The fossil record of sulids is quite extensive due to the many Miocene/Pliocene forms that have been recovered, but the lineage of sulids extends back to the Eocene, and all things (such as the Early Eocene frigatebird "Limnofregata") considered, the sulids seem to have diverged from the lineage leading to cormorants and darters around 50 million years ago (Mya), perhaps a bit earlier. The initial evolutionary radiation formed a number of genera that are now completely extinct, such as the freshwater "Masillastega" (which, as noted above, might not have been a modern-type sulid) or the bizarre "Rhamphastosula" (which had a bill shaped like an aracari's). The modern genera evolved (like many other living genera of birds) around the Oligocene-Miocene boundary about 23 Mya. "Microsula", which lived during that time, seems to have been a primitive booby that still had many symplesiomorphies with gannets. Like the other Phalacrocoraciformes, the sulids originated probably in the general region of the Atlantic or western Tethys Sea – probably the latter rather than the former, given that their earliest fossils are abundant in Europe, but absent from the well-studied contemporary American deposits.