Evolutionary oddball surfaces in Greenland.
Discovered on an expedition led by John S. Peel of the Geological Survey of Greenland and Simon Conway Morris of the University of Cambridge in England, the ancient creature bears the unofficial name Grasper, for a pair of appendages sticking out in front. Paleontologists have collected 50 or so partial skeletons of the animal, but they have found only one complete specimen. In a stroke of luck, the researchers discovered one half of the complete specimen in 1989 and then found the matching half when they returned to the same site in 1991.
"We knew Grasper was something different and very special," says Peel, recalling the initial find. But scientists did not begin studying the animal until after the discovery of its second half. In Chicago last week, at the Fifth North American Paleontological Convention, Graham E. Budd of Cambridge described the preliminary results of his work on the fossil.
Grasper and the other creatures found at the Greenland site provide a glimpse of life roughly 540 million years ago, soon after the "Cambrian explosion," an evolutionary burst that created the major existing divisions of animal life. During Precambrian time, which makes up some 87 percent of Earth's history, animal life evolved simple, coral-like and jellyfish-like forms about as complicated in shape as a dinner plate. These forms persisted for tens of millions of years, only to be replaced over a very short span by the appearance of the first complex animals in the early Cambrian. Paleontologists have found spectacularly preserved fossils of early Cambrian animals at three sites: the Burgess Shale in western Canada, Chengjiang in southwestern China and Sirius Passet in northern Greenland.
At all three sites, rocks have preserved a number of bizarre animals that do not readily fit into any phylum defined by modern organisms. Budd has found several strange features on Grasper. Most obvious are the long spines protruding from the front and rear of the body; these do not appear on any other known Cambrian animal, Budd says. In addition, Grasper has gill-like flaps along its sides -- a feature seen in only one other Cambrian animal, a weirdo called Opabinia that resembles a swimming vacuum cleaner.
But Grasper also has characteristics that may link it to some of its contemporaries. "The animal is bizarre; there's no doubt about it," says Budd. "But it's also important to look at the things that it appears to share in common with other animals, because that's the way you can try to classify it. It's quite easy to get bamboozled by the really bizarre aspects."
He points to several parts of Grasper's anatomy shared by animals called lobopods -- worm-like creatures with legs that look as though they have been inflated with a bicycle pump. Ancient lobopods and their modern counter-parts, in the phylum Onychophora, intrigue scientists because they may represent a link between two extremely successful phyla, Annelida (segmented worms) and Arthropoda.
Budd notes that Grasper has striations running across its back along with a double row of bumps -- both features found on Cambrian lobopods. The remarkable preservation of this animal also allowed Budd to study its internal musculature, where he found signs of circular muscles resembling those of modern onychophores. Furthermore, indentations on the fossil's underside suggest that it had stubby legs, a characteristic of Cambrian lobopods.
Yet Grasper's unique characteristics prevent it from fitting squarely into the lobopod group. Budd speculates that Grasper may be a lobopod that sported arthropod features such as gills. Other scientists say they hesitate to judge Budd's preliminary analyses because they have not yet had a chance to examine the new find. After viewing Budd's presentation last week, Desmond Collins of the Royal Ontario Museum in Toronto says he thinks Grasper looks more like an arthropod than a lobopod. Others don't know what to make of the beast.
The labels may seem of minor consequence, but the ultimate classification of the Cambrian oddballs will shape how scientists view patterns of animal evolution. If these creatures cannot fit into existing phyla, then the early seas held a great many more phyla than are recognized today.
In Wonderful Life: The Burgess Shale and the Nature of History (1989, Norton), paleontologist Stephen J. Gould of Harvard University argues that the Cambrian explosion created a great variety of fundamentally distinct body plans, most of which later disappeared, leaving the relatively few phyla found today. But a number of other scientists challenge that theory, saying that the number of phyla has remained relatively steady. Moreover, recent work has found homes for some of the most bizarre of the Cambrian animals, suggesting they do not represent unique phyla (SN: 5/18/91, p.310).
If Grasper is related to the lobopods, it may help scientists link other Cambrian oddballs, such as Opabinia, to existing phyla. Possessing characteristics of several phyla, the oddballs may represent intermediate forms that provide clues about how different body plans arose. Judging from Grasper's affinities with both lobopods and arthropods, Budd speculates that the arthropods may have developed from early gilled lobopods.
In the early Cambrian, he says, evolutionary forces apparently had great freedom to mix and match aspects of different phyla within a single organism. But soon after that period, the basic body plans emerged and the phyla grew distinct. "So the next challenge is to work out why it is that those changes could happen then, but don't appear to happen now," says Budd.
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|Title Annotation:||discovery of fossil remains of creature from Cambrian period|
|Date:||Jul 11, 1992|
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