Lecture+17-+Early+Hominin+Origins

EARLY HOMININ ORIGINS AND EVOLUTION - LECTURE 17

INTRODUCTION

  • Lecture by Dr. Schach in ANTH 1.
  • Focus on early hominin species including both pre-australopithecines and australopithecines.

EARLY HOMININ SPECIES

  • Categories:
    • Pre-Australopithecines
    • Australopithecines
  • Historic Timeline of Key Species:
    • 6 million years ago (mya): Sahelanthropus tchadensis, Orrorin tugenensis
    • 5-4 mya: Australopithecus (e.g., Au. anamensis, Au. afarensis)
    • 2 mya: Homo habilis, Homo erectus
  • Key Species:
    • Sahelanthropus tchadensis
    • Orrorin tugenensis
    • Ardipithecus (e.g., Ar. kadabba, Ar. ramidus)
    • Australopithecus species (e.g., Au. afarensis, Au. africanus, Au. robustus, etc.)
    • Homo habilis, Homo erectus

PRE-AUSTRALOPITHECINES

  • Definition:
    • Oldest identified members of Hominini.
    • Few fossil records that are fragmentary and exhibit more ape-like features than human-like.
  • Notable Species:
    1. Sahelanthropus tchadensis
    2. Orrorin tugenensis
    3. Ardipithecus kadabba
    4. Ardipithecus ramidus
SAHELANTHROPUS TCHADENSIS
  • Age: 7-6 million years old.
  • Discovery: Found in 2001 by Michel Brunet and colleagues in the Djurab Desert, Chad (NOT eastern Rift Valley).
  • Anatomical Features:
    • Small brain size (~350 cc).
    • Likely bipedal due to the positioning of the foramen magnum.
    • Unique chewing pattern (nonhoning).
    • Smallish canines and a massive brow ridge exceeding size of modern gorillas.
ORRORIN TUGENENSIS
  • Age: Approximately 6 million years old.
  • Discovery Location: Tugen Hills, Kenya.
  • Significant Findings:
    • Parts of at least five pre-australopithecine individuals found.
    • Partial femurs suggesting bipedalism.
    • Curvature of hand bones similar to living apes.
    • Nonhoning canines indicating dietary adaptations.
ARDIPITHECUS
  • Comprises two species found in Aramis, Middle Awash Valley, Ethiopia by a team led by Tim White.
ARDIPITHECUS KADABA
  • Age: 5.8 to 5.5 million years ago.
  • Physical Traits: Small brain, canines showing wear from tips (similar to humans) alongside partial honing (more ape-like).
  • Descriptions of enamel thickness are less than 1 meter (3.3 feet) tall; adapted to wooded settings.
ARDIPITHECUS RAMIDUS
  • Age: 4.4 million years ago.
  • Fossil Significance: Most complete early hominin skeleton with parts from 35 other individuals. Found during a 100,000-year depositional period.
  • Key Features:
    • Small brain size.
    • Nonhoning canines.
    • Thin enamel; estimated height of 120 cm (3.9 ft).
    • Likely bipedal but with adaptations for arboreal life.

AUSTRALOPITHECINES

  • Age Range: 4 to 1 million years ago.
  • Represented by hundreds of fossils and believed to encompass up to 10 species.
  • Trend Observed: Transition from pre-australopithecine to australopithecine features; teeth show wear on the tip of canines with modifications from honing patterns.
  • Physical Features: Vestiges of apelike traits diminish with time. Slight brain size increase observed over species.
AUSTRALOPITHECUS ANAMENSIS
  • Age: Approximately 4 million years old.
  • Discovery Locations: Near Lake Turkana, Kenya, and Awash River Valley, Ethiopia.
  • **Characteristics Transition