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ANTH-UA 2 Chapter Notes -Foramen Magnum, Canine Tooth, Hominidae

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Richard Bailey

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11 - Early Hominins
Early in hominin record we look for evidence of bipedalism
Look for human features in skull and dentition
Dental arcade of humans is parabolic
Dental arcade of apes is U-shaped
Lower vertebrates have homodont dentition
Mammals have heterodont dentition
CP3 = sectorial premolar complex; combination of canine and first premolar teeth that
form a self-sharpening apparatus
Reduced in hominins
First australopithecines show some reduction of the canine, absence or reduciton
of a diastema, and at least partial loss of the CP3 honing complex
Hominins have thicker enamel than apes (but thicker enamel probably arose several
times, so this alone does not guarantee a hominin tooth)
Throughout hominin evolution, brain size increases while face size decreases
De-emphasis of the masticatory system
Emphasis on brain size and probably intelligence
Early hominins lose cranial crests (bony ridges on the skull to which muscle
attach) and end up with more rounded braincase
First Hominins
Majority of fossil evidence of earliest hominins has come from the Great Rift Valley of
East Africa
The species to be discussed below are candidates for earliest hominin remains, but all
or some of them may represent fossil apes rather than hominins
Sahelanthropus Tchadensis (7.0-6.0 MYA)
French expedition led by Michel Brunet discovered a fossilized skull in the sands of the
Djurab Desert in northern Chad in 2001 (name means “Sahara hominin from Chad”)
Fossil consists of a fairly complete skull, mandibular fragments, and isolated teeth
Hominin features:
Less prognathic face than expected
Large browridge
Somewhat smaller canine teeth
Non-funcitonal CP3 honing complex
No diastema
Horizontal nuchal plane
Possibly an anterior placed foramen magnum (may indicate bipedality)
Apelike features:
Small brain size
U-shaped dental arcade
Somewhat thin enamel

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Orrorin Tugenensis (6.0 MYA)
Found in the Lukeino Formation of the Tugen Hills of Kenya by Martin Pickford and
Brigitte Senut (name means “hominin from the Tugen Hills”)
Consist of fragmentary cranial and postcranial remains, most importantly multiple
femoral fragments
Suite of postcranial characteristics indicate bipedal nature, but anatomy of the femur and
arm are not conclusive
Remains do indicate a larger body size than expected for late Miocene ape
Still have large upper canines
Ardipithecus Ramidus (4.4 MYA) & Ardipithecus Kadabba (5.8-5.2 MYA)
Tim White, Berhane Asfaw, Gen Suwa found fossilized remains of a very primitive
hominin in the northeastern part of Ethiopia near the Red Sea
Finds come from a site called Aramis in the Middle Awash region of an ancient
river delta called the Afar Triangle
Interesting because Aramis was forested (expect to find early hominins in
Ardipithecus ramidus (“ground-living root hominin”) is argued to be a primitive hominin,
but more primitive traits necessitates placement in the genus Ardipithecus
Thinner enamel, less postcanine enlargement (megadontia)
Hominin features: smaller canine with wear on tip rather than back side, anterior
position of the foramen magnum (bipedality)
Ardipithecus kadabba - earlier variant of Ar. ramidus
Australopithecus and Kin
Australopithecus = “southern ape”
Discoveries of australopithecines have revealed an adaptive radiation of early hominins
that filled a variety of habitat types in eastern, southern, and central Africa and are now
known to have lived from 4.2 to about 1.0 mya
Genus includes species of bipedal apes that are small bodied and small brained, had
moderately prognathic faces, and a mosaic of primitive and dervied cranio-dental
Australopithecus Anamensis (4.2-3.9 MYA)
Discovered by a team lead by Meave Leakey in the form of dozens of cranial and
postcranial bone fragments at separate sites near Lake Turkana, Kanapoi, and Allia Bay
(name means “southern ape of the lake”)
Incontrovertable evidence of bipedalism (tibia thickened at ends, tibial plateu is
Teeth and jaws are more primitive than those of later hominins but more derived than
those of early hominins
More primitive than Au. afaranesis (aspets of the mandible and dentition); should not
belong to the same species
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