Ardi - Ardipithecus ramidus

[touchingcloth]

...http://www.reasons.org/fossil-record/tr ... bipedalism

I'm not sure when this article was written, but it doesn't cite any research published after 2001...they seem to have mangled their figures a little.
The human-chimp last common ancestor was thought to have diverged ~8-6Ma, then for other hominids you get:

• Ardipithecus ~5.5-4.4Ma
• Australopithecus ~4-2Ma
• Homo ~2Ma

The ranges are quite broad here as we have an extremely limited number of fossils of early hominid so although you can say with some confidence when one individual lived, it's hard to put a figure on the time that species (or genus) spanned.
So given this you get:

• ~0.6-3.6My for a limited form of bipedalism to emerge and develop*
• ~0.4-3.5My for an improved form of bipedalism to emerge**
• ~2-4My for bipedalism as we know it to emerge (the genus is still extant)

*The article in Science has this to say

Ardipithecus ramidus now unveils how our skeleton became pro- gressively modified for bipedality. Although the foot anatomy of Ar. ramidus shows that it was still climbing trees, on the ground it walked upright. Its pelvis is a mosaic that, although far from being chim- panzee-like, is still much more primitive than that of Australopithecus.
The gluteal muscles had been repositioned so that Ar. ramidus could walk without shifting its center of mass from side to side. This is made clear not only by the shape of its ilium, but by the appearance of a special growth site unique to hominids among all primates (the anterior inferior iliac spine). However, its lower pelvis was still almost entirely ape-like, presumably because it still had massive hindlimb muscles for active climbing.
Changes made in the upper pelvis rendered Ar. ramidus an effec- tive upright walker. It could also run, but probably with less speed and efficiency than humans. Running would also have exposed it to injury because it lacked advanced mechanisms such as those that would allow it to decelerate its limbs or modulate collision forces at its heel. Australopithecus, which had given up its grasping foot and abandoned active climbing, had evolved a lower pelvis that allowed it to run and walk for considerable distances.

**From the same article

One of the oldest hominid pelves, that of Australopithecus afarensis (A.L. 288-1; “Lucy”), shows that her species had already evolved virtually all of the fundamental adaptations to bipedality. Even the kinetics of her hip joint were similar to ours.
...
In the second, from Ardipithecus to Australopithecus, modifications produced a pelvis and lower limb that facilitated more effective upright walking and running but that were no longer useful for climbing. Because climbing to feed, nest, and escape predators is vital to all nonhuman primates, both of these transitions would likely have been a response to intense natural selection.

[limerick]

Is this the stage where we all "agree to disagree"

[touchingcloth]

The species is to modern to be a common ancestor of humans and chimps - instead it is suspected to be on the branch between humans and the most recent common ancestor.

Exactly what I said...

The way you worded it, it sounded like you meant A. ramidus was a common ancestor of both us and chimps. Apologies.

[touchingcloth]

“Chalky”? “Squished”? “Badly crushed and distorted”? “Needed extensive digital reconstruction”? After all the media hype and overblown claims about importance of Ida, forgive me for having an initial reaction of skepticism. How far would you trust a “Rosetta stone” that was initially “crushed to smithereens” and “would turn to dust at a touch”?

Claims of bipedalism often depend upon precise measurements of the angles of key bones such as the pelvis, femur, and knee-bones. But if these bones were discovered in such a crushed, squished, etc. form, determining the precise contours of these bones might become a highly subjective exercise. I'm sure they spent a lot of time on their reconstructions (and it certainly sounds like they did) but at the end of the day, it's difficult to make solid claims about extremely unsolid bones.

The Science article on the emergence of upright walking goes into extensive detail about how they developed their reconstructions. A good number of the bone fragments were of a not unsubstantial size. They include estimated upper and lower bounds on the range of angles and sizes of the pelvis model. Sophisticated modeling techniques remove a lot of the subjectivity of the analysis. I'd agree with you that it's difficult to make a solid claim about the bones (A. ramidus' pelvis was Xmm wide) but it is possible to make some more general claims (i.e. it's clear that the pelvis structure is more suited to arboreal life than that of A. afarensis.).

