The word hominidae is used to describe the total member species of the human family
that have lived since the last common ancestor of both man and the apes.
A hominid is an individual species within that family.
- THE HUMAN LINEAGE
- The field of science which studies the human fossil record is known as paleoanthropology. It is the intersection of the disciplines of paleontology (the study of ancient life forms) and anthropology (the study of humans). Each hominid name consists of a genus name (e.g. Australopithecus, Homo) which is always capitalized, and a species name (e.g. africanus, erectus) which is always in lower case.
Some controversy exists on the time of this common ancestor to both ape and human, but it is believed to be about 5.5 million years ago. A key fossil record near that time is Ramapithecus, which was believed to be an early hominid for many years, but is now considered an ancient ape that lived near the fork in our common lineage. Ramapithecus is now thought to be an ancestor of the modern apes.
- History of Man
| SPECIES |
TIME PERIOD |
| Ardipithicus ramidus |
5 to 4 million years ago |
| Australopithecus anamensis |
4.2 to 3.9 million years ago |
| Australopithecus afarensis |
4 to 2.7 million years ago |
| Australopithecus africanus |
3 to 2 million years ago |
| Australopithecus robustus |
2.2 to 1.6 million years ago |
| Homo habilis |
2.2 to 1.6 million years ago |
| Homo erectus |
2.0 to 0.4 million years ago |
| Homo sapiens archaic |
400 to 200 thousand years ago |
| Homo sapiens neandertalensis |
200 to 30 thousand years ago |
| Homo sapiens sapiens |
200 thousand years ago to present |
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- The times of existence of the various hominid shown in the chart above are based on dated fossil remains. Each species may have existed earlier and/or later than shown, but fossil proof has not been discovered yet. There is also dispute concerning many overlapping species, for example, the overlap between Homo habilis and Homo erectus. It could well be that the two are continuing examples of the same species. The same dispute exists with Homo erectus, Homo sapiens archaic and homo sapiens sapiens. If all species have been discovered and the lineage of man lies within them, the most probable lineage would include all but the robust Australopithecines and the neandertal.
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- The Following Chronology is Abbreviated:
- The earliest fossil hominid, Ardipithecus ramidus, is a recent discovery. It is dated at 4.4 million years ago. The remains are incomplete but enough is available to suggest it was bipedal and about 4 feet tall. Other fossils were found with the ramidus fossil which would suggest that ramidus was a forest dweller. A new skeleton was recently discovered which is about 45% complete. It is now being studied.
A new species, Australopithecus anamensis, was named in 1995. It was found in Allia Bay in Kenya. Anamensis lived between 4.2 and 3.9 million years ago. Its body showed advanced bipedal features, but the skull closely resembled the ancient apes.
Australopithecus afarensis lived between 3.9 and 3.0 million years ago. It retained the apelike face with a sloping forehead, a distinct ridge over the eyes, flat nose and a chinless lower jaw. It had a brain capacity of about 450 cc. It was between 3'6" and 5' tall. It was fully bipedal and the thickness of its bones showed that it was quite strong. Its build (ratio of weight to height) was about the same as the modern human but its head and face were proportionately much larger. This larger head with powerful jaws is a feature of all species prior to Homo sapiens sapiens.
Australopithecus africanus was quite similar to afarensis and lived between three and two million years ago. It was also bipedal, but was slightly larger in body size. Its brain size was also slightly larger, ranging up to 500 cc. The brain was not advanced enough for speech. The molars were a little larger than in afarensis and much larger than modern human. This hominid was a herbivore and ate tough, hard to chew, plants. The shape of the jaw was now like the human.
Australopithecus aethiopicus lived between 2.6 and 2.3 million years ago. This species is probably an ancestor of the robustus and boisei. This hominid ate a rough and hard to chew diet. He had huge molars and jaws and a large sagittal crest. A sagittal crest is a bony ridge on the skull extending from the forehead to the back of the head. Massive chewing muscles were anchored to this crest. Brain sizes were still about 500cc, with no indication of speech functions.
Australopithecus robustus lived between two and 1.5 million years ago. It had a body similar to that of africanus, but a larger and more massive skull and teeth. Its huge face was flat and with no forehead. It had large brow ridges and a sagittal crest. Brain size was up to 525cc with no indication of speech capability.
Australopithecus boisei lived between 2.1 and 1.1 million years ago. It was quite similar to robustus, but with an even more massive face. It had huge molars, the larger measuring 0.9 inches across. The brain size was about the same as robustus. Some authorities believe that robustus and boisei are variants of the same species.
Homo habilis was called the handy man because tools were found with his fossil remains. This species existed between 2.4 and 1.5 million years ago. The brain size in earlier fossil specimens was about 500cc but rose to 800cc toward the end of the species life period. The species brain shape shows evidence that some speech had developed. Habilis was about 5' tall and weighed about 100 pounds. Some scientists believe that habilis is not a separate species and should be carried either as a later Australopithecine or an early Homo erectus. It is possible that early examples are in one species group and later examples in the other.
