The following is a précis of the Authors' summaries from the "Ardipithecus issue" of Science (2 October 2009).
Ardipithecus ramidus and the Paleobiology of Early Hominids
White et al., Science, vol. 326, 2009, pg. 64
... This species, substantially more primitive than Australopithecus, resolves many uncertainties about early human evolution, including the nature of the last common ancestor that we shared with the line leading to living chimpanzees and bonobos.
... we have learned that Ar. ramidus was a denizen of woodland with small patches of forest. We have also learned that it probably was more omnivorous than chimpanzees (ripe fruit specialists) and likely fed both in trees and on the ground. It apparently consumed only small amounts of open-environment resources, arguing against the idea than an inhabitation of grasslands was the driving force in the origin of upright walking.
... The numerous recovered teeth and a largely complete skull show that Ar. ramidus had a small face and a reduced canine/premolar complex, indicative of minimal social aggression. Its hands, arms, feet, pelvis, and legs collectively reveal that it moved capably in the trees, supported on its feet and palms (palmigrade clambering), but lacked any characteristics typical of the suspension, vertical climbing, or knuckle-walking of modern gorillas and chimps. Terrestrially, it engaged in a form of bipedality more primitive than that of Australopithecus, and it lacked adaptation to "heavy" chewing related to open environments (seen in later Australopithecus). Ar. ramidus thus indicates that the last common ancestors of humans and African apes were not chimpanzee-like and that both hominids and extant African apes are each highly specialized, but through very different evolutionary pathways.
The Geological, Isotopic, Botanical, Invertebrate, and Lower Vertebrate Surroundings of Ardipithecus ramidus
WoldeGabriel, Science, vol. 326, 2009, pg. 65
... Our combined evidence indicates that Ar. ramidus did not live in the open savanna that was once envisioned to be the predominant habitat of the earliest hominids, but rather in an environment that was humid and cooler than it is today, containing habitats ranging from woodland to forest patches.
Macrovertebrate Paleontology and the Pliocene Habitat of Ardipithecus ramidus
White et al., Science, vol. 326, 2009, pg. 67
... The Ardipithecus-bearing sediments at Aramis now provide fresh evidence that Ar. ramidus lived in a predominantly woodland setting. This and corroborative evidence from fossil assemblages of avian and small mammals imply that a grassland environment was not a major force driving evolution of the earliest hominids.
... These data suggest that the anatomy and behavior of early hominids did not evolve in response to open savanna or mosaic settings. Rather, hominids appear to have originated and persisted within more closed, wooded habitats until the emergence of more ecologically aggressive Australopithecus.
The Ardipithecus ramidus Skull and Its Implications for Hominid Origins
Suwa et al., Science, vol. 326, 2009, pg. 68
... These and an additional feature of the skull hint that, despite its small size, the brain of Ar. ramidus may have already begun to develop some aspects of later hominid-like form and function. The steep orientation of the bone on which the brain stem rests suggests that the base of the Ar. ramidus brain might have been more flexed than apes. In Australopithecus, a flexed cranial base occurs together with expansion of the posterior parietal cortex, a part of the modern human brain involved in aspects of visual and spatial perception.
Paleobiological Implication of the Ardipithecus ramidus Dentition
Suwa et al., Science, vol. 326, 2009, pg. 69
... In modern monkeys and apes, the upper canine is important in male antagonistic behavior, so its subdued shape in early hominids and Ar. ramidus suggests that sexual selection played a primary role in canine reduction. Thus, fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools.
... Lack of thick enamel indicates that Ar. ramidus was not as adapted to heavy chewing and/or eating abrasive foods as were later Australopithecus or even Homo. The combined evidence from the isotopic content of the enamel, dental wear, and molar structure indicates that the earliest hominid diet was one of generalized omnivory and frugivory and therefore differed from that of Australopithecus and living African apes.
Careful climbing in the Miocene: The Forelimbs of Ardipithecus ramidus and Humans are primitive
Lovejoy et al., Science, vol. 326, 2009, pg. 70
... Ardipithecus did not knuckle-walk like African apes and ... it lacked virtually all of the specializations that protect great ape hands from injury while they climb and feed in trees.
