Morphometric analysis of Antulsporites spores from the Middle Triassic of southwestern Gondwana: paleobiological, stratigraphic and paleoenvironmental implications

The Cerro de Las Cabras Formation (Middle Triassic) harbors a diverse assemblage of palynomorphs, including pollen grains, spores, algae, and fungi. However, despite extensive studies conducted on this unit, several forms of miospores remain unclassified or with an open nomenclature. Among them is a suite of spores attributed to the genus Antulsporites that exhibit broad morphological variability, complicating their taxonomic classification when relying on conventional methods. Multivariate statistical analyses are well-suited for distinguishing individuals based on their combined morphological (dis)similarities. Hierarchical clustering identified four morphogroups, designated as Blue, Green, Red, and Orange. Boxplot diagrams and PCA biplots reveal that the Blue group is the smallest, characterized by the fewest and smallest verrucae, followed by the Green group. Conversely, the Red and Orange groups show the lowest and highest number of constrictions in the cingulum, respectively. However, the LDA biplot shows significant overlap between the Blue and Green groups, suggesting that they represent a single morphological entity; nevertheless, the correlation seen between the distinct studied variables indicates that each recognized assemblage could correspond to groups of spores at different stages of development. Accordingly, three distinct taxa, linked through intermediate forms, are proposed: Antulsporites incipiens sp. nov., Antulsporites robustus sp. nov., and Antulsporites constrictus sp. nov. The occurrence of Antulsporites species in the upper Anisian–lower Ladinian of central-western Argentina marks the genus's earliest global record. Antulsporites' parent plant (Bryophytes) likely exhibited ruderal strategies and hygrophytic preferences, implying that increased spore abundance reflects brief, transient humidity spikes within an otherwise semi-arid environment.