[Gman]

The Science article on the emergence of upright walking goes into extensive detail about how they developed their reconstructions. A good number of the bone fragments were of a not unsubstantial size. They include estimated upper and lower bounds on the range of angles and sizes of the pelvis model. Sophisticated modeling techniques remove a lot of the subjectivity of the analysis. I'd agree with you that it's difficult to make a solid claim about the bones (A. ramidus' pelvis was Xmm wide) but it is possible to make some more general claims (i.e. it's clear that the pelvis structure is more suited to arboreal life than that of A. afarensis.).

I don't know about general claims... Not all researchers are on board with the evidence for bipedality.

"Some researchers, however, are unconvinced that Ardipithecus was quite so versatile.

"This is a fascinating skeleton, but based on what they present, the evidence for bipedality is limited at best," said William Jungers, an anatomist at Stony Brook University in New York State.

"Divergent big toes are associated with grasping, and this has one of the most divergent big toes you can imagine," Jungers said. "Why would an animal fully adapted to support its weight on its forelimbs in the trees elect to walk bipedally on the ground?"

Source: http://news.nationalgeographic.com/news ... midus.html

[Gman]

The way you worded it, it sounded like you meant A. ramidus was a common ancestor of both us and chimps. Apologies.

No problem TC...

[ageofknowledge]

Bipedialism didn't just appear, it was a gradual process typical of evolution. Recent studies have shown that the 'split' probably occured over 10 million years ago.

Wrong. Just in evolutionary theory there are more than twelve distinct hypotheses as to how and why bipedalism evolved in humans with much debate as to when. It sounded really authoritative the way you said it though.

It WAS a gradual process, a species didn't just wake up one morning and decide to walk on two legs.

Actually Adam did but but please carry on.. it's entertaining to hear you mash up the data so.

[limerick]

Bipedialism didn't just appear, it was a gradual process typical of evolution. Recent studies have shown that the 'split' probably occured over 10 million years ago.

Wrong. Just in evolutionary theory there are more than twelve distinct hypotheses as to how and why bipedalism evolved in humans with much debate as to when. It sounded really authoritative the way you said it though.

It WAS a gradual process, a species didn't just wake up one morning and decide to walk on two legs.

Actually Adam did but but please carry on.. it's entertaining to hear you mash up the data so.

Studies of fossils have indicated that it was a gradual process (naturally this cannot be proved 100% but what can?), what studies have indicated Adam was the clear first to so?

[touchingcloth]

Bipedialism didn't just appear, it was a gradual process typical of evolution. Recent studies have shown that the 'split' probably occured over 10 million years ago.

Wrong. Just in evolutionary theory there are more than twelve distinct hypotheses as to how and why bipedalism evolved in humans with much debate as to when. It sounded really authoritative the way you said it though.

It WAS a gradual process, a species didn't just wake up one morning and decide to walk on two legs.

You're both correct!
Bipedalism did gradually become a more and more commonplace type of locomotion - the first hominids to have ever walked bipedally would have done so far less than they knuckle walked or climbed trees. Gradually this will have become more dominant behaviour in certain hominids.
As to the driving force for the emergence of bipedalism, AoK is quite correct that there are different hypothesised pressures accounting for this (e.g. to facilitate tool-use, carrying food, reaching up to feed on fruit, changes in woodland habitats); the real reason is likely to be a combination of the hypotheses (and probably some others that have not been considered), and the change would have been adopted gradually. It could even be the case that one of the hypothesised reasons led to the emergence of bipedalism, whereas others led to the development and full adoption of bipedalism.

[Gman]

But you're not an evolutionist, and they DON'T believe this to be an embarrassment.

Not exactly, I said "if" I was an evolutionist I would be embarrassed at the claim...

One problem is that some portions of Ardi's skeleton were found crushed nearly to smithereens and needed extensive digital reconstruction.

The word 'portions' is important here, as not all of the remains were crushed. Therefore, a pretty good estimate could be made of the bones that were intact.

As for the fact that thye crunbled on touch, I'm sure in this day and age they found a way around it.

Portions? There are entire sections missing from the remains... As an example how does one come up with the rib cage here?

Just as a matter of interest, and I think I asked this before, but what do ye guys think it is?

It could be anything at this point... Possibly a primate, but hardly a smoking gun for evolution. That is why we disagree...

[touchingcloth]

Portions? There are entire sections missing from the remains... As an example how does one come up with the rib cage here?