... Our ancestors' hands differed profoundly from those of living great apes, and therefore the two must have substantially differed in the ways they climbed, fed, and nested. It is African apes who have evolved so extensively since we shared our last common ancestor, not humans or our immediate hominid ancestors. Hands of the earliest hominids were less ape-like than ours and quite differed from those of any living form.
Ardipithecus also shows that our ability to use and make tools did not require us to greatly modify our hands. Rather, human grasp and dexterity were long ago inherited almost directly from our last common ancestor with chimpanzees. We now know that our earliest ancestors only had to slightly enlarge their thumbs and shorten their fingers to greatly improve their dexterity for tool-using.
The Pelvis and Femur of Ardipithecus ramidus: The Emergence of Upright Walking
Lovejoy et al., Science, vol. 326, 2009, pg. 71
... Ar. ramidus thus illuminates two critical adaptive transitions in human evolution. In the first, from the human-chimp last common ancestor to Ardipithecus, modifications produced a mosaic pelvis that was useful for both climbing and upright walking. 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.
Combining Prehension and Propulsion: The Foot of Ardipithecus ramidus
Lovejoy et al., Science, vol. 326, 2009, pg. 72
... The foot of Ar. ramidus shows that none of these ape-like changes were present in the last common ancestor of African apes and humans. That ancestor, which until now has been thought to be chimpanzee-like, must have had a more monkey-like foot. ... We infer this because humans still have these characteristics, so we must have retained them from our last common ancestor.
... However, Ar. ramidus still had an opposable big toe, unlike any later hominid. Its ability to walk upright was therefore comparatively primitive. Because it had substantially modified the other four toes for upright walking, even while retaining its grasping big toe, the Ardipithecus foot was an odd mosaic that worked for both upright walking and climbing in trees. If our last common ancestor with the chimpanzee had not retained such an unspecialized foot, perhaps upright walking might never have evolved in the first place.
The Great Divides: Ardipithecus ramidus Reveals the Postcrania of Our Last Common Ancestors with African Apes
Lovejoy et al., Science, vol. 326, 2009, pg. 73
... The picture emerging from Ar. ramidus is that this last common ancestor had limb proportions more like those of monkeys than apes. Its feet functioned only partly like those of apes and much more like those of living monkeys and early apes such as Proconsul (which lived more than 15 million years ago). ... None of the changes that apes have evolved to stiffen their hands for suspension and vertical climbing were present, so its locomotion did not resemble that of any living ape.
The hominid descendant of the last common ancestor we shared with chimpanzees (the CLCA), Ardipithecus, became a biped by modifying its upper pelvis without abandoning its grasping big toe. It was therefore an unpredicted and odd mosaic. It appears, unlike Au. afarensis, to have occupied the basal adaptive plateau of hominid natural history.
Reexamining Human Origins in Light of Ardipithecus ramidus
Lovejoy, Science, vol. 326, 2009, pg. 74
... Ardipithecus ramidus ... shows that the anatomy of living African apes is not primitive but instead has evolved specifically within extant ape lineages. The anatomy and behavior of early hominids are therefore unlikely to represent simple amplifications of those shared with modern apes. Instead, Ar. ramidus preserves some of the ancestral characteristics of the last common ancestor with much greater fidelity than do living African apes. Two obvious exceptions are its ability to walk upright and the absence of the large projecting canine tooth in males, derived features that Ardipithecus shares with all later hominids.
... Ar. ramidus ... demonstrates that small canines occurred in hominids long before any of the dental modifications of Australopithecus or the use of stone tools.
... Ar. ramidus was fully capable of bipedality and had evolved a substantially modified pelvis and foot with which to walk upright. At the same time, it preserved the ability to maneuver in trees, because it maintained a grasping big toe and a powerful hip and thigh musculature. Because upright walking provided no energy advantage for Ar. ramidus (it lacked many of the adaptations that evolved in later hominids such as Australopithecus), reproductive success must have been central to its evolution in early hominids.
