Which evolved first in hominids

Additional hominin fossils from the crucial time period of million years ago must be discovered to conclusively determine the place of platyops in our evolution. Australopithecus africanus lived about 3. Skeletally, they were less ape-like than earlier species of australopithecines but were still usually small and light in frame like afarensis.

However, the teeth of africanus were in some ways more like humans than like afarensis. Specifically, the front teeth of africanus were relatively large like ours and their canine teeth did not project beyond the others. Microscopic wear patterns on africanus teeth suggest a diet consisting of relatively soft foods, which very likely included some meat along with plants.

This does not necessarily imply efficient hunting skills. More likely, they obtained meat by scavenging what remained on the abandoned corpses of large animals killed by lions and other predators.

It is possible that they also did some hunting of small animals in much the same inefficient manner of chimpanzees today. They probably ate insects and eggs as well. The classification of Australopithecus garhi is still very problematical.

This Ethiopian fossil has been dated to 2. Largely for that reason, some paleoanthropologists have suggested that garhi is a variant of africanus.

However, several features of the head of garhi look more like a holdover from the older afarensis species. On the other hand, the relative lengths of the arms and legs of garhi are more reminiscent of the first humans. The discovery of butchered animal bones with garhi suggests that their diet included at least some meat, as was the case with africanus.

Paranthropoid Species. T he australopithecines have been referred to collectively as gracile species literally "gracefully slender" of early hominins.

Most of them were relatively small, slender, and delicate boned compared to the somewhat more muscular, robust species paranthropoids that mostly came later. However, this is not always a reliable descriptive distinction because the range of variation in physical appearance of the two groups of species overlaps. Subsequently, some individual graciles were bigger than some of the robust ones.

However, the robust species shared some characteristics of their heads that dramatically show that they had diverged from the evolutionary line that would become humans. They had larger faces and jaws accompanied by pronounced sagittal crests in the case of males. They also had much larger back teeth premolars and molars and smaller front ones incisors compared to gracile australopithecines and early humans who were alive at the same time.

Australopithecus gracile body Paranthropus robust body Paranthropus teeth upper human teeth lower Little is known about Paranthropus a ethiopicus the "black skull" other than it apparently was one of the earliest robust species--it lived about 2. So far, this species has been found only in East Africa. Since it had a smaller brain than the other robust species and it was early, aethiopicus is thought to be a transitional form from one of the gracile species that came before.

It had an unusually large sagittal crest shown below. Paranthropus robustus was a South African robust species that lived about 2.

They had strong jaws and very large molar and premolar teeth with thick enamel. Males also had pronounced sagittal crests, though not as large as the species listed next. Paranthropus boisei was a super-robust East African species that lived about 2. They tended to be more massive and beefy-looking even than Paranthropus robustus. Male boisei were especially muscular.

Like their South African cousins, robustus , they had prominent sagittal crests and very large grinding teeth with thick enamel. These teeth would have been capable of cracking hard nuts and dry seeds. However, such food items may not have been important in their diet. Microscopic analysis of dental wear patterns and carbon isotope analysis of teeth indicate that what boisei predominantly ate was soft foods such as grasses, leaves, roots, and possibly even meat.

Early Hominin Body Size. The early hominins were significantly smaller on average than modern humans. Adult male australopithecines were usually only about 4. Females were much smaller and less muscular. They were usually 3. This is greater sexual dimorphism than is found in human populations today. In some australopithecine species, sexual dimorphism may have been nearly as great as among the great apes.

Possible Evolutionary Links. There has been a gap in the fossil hominin record for the crucial period before 4. New discoveries are now beginning to fill in the missing picture of evolution leading to the australopithecines at that early time. Beginning in , Tim White and several of his Ethiopian colleagues found fossils of what may be the immediate ancestor of the australopithecines at the Aramis site in the Middle Awash region of Northern Ethiopia.

The teeth of these very early fossils seem to have been transitional between apes and Australopithecus anamensis. Among the living apes, they were most similar to chimpanzees, however, they were not apes as we usually think of them today. These Aramis fossils date to about 4. Because of their primitiveness, White has given them a new genus and species designation Ardipithecus ramidus , nicknamed "Ardi" rather than include them with australopithecines.

Based on the time frame, body shape, and dentition similarities, it is reasonable to conclude that some of the early hominin species were ancestors of our genus Homo. Most likely, some of the australopithecines shown as red in the diagram below were in our line of evolution, but the later paranthropoids blue below were not. The first humans Homo habilis were contemporaries of the paranthropoids. As a result, they could not be our ancestors.

