Middle cambrian arthropod embryos with blastomeres.

A phosphatized Middle Cambrian ( approximately 510 million years ago) fauna from Duyun, southern China, has yielded fossil embryos that may be of arthropod affinity and could belong to the co-occurring eodiscid trilobite Pagetia sp. The shell was most likely flexible and possessed at least two thin layers. Four embryos reveal blastomeres, and two embryonic stages are represented. These embryos demonstrate that the basic paradigm for the growth of the invertebrate embryo has not changed in more than half a billion years.