The discovery, made on Bathurst Island in the Northwest Territories about 800 miles from the North Pole, shows vascular plants were more complex at that time than paleontologists previously believed and is significant for that reason, the UNC researcher said.
"These are not the earliest vascular plants ever found, but they are the earliest ever found of this size, complexity and degree of diversification," said Dr. Patricia G. Gensel, professor of biology at UNC. "They look something like medium-sized grasses, except that they branch."
The discovery adds to the sparse record of early land plants known from North America, Gensel said. Previously, most information on ancient plants has been based on fossils from Wales, Venezuela and China.
A report about the findings appears in the June issue of the American Journal of Botany. Besides Gensel, authors are UNC graduate student Michele E. Kotyk, Dr. James F. Basinger, professor of geology at the University of Saskatchewan, and Dr. Tim A. de Freitas, a Calgary, Canada geologist working for Nexen Inc.
Bits and pieces of the earliest known land plants date back almost 500 million years to the Ordovician Period, and their fragmentary remains indicate the plants were related to liverworts that exist today, Gensel said. The earliest vascular plants -- ones with water-conducting tissues -- so far are known to date back about 425 million years. Sparsely branched, they were about an eighth of an inch tall and grew a few reproductive bodies known as sporangia on their branches.
By contrast, the new plants, which lived only a few million years later, would have stood four or more inches tall, bore many branches with dense rows of sporangia and probably grew in clusters, she said. They more closely resembled much younger early Devonian plants from about 390 million years ago than any other Silurian forms.
"We found these previously unknown plants in rocky sediments we collected and brought back first by helicopter and then airplane from Bathurst in 1994," the biologist said. "Because of permafrost, digging is impossible, and we picked them up and chipped them out from exposed slopes on the almost completely barren island. Although we worked in July, some days it stayed near freezing all day long. When these plants were alive this land lay near the equator."
The team dated specimens by finding them in the same layers as several tiny invertebrate fossilized animals such as graptolites, which under the microscope resemble band saw blades, and conodonts, which resemble miniature jaws and teeth and represent the mouthparts of primitive vertebrates. Such animal remains are excellent index fossils - fossils that indicate time.
"We conclude that the Bathurst Island flora presents the best evidence to date of substantial diversity of form, complexity and stature of vascular plants in this period," Gensel said.
In 1996, she and colleagues in Virginia and Northern Ireland reported finding fossils of scorpions, millipedes and related arthropods dating back almost 400 million years. Those creatures, which predated dinosaurs and other reptiles by some 50 million to 100 million years, were the largest animals ever found on land up to that time in North America.
"Much of science is devoted to understanding and curing diseases, and that's as it should be," Gensel said. "However, we also need to understand where living things have come from, which we can do by studying fossils. That gives us a better perspective on why the Earth and life are as they are today."
Note: Gensel can be reached at (919) 962-6937 or email@example.com
Contact: David Williamson, (919) 962-8596.
By DAVID WILLIAMSON
UNC News Services