A fossil site in southern China that has held paleontologists captivated for a decade keeps relinquishing new treasures. Only 4 weeks ago, a Chinese team reported the oldest known vertebrates at the site, two fishlike creatures that lived 530 million years ago (ScienceNOW, 3 November). In this week's Nature, a rival team presents hundreds of astonishingly well-preserved fossils, which give researchers another eagerly awaited peek at the animals that set the stage for the evolution of the backbone.
The discovery was made in April at a site called Chengjiang near the city of Kunming, where 530-million-year-old fine-grained rocks have preserved even soft animal tissue in exquisite detail. A team led by Junyuan Chen from the Nanjing Institute of Paleontology and Geology found 305 specimens, 30 of them complete, of an early chordate--a member of a broad group that comprises not only vertebrates but also more primitive invertebrates such as sea squirts and lancelets. They have christened it Haikouella lanceolata, after the nearby town of Haikou.
Thanks to the stunning preservation, the researchers could not only discern a heart and a circulatory system in these 3-centimeter fossils, but also some of the hallmarks of chordates, such as a dorsal nerve cord and a notochord, a rod of stiff tissue that provides support along the back of the body. Haikouella also has a puffed-up back that seems to contain segmented muscles--another key chordate feature. What's more, the animal seems to have a relatively large brain, and what appear to be two eyes, suggesting that it may be a very early member of the vertebrates--which would put it somewhere on the first steps of the long road to humans.
Others question Haikouella's right to a place within the chordates. "I think they're trying to force too much advanced morphology into the animal," says paleontologist Simon Conway Morris from Cambridge University in the United Kingdom, who co-authored last month's paper. For one, Conway Morris isn't convinced that the bulging back does indeed contain chordatelike muscles; he thinks Haikouella may be further down the evolutionary tree, as a progenitor to chordates and to other invertebrates such as starfish and sea urchins.
But Chen and other researchers reject that idea. "There's no question that these things are chordates," says zoologist Nicholas Holland of the University of California, San Diego. The sheer quality of the specimens may eclipse last month's findings, he adds: "I think this is going to be an icon that we'll see in the textbooks for many years."