Something fishy...

Some paleontologists go the Gobi Desert and dig up petrified dinosaurs. Some watch lampreys rot. But it's all good.

Our knowledge of the earliest chordates, the ones that showed up in the Cambrian before the evolution of vertebrae and other bones, is sketchy. You'll see images, like the one of Pikaia here, but they're based on the interpretation of a small number of fossils formed when everything fell into place for the preservation of the soft parts remaining after their demise. The picture they paint of our 500 million year old ancestors is nebulous and, perhaps, flawed. And it took rotting lampreys to tell us that.

Researchers at the University of Leicester report in Nature on a study in which they observed the decomposition of the larvae of the modern-day lamprey of genus Lampetra and the lancelet Branchiostoma. These animals are the closest living analogues to the earliest living chordates. What they found may force a rethinking of our interpretation of these earliest chordate fossils?

The research team, led by Mark Purnell of Leicester's Department of Geology, found that the the decomposition process proceeded in a non-random fashion. While some features, like the liver, persisted for months, others, like the heart, were gone within two weeks. Some of the features most important in recognizing advancements in the early chordates are among the most rapid to decay. This raises the real possibility that fossils interpreted as very primitive chordate ancestors may actually be more complex organisms in which key features had simply rotted away prior to preservation. New information such as this may lead to some reevaluation of our ideas about what evolved when. However, caution is in order. The fact that a structure might have been lost to decay doesn't mean it was.