Re: dense bones equal fast runners, proven
- From: Lee Olsen <paleocity@xxxxxxxxxxx>
- Date: Wed, 30 Jul 2008 15:26:06 -0700 (PDT)
http://www.naturalhistorymag.com/master.html?http://www.naturalhistorymag.com/1206/1206_samplings.html
Faster than a kudu.
On Jul 29, 11:53 pm, Marc Verhaegen <m_verhae...@xxxxxxxxx> wrote:
Bone Thickness in Homo erectus
Kennedy GE 1985 JHE 14: 699-708
The presence of such thickened bone (in erectus) is extraordinary; very
few animals (mammal or non-mammal) show similar generalized thickened bone.
Within the order Sirenia, the families Manatidae (Manatees) and the
Halicoridae (dugongs) show not merely thickened bone and medullary stenosis
but complete lack of medullary canal (Fawcett 1942) © The adaptive advantage
of such heavy, dense bone to the sirenians is apparently to counterbalance
the buoyancy of their large lung volume while submerged. Amedullary bones,
presumably reflecting a similar selective pressure, are also found in
certain Mesozoic marine reptiles (Fawcett 1942) and in living humpback
whales (Ogden 1980).
A morphometric and taxonomic assessment of a hominine femur from the lower
member, Koobi Fora, Lake Turkana
GE Kennedy AJPA 61:429-436
The femoral shaft of Homo erectus, relative to H.sapiens, demonstrates
small anteroposterior diameters, a distally placed point of minimum shaft
breadth, and increased cortical thickness resulting in medullary stenosis.
This pattern has been identified in specimens from Choukoutien (I and IV),
Olduvai (OH 28), and Lake Turkana (KNM ER 737) ... Known H.erectus femora
extend over a broad span and yet show very low, variability; this pronounced
stasis would strongly suggest that, at least in this portion of the
postcranium, H.erectus was in a period of profound morphological stasis.
Body proportions of Homo habilis reviewed
Martin Haeusler & Henry M. McHenry 2004 JHE 46:433-465
... early Homo femora are said to possess an extremely thick femoral
cortex compared to both Australopithecus & modern humans ... medullar
stenosis seems to be typical mainly for later Eurasian H.erectus ...
NT Boaz & RL Ciochon 2004 Oxford UP
Dragon Bone Hill: An Ice-Age Saga of Homo erectus
H.erectus skull bone can be technically descibed as "pachyostotic"
(literally "thick-boned") ... Some species such sirenians have dense bones
throughout their bodies to give them negative buoyancy in the water.
THE POSTCRANIAL SKELETON OF EARLY EOCENE PAKICETID CETACEANS
SI Madar 2007 J.Paleontol.
Osteosclerosis is an increased thickness of the cortex, due to
replacement of trabecular bone with compact bone ...
Evidence of aquatic dependence from bone microstructure. - The
morphological adaptations for aquatic locomotion described above may appear
to suggest that pakicetids represent a very early stage of transition to
life in water, that these animals were not fully committed to an aquatic
environment, and remained better suited for terrestrial than aquatic
pursuits. However, evidence from bone microstructure demonstrates the
contrary - pakicetids were highly derived semiaquatic mammals. Skeletal
ballast was present in all pakicetid taxa (Fig.7). Hyperostosis and
osteosclerosis are found in all regions of the skeleton and are similarly
developed in juvenile and adult individuals of all 3 taxa. Long bone & rib
marrow cavities are either miniscule or absent due to thick cortices or
dense trabecular infill. Even vertebrae have hyperthick cortices.
Bone ballast in the form of osteosclerosis and hyperostosis is an
unmistakable hallmark of an aquatic lifestyle (Fish & Stein 1991; Domning &
de Buffrénil 1991; Taylor 1994; Madar 1998). Skeletal ballast has already
been described in early marine cetaceans (Buffrénil et al.1990; Madar 1998;
Uhen 2004) including Ambulocetus, Basilosaurus Harlan 1834, and Dorudon
Gibbes 1845. Pakicetids differ most from Ambulocetus & subsequent taxa in
their greater diaphyseal osteosclerosis, though all exhibit complete or near
complete infill of marrow cavities by trabecular bone. The increased
trabecular density & cortical hypertrophy found throughout the pakicetid
skeleton suggest an adaptation toward bottom walking or wading, as heavy
skeletons counteract buoyant effects of inflated lungs & furtrapped air. The
increased density of the pakicetid skeleton would have left these early
cetaceans wholly unsuited to running, or even prolonged terrestriality, as
heavy skeletons are energetically expensive to move. In addition, the
hypermineralization (osteopetroses) of pakicetid load bearing elements put
them at increased risk for fracture during terrestrial loading (de Vernejoul
& Bénichou 2001), a risk that rises with velocity. Thus, although they look
superficially similar to their cursorial relatives, it is likely that
pakicetids made few sustained terrestrial forays. The summed evidence of
bone gross morphology and microstructure indicates that pakicetid cetaceans
were fully committed to an aquatic lifestyle, and bore marked adaptations
for bottom walking, paddling, and undulatory swimming modes.- Hide quoted text -
- Show quoted text -
.
- References:
- osteosclerosis = hallmark of an aquatic lifestyle
- From: Marc Verhaegen
- Re: dense bones equal fast runners
- From: Lee Olsen
- Re: dense bones equal fast runners :-DDD
- From: Marc Verhaegen
- osteosclerosis = hallmark of an aquatic lifestyle
- Prev by Date: Re: dense bones equal fast runners :-DDD
- Next by Date: A dinosaur stepped on a human footprint: repent now.
- Previous by thread: Re: dense bones equal fast runners :-DDD
- Next by thread: Authentic Air Max 87 88 89 90 shoes china stoer www.Allnicesneakers.com discount airmax ltd trainers, Airmax china stoers
- Index(es):
Relevant Pages
|
