# Introduction to Paleoanthropology/Hominids Early



## Overview of Human Evolutionary Origin

The fossil record provides little information about the evolution of the
human lineage during the Late Miocene, from 10 million to 5 million
years ago. Around 10 million years ago, several species of large-bodied
hominids that bore some resemblance to modern orangutans lived in Africa
and Asia. About this time, the world began to cool; grassland and
savanna habitats spread; and forests began to shrink in much of the
tropics.

The creatures that occupied tropical forests declined in variety and
abundance, while those that lived in the open grasslands thrived. We
know that at least one ape species survived the environmental changes
that occurred during the Late Miocene, because molecular genetics tells
us that humans, gorillas, bonobos and chimpanzees are all descended from
a common ancestor that lived sometime between 7 million and 5 million
years ago. Unfortunately, the fossil record for the Late Miocene tells
us little about the creature that linked the forest apes to modern
hominids.

Beginning about 5 million years ago, hominids begin to appear in the
fossil record. These early hominids were different from any of the
Miocene apes in one important way: they walked upright (as we do).
Otherwise, the earliest hominids were probably not much different from
modern apes in their behavior or appearance.

Between 4 million and 2 million years ago, the hominid lineage
diversified, creating a community of several hominid species that ranged
through eastern and southern Africa. Among the members of this
community, two distinct patterns of adaptation emerged:

-   One group of creatures (Australopithecus, Ardipithecus,
    Paranthropus) evolved large molars that enhanced their ability to
    process coarse plant foods;
-   The second group, constituted of members of our own genus Homo (as
    well as Australopithecus garhi) evolved larger brains, manufactured
    and used stone tools, and relied more on meat than the
    Australopithecines did.

## Hominid Species

!Map of hominid fossil sites in East
Africa.svg "Map of hominid fossil sites in East Africa")

  ------------------ ----------------------- ----------------- --------------------------
  **Species**        **Type**                **Specimen**      **Named by**
  Sahelanthropus     tchadensis \"Toumai\"   TM 266-01-060-1   Brunet et al. 2002
  Orrorin            tugenensis              BAR 1000\'00      Senut et al. 2001
  Ardipithecus       ramidus                 ARA-VP 6/1        White et al. 1994
  Australopithecus   anamensis               KP 29281          M. Leakey et al. 1995
  Australopithecus   afarensis               LH 4              Johanson et al. 1978
  Australopithecus   bahrelghazali           KT 12/H1          Brunet et al. 1996
  Kenyanthropus      platyops                KNM-WT 40000      M. Leakey et al. 2001
  Australopithecus   garhi                   BOU-VP-12/130     Asfaw et al. 1999
  Australopithecus   africanus               Taung             Dart 1925
  Australopithecus   aethiopicus             Omo 18            Arambourg & Coppens 1968
  Paranthropus       robustus                TM 1517           Broom 1938
  Paranthropus       boisei                  OH 5              L. Leakey 1959
  Homo               habilis                 OH 7              L. Leakey et al. 1964
  ------------------ ----------------------- ----------------- --------------------------

### *Sahelanthropus tchadensis* (\"Toumai\")

!Sahelanthropus tchadensis - commonly called \"Toumai\". A hominid
skulll from 6-7 million years
ago

-   Named in July 2002 from fossils discovered in Chad.
-   Oldest known hominid or near-hominid species (6-7 million years
    ago).
-   Discovery of nearly complete cranium and number of fragmentary lower
    jaws and teeth:
    -   Skull has very small brain size (ca. 350 cc), considered as
        primitive apelike feature;
    -   Yet, other features are characteristic of later hominids: short
        and relatively flat face; canines are smaller and shorter; tooth
        enamel is slightly thicker (suggesting a diet with less fruit).
-   This mixture of features, along with fact that it comes from around
    the time when hominids are thought to have diverged from
    chimpanzees, suggests it is close to the common ancestor of humans
    and chimpanzees.
-   Foramen magnum is oval (not rounded as in chimps) suggesting upright
    walking position.

