Assuming it true and lack of the Pan-Australopith LCA in Africa, it may be speculated that a western group of the later Miocene Siwalik Sivapithecus or the like hominoid migrated to Africa and gradually evolved to Australopith.

To date it is widely believed that the last common ancestor was an African one. Evidences have also supported it. Unless new evidences are unearthed, I feel we have to go with the same belief. 

Amit- you are right; this is but only a belief, and there is no hard fossil evidence to make the belief a scientific basis.

If there is an orang-australopith hypothesis (Jeffrey Schwartz?), it's wrong according to anatomical evidence (see e.g. my Hum.Evol.papers).

Sivapith, Lufengpith, Gigantopith & probably Ankarapith are probably pongid (Asian great apes), but australopiths are hominid (African great apes-humans), although both groups (pongis // hominids) probably partly evolved in parallel, e.g. African // Asian apes got longer arms & hands, longer iliac blades, larger canine teeth.

Whereas both hominids (incl. ausralopiths) & pongids (in //) generally became more apelike, one hominid branch (Homo) took a very different evolutionary direction, evolving much large brains, external noses, much longer legs etc. (probably during the Pleistocene, when archaic Homo dispersed intercontinentally along African & Eurasian coasts & rivers, see file attached).

Until and unless we identify the Pan-australopith last common ancestor in African fossil record, it remain only a view. Homo-Pan DNA closeness may be sympleisiomorphic until australopith DNA is known.

Of course, the pongid lineage was more wide spread compared to the panid lineage.

Will it ever be possible to extract DNA from apith fossils? I don't know.

Before c 20 Ma, early hominoids lived in Africa, but when the Afro-Arabian plate hit the Eurasian plate, first hylobatids (c 18 Ma?) and then pongids or hominids-pongids followed (c 16 Ma?) along the Tethys coastal forests. IMO these early "apes" were "aquarboreal" (google), spending part of their time in the branches (arbor), part in the swamps (aqu-), perhaps somewhat comparable to lowland gorillas today collecting papyrus sedges & frogbit in tropical forest bais (google "gorilla Ndoki bai" or so). They were "upright" (vertical lumbar spine, orthograde), not for walking bipedally on dry land, but IMO for wading on 2 legs, floating vertically in swamps & climbing arms overhead in the branches above the swamps, as lowland gorillas still do parttime. Probably pongids colonized the eastern Tethys coastal forests (now along the Indian Ocean), and possibly, hominids colonized the western Tethys & para-Tethys coastal forests (now Medit.-Black-Caspian seas). After c 12 Ma or so, hominids went south (cf late-Miocene cooling?), e.g. we find Oreopithecus c 7 Ma on an Italian island, Sahelanthropus c 7 Ma in Chad (via Lybian shallow seas & wetlands?) & Orrorin c 6 Ma in Kenya.

Sahelanthropus, Orrorin, Ardipith & australopiths are no exclusive human ancestors. IMO australopith human-like traits (e.g. thick enamel, rel.small canines, vertical spine, low iliac blades) are not derived in the human direction ("hominin"), but are primitive (early-hominid or older): Pan & Gorilla (in //) had orthograde apith ancestors, recently evolving longer arms (esp.Pan), knuckle-walking (Gorilla>Pan), larger canines (esp.males, less in bonobos), thinner enamel (esp.Gorilla). East-African australopiths have more gorilla features than South-African ones (e.g. very large airsacs), and South-Afr.apiths have more bonobo-chimp-like features than East-African ones (see my Hum.Evol.papers), so IMO Au.afarensis-aethiopicus-boisei (incl.Lucy) were fossil relatives of gorillas, and Au.africanus-sediba-robustus of bonobos-chimps.

According to DNA comparisons, Gorilla & Homo-Pan split c 8 or 7 Ma. Presumably (cf Jon.Kingdon) gorilla relatives lived in the Rift-Nile-Congo papyrus swamps, wetlands etc., and Homo-Pan relatives lived in the coastal forests around the Zambesi mouth. Homo & Pan split c 5 Ma: chimps remained in Africa, and our branch colonized the Indian Ocean coastal forests (cf absence of retroviral DNA in humans, google "Yohn 2005 PLoS"). With the Pleistocene coolings (after c 2.5 Ma), when sea-levels dropped, and vast, presumably tree-poor & shellfish-rich areas came "free" for intelligent, tool-using & dextrous "apes", Homo began beach-combing, diving & wading bipedally in Eurasian & African coasts & rivers for littoral, shallow aquatic & waterside foods (google "researchGate marc verhaegen"): this explains human (vs chimp) fur loss, thick SC fat, external nose, poor sense of smell, small mouth & dentition, voluntary breathing (parttime diving), huge brain (DHA in seafood), etc.

