Over 100 million years ago, the understory of late Mesozoic forests was dominated by a diverse group of plants of the class Equisetopsida. Today, only one genus from this group, Equisetum (also known as horsetail or scouring rush), existsand it is a prime candidate for being the oldest extant genus of land plant.
There is some debate as to the evolutionary beginnings of the genus Equisetum. Molecular dating places the divergence of the 15 extant species of the genus around 65 million years ago (mya), yet the fossil record suggests that it occurred earlier than that, perhaps around 136 mya. A discovery of a new fossil Equisetum species now places this genus at 150 mya, living in an environment where it still can be found todayhot springs.
Hot spring ecosystems and how they become fossilized are the main areas of research interest for Alan Channing, a geobiologist at Cardiff University, Wales. When he and colleagues from Wales and Argentina discovered the abundant fossilized remains of a species of Equisetum in southern Patagonia, they realized that not only could these fossils shed light on the phylogenetic age of this group of ancient plants, but they could also tell us something about how these plants lived, what types of environments they were adapted to, and their ecology and physiology. Moreover, they were intrigued to find out how closely these aspects might match extant species of Equisetum, especially those living in similar environments today. Their findings are published in the April issue of the American Journal of Botany (http://www.amjbot.org/cgi/reprint/98/4/680).
When Channing and his colleagues first began working in the remote Deseado Massif of Santa Cruz Province, Argentinaan area of ancient volcanic rocksthey did not know if they would find plant fossils. But the discovery of a near-intact and extremely well-exposed fossil hot spring deposit of Jurassic age at San Agustin
|Contact: Richard Hund|
American Journal of Botany