Answer: silurian

AnswerCrossword Clue
SILURIANPeriod in which early invertebrate land animals appeared
SILURIANOf a geological period.
SILURIANGeological era
silurianformed in the third period of the Palaeozoic era
silurianthe Silurian Period or System of rocks
silurianof or pertaining to the Silures or their country
siluriannoting or pertaining to a period of the Paleozoic Era, occurring from 425 to 405 million years ago, notable for the advent of air-breathing animals and terrestrial plants