Journal of Paleontology, Vol. 64, No. 2 (Mar., 1990), pp. 255-277 (23 pages) Up to four discrete protaspid larval stages are described for calymenid trilobites of Ordovician to Devonian age. The ...

In Earth’s modern history (meaning the time since complex life evolved on Earth), there have been five mass extinctions. These “big five” are the End Ordovician (roughly 440 million years ago), the ...

This column is part of a series where Verge staffers post highly subjective reviews of animals. Up until now, we’ve written about animals without telling you whether they suck or rule. We are now ...

Throughout the past 600 million years there have been five major mass extinction events that devastated life on Earth. While some of these events are very well studied, such as the killer asteroid ...