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) harbours 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 morphogroup is the smallest, characterised by the fewest and smallest verrucae, followed by the green morphogroup. Conversely, the red and orange morphogroups show the lowest and highest number of constrictions in the cingulum, respectively. However, the LDA biplot shows significant overlap between the blue and green morphogroups, suggesting that they represent a single morphological entity; nevertheless, the correlation seen between the distinct studied variables indicates that each recognised assemblage could correspond to groups of spores at different stages of development. Irrespective of the underlying causes of morphological variation, multivariate statistical analyses consistently support the recognition of three distinct taxa. However, the presence of intermediate forms exhibiting continuous variation in diagnostic traits suggests phenotypic continuity, which justifies the integration of these assemblages within the Antulsporites incipiens morphon. Accordingly, we propose the following species: Antulsporites incipiens sp. nov. (blue + green morphogroups), Antulsporites robustus sp. nov. (red morphogroup) and Antulsporites constrictus sp. nov. (orange morphogroup). 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.