That much about the role of current ecological conditions. Explanations of biodiversity patterns may also be historical: such as whole long time has been available for evolution within a certain area. So, let us look at the historical origin of passerine birds. Actually passerine birds originated sometime in the early Tertiary here in Antarctica. We see here a simplified phylogeny of the group, based on DNA data. In the data analysis, the computer back-calculates from current distributions the most likely area of origin at each node of the tree. The earliest lineages to develop here are, at the top, the New Zealand wrens, then a large group of suboscines, the majority of these are in South America (marked with light blue at the base), and then several lineages in Australia (with a purple colour on the graph), and then we have large terminal radiations, with the majority of species, in various parts of the world but mainly in the Old World tropics; all this points to an origin in the south and later diversification in the northern hemisphere. This is also the case for the sister group of passerines, the parrots, which are mainly South American and Australian; and their common sister group, in turn, appears to be rooted in South America. Thus, this all points to an ancient history in the south, near the Cretaceous-Tertiary transition some 65 million years ago. So, what did the world look like at this time? In this slide we see what the world looked like from the south. So with Antarctica in the center, and the earliest passerine lineages are in New Zealand, South America and Australia, so it seems plausible to assume that they were actually distributed all the way across the intervening land area, Antarctica. So, the passerine birds could provide a major natural experiment to test one of the many possible explanations of the global variation in biodiversity, namely where there is species richness, it reflects the time available for evolution. We should expect a lot of passerine species in Antarctica, and this is obviously not the case. Even Australia is quite poor, so although we find some ancient passerine groups here, they are not particularly diverse. This may have to do with of course cold in Antarctica, aridity in Australia. Earth history data provide a plausible explanation here. Antarctica was connected with South America and Australia; the marine circulation systems did not allow accumulation of cold weather in Antarctica. The coloured arrows on the map illustrate the course of sea currents at that time. Red - thus, warm currents from the tropical seas reached the Antarctic coasts (except over to the west side of the Antarctic Peninsula and southern tip of South America). Thus, even through the winter darkness, where there would have been cold in the inland, the Antarctic coastal zones had tolerable climatic conditions and they were forested thus providing suitable conditions for a diversity of birds. Antarctica became cold much later, as it was separated from South America and Australia and this allowed new sea currents to develop around � cold currents going around Antarctica and this was established from 34 million years ago (around the Eocene-Oligocene cooling event), and this caused an accumulation of cold on Antarctica, and the first glaciation of the continent. Since then, the passerine birds could evolve in splendid isolation in South America and Australia, and it was only much later that an opportunity arose for leaving Australia. Because of the large amounts of new molecular data we now know that the global expansion of passerine birds started in the Oligocene period, from Australia. It comprised two cases of dispersal of species of songbirds, Oscines. One of them is called the Passerida, and comprises the enormous diversity of groups of warblers, babblers, thrushes, sparrows, finches etc., altogether 3,500 species, which can now be found all over the world. I will examine now only the expansion of one smaller group, the crow-like birds, the Corvida. So here we have one species of crow, but the whole group of crow-like birds is actually a lot more � a quite diverse group as we see here � at the top the Australian raven, which is a crow, but then there are a number of other birds of Paradise, drongos, bush shrikes in Africa etc. They are in all parts of the world today. So we will look at the phylogeny of these groups. On the next slide I will explain quite quickly how this is made. This is from a big phylogeny covering more than 80% of all the species. We have made a more simplified one and the computer has back-calculated at each node what is the most likely area of origin and we see a big group with black at the base � black means the Papuan Island distribution in New Guinea, so we can see that there is an almost explosive radiation starting with Papuan origin and it apparently corresponds in time to when the Papuan Islands emerged from the epi-continental seas that covered the northern rim of the Australian plate during the Oligocene period. Comparing the phylogeny with plate tectonics reconstructions we can see that the origin of the expansion of songbirds correspond to a great Earth history change that provided new opportunities: as a consequence of the continental drift and movement of the Australian plate towards the north, the �anterior� edge of that plate, that until then had been covered by shallow seas, tipped up to the surface, giving rise to archipelagos of calcareous islands, a short distance off the Australian coast. At the same time, oceanic islands emerged because of volcanism along the edge of the Pacific plate further up in the ocean. And emerging island arcs were gradually squeezed towards the west; some of them were �docked� on to the northern coast of New Guinea, and turned into coastal mountains that we see today. Others were piled up in large archipelagos in the area we now know as Indonesia and the Philippines. This created a tremendous island world in the gateway between the Pacific and Indian Oceans. The islands were surrounded by constantly warm seas; thus, enormous and dynamic opportunities for rapid development of luxurious vegetation and resources for colonizing birds � really good opportunities. So what happened was apparently that two lineages out of the ancient Australian songbird groups managed to colonize the islands corresponding to New Guinea, underwent rapid adaptive radiation, and then took opportunities in these archipelagos to rapidly move onwards.
