Taxonomic position and palaeoecology of Palaeoaplysina: insights from the lower Permian (Asselian) of Svalbard

초록

Relatively large organisms that build massive reefs are often absent from late Carboniferous and early Permian reefs, which are instead dominated by smaller constructors such as calcareous algae, calcified sponges, and bryozoans. Palaeoaplysina Krotov, 1888 was a unique and enigmatic reef-builder during this time interval, and is notable for its relatively short stratigraphical range. The biological affinity of this organism is debated. This study investigates the growth behaviour and palaeoecological role of Palaeoaplysina within biostromal buildups dominated by this taxon from the Asselian part of the Tyrrellfjellet Member, Wordiekammen Formation (lower Permian), Svalbard, Norway. Palaeoaplysina characteristically consists of thin plates with consistent thickness. The thallus displays regularly distributed pores of varying sizes, resulting in the differentiation of hypothallus and perithallus. The pores are infilled with either micritic sediment or sparry cement. The pore openings in the perithallus gradually narrow upwards. The intraskeletal architecture is partially preserved, with characteristic circular to polygonal cellular patterns. Evidence indicates that Palaeoaplysina displayed encrusting and recumbent growth habits on unconsolidated substrates, and thus most likely performed a role of sediment stabilisation and formation of cryptic microhabitats for small encrusters such as bryozoans and foraminifers. The distribution of encrusting organisms indicates a strong ecological partitioning, with cryptobionts preferentially colonising the undersides of Palaeoaplysina plates. Comparative morphological and structural analysis supports an algal affinity for Palaeoaplysina, most likely among coralline red algae, rather than a poriferan or hydrozoan affinity. The palaeogeographical distribution of Palaeoaplysina was largely restricted to the northern margin of Pangaea, with an outlier occurrence in Japan, likely reflecting preservation bias. Alternatively, Palaeoaplysina may have been a provincial coralline alga, related to Archaeolithophyllales. Taken together, these results indicate that Palaeoaplysina, with its recumbent growth habit, contributed to sediment stabilisation and the development of small-scale habitats in late Carboniferous to early Permian carbonate platforms during a prolonged interval of reef recovery following the Late Devonian biotic crisis. (c) 2026 Nanjing Institute of Geology and Palaeontology. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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