Homo erectus lived between 1.8 million and 300,000 years ago. It was a successful species for a million and a half years. Early examples had a 900cc brain size on the average. The brain grew steadily during its reign. Toward the end its brain was almost the same size as modern man, at about 1200cc. The species definitely had speech. Erectus developed tools, weapons and fire and learned to cook his food. He traveled out of Africa into China and Southeast Asia and developed clothing for northern climates. He turned to hunting for his food. Only his head and face differed from modern man. Like habilis, the face had massive jaws with huge molars, no chin, thick brow ridges, and a long low skull. Though proportioned the same, he was sturdier in build and much stronger than the modern human.
Homo sapiens (archaic) provides the bridge between erectus and Homo sapiens sapiens during the period 200,000 to 500,000 years ago. Many skulls have been found with features intermediate between the two. Brain averaged about 1200cc and speech was indicated. Skulls are more rounded and with smaller features. Molars and brow ridges are smaller. The skeleton shows a stronger build than modern human but was well proportioned.
Homo sapiens neandertalensis lived in Europe and the Mideast between 150,000 and 35,000 years ago. Neandertals coexisted with H.sapiens (archaic) and early H.sapiens sapiens. It is not known whether he was of the same species and disappeared into the H.sapiens sapiens gene pool or he may have been crowded out of existence (killed off) by the H.sapien sapien. Recent DNA studies have indicated that the neandertal was an entirely different species and did not merge into the H. sapiens sapiens gene pool. Brain sizes averaged larger than modern man at about 1450cc but the head was shaped differently, being longer and lower than modern man. His nose was large and was different from modern man in structure. He was a massive man at about 5'6" tall with an extremely heavy skeleton that showed attachments for massive muscles. He was far stronger than modern man. His jaw was massive and he had a receding forehead, like erectus.
Homo sapiens sapiens first appeared about 120,000 years ago. Modern humans have an average brain size of about 1350 cc.
- Bipedal Locomotion
- The principle feature which binds all hominids together into a unique group is their choice of locomotion. All hominids exhibit features of their anatomy which indicate habitual bipedalism. There are a great many features which provide direct or subtle evidence for this behavior; a some of the main features of the skeletal system include:
1. Shape and proportioning of the pelvic girdle
2. Positioning of the head and neck of the femur
3. Position of the big toe (abducted, as opposed to divergent)
4. Position of the foramen magnum, the hole on the underside of the cranium which transmits the brainstem and spinal cord
Other features include asymmetry of the distal femoral condyles and proximal tibial condyles; relative positioning of the ischium and the iliac crest; angle of the femoral neck. Additionally, reconfiguration of muscular attachments, especially the hip abductors, is required to maintain proper balance while moving in a bipedal gait. These characteristics, when observed in fossilized skeletal elements, argue for an organism which utilized a highly specialized mode of locomotion shared with all human beings today.
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- Laetoli Trackways
- Two diagrams show the location of the hominid footprints found by archaeologist Mary Leakey's team at Laetoli. Other animal tracks are also visible. These tracks, at least 3.6 million years old, were the first evidence paleontologists found of upright walking, an ability unique to humans. According to Ian Tattersall: "Usually behavior has to be inferred indirectly from the evidence of bones and teeth, and there is almost always argument over inferences of this kind. But at Laetoli, through these footprints, behavior itself is fossilized."
- Thank goodness for the irrepressible urge of humans (and other animals) to joke and play around in nearly any situation. Sometimes, it pays big dividends. It certainly did in 1976, when paleoanthropologist Andrew Hill and a colleague were tossing elephant dung at each other in Laetoli, a hominid archeological site in Tanzania. As Hill dived out of the way, he stumbled on what turned out to be one of the wonders of prehistoric finds: a trail of hominid footprints about 3.6 million years old.
The majority of the Laetoli footprint site was excavated in 1978. Until then, the oldest known footprints of human ancestors were tens of thousands of years old. But this trail, some 80 feet long and preserved in cementlike volcanic ash, had been made by some of the first upright-walking hominids. An almost unimaginable sequence of events preserved what paleontologist Ian Tattersall calls a fossil of human behavior -- prehistoric walking.
Initially, a nearby volcano called Sadiman erupted a cloud of fine ash, like beach sand, that left a layer on the landscape. Then a light rain fell onto the ash to create something like wet cement -- an ideal material for trapping footprints. Birds and mammals left a great number of prints, but, spectacularly, so did a pair of hominids, one large and one small, trekking across the ash. (Some analysts conclude that it is possible to detect the trail of a third, smaller individual whose tracks overlap the footprints left by one of the others.) A subsequent eruption from Sadiman dropped more ash, sealing the footprints like a laminated driver's license. Finally, erosion over millions of years unveiled the prints for Hill and other researchers in Mary Leakey's group to discover.
The prints, say experts on hominid body structure, are strikingly different from those of a chimpanzee, and in fact are hardly distinguishable from those of modern humans. The only known hominid fossils of that age in that location are those of Lucy and her kind, the small-brained but upright-walking hominids classified as Australopithecus afarensis. Some analysts have noted that the smaller of the two clearest trails bears telltale signs that suggest whoever left the prints was burdened on one side -- perhaps a female carrying an infant on her hip. While the detailed interpretation of the prints remains a matter of debate, they remain an extraordinary and fascinating fossil find, preserving a moment in prehistoric time.
