Equisetaleans from the Bajo de Veliz Formation (Gzhelian-Asselian): a new key in the evolution of Gondwanan reproductive structures

ABSTRACT

Equisetaleans are a frequent floral element in the upper Palaeozoic of Gondwana and traditionally have been assigned to a few species of Phyllotheca based mainly on vegetative features. However, studies have suggested that the reproductive organs of Gondwanan equisetaleans may be more complex than previously thought, and new Gondwanan taxa have been reported during recent decades. The evolution of these plants is believed to have been driven by changes in their reproductive organs, including the emergence of simple sporangia or cruciate sporangiophores at the internodes as well as the development of strobilar structures. Here, we describe new records of Cruciatheca Cúneo et Escapa and Conustheca gen. nov. from Gzhelian-earliest Cisuralian deposits in the southeastern boundary of the Paganzo Basin, Argentina. The new species with whorls of strobilus-like structures provides further evidence of a diverse equisetalean flora across the southern continents. These records also suggest that the evolution of these equisetaleans was complex, with multiple lineages and distinct morphologies.

KEYWORDS:

• Equisetales
• sporangiophore
• strobilus
• latest Pennsylvanian
• Gondwana

Acknowledgments

We would like to thank Evelyn Kustatscher and Alexandru Tomescu for reviewing the manuscript and helpful suggestions. Ezequiel Vera provided useful comments on taxonomic issues. To Ignacio Escapa (Museo Egidio Feruglio) for providing some photographs of Cruciaetheca, and to Emmanuel Robert (Lyon University) for sending images of Autophyllites´s lectotype and paralectotypes for comparisons. Marian A. Tanuz (Palaeontological Repository, Buenos Aires University), Augusto Haro and Gladys Ortega (Palaeontological Museum, Córdoba University) facilitated the observation of the specimens in their collections. Jorge Chiesa is thanked for his valuable advice as co-director of Fernandez’s thesis. Grants PROICO 03-0218 (Chiesa) and PICT 2020-1294 (Césari) supported this research.

Disclosure statement

No potential conflict of interest was reported by the author(s)

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.