Azolla Sporophytes and Spores from the Late Cretaceous and Paleocene of Patagonia, Argentina

Abstract

Premise of research. While Azolla has a rich fossil record based on dispersed megaspore apparatuses and microspore massulae, fossil sporophytes are relatively rare. In this contribution, we describe two fossil Azolla species based on both sporophytes and spores from Chubut Province, Patagonia, Argentina: Azolla coloniensis De Benedetti & Zamaloa, emend. Hermsen et al., and A. keuja Jud et al., sp. nov. Azolla coloniensis and A. keuja are the first fossil species of Azolla to be represented by vegetative structures (i.e., leaves, stems, and roots) from both South America and the Southern Hemisphere. Methodology. We examined sporophyte material of A. coloniensis from the Cañadón del Irupé locality, Upper Cretaceous, La Colonia Formation, and A. keuja from the Palacio de los Loros locality PL-2, Paleocene, Salamanca Formation. Spores of A. keuja were obtained from a sporophyte specimen and its surrounding rock matrix. Material was studied using standard light microscopy, epifluorescence microscopy, and scanning electron microscopy. Fossils are held at the Museo Paleontológico Egidio Feruglio,

Understanding the appearance of heterospory and derived plant reproductive strategies in the Devonian

“…The general lack of heterospory origins after the Carboniferous may also reflect the dominance of one specialized heterosporous clade, seed plants, which replaced free-sporing plants as primary components of wetland ecosystems following the climate-driven collapse of equatorial Pennsylvanian coal swamps (DiMichele et al 2001, 2006). For example, heterosporous lycopsids continued to exist after the Paleozoic, but as increasingly minor components of seed plant–dominated ecosystems (later forms reviewed in Pigg 2001), and ecological opportunities for new heterosporous lineages were likely reduced (although they obviously did occur, as shown by the evolution of very specialized heterosporous filicalean ferns in the Mesozoic; Lupia et al 2000; Yamada and Kato 2002; Hermsen et al 2019).…”

“…lycopsids continued to exist after the Paleozoic, but as increasingly minor components of seed plant-dominated ecosystems (later forms reviewed in Pigg 2001), and ecological opportunities for new heterosporous lineages were likely reduced (although they obviously did occur, as shown by the evolution of very specialized heterosporous filicalean ferns in the Mesozoic; Lupia et al 2000;Yamada and Kato 2002;Hermsen et al 2019).…”

Patagonia’s diverse but homogeneous early Paleocene forests: Angiosperm leaves from the Danian Salamanca and Peñas Coloradas formations, San Jorge Basin, Chubut, Argentina

“…endocarp, associated with a diagnostic leaf of the family (Jud et al, 2018b). In addition fertile sporophytes of the aquatic fern Azolla Lamarck, 1783 were recently reported (Hermsen et al, 2019). Insect-feeding damage on the fossil angiosperm and conifer leaves supported the first analyses of the effects of the Cretaceous-Paleogene (K-Pg) extinction on plant-insect food webs in the Southern Hemisphere (Donovan et al, 2016(Donovan et al, , 2018(Donovan et al, , 2020.…”

Reinterpretation ofPaleoazolla: a heterosporous water fern from the Late Cretaceous of Patagonia, Argentina

“…Fossils with putative affinities to Marsileaceae have been recorded from the Late Jurassic or Early Cretaceous (Yamada and Kato, 2002), although most of the macrofossils remains have been recovered from Late Cretaceous deposits (Sahni and Sitholey, 1943;Chitaley and Paradkar, 1972;Banerji, 1987;Skog and Dilcher, 1992;Lupia et al, 2000;Rich et al, 2001;Nagalingum, 2007;Hu et al, 2008;Herman and Kvaček, 2010;Cúneo et al, 2013;Hermsen et al, 2013;Puebla et al, 2014;Sender et al, 2014;Sun et al, 2014;Monje Dussán et al, 2016;Vallati et al, 2017;Estrada-Ruiz et al, 2018;Hermsen, 2019). The fossil record of Salviniaceae starts later, in the Late Cretaceous, and it is mostly based on dispersed megaspores and microspore massulae, while sporophytes are scarcely recorded (Hall, 1968;Bůžek et al, 1971Bůžek et al, , 1988Sweet and Chandrasekharam, 1973;Lucas and Ducket, 1980;Melchior and Hall, 1983;Kovach and Batten, 1989;Batten and Kovach, 1990;McIver and Basinger, 1993;Hoffman and Stockey, 1994;Collinson et al, 2013;Wang et al, 2014;Vallati et al, 2017;De Benedetti et al, 2018;Hermsen et al 2019).…”