### *Orrorin tugenensis*

-   Named in July 2001; fossils discovered in western Kenya.
-   Deposits dated to about 6 million years ago.
-   Fossils include fragmentary arm and thigh bones, lower jaws, and
    teeth:
    -   Limb bones are about 1.5 times larger than those of Lucy, and
        suggest that it was about the size of a female chimpanzee.
-   Its finders claimed that Orrorin was a human ancestor adapted to
    both bipedality and tree climbing, and that the australopithecines
    are an extinct offshoot.

### *Ardipithecus ramidus*

!Skeleton of *Ardipithecus
ramidus*

-   Recent discovery announced in Sept. 1994.
-   Dated 4.4 million years ago.
-   Most remains are skull fragments.
    -   Indirect evidence suggests that it was possibly bipedal, and
        that some individuals were about 122 cm (4\'0\") tall;
    -   Teeth are intermediate between those of earlier apes and
        Austalopithecus afarensis.

### *Australopithecus anamensis*

-   Named in August 1995 from fossils from Kanapoi and Allia Bay in
    Kenya.
-   Dated between 4.2 and 3.9 million years ago.
-   Fossils show mixture of primitive features in the skull, and
    advanced features in the body:
    -   Teeth and jaws are very similar to those of older fossil apes;
    -   Partial tibia (inner calf bone) is strong evidence of
        bipedality, and lower humerus (the upper arm bone) is extremely
        humanlike.

### *Australopithecus afarensis*

!\"Lucy\", an *Australopithecus afarensis*
skeleton

-   Existed between 3.9 and 3.0 million years ago.
-   *A. afarensis* had an apelike face with a low forehead, a bony ridge
    over the eyes, a flat nose, and no chin. They had protruding jaws
    with large back teeth.
-   Cranial capacity: 375 to 550 cc. Skull is similar to chimpanzee,
    except for more human-like teeth. Canine teeth are much smaller than
    modern apes, but larger and more pointed than humans, and shape of
    the jaw is between rectangular shape of apes and parabolic shape of
    humans.
-   Pelvis and leg bones far more closely resemble those of modern
    humans, and leave no doubt that they were bipedal.
-   Bones show that they were physically very strong.
-   Females were substantially smaller than males, a condition known as
    sexual dimorphism. Height varied between about 107 cm (3\'6\") and
    152 cm (5\'0\").
-   Finger and toe bones are curved and proportionally longer than in
    humans, but hands are similar to humans in most other details.

### *Kenyanthropus platyops* (\"flat-faced man of Kenya\")

!Skull of *Kenyanthropus
platyops*.JPG "Skull of Kenyanthropus platyops")

-   Named in 2001 from partial skull found in Kenya.
-   Dated to about 3.5 million years ago.
-   Fossils show unusual mixture of features: size of skull is similar
    to *A. afarensis* and *A. africanus*, and has a large, flat face and
    small teeth.

### *Australopithecus garhi*

-   *A. garhi* existed around 2.5 Myrs.
-   It has an apelike face in the lower part, with a protruding jaw
    resembling that of *A. afarensis*. The large size of the palate and
    teeth suggests that it is a male, with a small braincase of about
    450 cc.
-   It is like no other hominid species and is clearly not a robust
    form. In a few dental traits, such as the shape of the premolar and
    the size ratio of the canine teeth to the molars, *A. garhi*
    resembles specimens of early Homo. But its molars are huge, even
    larger than the *A. robustus* average.
-   Among skeletal finds recovered, femur (upper leg bone) is relatively
    long, like that of modern humans. But forearm is long too, a
    condition found in apes and other australopithecines but not in
    humans.

