroidium (the low fern-like plants, above), while extensive coniferous forests (background) may have occupied the basin periphery. A Note on Lystrosaur Species: Although a number of species are known, these differ in only minor details, and some may still rturn out to be synonyms. The following species are listed on Early Triassic World - Vertebrates (only some of the synopnyms shown here): Lystrosaurus curvatus (Owen 1876) (= L. youngi) - Lystrosaurus Assemblage Zone, Middle Beaufort Beds, South Africa South Africa; Halfmoon Bluff, Fremouw Fm, Antarctica; Junggar and Turpan Basin, Xinjiang, Jiucaiyuan Fm, Tunghungshan Series, China. Lystrosaurus declivis (Owen 1860) - Lystrosaurus Zone, South Africa Lystrosaurus georgi Kalandadze 1975 - Vetluga River, Nizhegorodskaya Region, central European Russia Lystrosaurus hedini Young 1935, Jiucaiyuan Formation, Tunghungshan Series, China. Lystrosaurus mccaigi Seeley 1898 (= L. putterilli, L. amphibius) - Lystrosaurus Zone, South Africa; Panchet Fm, India; Shenk Peak, Fremouw Fm., Antarctica, Lystrosaurus murrayi (Huxley 1859) (= L. orientalis, L. frontosus, Prolystrosaurus natalensis, L. broomi, L. rubidgei, etc); Lystrosaurus Zone, South Africa; Fremouw Fm, Coalsack Bluff, Antarctica; Panchet Fm, India; Jiucaiyuan Fm, China. Lystrosaurus oviceps Haughton 1915 (= L. breyeri) - Lystrosaurus Zone, South Africa; Lystrosaurus platyceps Seeley 1898 (= L. andersoni) - Lystrosaurus Zone, South Africa; Panchet Fm, India. Lystrosaurus rajurkari Tripathi & Satsangi 1963 - Panchet Fm, India Lystrosaurus robustus (Sun 1973) (= L. latifrons) Jiucaiyuan Fm, China Lystrosaurus shichanggouensis Cheng 1986 - Jiucaiyuan Fm, China. Lystrosaurus weidenreichi Young 1939 - Jiacaiyuan Fm, China |
 illustration by Steve Kirk - Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals
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| Thrinaxodon liorhinus Seeley 1894 was a fairly small (total length about 50 cm) early cynodont, known from the Lystrosaurus zone, South Africa, and the Fremouw Formation of Antarctica; a furry creature on the direct line to the mammals. Although technically a reptile, it would have appeared mammal-like in form. Thrinaxodon fed on large invertebrates and smaller vertebrates, and during the Olenekian gave rise to larger and more advanced forms like Cynognathus. It is usually placed in the (paraphyletic) family Galesauridae |
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