midCambrian

Mid-Cambrian refers to the middle portion of the Cambrian period, a major division of the Paleozoic era. In most global timescales the Cambrian spans about 541 to 485 million years ago, and the mid-Cambrian covers roughly the middle of that interval, commonly placed around 513 to 509 million years ago, though exact boundaries vary regionally.

During this interval, Earth's oceans were warm and commonly shallow seas flooded many continents; high sea levels promoted extensive carbonate platforms and widespread sedimentation. Atmospheric oxygen levels were rising, which supported greater biological complexity in marine ecosystems.

The mid-Cambrian saw continued diversification of marine invertebrates. Arthropods, mollusks, brachiopods, echinoderms, and other invertebrates diversified, and early representatives of several major animal groups appeared. The fossil record includes Burgess Shale-type deposits dating to around 508 million years ago, preserving a wide range of soft-bodied organisms and illuminating the structure of early marine ecosystems.

Stratigraphically, mid-Cambrian rocks are used to correlate marine deposits across regions and to study patterns of diversification after the initial Cambrian explosion. The interval is notable for preserving a snapshot of early ecosystem evolution and the ongoing expansion of marine life in a world of high sea levels.

Terrestrial ecosystems were limited at this time; life remained primarily marine, with land habitats remaining largely uncolonized by complex organisms.