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An elephant-sized Late Triassic synapsid with erect limbs

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Science  04 Jan 2019:
Vol. 363, Issue 6422, pp. 78-80
DOI: 10.1126/science.aal4853

A proto-mammalian giant

Early terrestrial amniotes evolved into two groups: the sauropsids, which led to the bird and dinosaur lineages, and the synapsids, which led to mammals. Synapsids were diverse during the Permian but were greatly reduced after the end-Permian extinction (about 252 million years ago). The few groups that survived into the Triassic were mostly small and retained a sprawling gait. Sulej and Niedźwiedzki, however, describe a dicynodont from the Late Triassic of Poland that is as large as some coexisting dinosaurs and appears to have had an erect gait—like modern mammals. Thus, megaherbivores in the Triassic were not only dinosaurs.

Science, this issue p. 78

Abstract

Here, we describe the dicynodont Lisowicia bojani, from the Late Triassic of Poland, a gigantic synapsid with seemingly upright subcursorial limbs that reached an estimated length of more than 4.5 meters, height of 2.6 meters, and body mass of 9 tons. Lisowicia is the youngest undisputed dicynodont and the largest nondinosaurian terrestrial tetrapod from the Triassic. The lack of lines of arrested growth and the highly remodeled cortex of its limb bones suggest permanently rapid growth and recalls that of dinosaurs and mammals. The discovery of Lisowicia overturns the established picture of the Triassic megaherbivore radiation as a phenomenon restricted to dinosaurs and shows that stem-group mammals were capable of reaching body sizes that were not attained again in mammalian evolution until the latest Eocene.

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