Did Metoposaurus Aestivate in the Carnian Triassic of Poland?

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Krasiejów, Poland was a vastly different place 230 million years ago during the Triassic Period. It was part of a giant continent called Pangea, had a warm climate throughout the year, and was populated by giant amphibians that weighed half a ton and were 10 feet long. Metoposaurus diagnosticus was one of these giant amphibians, and its environment had only two seasons: wet and dry. Like modern amphibians, Metoposaurus needed water for its lifestyle, but the extremely long dry season in Triassic Krasiejów drove this species to burrow underground and go dormant when water was scarce.

The burrowing behavior of Metoposaurus was recently discovered by Dorota Konietzko-Meier of the University of Opole, Poland and the University of Bonn, Germany, and P. Martin Sander also of the University of Bonn and was recently published in a study in the Journal of Vertebrate Paleontology. This study examined both the overall structure of the skeleton of Metoposaurus as well as the microscopic structure of its bones.

The broad, flat head, broad flat arm bones, wide hands, and large tail of Metaposaurus diagnosticus led the investigators to conclude that this species swam in ephemeral lakes during the wet season and used its broad, flat head and forearms to burrow under the ground when the dry season began. The authors also examined cross-sections of the bones of Metoposaurus looking for growth rings, called annuli. These annuli are similar to tree rings, where a band of light and a band of dark indicate one year of growth. In other early amphibians one annulus usually consists of a broad zone of rapid growth (wet season) followed by a thin band of slow growth (dry season), but in Metoposaurus, a period of prolonged slow growth was followed by a cessation of growth during the dry season. According to lead author Dorota Konietzo-Meier, "The histology of Metoposaurus long bones seems to be unique. In our interpretation it corresponds to the two-seasonal climate with a short, more favorable wet season and a long dry part of the year when life conditions were worse."

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