### *Australopithecus africanus*

-   First identified in 1924 by Raymond Dart, an Australian anatomist
    living in South Africa.
-   *A. africanus* existed between 3 and 2 million years ago.
-   Similar to *A. afarensis*, and was also bipedal, but body size was
    slightly greater.
-   Brain size may also have been slightly larger, ranging between 420
    and 500 cc. This is a little larger than chimp brains (despite a
    similar body size).
-   Back teeth were a little bigger than in *A. afarensis*. Although the
    teeth and jaws of *A. africanus* are much larger than those of
    humans, they are far more similar to human teeth than to those of
    apes. The shape of the jaw is now fully parabolic, like that of
    humans, and the size of the canine teeth is further reduced compared
    to *A. afarensis*.

NOTE: *Australopithecus afarensis* and *A. africanus* are known as
gracile australopithecines, because of their relatively lighter build,
especially in the skull and teeth. (Gracile means \"slender\", and in
paleoanthropology is used as an antonym to \"robust\"). Despite the use
of the word \"gracile\", these creatures were still more far more robust
than modern humans.

### *Australopithecus aethiopicus*

-   *A. aethiopicus* existed between 2.6 and 2.3 million years ago.
-   Species known mainly from one major specimen: the Black Skull
    (KNM-WT 17000) discovered at Lake Turkana.
-   It may be ancestor of *P. robustus* and *P. boisei*, but it has a
    baffling mixture of primitive and advanced traits:
    -   Brain size is very small (410 cc) and parts of the skull
        (particularly the hind portions) are very primitive, most
        resembling *A. afarensis*;
    -   Other characteristics, like massiveness of face, jaws and
        largest sagittal crest in any known hominid, are more
        reminiscent of *P. boisei*.

### *Paranthropus boisei*

!Skull of *Paranthropus
boisei*

-   *P. boisei* existed between 2.2 and 1.3 million years ago.
-   Similar to *P. robustus*, but face and cheek teeth were even more
    massive, some molars being up to 2 cm across. Brain size is very
    similar to P. robustus, about 530 cc.
-   A few experts consider *P. boisei* and *P. robustus* to be variants
    of the same species.

### *Paranthropus robustus*

-   *P. robustus* had a body similar to that of *A. africanus*, but a
    larger and more robust skull and teeth.
-   It existed between 2 and 1.5 million years ago.
-   The massive face is flat, with large brow ridges and no forehead. It
    has relatively small front teeth, but massive grinding teeth in a
    large lower jaw. Most specimens have sagittal crests.
-   Its diet would have been mostly coarse, tough food that needed a lot
    of chewing.
-   The average brain size is about 530 cc. Bones excavated with *P.
    robustus* skeletons indicate that they may have been used as digging
    tools.

*Australopithecus aethiopicus*, *Paranthropus robustus* and *P. boisei*
are known as robust australopithecines, because their skulls in
particular are more heavily built.

### *Homo habilis*

!Skull of *Homo
habilis*

-   *H. habilis* (\"handy man\")
-   *H. habilis* existed between 2.4 and 1.5 million years ago.
-   It is very similar to australopithecines in many ways. The face is
    still primitive, but it projects less than in A. africanus. The back
    teeth are smaller, but still considerably larger than in modern
    humans.
-   The average brain size, at 650 cc, larger than in
    australopithecines. Brain size varies between 500 and 800 cc,
    overlapping the australopithecines at the low end and *H. erectus*
    at the high end. The brain shape is also more humanlike.
-   *H. habilis* is thought to have been about 127 cm (5\'0\") tall, and
    about 45 kg (100 lb) in weight, although females may have been
    smaller.
-   Because of important morphological variation among the fossils, *H.
    habilis* has been a controversial species. Some scientists have not
    accepted it, believing that all *H. habilis* specimens should be
    assigned to either the australopithecines or Homo erectus. Many now
    believe that *H. habilis* combines specimens from at least two
    different *Homo* species: small-brained less-robust individuals (*H.
    habilis*) and large-brained, more robust ones (*H. rudolfensis*).
    Presently, not enough is known about these creatures to resolve this
    debate.

