Fossil wood of the Mimosoideae from the early Paleocene of Patagonia, Argentina

Abstract

Brea, M., Zamuner, A.B., Matheos, S.D., Iglesias, A. & Zucol, A.F., December, 2008. Fossil wood of the Mimosoideae from the early Paleocene of Patagonia, Argentina. Alcheringa 32, 427–441. ISSN 0311-5518.

An anatomically preserved mature stem from the Salamanca Formation (early Paleocene) at Palacio de Los Loros, central Patagonia, Argentina, is described and assigned to Paracacioxylon frenguellii sp. nov. The material was preserved by siliceous permineralization and shows features of the secondary xylem typical of subfamily Mimosoideae. This species represents the oldest record of the genus and of the Leguminosae along the western border of Gondwana, and is the world's second oldest record of Leguminosae wood. The species is characterized by ring-porous to semi-ring-porous vessels that are solitary, in multiples of 2–4 and clustered, simple perforation plates, alternate and vestured inter-vessel pitting, homocellular 1–6 seriate rays, tyloses, crystals and diffuse apotracheal, vasicentric paratracheal and confluent axial parenchyma. Paracacioxylon frenguellii has anatomical similarities to Acacia Miller. The presence of Paracacioxylon frenguellii associated with pulvinate leaves suggests that the legumes might have been a component of mesothermal forests developed along the western margin of the Golfo San Jorge Basin during the early Paleocene.

Key words:

• Argentina
• Patagonia
• early Paleocene
• Salamanca Formation
• fossil wood
• Mimosoideae
• Paracacioxylon

Acknowledgements

The authors would like to express their thanks to Elisabeth Wheeler and Imogen Poole for their valuable help in providing critical and constructive comments on a previous version of the manuscript. Their observations have substantially improved the text. We are also grateful to Patricia Sarmiento who took the scanning electron micrographs in Fig. 5. This work was financially supported by the ‘Consejo Nacional de Investigaciones Científicas y Técnicas’, Project PIP-CONICET 1050/98, PIP-CONICET 5079/05 and ‘Agencia Nacional de Promoción Científica y Técnológicas’, Project PICT 07-08671. We gratefully acknowledge the National Science Foundation Grant DEB-0345750 for technical support. The authors are thankful to the Secretaria de Cultura del Chubut, Panamerican Energy, V. Szlápelis, C. Salazar and H. Visser for the land permits. The authors express their acknowledgement to the Editor and reviewers of Alcheringa for correcting the English text and for critically appraising the manuscript.