Ordovician extinctions

Megalograptidae are a family of eurypterids, an extinct group of aquatic chelicerate arthropods commonly known as "sea scorpions".

Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had an extratropical distribution, and there is evidence that they lived in darker parts of the water column (around 175m deep). Cyclopygids are characterized by enlarged eyes, with a wide angle of view, both horizontal and vertical, reminiscent of the eyes of dragonflies. These typically touch the glabella directly on the side. Cyclopygids all lack genal spines, but Symphysops carries a forward directed frontal spine on the glabella. It is presumed that at least the members of the genus Pricyclopyge swam upside do

Trinucleidae is a family of small to average size asaphid trilobites that first occurred at the start of the Ordovician and became extinct at the end of that period. It contains approximately 227 species divided over 51 genera in 5 subfamilies. The most conspicuous character is the wide perforated fringe of the head.

Asaphidae is a family of asaphid trilobites. Although the first genera originate in Upper Cambrian marine strata, the family becomes the most widely distributed and most species-rich trilobite family during the Ordovician.

Markuelia is a genus of fossil worm-like bilaterian animals allied to Ecdysozoa and known from strata of Lower Cambrian to Lower Ordovician age containing five species.