in the evolution of the group. Other eukaryotes with chloroplasts appear to have gained them by engulfing a single-celled archaeplastidan with its own bacterially-derived chloroplasts. Because these events involve endosymbiosis of cells that have their own endosymbionts, the process is called secondary endosymbiosis. The chloroplasts of such eukaryotes are typically surrounded by more than two membranes, reflecting a history of multiple engulfment. The chloroplasts of euglenids, chlorarachniophytes and a small group of dinoflagellates appear to be captured green algae, whereas those of the remaining photosynthetic eukaryotes, such as heterokont algae, cryptophytes, haptophytes, and dinoflagellates, appear to be captured red algae. Fossil record Perhaps the most ancient remains of Archaeplastida are putative red algae (Rafatazmia) within stromatolites in 1600 Ma (million years ago) rocks in India. Somewhat more recent are microfossils from the Roper group in northern Australia. The structure of these single-celled fossils resembles that of modern green algae. They date to the Mesoproterozoic Era, about 1500 to 1300 Ma. These fossils are consistent with a molecular clock study that calculated that this clade diverged about 1500 Ma. The oldest fossil that can be assigned to a specific modern group is the red alga Bangiomorpha, from 1200 Ma. In the late Neoproterozoic Era, algal fossils became more numerous and diverse. Eventually, in the Paleozoic Era, plants emerged onto land, and have continued to flourish up to the present. Notes References External links Tree of Life Eukaryotes Bikont unranked clades