Ardipithecus ramidus and the Paleobiology of Early Hominids
White et al., Science, vol. 326, 2009, pg. 64
... This species, substantially more primitive than Australopithecus, resolves many uncertainties about early human evolution, including the nature of the last common ancestor that we shared with the line leading to living chimpanzees and bonobos.
... we have learned that Ar. ramidus was a denizen of woodland with small patches of forest. We have also learned that it probably was more omnivorous than chimpanzees (ripe fruit specialists) and likely fed both in trees and on the ground. It apparently consumed only small amounts of open-environment resources, arguing against the idea than an inhabitation of grasslands was the driving force in the origin of upright walking.
... The numerous recovered teeth and a largely complete skull show that Ar. ramidus had a small face and a reduced canine/premolar complex, indicative of minimal social aggression. Its hands, arms, feet, pelvis, and legs collectively reveal that it moved capably in the trees, supported on its feet and palms (palmigrade clambering), but lacked any characteristics typical of the suspension, vertical climbing, or knuckle-walking of modern gorillas and chimps. Terrestrially, it engaged in a form of bipedality more primitive than that of Australopithecus, and it lacked adaptation to "heavy" chewing related to open environments (seen in later Australopithecus). Ar. ramidus thus indicates that the last common ancestors of humans and African apes were not chimpanzee-like and that both hominids and extant African apes are each highly specialized, but through very different evolutionary pathways.
The Geological, Isotopic, Botanical, Invertebrate, and Lower Vertebrate Surroundings of Ardipithecus ramidus
WoldeGabriel, Science, vol. 326, 2009, pg. 65
... Our combined evidence indicates that Ar. ramidus did not live in the open savanna that was once envisioned to be the predominant habitat of the earliest hominids, but rather in an environment that was humid and cooler than it is today, containing habitats ranging from woodland to forest patches.
Macrovertebrate Paleontology and the Pliocene Habitat of Ardipithecus ramidus
White et al., Science, vol. 326, 2009, pg. 67
... The Ardipithecus-bearing sediments at Aramis now provide fresh evidence that Ar. ramidus lived in a predominantly woodland setting. This and corroborative evidence from fossil assemblages of avian and small mammals imply that a grassland environment was not a major force driving evolution of the earliest hominids.
... These data suggest that the anatomy and behavior of early hominids did not evolve in response to open savanna or mosaic settings. Rather, hominids appear to have originated and persisted within more closed, wooded habitats until the emergence of more ecologically aggressive Australopithecus.
The Ardipithecus ramidus Skull and Its Implications for Hominid Origins
Suwa et al., Science, vol. 326, 2009, pg. 68
... These and an additional feature of the skull hint that, despite its small size, the brain of Ar. ramidus may have already begun to develop some aspects of later hominid-like form and function. The steep orientation of the bone on which the brain stem rests suggests that the base of the Ar. ramidus brain might have been more flexed than apes. In Australopithecus, a flexed cranial base occurs together with expansion of the posterior parietal cortex, a part of the modern human brain involved in aspects of visual and spatial perception.
Paleobiological Implication of the Ardipithecus ramidus Dentition
Suwa et al., Science, vol. 326, 2009, pg. 69
... In modern monkeys and apes, the upper canine is important in male antagonistic behavior, so its subdued shape in early hominids and Ar. ramidus suggests that sexual selection played a primary role in canine reduction. Thus, fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools.
... Lack of thick enamel indicates that Ar. ramidus was not as adapted to heavy chewing and/or eating abrasive foods as were later Australopithecus or even Homo. The combined evidence from the isotopic content of the enamel, dental wear, and molar structure indicates that the earliest hominid diet was one of generalized omnivory and frugivory and therefore differed from that of Australopithecus and living African apes.
Careful climbing in the Miocene: The Forelimbs of Ardipithecus ramidus and Humans are primitive
Lovejoy et al., Science, vol. 326, 2009, pg. 70
... Ardipithecus did not knuckle-walk like African apes and ... it lacked virtually all of the specializations that protect great ape hands from injury while they climb and feed in trees.
