During the Triassic period, between 252 and 201 million years ago, animals (reptiles according to some classifications) similar to mammals and called therapsids, coexisted with dinosaur ancestors, crocodiles, mammals, pterosaurs, turtles, frogs and lizards.
One group of these therapsids are the dicynodonts. Researchers from the University of Uppsala (Sweden), together with scientists from Poland, have discovered fossils of a new genus and species of gigantic dicynodont: Lisowicia bojani, described this week in the journal Science.
Dicynodonts were among the synapsids (early quadruped land vertebrates that gave rise to modern mammals) more abundant and diverse since the Middle Permian, between 299 and 251 million years ago, until the Early Upper Triassic –About 237 million years ago–.
All dicynodont species were herbivores and they varied greatly in size depending on the species. They survived the Permian period mass extinction and they became the dominant terrestrial herbivores in the Triassic middle and late.
It was believed that would have become extinct before the dinosaurs became the dominant form of tetrapods on Earth.
«Lisowicia's discovery changes our thinking about the more recent history of dicynodonts, Triassic relatives of mammals. It also raises a lot more questions about what really made them and the dinosaurs so big.«Says Tomasz Sulej of the Polish Academy of Sciences.
The Lisowicia fossils constitute the first important finds of dicynodonts in European lands. This giant animal was much larger than other quadrupeds of the time not classified as dinosaurs.
It is estimated that it would weigh about nine tons. His forelimbs were also erect, which suggests an upright posture, like that of large modern mammals such as the rhinoceros and the hippopotamus.
The first finds of its fossils were discovered in Poland in 2005 by Robert Borzęcki and Piotr Menducki. Since then, more than 1,000 bones and bone fragments have been collected in the area, including Lisowicia fossils. The area is believed to have been a fluvial deposit during the late Triassic.
«Dicynodonts were incredibly successful animals during the middle and late Triassic. Lisowicia is the youngest dicynodont and the largest terrestrial tetrapod, other than a dinosaur, from the Triassic. It is natural to want to know how dicynodonts became such large animals. Lisowicia's find is exciting because it shakes many of our classic ideas about mammalian-like reptiles”Says Grzegorz Niedzwiedzki from Uppsala University.
This finding suggests that the evolutionary history of the dicynodont in the Late Triassic is poorly documented. and their remains in Europe call into question theories that giant dicynodonts were highly geographically restricted.
The authors postulate that selection pressures on animals, perhaps to protect yourself from large predators or to conserve more energy, they were the engines of the evolution of the upright posture and the gigantic size of this animal.
«The discovery of such an important species is a once-in-a-lifetime find«Sulej concludes.
Tomasz Sulej, Grzegorz Niedźwiedzki. "An elephant-sized Late Triassic synapsid with erect limbs" Science http://science.sciencemag.org/lookup/doi/10.1126/science.aal4853.
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