 It was understood that not only had there been an "age of reptiles" preceding the current "age of mammals", but there had been a time (during the Cambrian and the Silurian) when life had been restricted to the sea, and a time (prior to the Devonian) when invertebrates had been the largest and most complex forms of animal life.This rapid progress in geology and paleontology during the 1830s and 1840s was aided by a growing international network of geologists and fossil specialists whose work was organized and reviewed by an increasing number of geological societies.Many of these geologists and paleontologists were now paid professionals working for universities, museums and government geological surveys.