Only complete idiots believe H.erectus ran after antelopes:

"Evolution of Sirenian Pachyosteosclerosis"
Vivian de Buffrénil cs 2010
J.Mammal.Evol.17:101–120
Osteo-sclerosis (OS, inner bone compaction) & pachy-ostosis (PO, outer hyperplasy of bone cortex) are typical of tetrapods secondarily adapted to life in water ... spectacularly exemplified by the ribs of extant & extinct Sirenia ...
- PO evolved 1st (mid-Eocene),
it is a basal feature of Sirenia, but subsequently regressed in some taxa.
- OS was only incipient in Pezosiren portelli ~50 Ma, its full development occurred later (end-Eocene).
These 2 structural specializations of bone are variably pronounced in extinct & extant Sirenia,
PO & OS are rel. independent from each other, but frequently associated.  
.... Incipient acquisition of aquatic habits by the earliest forms induced the need for ballast, allowing a passive control of buoyancy & trim ...
This evol.process was rapid, already completed in animals that basically remained terrestrial anatomically.
(!! --mv)
OS also occurred early in sirenian evolution, but as a progressive, somewhat slower process, not closely synchronous with PO.
Pezosiren typifies an initial adaptive stage, combining advanced PO + incomplete OS + nearly non-existent gross morphological specializations for life in water, at least for the bones involved in locomotion (the nasal region suggests some aquatic adaptation) …
(google "Oi, big nose!" --mv)
PO & OS are by no means unique to the Sirenia. They are also encountered in the long bones of most, if not all, other aquatic tetrapods at incipient stages of their adaptation to life in seas ...
The OS or POS stages thus seem to be mandatory passages in the history of marine tetrapods.
In semi-aquatic forms or fresh-water dwellers, there is just a limited increase in bone density …
(IOW, H.erectus was coastal –mv)
All authors consider that OS and/or PO have a hydrostatic role, and contribute, as ballast, to regulating buoyancy & trim in tetrapods incipiently adapting to life in water, or specialized in feeding on fixed or slow-moving prey in shallow waters.

(neandertal ear exostoses also prove frequent swimming --mv)

littor...@gmail.com wrote:
> Only complete idiots believe H.erectus ran after antelopes:
>
> "Evolution of Sirenian Pachyosteosclerosis"