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- "LUCY'S BABY" -- World's Oldest Child
- The world's oldest known child has been discovered in East Africa in an area known appropriately as the Cradle of Humanity.
The 3.3-million-year-old fossilized toddler was uncovered in north Ethiopia's badlands along the Great Rift Valley. The skeleton, belonging to the primitive human species Australopithecus afarensis, is remarkable for its age and completeness, even for a region spectacularly rich in fossils of our ancient ancestors, experts say.
The new find may even trump the superstar fossil of the same species: "Lucy," a 3.2-million-year-old adult female discovered nearby in 1974 that reshaped theories of human evolution. Some experts have taken to calling the baby skeleton "Lucy's baby" because of the proximity of the discoveries, despite the fact that the baby is tens of thousands of years older.
"This is something you find once in a lifetime," said Zeresenay Alemseged of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the team that made the discovery.
A Complete Find
The child was probably female and about three years old when she died, according to the researchers. Found in sandstone in the Dikika area, the remains include a remarkably well preserved skull, milk teeth, tiny fingers, a torso, a foot, and a kneecap no bigger than a dried pea. Archaeologists hope that the baby skeleton, because of its completeness, can provide a wealth of details that Lucy and similar fossils couldn't. The age of death makes the find especially useful, scientists say, providing insights into the growth and development of human ancestors.
"Visually speaking, the Dikika child is definitely more complete [than Lucy]," team member Fred Spoor of University College London (UCL) said.
"The most impressive difference between them is that this baby has a face," Zeresenay added.
That face, no bigger than a monkey's, was spotted peering from a dusty slope in December 2000. Its smooth brow and short canine teeth identified it as a hominin, a group that encompasses humans and their ancestors.
New Questions
The fossil child, who died at nursing age, offers important clues to the development of early humans, says Spoor, of UCL. "It will teach us how our early ancestors grew up," he said. "The only way you can evolve from one type of species into another is by growing up in a different way, because that's how you change." For instance, a prolonged, dependent childhood allowed later human species to grow larger brains, which need more time to develop after birth. "As far as we can tell, it is not yet happening [with Lucy's baby]," Spoor said.
While the adult A. afarensis is thought to have had a brain slightly larger than a chimpanzee's, the hominin child's brain appears to have been smaller than an average chimp brain of the same age. "For the first time we have insights that they may have grown their brains a little bit slower than your average chimp," Spoor said.
"If you take more time to form your brain, it may well be that you make more intricate connections inside," the researcher added. "Or it may not be a positive thing—perhaps you live on poorer food or are a bit behind."
Spoor favors the latter explanation in the case of these early hominins. "They haven't progressed over great apes at all," he said. "They've just changed their locomotion for whatever reason, but they were not necessarily any more clever than chimps were." The new fossil also supports the theory that A. afarensis walked upright on two legs, but it hints that human ancestors hadn't completely left the trees by that time. The skeleton's ape-like upper body includes two complete shoulder blades similar to a gorilla's, so it could have been better at climbing than humans are. "This was a bit of a surprise, and controversial," Spoor said.
Some researchers will say the feature was inherited from an ancestor and reveals little about this hominin's lifestyle, Spoor adds. "Other people will say it shows they are still using their arms for climbing quite a lot," he said.
"The question is not whether they spent all day swinging around in the trees. But it may be true there was still some climbing aspect, for instance, for building nests at night or to forage in the trees."
A Record Find
Louise Humphrey, a paleontologist at the Natural History Museum in London who wasn't part of Zeresenay's team, describes the find as "an extremely valuable addition to the hominin fossil record."
"The fossil also preserves parts of the skeleton not previously documented for A. afarensis," she added. These included a hyoid bone in the throat area that later went on to form part of the human voice box. "Detailed analysis of the skeleton will reveal a lot more about the [locomotion] and foraging behavior of this young hominin," Humphrey said. How the child died is unclear, though it appears the body was rapidly covered by sand and gravel during a flood.
"It was buried just after it died," Zeresenay said. "That's why we found an almost complete skeleton, so maybe [drowning] could be the cause of its demise." Like Lucy and many other hominin fossils, the child was uncovered in the low-lying northern end of Africa's Great Rift Valley.
Researchers say the region was once much less arid. Hominins shared the area's lush woods and grasslands with extinct species of elephants, hippos, crocodiles, otters, antelopes, and other animals whose fossils have been found nearby. For these remains to be preserved and discovered, Zeresenay says, they needed to be covered in sediments and then exposed by tectonic activity, as has happened in the Great Rift Valley.
"These deposited environments were subsequently exposed by tectonics for us to go there and find the hominins," he added. The Ethiopian paleoanthropologist says several more years of painstaking work will be needed to remove the remaining hard sandstone encasing much of the fossil child's skeleton.
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