Assembling a Jurassic puzzle: anatomically preserved conifer remains in hot spring deposits from Santa Cruz Province, Argentina.

ESCAPA I.E.; GARCIA MASSINI J.L.; NUNES, CRISTINA; D. M. GUIDO

Minnesota

Congreso; Botanical Society of America congress; 2018

Jurassic hot-spring chert deposits in the Deseado Massif (Patagonia, Argentina) have been known for over two decades, but the associated biota has only begun to be documented recently, and thus far only from a small number of localities. Paleo-hot spring sites of the Deseado Massif include a total of 23 locations, several of which have differentially preserved biotic components of the Jurassic ecosystems in Patagonia. The chert samples contain exceptionally preserved, in-situ and transported, tri-dimensionally silicified plants, animals and microorganisms. The Jurassic flora from Santa Cruz Province is well known for two emblematic conifer taxa, Araucaria mirabilis (Araucariaceae) and Pararaucaria patagonica (Cheirolepidaceae), delimiting an association with an important role in the Jurassic forests of both hemispheres. Paleobiological information on these taxa has been based primarily on anatomically preserved seed cones. Here we report the discovery of anatomically preserved leafy twigs, pollen cones and isolated seeds. Two different types of leaves were found, both of Brachyphyllum type, but with marked anatomical differences (e.g., number of vascular bundles, presence/absence of resin canals). Well preserved mycorrhizal root nodules are also present, displaying fungal arbuscules, hyphal coils, and putative vesicles. Altogether, this geothermally preserved biota provides a unique opportunity to develop more complete plant concepts for Araucaria and Pararaucaria, and to understand their biological interactions in the context of the Jurassic ecosystems in Gondwana.