... Our ancestors' hands differed profoundly from those of living great apes, and therefore the two must have substantially differed in the ways they climbed, fed, and nested. It is African apes who have evolved so extensively since we shared our last common ancestor, not humans or our immediate hominid ancestors. Hands of the earliest hominids were less ape-like than ours and quite differed from those of any living form.
Ardipithecus also shows that our ability to use and make tools did not require us to greatly modify our hands. Rather, human grasp and dexterity were long ago inherited almost directly from our last common ancestor with chimpanzees. We now know that our earliest ancestors only had to slightly enlarge their thumbs and shorten their fingers to greatly improve their dexterity for tool-using.
The Pelvis and Femur of Ardipithecus ramidus: The Emergence of Upright Walking
Lovejoy et al., Science, vol. 326, 2009, pg. 71
... Ar. ramidus thus illuminates two critical adaptive transitions in human evolution. In the first, from the human-chimp last common ancestor to Ardipithecus, modifications produced a mosaic pelvis that was useful for both climbing and upright walking. 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.
Combining Prehension and Propulsion: The Foot of Ardipithecus ramidus
Lovejoy et al., Science, vol. 326, 2009, pg. 72
... The foot of Ar. ramidus shows that none of these ape-like changes were present in the last common ancestor of African apes and humans. That ancestor, which until now has been thought to be chimpanzee-like, must have had a more monkey-like foot. ... We infer this because humans still have these characteristics, so we must have retained them from our last common ancestor.
... However, Ar. ramidus still had an opposable big toe, unlike any later hominid. Its ability to walk upright was therefore comparatively primitive. Because it had substantially modified the other four toes for upright walking, even while retaining its grasping big toe, the Ardipithecus foot was an odd mosaic that worked for both upright walking and climbing in trees. If our last common ancestor with the chimpanzee had not retained such an unspecialized foot, perhaps upright walking might never have evolved in the first place.
The Great Divides: Ardipithecus ramidus Reveals the Postcrania of Our Last Common Ancestors with African Apes
Lovejoy et al., Science, vol. 326, 2009, pg. 73
... The picture emerging from Ar. ramidus is that this last common ancestor had limb proportions more like those of monkeys than apes. Its feet functioned only partly like those of apes and much more like those of living monkeys and early apes such as Proconsul (which lived more than 15 million years ago). ... None of the changes that apes have evolved to stiffen their hands for suspension and vertical climbing were present, so its locomotion did not resemble that of any living ape.
The hominid descendant of the last common ancestor we shared with chimpanzees (the CLCA), Ardipithecus, became a biped by modifying its upper pelvis without abandoning its grasping big toe. It was therefore an unpredicted and odd mosaic. It appears, unlike Au. afarensis, to have occupied the basal adaptive plateau of hominid natural history.
Reexamining Human Origins in Light of Ardipithecus ramidus
Lovejoy, Science, vol. 326, 2009, pg. 74
... Ardipithecus ramidus ... shows that the anatomy of living African apes is not primitive but instead has evolved specifically within extant ape lineages. The anatomy and behavior of early hominids are therefore unlikely to represent simple amplifications of those shared with modern apes. Instead, Ar. ramidus preserves some of the ancestral characteristics of the last common ancestor with much greater fidelity than do living African apes. Two obvious exceptions are its ability to walk upright and the absence of the large projecting canine tooth in males, derived features that Ardipithecus shares with all later hominids.
... Ar. ramidus ... demonstrates that small canines occurred in hominids long before any of the dental modifications of Australopithecus or the use of stone tools.
... Ar. ramidus was fully capable of bipedality and had evolved a substantially modified pelvis and foot with which to walk upright. At the same time, it preserved the ability to maneuver in trees, because it maintained a grasping big toe and a powerful hip and thigh musculature. Because upright walking provided no energy advantage for Ar. ramidus (it lacked many of the adaptations that evolved in later hominids such as Australopithecus), reproductive success must have been central to its evolution in early hominids.
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