A worm so early, there was no bird

In 1977, scientists identified Hallucigenia, which measured 1-5 centimeters (0.4-2 inches), as its own organism, but then spent decades puzzling over the spikes on its back (which they thought were legs) and its limbs (which they thought were tentacles). On Wednesday, however, Nature reported that researchers reconstructed it in reverse - finding a pair of eyes and a toothy mouth in what scientists had long considered the worm's backside.

"Prior to our study, a large balloonlike orb at one end of the specimen had been interpreted as an amorphous head," University of Cambridge scientist Martin Smith said. "We can now demonstrate that this actually wasn't part of the body at all but a dark stain representing decay fluids or gut contents that oozed out of the anus as the animal was compressed during burial," he told news agency AFP by email.

Smith and co-researcher Jean-Bernard Caron, of the University of Toronto, used an electron microscope to analyze dozens of Hallucigenia fossils in museum collections, uncovering "astounding new detail" of the worm that had lived on the sea floor about 505-515 million years ago. After identifying the worm's derriere, they decided to take a closer look at the other end - removing the sediment covering several of the fossilized heads.

"We were astonished when we found not just a pair of eyes, but also a cheeky grin - a set of teeth smiling back at us," Smith said.

A turtle, too

The velvet worm - a leggy, slimy, antennaed invertebrate that lives in eucalyptus logs - remains Hallucigenia's closest descendant. They belong to the ecdysozoa family: insects, lobsters and spiders that shed their exoskeletons. Hallucigenia's newly discovered choppers has led Smith and Caron to conclude that the ancestor of ecdysozoa must also have had a toothy mouth and throat.

Scientists date ecdysozoa to the Cambrian explosion, a roughly 20-million-year period when the ancestors of most modern fauna phyla emerged. A water-dweller anyway, Hallucigenia, which did not survive the Cambrian period, predated its descendants' most-cliched predators by a good 350 million years: Birds did not arrive in a package resembling their present form until roughly 150 million years ago, at the end of the Jurassic era.

Nature also announced that US scientists had discovered fossils from a turtle that lived over 240 million years ago, shedding new light on another of evolution's great mysteries. Broad-ribbed and shell-less, the 20-centimeter sample represents a link between the first turtles and their modern descendants.

As scientists continue to discover new clues to evolution, others are concerned about the possibility of fresh extinctions.

mkg/bw (EFE, AFP)