Eeb 210 Spring 2008 Lecture #11: Early hominins Summary of hominin ancestry as known from the fossil record




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EEB 210

Spring 2008
Lecture #11: Early hominins
Summary of hominin ancestry as known from the fossil record:
Possible common ancestors of apes and hominins, or very early hominins:


  1. Sahelanthropus tchadensis

  2. Ardipithecus ramidus

  3. Orrorin tugenensis

These species lived 5-7 mya, within the time frame suggested by genetic evidence for the common ancestor of apes and humans.

Australopithecines (or gracile australopithecines):


  1. A. animensis 4.2 - 3.8 mya

  2. A. afarensis 4 – 3 mya

  3. A. africanus 3 – 2.2 mya

  4. A. gahri 2.5 mya


Paranthropus (or robust australopithecines---these species often classified in genus Australopithecus):
a. P. aethiopicus 2.5 mya

b. P. robustus 1.8 – 1.0 mya

c. P. boisei 2.2 – 1.3 mya
Paranthropus has broad face with prominent cheeks and sagittal crest on top of skull.

Robert Broom originally (1938) described Paranthropus robustus; this species later reclassified as A. robustus (a robust australopithecine)---now often reclassified again as P. robustus along with other robust species. Some taxonomists currently place all 3 species of genus Paranthropus in genus Australopithecus (hence A. aethiopicus, A. robustus, and A. boisei)


Jaw musculature: Chewing motions of jaws controlled by masseter muscles and

temporalis muscles
Zygomatic arches: cheek bones
Temporal fossa: opening between zygomatic arches and skull allowing for passage of temporalis muscles-----zygomatic arches are flaring and pronounced in Paranthropus---larger temporal fossa allowing for large temporalis muscles
Sagittal crest: (bony ridge) at top of skull of Paranthropus provides more bone surface for attachment of temporalis muscle, which works the jaw. These “robust” hominins probably ate some foods that required strong muscles for chewing.
Kenyanthropus platyops 3.5 – 3.2 mya
Homo:

  1. H. habilis 2.4 – 1.5 mya

  2. H. rudolphensis 1.8 mya

c. H. ergaster 1.9 – 1.0 mya

d. H. erectus 1.6 – 0.4 mya

e. H. heidelbergensis 0.6 mya

f. H. neaderthalensis 0.13 – 0.03 mya

g. H. sapiens 0.2 mya to present

H. habilis:
a. earliest species in genus Homo (but is sometimes classified in genus

Australopithecus [A. habilis])

b. likely made earliest stone tools


H. ergaster :


  1. developmental stages of teeth and skull suggest that H. ergaster showed slower development that australopithecines

  2. sex dimorphism in body size is less than for most australopithecines and more like H. sapiens

  3. most complete fossil was so-called Nariokotome boy (10 year-old boy), discovered by Richard Leakey; this fossil from about 1.8 mya, found near Lake Turkana, Kenya

  4. H. ergaster had proportionally shorter arms compared to australopithecines, suggesting a strictly terrestrial (not arboreal) lifestyle


H. erectus:


  1. thought to have speciated (diverged) from a population of H. ergaster about 1.6 mya and then migrated to Asia

  2. found in Asia and Java


H. heidelbergensis:


  1. may have speciated from a population of H. ergaster and migrated into Europe

  2. may be ancestral to both H. neanderthalensis and H. sapiens

  3. at least one population of H. heidelbergensis evolved some Neandertal features (i.e., arched brow ridges) by about 300,000 ya

  4. H. heidelbergensis may have co-existed with H. erectus in eastern Asia about 250,000 – 200,000 ya


H. neanderthalensis:
a. first appeared in western Eurasia about 130,000 ya; became extinct about

30,000 ya

b. stocky bodies and relatively short limbs of Neandertals probably adaptations to

cold climate



  1. brain case was slightly larger than for modern H. sapiens (but perhaps not

larger in relation to body size)

d. probably buried their dead


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