New creatures from Cambrian.

At the turn of the century paleontologist Charles Walcott stumbled upon a remarkable fossil find in the shale layers of Mt. Burgess in British Columbia. The well-preserved remains of more than 100 species of arthropods (invertebrates such as insects, scorpions and millipedes), sponges and other creatures, embedded in the Burgess shale since the Middle Cambrian 530 million years ago, provided scientists with a distinctly rare glimpse of life near its very beginnings.

Now a new assemblage of Middle Cambrian fossils has been unearthed, giving paleontologists another peek at early life. The fossils were found on Mt. Stephen, 5 kilometers to the south of Walcott's site, in rocks that are slightly older than the Burgess shale. According to Desmond H. Collins, a curator at the Royal Ontario Museum in Toronto, Canada, who reported the find at the recent meeting of the Geological Society of America in Orlando, Fla., the Mt. Stephen assemblage is one of the largest and most significant discoveries since Walcott's find.

Included in the new assemblage of more than 1,000 specimens are the first representatives of modern chaetognaths (arrowworms) and ctenophores (jellyfish). Collins's group also found the largest Cambrian animal known, Anomalocaris nathorsti -- a half-meter-long monster with a circular mouth, radiating teeth and claws in the front. In addition, there are a few animal forms of unknown affinities, including a leggy creature that Collins describes as looking most like an inch-long cameo of a stegosaurus (a dinosaur with a small head and club tail). "It's like nothing I've ever seen," he says.

But the real prize of the Mt. Stephen assemblage is an arthropod Collins has dubbed "Santa Claws" because of the five pairs of claws attached to its head (and because Collins thought of the fossil as a gift). Santa Claws has two unusual flaps on its side and a beaverlike tail, both of which Collins suspects helped to steer the fearsome creature. Collins also believes that Santa Claws is the earliest ancestor of sea scorpions, which thrived during the Ordovician period after the Cambrian and which later gave rise to scorpions, the first land animals.

The Mt. Stephen assemblage, as well as another recent discovery of many similar fossils of older and younger ages made in Utah by Richard A. Robinson of the University of Kansas in Lawrence, shows that by the middle of the Cambrian virtually every invertebrate group was represented and well developed. Moreover, by providing views of life several million years before the animals in the Burgess shale died, the two recent finds indicate that the Middle Cambrian animals were not evolving very rapidly. This suggests to Collins that Cambrian fauna had been evolutionarily stable for some time--which may imply that early evolution occurred either faster or even earlier than paleontologists commonly suppose.