I have to revise my view on early hominoid evolution (thanks, Kathelijne):
I thought: c 30 Ma, some catarrhines reached islands between India & S-Eurasia, but 30 Ma, India had already collided with Asia...
https://upscwithnikhil.com/article/geography/movement-of-the-indian-plate
More likely IMO now, the ape/OWM split (30-25 Ma?) happened before Arabafrica (the Red Sea didn't yet exist) hit Eurasia, not unlikely on islands then between both continents: cercopithecoids (Old World monkeys) in Arabafrica, hominoids in S-Asian
coastal forests (on islands?), where the earliest "apes" c 25 Ma became aquarboreal (aqua=water, arbor=tree): vertically=bipedally wading upright & climbing arms overhead in the branches above the water:
- larger size (much later secondarily reduced in hylobatids, who still have a long gestation period, but not in the other apes),
- broad pelvis (+ lateral movements of legs),
- broad thorax & broad a sturdy breast-bone (Hominoidea=Latisternalia) + dorsal scapulas (+ lateral & upward arm movements), unlike monkeys & most mammals,
- longer arms (later evolving into brachiation, esp. in hyobatids),
- centrally-placed spine (vs dorsally in most, pronograde mammals) + probably lumbar spine shortening,
- complete loss of the external tail (unexpected in purely arboreal fast mammals: "equilibrium organ"?).
Thus, my view on the location of early-hominoid evolution (early-Miocene?) has changed, but my scenario remains (provisionally?) the same:
- The Mesopotamian Seaway closure (15-13 Ma?) caused the hominid/pongid (E/W? dryopith/sivapith?) split.
- Hominids died out, except in the (incipient) Red Sea, where 8-7 Ma Gorilla-Praeanthropus followed the incipient northern Rift ->afarensis->boisei etc.
- When the Red Sea opened into the Gulf (6-5 Ma?), Pan went right (E.Afr.coast -> southern Rift ->afrcanus->robustus etc.), and Homo went left: S.Asian coast, and (early-Pleist.?) became shallow-divers for shellfish, as proven by several independent
facts, e.g. H.erectus s.l.:
• archaic Homo's atypical tooth-wear was caused by "sand and oral processing of marine mollusks", Towle cs 2022
https://onlinelibrary.wiley.com/doi/10.1002/ajpa.24500
• H.erectus s.s. fossilized typically (always?) in coastal sediments, e.g. Mojokerto amid barnacles & corals; Trinil amid Pseudodon & Elongaria; Sangiran-17 in "brackish marsh near the coast",
• Stephen Munro's sea-shell engravings made by H.erectus: Joordens cs 2015 Nature 518:228-231
https://pubmed.ncbi.nlm.nih.gov/25470048/
• ear-exostoses (in H.erectus & H.neand.) develop after years of cold(er) water irrigation
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5696936/
• pachy-osteo-sclerosis is typically & exclusively seen in slow+shallow-diving tetrapods (de Buffrénil cs 2010 J.Mamm.Evol.17:101-120), e.g. erectus’ parietal bone is 2x as thick as in gorillas,
• brain size in erectus (2x apes-australopiths) is facilitated by sea-food, e.g. DHA docosahexaenoic acid in shellfish etc., e.g. Odontocetes, Pinnipedia,
• Pleistocene Homo even colonized islands far oversea (Flores & later even Luzon)
https://www.academia.edu/36193382/Coastal_Dispersal_of_Pleistocene_Homo_2018
• Homo’s stone tool use & dexterity is typical for molluscivores, cf. sea-otters etc.
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