However, it is likely that Australopithecus afarensis and Australopithecus africanus were in our evolutionary line. We have not yet been able to extract DNA from the bones of any australopithecine for comparison with modern human DNA.

When we can do this, it is almost certain that we will discover many of their genes still in us today. He based this on the fact that the natural range of our nearest living relatives, chimpanzees and gorillas, is limited to Africa.

He concluded that we ultimately must have shared a now extinct common ancestor with those apes in Africa. This view was mostly rejected by the scientific world of the time. Before the 's, knowledge of our fossil ancestors only went back to the Neandertals in Europe and some presumably earlier human-like forms from Java, in Southeast Asia. Few researchers were willing to estimate the time period of the earliest hominins at much more than , years, and there was no inkling of anything older from Africa.

In addition, there was a bias among the predominantly European paleoanthropologists against accepting early Africans as the ancestors of all humanity. In , Raymond Dart , an Australian anatomy professor at the University of Witerwatersrand in Johannesburg, South Africa, obtained a fossil skull that had been blasted out of a nearby limestone quarry at Taung. It took him 73 days to chisel the skull free from its surrounding stone matrix and 4 years of spare time to free the jaw and the fossilized brain.

However, long before then, Dart recognized the importance of this find. In he named it Australopithecus africanus literally "southern ape from Africa".

Because of its small size, he called it the "Taung baby. Despite its relatively small brain, he concluded that this species was intermediate between apes and humans. He based this mainly on the shape and position of the base of the brain cast. It indicated that the foramen magnum , or hole in the skull through which the spinal cord passes, pointed downward and was nearly at the central balance point of the skull.

This meant that the Taung child must have been bipedal. In addition, the canine teeth were relatively short. In both of these traits, the Taung child was much more like a human than an ape.

Most paleoanthropologists in the 's rejected Dart's claims that Australopithecus africanus was intermediate between apes and humans in favor of the view that it was just an ape. Dart's claims were not widely accepted until the late 's. Following Dart's discovery, several other caves were investigated in South Africa. Most of the work was done by Robert Broom from through the 's. Broom was a medical doctor and an enthusiastic amateur paleontologist from Scotland.

In , he was appointed professor of geology at the University of Stellenbosch in South Africa and became internationally respected for his studies of early mammal-like reptiles. His insistence on the correctness of the theory of evolution led to his dismissal from this conservative religious university in Consequently, he returned to being a medical doctor in a rural town in South Africa but continued paleontological research in his spare time.

In , at the age of 68, he retired from his medical practice and joined the staff of the Transvaal Museum in Pretoria as a paleoanthropologist.

The rest of his life was spent searching for early hominin fossils. Robert Broom's most important discoveries were made in the Sterkfontein valley of South Africa. It was there in that he found the first known adult Australopithecus africanus while excavating in Sterkfontein cave.

In , he discovered more fossil remains of africanus and other early hominins in Kromdraai cave. Some of these fossils were larger boned and more muscular with powerful jaws. Broom named them Paranthropus robustus Paranthropus means "parallel to man". Significantly, these robust hominins also differed in having a sagittal crest , or ridge of bone extending from front to back, along the midline of the top of the skull.

A sagittal crest serves as an anchor attachment for exceptionally large, strong jaw muscles. This skeletal feature is also present in large apes but not in africanus or humans. Paranthropus robustus NOTE: Some paleoanthropologists lump Paranthropus robustus and other paranthropoids into the genus Australopithecus. They consider them to be a physically robust subgroup of australopithecines.

Following that excavation, he dedicated the rest of his life to writing everything known about all of the early hominins.

H e completed this compendium work in He was 85 years old and ill. As he finally finished his writing, he reportedly said "now it is done and so am I. Leopard canines fit punctures in hominin skull from Swartkrans Between and , Swartkrans cave was carefully reinvestigated by another South African paleoanthropologist, C.

Brain, using more thorough field and laboratory techniques than had been used by Robert Broom a generation earlier. Many thousands of bone fragments, including the remains of individual hominins, were recovered by Brain. These bones were from australopithecines and paranthropoids as well as early members of our genus, Homo. Because many of the bones had chewing marks and at least one of the skulls had peculiar depressions reminiscent of punctures made by the canine teeth of a leopard, Brain hypothesized that some of the Swartkrans hominins had been eaten by these big cats.

The early hominin fossil-bearing strata in the cave also contained stones that were from locations distant from the cave. Brain believed that 30 of them may have been used as tools or weapons. In any case, the presence of these stones suggests that not all of the early hominins in the cave were there as a result of being the victims of carnivores.

