Shorter jaws with smaller teeth

As our ancestors evolved, their jaws and teeth changed in many ways. Some tooth changes were apparent five million years ago and additional changes have occurred since then.

Side view of a chimpanzee skull

Helen Beare © Australian Museum

Developing shorter jaws with smaller teeth

About seven million years ago our early ancestors had long jaws which resulted in projecting face profiles. They also had long, pointed canines and parallel tooth rows.

By 5.5 million years ago, our ancestors’ canines were starting to become smaller.

By 3.5 million years ago, our ancestors’ teeth were arranged in rows that were slightly wider apart at the back than at the front.

By 1.8 million years ago, our ancestors’ canines had become short and relatively blunt like ours. Their jaws had also become much shorter. This made the face more vertical and forced the side rows of teeth to bend into a rounded arc shape.

By 250,000 years ago, our direct ancestors had very short jaws and had developed a pointed chin for added strength. To fit into the small jaw, the teeth were now smaller and arranged in a tightly parabolic arc. Faces were now vertical rather than projecting.

 

Comparing then to now

Seven million years ago

Seven million years ago, our ancestors’ jaws and teeth were similar to those of modern chimpanzees.

Dental arcade and tooth rows:

  • teeth were arranged in the jaw in a rectangular or U-shape
  • a diastema (gap) was present next to each canine tooth. These gaps were spaces the large canines could fit into when the jaws closed. In the upper jaw, the gap was in front of the canine. In the lower jaw, it was behind the canine.

Jaw and face profile:

  • jaw was long which resulted in a projecting face profile.
  • there was no chin


Teeth:

  • incisors (the four front teeth on the top and the bottom) were relatively large
  • upper incisors were broad and projected outward
  • canines were very long, pointed and much larger in males than in females
  • molars (back teeth) were large
  • premolars and molars had high cusps (bumps) on the grinding surface
  • teeth were covered by a thin layer of enamel

Now

The evolution of modern humans has involved the development of distinctive facial and dental features.

Dental arcade and tooth rows:

  • teeth are arranged in a parabolic or rounded arc shape within the jaw.
  • there is no diastema (gap) next to the canines.

Jaw and face profile:

  • jaw is very short so that there is almost no projection of the face
  • a pointed chin is present

Teeth:

  • incisors are relatively small
  • incisors are narrow and quite vertical
  • canines are short (almost level with the other teeth), relatively blunt and are similar in size in males and females
  • molars (back teeth) are small and impacted ‘wisdom teeth’ often result because there is not enough room for them in the shortened jaw
  • premolars and molars are relatively flat with low, rounded cusps (bumps) on the grinding surface
  • teeth are covered by a thick layer of enamel


Fran Dorey , Exhibition Project Coordinator
Beth Blaxland , Education Project Officer
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