I'm not sure on this one so I'll have to go do some reading - but I think the featured picture is of the Ardi individual; there were other (15 in total, IIRC) individuals whose remains were collected so the rib structure was probably derived from those samples.

[Gman]

I'm not sure on this one so I'll have to go do some reading - but I think the featured picture is of the Ardi individual; there were other (15 in total, IIRC) individuals whose remains were collected so the rib structure was probably derived from those samples.

So in other words, we don't have enough evidence here so we will take them from another site? A Frankenstein approach? Oh, well the possibilities are endless then... Anyone could do that, even a boy scout, and call it science to boot...

[limerick]

GMAN SAID

It could be anything at this point... Possibly a primate, but hardly a smoking gun for evolution. That is why we disagree...

They are not claiming it to be a smoking gun for evolution, as far as they are concerned evolution is fact, this just helps them further in understanding how hominoids evolved.

It could be anything at this point... Possibly a primate, but hardly a smoking gun for evolution. That is why we disagree...

As I said we agree to disagree

Touchingcloth said

I'm not sure on this one so I'll have to go do some reading - but I think the featured picture is of the Ardi individual; there were other (15 in total, IIRC) individuals whose remains were collected so the rib structure was probably derived from those samples.

Thats what I was trying to get at when I said they were working on this for fifteen years.

[touchingcloth]

I'm not sure on this one so I'll have to go do some reading - but I think the featured picture is of the Ardi individual; there were other (15 in total, IIRC) individuals whose remains were collected so the rib structure was probably derived from those samples.

So in other words, we don't have enough evidence here so we will take them from another site? A Frankenstein approach? Oh, well the possibilities are endless then... Anyone could do that, even a boy scout, and call it science to boot...

Well, not. Not if Ardi was the single best preserved individual, but it was clear that other individuals were of the same species. It's not like they would have found, say, and elephant's rib cage and thought "yep, that'll do.".

[ageofknowledge]

Bipedialism didn't just appear, it was a gradual process typical of evolution. Recent studies have shown that the 'split' probably occured over 10 million years ago.

Wrong. Just in evolutionary theory there are more than twelve distinct hypotheses as to how and why bipedalism evolved in humans with much debate as to when. It sounded really authoritative the way you said it though.

It WAS a gradual process, a species didn't just wake up one morning and decide to walk on two legs.

Actually Adam did but but please carry on.. it's entertaining to hear you mash up the data so.

Studies of fossils have indicated that it was a gradual process (naturally this cannot be proved 100% but what can?), what studies have indicated Adam was the clear first to so?

Yes studies on bipedalism have been conducted. And here's what they find:

The prevailing evolutionary theory to account for the appearance of bipedalism is that the habitat of the hominids changed from woodland to open savanna. Under these conditions, erect posture would be helpful in detecting predators and maintaining body temperature. However, with recent studies pushing bipedalism back to at least 4 million years, the woodland habitat does not provide the proper driving force to select for the appearance of a bipedal stance.

Bipedalism uses twice the energy as mammalian quadrupedalism. Therefore, one would expect to find a fairly robust theory to explain why hominids opted to use so much energy to get around.

Most evolutionary theories constructed to account for the appearance of bipedalism have serious problems, since they rely upon the change from woodland to savanna habitat, which occurred after bipedalism arose. This eliminates the ecology, the thermoregulation, and the enhanced vision hypotheses. The original hunting hypothesis (proposed by Charles Darwin) has been invalidated, since the appearance of hunting tools were much later than the appearance of bipedalism.

The male provider model states that monogamous males provided for pregnant/nursing mates and their offspring. All available evidence indicates that early hominids were polygynous and not monogamous and that male provisioning of immobile females and offspring was unlikely. No monogamous primate species is known to have a male who provides food for the female and her offspring. Even so, in hunter/gatherer societies, the average human female gathers an estimated 12,000 calories per day in food while the male averages only about 7,230 calories. So much for male provisioning!

The final explanation was that scarce dietary resources required an efficient means of travel. In the late Miocene, hominid dietary resources become thinly dispersed in some areas, requiring possible extensive travel to exploit those resources. Why energy-consuming bipedalism, as opposed to quadrupedalism, would be chosen as the means of travel, remains a question.

Like I said, keep talking. It's entertaining.