Marc- you have made a beautiful theory and explaining convincingly. Ecological explanations are quite flexible and can be stretched to any side. My only concern is 'can we lay our hand on the African LCA among all known fossil taxa? 'If you clearly name it, then we may discuss that further. While ancestral orthograde gorillas or chimpanzee became quadrumanuous and knuckle-walker rather than pursuing  orthogrady and bipedalism -which provided greater selective advantage to the hominids? Of course, dietary adaptation to frugivory is a standard explanation - also given for thinning of the molar enamel and shedding away omnivory in gorilla-chimp lineage. But, restricts their home rage and dietary regime as well as survival vis-avis the omnivorous hominids. Why evolution for reduction of enamel thichness when it is selectively advantageous for hominids and Asian pongids and enhanced their territory and greater adaptive radiation?

Hi Anek. My view is not based on ecological data, but on fossil, paleo-environmental, dentitional, comparative etc.data. Fossil LCAs are almost a contradictio in terminis: fossils appear typically a few millions of years after the LCA. DNA suggests that Pan & Homo split some 5 Ma: the appearance of Homo at 1.8 Ma in Dmanisi & probably Mojokerto therefore is what could be expected if Homo after the split with Pan followed the Indian Ocean coasts (cf absence of African retro-viral DNA in Homo, google "Yohn 2005 PLoS"). Pan-like australopiths appeared a bit earlier (c 3 Ma S.Africa): therefore it's difficult to say whether e.g. A.africanus belonged to Pan or to a side-branch of Homo-Pan. But since there's so much parallel, convergent & reverse evolution in the fossil record (of hominids & other animals), this is not so important: it's very difficult to know where exactly we can put any hominid fossil on anatomical evidence (i.e. without DNA evidence).

Homo-Pan (incl.S.Afr.apiths) was apparently generally a lot more omnivorous than the more herbivorous Gorilla (incl.E.Afr.apiths). The superthick enamel in e.g. A.boisei might have been for wetland foods such as calorie-poor papyrus sedges (which can contain hard-shelled invertebrates HSI), see the work of Lloyd du Brul, P-F Puech, Alan Shabel, Nik.vd Merwe etc. A.bosei fossils are found in lagoons (Baringo), amid papyrus roots (Olduvai), montane forests (Koobi Fora) & wetlands (all?). The thin enamel in living gorillas, as in other herbivores, is probably an adaptation to their diet of herbaceous vegetation (aquatic AHV & terrestrial THV): thin enamel is probably better (sharper) for slicing leaves etc. The thick enamel (brittler but harder e.g. for diets including hard parts) in Homo & Pongo is not unexpected in these omni- & frugivores. For a more thorough discussion, see e.g. our papers (with P-F Puech 2000) "Hominid lifestyle and diet reconsidered: paleo-environmental and comparative data" Hum.Evol.15:175-186, and (+ St.Munro 2002) "Aquarboreal ancestors?" Trends Ecol.Evol.17:212-7, google "aquarboreal".

Hi Marc- thanks for your further explanations and valuable insight- more of which are made by you earlier; I appreciate your interpretations on aquaboreal line and like your strong conviction.

In fact, many use DNA  or/and morphology conveniently- partly one and partly the other..

Many accuse fossil record as incomplete,.so much parallel, convergent & reverse evolution. But,.If you look carefully this is also true for DNA genomic sequences- there are frequent back and parallel mutations and you cannot distinguish between symplesiomorphies and synapomorphies.

Why Homo-Pan DNA similarities are not symplesiomorphies and why should be assume these as synapomorphies- I am yet to be convinced.

Also, I am yet to be convinced with australopith as gorilla-Pan closest ancestors/allies because they display different  dental patterns - obviously attained through  different  long evolutionary history /ecological settings- partly aquaboreal. 

Hi Anek, it has nothing to do with conviction, only with facts.

With "dental patterns", you probably mean esp. the huge canines in male gorillas & chimps (more than in bonobos). Note that some H.erectus skulls from Java had canine gaps (diastemata on the opposite jaw) of 4 mm, more than in many orangutans, that many afarensis & other apiths had rel.large canines, that e.g. female bononos have no larger canines than most humans, etc.

Google "aquarboreal", not "aquaboreal", it's from Latin "aqu-" (water) + "arbor" (tree): the swamp/mangrove/flooded forests where most fossils of Mio-Pliocene hominoids including australopiths are found.

Thanks Marc. From dental pattern I meant not canine alone but thick enamel- megadonty n associated trait which r distinct in african apes n apiths- entirely different adaptations

Yes, enamel thickness I had tried to answer in my previous answer & in our "aquarboreal" papers (in TREE & see file attached). Most Mio-Pliocene hominoids had thick enamel (arguable as an adaptation to harder foods such as coco or other nuts or hard-shelled invertebrates HSIs, as seen in e.g. capuchins, who e.g. open mangrove oysters with oyster shells, see refs in papers above). Some hominoid spp developed superthick enamel (e.g. Ouranopith, aethiopicus-boisei, robustus), some got (directly or again) thinner enamel (Pan & esp.Gorilla), others kept or re-evolved thick enamel (Homo, Pongo). Generally, AFAICS (see attachment), in hominoids we see thick enamel in omnivores in coastal forests, superthick enamel in herbivores in open wetlands, and thinner enamel in foli-herbivores in tropical forests, but this provisionel impression requires a lot more detailed study.