Graptolite Fossils Offer New Insights On Colony Complexity
October 3, 2012

Old Graptolite Fossils Offer New Insights Into Colony Complexity

Alan McStravick for - Your Universe Online

In what is perhaps the best outcome of hoarding ever, researchers revisited the fossil records of a specimen that has been stored in a museum for over a century. Dr. Jan Zalasiewicz of the Department of Geology at the University of Leicester reviewed the fossil of the graptolite, a member of a planktonic colony that existed nearly a half billion years ago. This specific specimen was found in the Southern Uplands of Scotland.

Existing primarily during the Cambrian Period some 500 million years ago and surviving into the Early Carboniferous Period roughly 350 million years ago, graptolite is part of a group of aquatic colonial animals. Lacking any mineralized internal structure and having an exoskeleton that is best described as “fingernail-like,” the graptolite fossil record usually shows up preserved in carbonaceous impressions on black shale. These fossils, made up of flat impressions in the shale, usually lack any significant detail.

Long thought to have been extinct, the graptolite was re-discovered on the seafloor near New Caledonia in 1992 by Noel Dilly. While sorting through a whole host of specimens retrieved by French oceanographers, Dilly quickly realized that he had stumbled upon a creature that had been presumed extinct for more than 300 million years.

Dilly exclaimed, “I don´t want to sound arrogant, but I feel I must almost be in the same bracket as Dr. (J.L.B.) Smith.” The Dr. Smith to whom he referred was a South African chemist who, in 1938, while examining a sketch of a fish that was caught off Madagascar, realized he was looking at a coelacanth, an ancient lobe-finned fish thought to have been extinct for the better part of 100 million years.

Dilly continued, “Here I am, a complete outsider, who by virtue of an incredible stroke of good fortune has stumbled across something that is very exciting and very interesting.”

“I remember the morning vividly,” recounts Dilly, of the day he received the specimens. “I thought, ℠Oh my God, not another boring collection to hack through.´ And then when I took the first one out of the pot I thought, ℠This is like nothing I´ve seen.´ I saw those long needle-like processes, (a definitive characteristic of graptolite fossils), and thought, ℠I don´t believe this. There was about a 40-minute period when I was looking at these things through the microscope and waiting to wake up from a dream.”

Graptolites, floating organisms that once enjoyed wide global distribution due to ocean currents, have been found as fossils in a variety of locations around the planet.

In a study published in Geological Magazine, Dr. Zalasiewicz provides new evidence that these early organisms had developed highly specialized roles, showing a level of cooperation that had not even been considered previously. Specifically, the study focused on the multi-story floating ℠homes´ that the small graptolite constructed. Similar to how modern home builders utilize specialized laborers in the construction of homes — bricklayers, plasterers, decorators, etc. — the graptolite colonies displayed a sort of cooperative symbiosis and division of labor between different types of specialized workers.

While reviewing the fossils, Dr. Zalasiewicz noticed something that had been previously overlooked. Because the animals themselves are soft-bodied and decompose relatively quickly, the fossils tend not to show the animals themselves but rather the connections that existed between the animals.

These connections indicate that the animals of the colony could not have been all basically the same, as had been assumed. Rather, they must have been very different in shape and organization in different parts of the colony.

Dr Zalasiewicz said, "The light caught one of the fossils in just the right way, and it showed complex structures I had never seen in a graptolite before. It was a sheer stroke of luck “¦ one of those Eureka moments.”

“In some parts of the colony, these fossilized connections look like slender criss-crossing branches; others look like little hourglasses. Hence, a key element in the ancient success of these animals must have been an elaborate division of labor, in which different members of the colony took on different tasks, for feeding, building and so on. This amazing fossil shows sophisticated prehistoric co-operation, preserved in stone."

It has been a mystery how such tiny 'lowly' prehistoric creatures could have cooperated to build such impressively sophisticated living quarters. Now, this single fossil which has been carefully preserved in the collections of the British Geological Survey since 1882, sheds light on these ancient master builders.

Over that past century, the fossil slab had been examined by some of the world's leading experts on these fossils because it includes numerous specimens of a rare and unusual species.

Dr. Mike Howe, manager of the British Geological Survey's fossil collections and a co-author of the study, commented "This shows that museum collections are a treasure trove, where fossils collected long ago can drive new science."

This study was funded primarily by the British Geological Survey (BGS), a part of the Natural Environment Research Council (NERC).