Characteristics of Primates- Dentition and Vision (17) Flashcards
What are the two areas of evolutionary changes that takes place in dentation
- number of teeth/ arrangement
2. Structure
What are the two sets of teeth for primates
deciduous and permanent
Whats a dental formula
- # of each type of tooth that a species has can be expressed as a dental formulagives number of each type of tooth in ¼ of jaw
Explain the dental comb
Lemurs and lorises= unusual specialisation of incisor teeth= lower front incisors= slanted forward with crowns= narrow + closely spaced to form dental comb
• Used for grooming fur, only rarely for feeding/fighting
Explain distema
o large lower have a gap (distema) b/w upper and 2nd incisor + upper canine to accommodate large lower canine
o To allow large upper canine= crown of 1st premolar slanted back + sharp edged
How is canines sharpened
pper canine fits tightly against this premolar +sharpened by the grinding that occurs
what is the general change in molar teeth
- little change from early mammals
o May be related to generalized diets
Explain the evolution in cusps of molars
- 3 cusped molars of early mammals= evolved to 4 cusp pattern in Old World Monkeys
- Further trend= seen with apes + humans where lower molars- 5 cusps forming 4-5 pattern
o
Pattern useful identifying teeth of fossil apes + humans= presumed to have evolved due to predominantly fruit diet of apes
What does the hard enamel of teeth allow
resist decomposition
Example of why care needs to be taken when using teeth to indicate diet
- Large canine teeth of old world monkeys + apes more important in predator defence and social displays that for meat-eating
Is there an emphasis on vision in evolution and why
Arboreal life= emphasis on vision
Due to arboreal life and increase in emphasis on vision, what decreased
- reliance on sense of smell, olfaction
- shift in sensory orientation
what did the shift in sensory orientation (focus on vision and not smell) be accompanied by
overall change in shape of skull compared with other mammals
what was the general skull evolution in result of chignon sensory orientation
- General tendency for facial portions of skull, particularly region around nose and snout, to become smaller and flatter
o While region that houses the brain has become larger
What evidence is used that supports shift of increase emphasis on vision > decrease on other sensory > nose flatter
Observable behaviour
o E.g. lemurs= use their snout and teeth for what apes use eyes and hands for (investigating an object, grooming, communicating)
What is an important evolutionary trend of forward facing eyes
- Flattening face of primates + movement of eyes to face fully forward= important evolutionary trend
- Forward facing eyes= allow for stereoscopic (three-dimensional) vision
explain difference in eye sockets of other mammals and primates
- Most mammals have eye socket that face sideways, but primates developed eye sockets that face forward
what has change in eye sockets of primates allowed
o Enables fields of vision of each eye to overlap= distances judged accurately
o = important adaption for a tree living animals
Why is depth perception important
- For primates: evolved for life in trees, the importance of depth perception cannot be overemphasized
o A mistake in judging distances= fatal
What is the ‘negative’ result of forward facing eyes
o However with both eyes facing forward, field of view much narrower than if the eyes face sideway
How has primates compensated for narrower field of vision
♣ Primates compensate for this by evolving a highly mobile head and neck
How has colour vision increased and allowed
♣ In addition= most primates have rods and cones in retina
• Rods= important for vision in dim light
• Cones= fine visual discrimination and colour vision (nocturnal= only has rods)
♣ Nerves connecting rods and cones to brain also improved // vision is more acute in each eye and coordination b/w two eyes far better than other mammals
♣ These modifications also enhanced stereoscopic vision
Explain development of the eye socket and evidence in fossil skulls
- As eyes become more forward= bony eye socket developed to give protection
Gradual change in eye socket clearly visible in fossil primate skulls
o As position of eye socket changed for eyes to face forward, bone gradually closed in side and rear of socket
How has brain developed in association with vision
- Increasing importance of vision= region of brain concerned with interpretation of visual information increased in size
o While that concerned with olfaction decreased
