Temperature: 16 °C
Atmospheric oxygen: 13.5%
The Ordovician is the second of six periods of the Paleozoic era. During this period ancient oceans separated the barren continents of Laurentia, Baltica, Siberia and Gondwana. The end of the Ordovician was one of the coldest times in Earth history. Ice covered much of the southern region of Gondwana.
Orthoceras is a genus of extinct nautiloid cephalopod endemic to Middle Ordovician-aged marine limestones of the Baltic States and Sweden. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera, Orthocerus or Orthoceros.