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Posted to original Thread in LBN by gottaB (1000+ posts) Thu Jan-20-05 04:24 AM
You basically take a list of features that distinguish humans from apes. If a specimen or group of specimens has a lot of human characteristics, call it a hominid. Then you spend twenty years arguing about it, all the while new data are coming in.
There are cases of hominids that aren't ancestral, for example among the Austrolopithecenes. To find the ancestors, you basically do the same thing in that group and weed out the ones with unusual features, like robustus. The reasoning is that once a successful adaptation takes place, it's not likely to revert to a more primordial state and start again. So you can't say with absolute certainty that A. robustus is not an ancestor, but it would be extremely unlikely. A. afarensis, on the other hand, is almost certainly an ancestor.
Here's a chart:
http://www.archaeologyinfo.com/species.htm In the case of ramidus, we see features associated with an adaptation for bipedalism. The position of the foramen magnum was mentioned in the Times article. There's also the phalanx that was unearthed. There is also a femur, which has a large balled head suggestive of bipedalism. Taken together it's pretty strong evidence of both a divergence from the line leading to modern Chimps, and the begining of the line leading to Homo sapiens.
Well, I'm not much on dentition, but here goes....
I think the teeth are basically ape teeth with a couple of features only present in later hominids.
One description:
A morphological description of the initial, mainly dental, fossil remains of Ardipithecus ramidus was published by White et al, 1994. The physical attributes of this hominid show a range of primitive traits, which are most likely character retentions from the last hominid/chimpanzee ancestor. At the same time, some hominid innovations are equally apparent. The currently known traits of Ardipithecus ramidus, in general, can be placed within two categories: ape-like traits and Australopithecine-like traits.
Much of the dentition is ape-like and this hominid most likely had a significantly different dietary niche than did later hominids. A small canine-incisor to postcanine dental ratio, typical of all other known hominids, is strikingly absent in Ardipithecus ramidus. In addition to the presence of a relatively large anterior dentition, tooth enamel is thin. Though slightly greater than in teeth of modern chimpanzees, enamel thickness of A. ramidus is extremely thin by hominid standards.
Premolar and molar morphology also point to niche affinities with the great ape ancestors. Strong crown asymmetries, in particular enlarged buccal cusps, characterize the upper and lower premolars. Additionally, an ape-like molar shape prevails. The length (in the mesiodistal plane) to breadth (in the buccolingual plane) ratio, which is roughly equal to 1 in later hominids, is much greater in A. ramidus.
Some important derived features, link Ardipithecus ramidus with the Australopithecines. Hominid-like canines are present. These are low, blunt, and less projecting than the canines of all other known apes. Upper and lower incisors are larger than those of the Australopithecines, but are smaller than those of chimpanzees. This character state can thus be considered transitional between apes and Australopithecines. Additionally, the lower molars are broader than those of a comparably-sized ape. This trait, too, approaches the common hominid condition.
http://www.archaeologyinfo.com/ardipithecusramidus.htm In my view bipedalism represents a huge adaptation. By huge I mean it really alters the gross anatomy in a variety of ways. One could imagine such dramatic changes happening twice, but it would be unusual. The most parsimonious explanation is that it happened once in the human lineage, and that explanation does not appear to be inconsitent with the fossil record.
So in short I am not bothered much by ramidus' dentition, not to the point of putting it off to the side. I don't know. There is A. kadabba or A. ramidus kadabba, depending upon your preference. I suppose it will be argued for another decade at least.
Check this out:
http://www.cmnh.org/collections/physanth/documents/60B6 ...
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posted to original thread by Nothing Without Hope (990 posts) Thu Jan-20-05 04:23 AM
Interesting that they ate a plant-based diet and that the canines, which some apes use for dominance fights, were small. So they sound less like the relatively warlike chimpanzees and more like the make-love-not-war bonobos. At least that is a pleasant speculation. Perhaps there was a sort of Garden of Eden after all.
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