Early life forms had a modular structure

Science News, July 31, 2004

A cache of fossils recently unearthed in northeastern Newfoundland reveals that some of Earth's earliest large organisms had modular body plans whose main architectural element was a branching, frondlike structure.

The organisms--scientists debate whether they were animals, plants, or neither--grew into flat, plumed, and floral shapes. The ancient creatures were entombed in fine-grained mud deposited on the seafloor about 565 million years ago, says Guy M. Narbonne, a paleontologist at Queen's University in Kingston, Ontario. The sediments, some of which infiltrated the soft-bodied organisms, preserved internal and external body features as small as 30 micrometers across.

The Canadian fossils are the oldest known examples of large, multicellular creatures and the first of their type to be found preserved as three-dimensional casts. Some of the organisms grew on stalks from the ocean floor and reached 1 meter or so in length; other species that lay on the sea bottom grew up to 2 m long. Narbonne describes the relics in an upcoming Science.

The fossils include multiple frondlike structures, each of which is approximately 3 centimeters long and made up of branching tubes. The largest tubes are a few millimeters in diameter, and the ones that grow directly from them average about 0.5 mm across. The smallest tubes in the structures measure less than 0.15 mm in diameter. Narbonne notes that this type of creature--known as a rangeomorph--became extinct about 540 million years ago and doesn't appear to be related to any organisms that have lived since.--S.P.