Eucalyptus Fossils from Argentina
Eucalyptus trees may be restricted to Australia and its outlying islands these days but new fossil evidence suggests that this ancient type of tree may have flourished in South America. Fossils of leaves, flowers, fruits and buds found in Patagonia (Argentina) indicate that this type of tree was around in the Palaeogene and they represent the only scientifically validated Eucalyptus macro-fossils identified from outside Australasia.
The fossils have been dated to approximately 52 million years ago and represent a sub-genus of Eucalyptus known as Symphyomyrtus, which makes this sub-genus much more ancient than previously thought.
The research team identified a number of structures characteristic of Eucalyptus in the morphology (shape) of imprints of plant material preserved as fossils. Some key features included, long, thin leaves with smooth edges, dots on the leaves that reveal oil glands and scars on the fruits where petals and sepals fell off. The evolution of the Eucalyptus and its relatives has been poorly documented, due to the lack of fossil evidence. In the past, a few scientists had claimed to identify Eucalyptus fossils from South America but those records failed to hold up to formal scientific scrutiny using modern research techniques.
Maria A. Gandolfo, a senior researcher in the Dept. of Plant Biology at Cornell University and one of the lead authors on the paper stated:
“The genus Eucalyptus is restricted to Australia and a few surrounding islands, and it is completely extinct in South America which makes this discovery very significant not only for botanists and palaeobotanists but also for [its] biogeographical implications.”
The fossils were found at a site called Laguna del Hunco, northwestern Chubut Province in Patagonia. Although petroleum exploration geologists first discovered fossils at this site in 1932, a team of researchers from the United States and Argentina including Gandolfo and Elizabeth Hermsen, a postdoctoral associate working in Gandolfo’s lab, collected important fossils in 2009 that included fruits, branching structures that support the fruits, three flower buds and a flower.
Elizabeth, who is also a lead author on the scientific paper detailing the research team’s work said:
“The buds provided important information that placed them within the genus Eucalyptus; they really helped clinch the identity of the fossils.”
The researchers also used a computer programme and analysis of the morphology to create a phylogeny, a branching diagram that depicts the evolutionary relatedness among groups of organisms (species, populations and so on), of Eucalyptus. Because the researchers were able to accurately date the fossils and then place them in a phylogenetic context in relation to living plants, the findings may now be used as a reference point to test the results of recent molecular dating studies that have calculated the age of the Eucalypts.
The research was conducted in collaboration with colleagues from Pennsylvania State University, the Denver Museum of Nature and Science, the Universidad de Buenos Aires and Museo Paleontológico E. Feruglio, Argentina. The work was funded by an American Recovery and Reinvestment Act Grant from the National Science Foundation to Gandolfo.