What is the Rhynie Chert?

The Rhynie chert is a fossil bed located near the village of Rhynie in Scotland. It is famous for containing exceptionally preserved fossils of some of the earliest known terrestrial life, including both plants and animals (arthropods). The Rhynie chert is dated to the Early Devonian, about 396 million years ago. The preservation is so remarkable that the outlines of individual cells can be observed when the chert is polished.

Chert is a sedimentary rock composed of an agglomeration of several different quartz varieties. At Rhynie, the fossiliferous strata formed when a hot spring released silicaeous water which rose and preserved the plants and animals in situ. The ecosystem was mineralized in excellent condition, for us to discover 396 million years later. A modern-day example of this phenomenon would be at the hot springs at Yellowstone Park in the United States.

The land plant fossils preserved in the Rhynie chert are the best and most diverse of their age, making the chert a cornerstone of paleobotany. Although land plants, such as algae and mosses, had existed since the Late Cambrian, about 500 million years ago, they didn't diversify until the Silurian, about 420 million years ago. Around the time of the Rhynie chert, the first plants with vascular tissues appeared. Vascular tissues are used to ferry water and nutrients around within plants. Without them, plants are basically mosses and close relatives, and can't grow more than a few inches tall.

Some of the plant varieties found in the Rhynie chert include Aglaophyton, Asteroxylon, Horneophyton, Nothia, Rhynia, Trichopherophyton, and Ventarura. Five of seven genera of land plants from the Rhynie chert contain vascular tissue. These plants were between 15 and 40 cm (6 - 16 in) in height, small for today, but large for the time. The plants had extensive subterranean branching networks of rhizomes, bulbs covered with root hairs to absorb nutrients. There is evidence of symbiosis with fungi in the roots, a symbiosis that continues in the majority of land plants to this day. Plants exploit the greater surface area of the tiny fungal hyphae to absorb nutrients, while the fungi take a cut of the nutrients for their own survival.

The arthropods unearthed with the Rhynie chert are all relatively tiny, and include springtails (Collembola), harvestmen (also known as daddy long-legs), pseudoscorpions (tiny scorpion-like predators), mites (Acari), myriapods (ancestors of centipedes), small crustaceans (in the freshwater portion), odd aquatic organisms called Euthycarcinoids, and Trigonotarbids (extinct relatives of spiders). No winged insects have been found, but some show derived chracteristics often associated with winged insects, so it is possible that insect flight evolved millions of years prior.