Contents
Vol 277, Issue 5332
Contents
This Week in Science
Editorial
ScienceScope
Random Samples
Research News
Books et al.
Book Reviews
Perspectives
Tech.Sight
Summary
Letter
Correction
News and Comment
Articles
Reports
Technical Comments
The radiation of animal life around the Precambrian-Cambrian boundary (the "Cambrian Explosion") was a major event in the history of life. The cover shows phosphatized fossil embryos (~0.5 millimeters in diameter) of two animals from that time, a probable cnidarian (rear) and a segmented worm (front). Both appear to have been direct developers (no larval stage) with large, yolk-filled eggs. The fossilization of soft embryos opens windows on the study of developmental biology of extinct organisms. See 1645. [Image: S. Bengtson and Y. Zhao]