Taxonomy and palaeoecology of the Mesozoic family Duotaxidae Mikhalevich (Foraminifera)

This paper addresses the long-standing taxonomic issue of the supra-species classification of Mesozoic taxa with an agglutinated wall originally included in the genus Tetrataxis, the type species of which, Tetrataxis conica, ranges into the Palaeozoic and has a different wall texture. Our investigation is based on the re-examination of the types of Mesozoic species assigned to Tetrataxis, and to the co-occurring genus Duotaxis. Moreover, we document their morphological variability and occurrences in different lithofacies types of two Tethyan carbonate platform sections, Mt Messapion (Pelagonian Platform, Greece) and Valle Agricola (Apennine Platform, Italy), encompassing the interval of the end-Triassic extinction (ETE). Our taxonomic investigation supports the validity of the genus Duotaxis and the necessity to erect a new genus named Kristanita to accommodate Mesozoic species incorrectly assigned to Tetrataxis. Duotaxis and Kristanita represent the only known genera of the family Duotaxidae (Class Spirillinata). This group possesses a well-developed umbilical cavity, a keeled periphery and supplementary structures on the umbilical side. Our study suggests that the Duotaxidae lived clinging or attached to rock or biogenic substrates in carbonate platform environments characterized by water turbulence and tolerated a high nutrient supply and sharp environmental changes. Both genera survived the ETE and were among the first colonizers of carbonate platforms long after the biotic crisis (Lazarus taxa). The eurytopic ecology and resilience to one of the big five extinctions in Earth's history may explain the long evolutionary history of Spirillinata and highlight their important role in the post-crisis recovery of benthic ecosystems.