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Lecture 16

BIOLOGY 1M03 Lecture Notes - Lecture 16: Foramen Magnum, Canine Tooth, Human Embryogenesis

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Ben Evans

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- Dispersal of OWMs
- Dentition and diet
- Primate phylogeny
- Hominoid (ape) diversification in time and space
- Hominoid social systems; origins of violence in human societies
- Hominin (human lineage) diversification
- Evolution of suspensory locomotion and bipedalism
- Ambiguous phylogenetic relationships among Hominins
- Hunting
- Tool use
Practice Question
Ben recently had a “brachial cleft cyst” removed from his neck. This cyst was formed
from tissue that normally is reabsorbed during human embryogenesis, but which in fish
normally develops into a gill. Which of the following statements below is accurate?
a) This tissue is an example of homoplasy, because it evolved independently in
humans and in fish
b) This tissue is an example of homology, because it was present in the MRCA
of humans and fish
c) This tissue is an example of homoplasy, because it was present in the MRCA of
humans and fish
d) This information indicates that this tissue is currently under diversifying selection
How are Humans Different From Other Apes?
- Fully bipedal
- Parabolic dental arcade, thick molar enamel, reduced canine teeth, large molars
relative to other teeth
- Long juvenile period
- Large brains relative to brain size; spoken language; symbolic culture
- Ancestral hominins shared some of the features of humans and some features of
contemporary chimpanzees
Hominins lineage that includes all organisms and fossil species that are more closely
related to humans than chimpanzees or bonobos
Late Miocene/Pliocene Primates
- Global cooling was associated with decreased rainfall and seasonality, including dry
- Tropical rainforests shrank in size; dry woodland and grassland habitat expanded
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- Ancestors of humans (the hominins) moved into grassland habitat and began to
Chimp-Humans Split (5-7 mya)
- The shift from 4 to 2 legs. Anatomical changes were required for the shift, especially
in the structure of the skull, spine, legs and feet
- Changes from the ancestor of chimps and humans to humans today included the
movement of the foramen magnum (the hole in the skull which the spinal cord
passes), it was repositioned so the human skull balances directly onto of the vertebral
- The human spine is upright and S-shaped so weight is directly over the pelvis
- The pelvis was reconfigured for an upright position, with internal organs over it. Legs
are longer to enable long stride length for efficient movement and their anatomy
altered so the legs are directly under the body
- Tibia and femur are directly on top of each other and directly underneath pelvis
- The foot is narrower and has a more developed heel and larger big toe, which
contributes to a springier foot, there is also an arch
Hominin Fossil Record
- We are the only hominin on the planet for the 1st time in 6 million years
- Hominins were very diverse
- Many different fossils were around in Africa at the same time as our evolution
Chimp-Humans Split (5-7 mya)
- Genetic data suggest that the most recent common ancestor (MRCA) of chimps and
humans lived about 5-7 million years ago
- 3 major fossils have illuminated what this ancestor was like: Ardipithecus ramidus,
Orrorin tugenensis, and Sahelanthropus tchadensis DO NOT NEED TO KNOW
- These fossils had a mixture of
- Primitive features thick enamel, ape-sized brains
- Derived features shorter arms than other apes, upright posture, less
prognathism (the extent to which your mouth bulges out) than chimps, long
femoral neck (has to do with evolution of bipedalism), foramen magnum under
Hominins (4-6 mya)
- Ancestral features of these fossils included
- Small molars
- Thin enamel
- Canines larger than in humans
- Large brow ridge
- Small braincase relative to modern humans
- Derived features of these fossils included:
- Forward location of the foramen magnum: this is a signature of bipedalism
- Relatively small canine teeth compared to chimps that are not sharpened by first
lower premolar
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