Abstract Detail



Paleobotany

De Benedetti, Facundo [1], Zamaloa, Maria Del Carmen [2], Gandolfo, Maria [3], Cuneo, Nestor [4].

Late Cretaceous heterosporous water ferns from Patagonia: assessing heterochrony and monomegaspory.

Marsileaceae and Salviniaceae form a monophyletic group of heterosporous water ferns. Extant Marsileaceae comprises three genera (Marsilea, Regnellidium, and Pilularia) while Salviniaceae includes two genera (Azolla and Salvinia). Although the fossil record of water ferns starts at the Late Jurassic, they diversified during the late Cretaceous at the same time that the flowering plants, nevertheless after the K/pg boundary they rapidly declined in diversity. Their fossil record is mostly based on dispersed megaspores and microspores or microspore massulae encompassing many genera and species. Among these species, it is the Late Cretaceous Paleoazolla patagonica from Patagonia, Argentina, which was placed within Salviniaceae. The original diagnosis of Paleoazolla denotes that the megaspore apparatus has a single megaspore and a complex of three to four floats covered by multibarbed hairs, the microspore massulae contain numerous rounded microspores and have multibarbed glochidia. However, recently collected specimens and additional observations of the original material allow a new interpretation of Paleoazolla’s morphological and ultrastructural features. Our interpretation suggests that the heterosporangiate sorus is composed of one ellipsoidal megasporangium surrounded by three to four oval microsporangia; the megasporangium bears a single hairy massula that encloses two megaspores (rarely one or three) whereas the microsporangia contain numerous microspore massulae with non-septate multibarbed glochidia, and one microspore per massula. Based on this evidence, we propose that heterochronic processes were probably involved in the evolution of the homosporangiate sori in Azolla. Furthermore, the presence of two megaspores in Paleoazolla’s megasporangium definitely reveals critical gaps in our current knowledge on the evolution of monomegaspory in heterosporous water ferns and emphasizes the need for phylogenies including fossils for elucidating patterns of character acquisition.


1 - Museo Paleontológico Egidio Feruglio, Avenida Fontana 140, Trelew, U, 9100, Argentina
2 - Universidad De Buenos Aires, Ecologia, Genética Y Evolucion, Ciudad Universitaria. Pab 2. Piso 4, Buenos Aires, 1428, Argentina
3 - Cornell University, L.H. Bailey Hortorium, Section Of Plant Biology, 410 Mann Library Building, Ithaca, NY, 14853.0, United States
4 - MEF, Av. Fontana 140, Trelew-Chubut, U, 9100, Argentina

Keywords:
water ferns
heterochrony
fossil
megaspores
Late Cretaceous
Patagonia.

Presentation Type: Oral Paper
Number: 0004
Abstract ID:117
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award


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