An updated stratigraphic and environmental framework for the distribution of Silurian vertebrates on Gotland

Abstract

In this work, previously published occurrences of vertebrates from the latest Llandovery to end-Ludlow successions of Gotland, Sweden, are gathered and summarized in an updated stratigraphic framework, which also incorporates facies differences of sedimentary units. Even though the taxonomy of vertebrates from Gotland is in need of revision, their occurrences are here reported on a group level in order to give preliminary indications of where the focus of continued sampling should lie. Indeed, there are parts of Gotland that are poorly represented by the samples at hand and others that have been extensively sampled but still have not yielded any vertebrates. Preliminary investigations of new samples indicate that the lack of vertebrates in older sediments of Gotland may be because of sampling bias, while the reasons for a complete absence of vertebrates in other parts remain unknown. Our results also emphasize a sudden appearance of acanthodians on Gotland in the early Ludfordian. To investigate these preliminary results, complementary sampling and more confined facies-categorization will be needed. Combined with a higher taxonomical resolution, this will also help us understand how the vertebrate faunas were affected by the events coupled with extinctions that have been identified on Gotland and on a global scale. One of these events has been shown to affect the Gotland vertebrates before. Our results indicate that this may be true for several of the events. When an increased understanding of the vertebrate faunas of Gotland has been established, the goal is to use up-to-date correlations to compare Gotland with other parts of the Baltic Basin to render a better picture of early vertebrate evolution during the Silurian.

Keywords

• vertebrate distribution
• stratigraphy
• facies
• Silurian events
• Gotland
• Sweden.