Science has a short essay by Terry Harrison this week about Miocene ape evolution: "Apes among the tangled branches of human origins."
This is the sort of article that shows just how frustrating the Miocene apes can be. It's short, probably not even 1500 words, and it has more than 20 genus names stacked into it -- and he doesn't even list Proconsul and its Early Miocene ilk.
I've been trying to give a longer account of Miocene ape evolution here, by dribs and drabs. You can get most of the list under my "Miocene" category. Last fall's account of "Late Miocene apes from Africa" expands significantly on a topic that Harrison glosses -- what do we know about African apes during the time that chimpanzees, gorillas, and humans were diverging?
There are two phylogenetic issues related to Miocene apes that command a lot of attention. Where did hominins come from? -- that's one issue. The other is, how are Asian and African apes related?
This latter question is important because it helps to establish the timeline of orangutan divergence from us and subsequent evolution. It also determines the position of the European apes -- and thereby, whether their locomotor and dietary diversity is relevant to later ape evolution.
Harrison comes down in favor of the hypothesis that Dryopithecus and most other European apes were stem hominids -- that is, collaterals of all living great apes, not specially related to the African apes and humans. The main alternative to that view is that the European apes mostly represent the African side of an early Asia-Africa biogeographic split, such that chimpanzees, gorillas and humans (the hominines) descend from Dryopithecus or some similar lineage closely aligned with these European apes. Harrison is willing to admit the Late Miocene Greek ape Ouranopithecus to the African ape lineage, but in his view the earlier European apes belong to one or more side-branches of the great apes.
A question: If Harrison is correct here, does that affect the paleontological evidence for the human-orangutan divergence? That is, if Dryopithecus were a hominine, it is plausible that the Asian/African ape divergence actually happened in Eurasia not long before 12 million years ago. If Dryopithecus branched off before the African and Asian ape divergence, and Sivapithecus was derived from an African ape, does that make the divergence earlier or later?
I'll consider that over the weekend.
Harrison T. 2010. Apes among the tangled branches of human origins. Science 327:532-534. doi:10.1126/science.1184703