Fossils of Ancient Member of the Daisy Family Discovered in Argentina

The Dutch born, post impressionist, artist Vincent Van Gogh famously painted a number of still life pictures of sunflowers.  One such painting was sold at auction in the late 1980s for a little under $40 million USD.  However, researchers at the Argentinian Museum of National Sciences have discovered their own “portrait of sunflowers” with the finding of two exquisitely preserved fossilised flowering heads in southern Patagonia (Argentina).  Sunflowers are members of the Asteraceae (otherwise known as Compositae – we think) Family.  This family of flowering plants (Angiosperms), is one of the most diverse and widespread of all the plant families.  This family includes plants such as the daisy, dandelion and commercially important plants such as the tea bush and sunflowers.

Plant material is rarely preserved as a whole fossil, for instance, a fossil of the entire plant with roots, leaves and flowers all together.  Fossils normally occur as isolated individual parts such as cones, pollen grains, pieces of trunk and such like.  Delicate flowering heads (capitula) are extremely rare in the fossil record.  However, the discovery of a fossil that shows two complete flower heads, winged seeds and the flower stem is helping scientists to understand the evolution of this very important group of plants.

The fossil has been dated to approximately 47.5 million years ago (Eocene Epoch) and it was found in strata along the Pichi Leufu river.  During the Eocene, this part of the world had a sub-tropical climate with average temperatures of around 19 degrees Celsius.  The dense flower-head would have been attractive to pollinating insects, suggesting that flowers such as these primitive ancestors of the sunflower already had a long established relationship with insect pollinators.

Sunflowers

Dr Viviana Barreda, one of the authors of the paper, the details of which have been published in the journal “Science”, suggests that the finding of this fossil supports the hypothesis that the ancestors of the Asteraceae Family evolved in the southern region of Gondwanaland and spread to most of this super-continent before this landmass began to break up.  This would explain the wide geographical dispersal of related genera.

Scientists believe that the common ancestor to a number of related plant families first evolved in sub-tropical Antarctica, (which was part of Gondwanaland), before migrating to Australia and South America as Antarctica cooled and became an unfavourable climate for most plant species.

Commenting on the discovery, University of Vienna (Austria) botanist, Dr Tod Stuessy stated that this fossil and the related pollen grains were clear evidence of the existence of the sunflower sub-family at the early stages of Asteraceae diversification.  Dr Stuessy wrote an accompanying article to the Argentinian scientific paper.  He went on to add that little is known about the origins of sunflowers and there is much still to learn about how these plants evolved and spread all over the world or indeed how members of the Asteraceae became so “incredibly diverse.”

The scientific paper on which the journal article is based is the culmination of two years of research.

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