Unfortunately, most of the South African sites where early hominin fossils have been found are not easily dated because they lack association with volcanic deposits that would readily allow radiometric dating. That is not the case with most of the early hominin sites in East Africa. The oldest fossil hominins have been recovered from sites in East Africa, especially in the Great Rift Valley.

One of the most important sites there is Olduvai Gorge. It is an approximately 30 mile 48 km. It is only about feet 90 m. The remains of many australopithecines, paranthropoids, and early humans have been found at Olduvai. When these ancient hominins lived there, it was a lake margin grassland area that had abundant plant food and meat sources that could be exploited by scavenging.

Her bones were so brittle that they crumbled when touched. The researchers spent three field seasons digging out entire blocks of sedimentary rock surrounding the fossils, encasing the blocks in plaster and driving them to the National Museum of Ethiopia in Addis Ababa. In the museum lab, White painstakingly injected glue from syringes into each fragment and then used dental tools and brushes, often under a microscope, to remove the silty clay from the glue-hardened fossils.

Meanwhile, Suwa, today a paleoanthropologist at the University of Tokyo, analyzed key fossils with modified CT scanners to see what was inside them and used computer imaging to digitally restore the crushed skull.

Finally, he and anatomist C. Owen Lovejoy worked from the fossils and the computer images to make physical models of the skull and pelvis. This came as a surprise to researchers who had proposed that the earliest hominids would look and act a lot like chimpanzees.

They are our closest living relatives, sharing 96 percent of our DNA, and they are capable of tool use and complex social behavior. If Lovejoy is right, this means Ardi—and our upright-walking ancestors—never went through a knuckle-walking stage after they came down from the trees to live on the ground, as some experts have long believed.

They would have let her balance on one leg at a time while walking upright. And she had an opposable big toe, so her foot was able to grasp branches, suggesting she still spent a lot of time in the trees—to escape predators, pick fruit or even sleep, presumably in nests made of branches and leaves. He and his colleagues have proposed that Ardi represents an early stage of human evolution when an ancient ape body plan was being remodeled to live in two worlds—in the trees and on the ground, where hominids increasingly foraged for plants, eggs and small critters.

The Ardi research also challenged the long-held views that hominids evolved in a grassy savanna, says Middle Awash project geologist Giday WoldeGabriel of Los Alamos National Laboratory. Analyzing thousands of specimens of fossilized plants and animals, as well as hundreds of samples of chemicals in sediments and tooth enamel, the researchers found evidence of such forest species as hackberry, fig and palm trees in her environment.

Ardi lived alongside monkeys, kudu antelopes and peafowl—animals that prefer woodlands, not open grasslands. Ardi is also providing insights into ancient hominid behavior. Moving from the trees to the ground meant that hominids became easier prey. At the same time, A. As hominids began increasingly to work together, Lovejoy says, they also adopted other previously unseen behaviors—to regularly carry food in their hands, which allowed them to provision mates or their young more effectively.

This behavior, in turn, may have allowed males to form tighter bonds with female mates and to invest in the upbringing of their offspring in a way not seen in African apes. All this reinforced the shift to life on the ground, upright walking and social cooperation, says Lovejoy. Not everyone is convinced that Ardi walked upright, in part because the critical evidence comes from her pelvis, which was crushed.

While most researchers agree that she is a hominid, based on features in her teeth and skull, they say she could be a type of hominid that was a distant cousin of our direct ancestor—a newfound offshoot on the human family tree.

As researchers sort out where Ardi sits in the human family tree, they agree that she is advancing fundamental questions about human evolution: How can we identify the earliest members of the human family? How do we recognize the first stages of upright walking? What did our common ancestor with chimpanzees look like? A toe bone suggested its owner had walked upright. The bones looked so much like a primitive version of A.

In , Martin Pickford of the College of France and Brigitte Senut of the National Museum of Natural History in Paris announced their team had found an even older hominid—13 fossils representing a species that lived six million years ago in the Tugen Hills of Kenya. Two of the fossils were thighbones, including one that provided the oldest direct evidence of upright walking in a hominid. Informally, in honor of its year of discovery, they called it Millennium man.

Hot on the heels of that discovery came the most surprising one of all—a skull from Chad, about 1, miles west of the Great Rift Valley of eastern Africa where many of the most ancient hominids have been found. A Chadian student named Ahounta Djimdoumalbaye picked up a ball of rock on the floor of the Djurab Desert, where windstorms blow sand dunes like waves on a sea and expose fossils buried for millions of years.