The discovery that extinct marine organisms called trilobites laid eggs provides the first direct evidence for how they reproduced.
Trilobites lived between 520 million and 250 million years ago, and are one of the earliest known groups of arthropods (invertebrates, including modern insects, with exoskeletons and segmented bodies). Thomas Hegna of Western Illinois University in Macomb and his colleagues report the discovery of ancient trilobite eggs in New York State, in rocks about 450 million years old. The eggs are spherical, almost 200 micrometres in diameter, and lie near several well-preserved trilobite fossils (pictured).
Trilobites may have released eggs and sperm through genital pores at or near the backs of their heads, the authors say.