The recent discovery of the gargantuan four-legged creature Lisowicia bojani, from the Late Triassic period of Poland, has overturned established beliefs that the only giant herbivores to roam Triassic lands were dinosaurs, report Tomasz Sulej and Grzegorz Nied?wiedzki. Mammalian ancestors during the time were also capable of reaching gigantic body sizes, the finding suggests, opening the door to a flurry of new theories regarding the evolution, expansion and characteristics of dicynodonts during the Triassic. Dicynodonts were among the most abundant and diverse synapids (early four-legged land vertebrates that gave rise to modern-day mammals) from the middle Permian (around 299 to 251 million years ago) to the early Late Triassic (around 237 million years ago). Despite their dominance among herbivores during the Middle to Late Triassic, fossils of Triassic dicynodonts have only been abundant in Africa, Asia and North and South America, and comparatively scarce in regions like Europe. Lisowicia fossils were the first substantial dicynodont finds in European land. Estimated at 9,000 kilograms (nine tons), much bigger than other four-legged, non-dinosaur animals of the time, Lisowicia also had erect-gait forelimbs, suggesting upright limb posture, like that of modern large mammals such as rhinoceroses and hippopotami. Previously, Triassic dicynodonts were characterized only with sprawling forelimbs (the gait of reptiles).The discovery of Lisowicia suggests that dicynodont evolutionary history in the Late Triassic is more poorly documented than believed, and its excavation in Europe calls into question theories that giant dicynodonts were highly geographically restricted. The authors postulate that selection pressures on the animals, perhaps to protect themselves from large predators or to conserve more energy, were likely drivers of the evolution of Lisowicia's distinct upright posture and massive size.
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Journal
Science