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Depositional palaeoenvironments in a tide-influenced delta plain with amphibian and Cycadophyta remains – the Triassic Zarzaitine Formation (Algerian eastern Sahara)

Mazrou S., Lasnami Y., Amer J., Boutaleb A.

Geologos

2024

Vol. 30, No. 3

209--229

In the region of In Amenas (south-eastern Algeria) Triassic deposits crop out, on top of Palaeozoic rocks under an angular unconformity. A study of their sedimentological and palaeoenvironmental characteristics has revealed a sandy-clay unit with vertebrate remains, tree trunks and ichnofossils of Middle-Late Triassic age. This so-called Zarzaitine Formation, which reflects deposition in a deltaic environment, shows three facies associations. The first defines an upper and shallow intertidal mixed flat zone with in-situ temnospondyl capitosauroid remains, associated with Skolithos ichnofacies, while the second one defines a lower intertidal delta plain zone, composed of sandstone, distributary channels and muddy interdistributary areas,which record daily tidal rhythmites and monthly tidal bundles. The third, and last, facies association represents an upper delta plain of the supratidal zone, characterised by coarse sandstone deposits of braided rivers and a Cycadophyta palaeosol. Previous work, which led to considering these Triassic deposits as a series composed of four formations, deposited in a braided rivers environment, whose lower floodplains constituted ecological niche for a temnospondyl fauna, under hot and dry climatic conditions and plants belonging to this same formation, for mushrooms and algae, will also be considered.

Morphometrics of the mandible of Metoposaurus krasiejowensis Sulej, 2002 and its ecological implications

Quarto Luka F., Antczak Mateusz

Acta Geologica Polonica

2024

Vol. 74, no. 3

art. no. e18

Amphibians, due to their ecological plasticity, are some of the best environmental indicators among vertebrates nowadays and in the fossil record. One such example is the extinct family Metoposauridae Watson, 1919. Metoposaurids were abundant amphibians in Late Triassic Pangea. The remains of the genus Metoposaurus Lydekker, 1890 have been found in Germany, Poland and Portugal with three species, respectively Metoposaurus diagnosticus (Meyer, 1842), Metoposaurus krasiejowensis Sulej, 2002 and Metoposaurus algarvensis Brusatte, Butler, Mateus and Steyer, 2015. Since the majority of studies concern the skull and the pectoral girdle, in this work M. krasiejowensis has been analysed through a morphometric study of the mandible. This was made possible by the high abundance of fossils found in Krasiejów (SW Poland) in the last 20 years. The characteristics considered are the morphology of the mandible corpus and its most relevant bones, the adaptation to stress during biting and the dermal ornamentation. The results reveal that not only do these characters have great intraspecific variability, but that at least two groups of a single population of M. krasiejowensis probably had different lifestyles, one more aquatic and the other more terrestrial.