Question

1. How is it that Anthropoids differ from Prosimians (what are the primary morphological differences)?
2. Explain the adaptive purpose/significance of the closure of the eye orbits. Do you think that this morphological change could also relate to the fused mandible?

c

Answer 1

Answer :

a)

PROSIMIANS

Includes bush babies of Africa, lemurs of Madagascar, lorises, pottos and tarsiers of south east Asia.

They tend to be nocturnal.

Smaller size.

Smaller brain.

Snouty wet noses.

Most are leaping.

ANTHROPOIDES

They include monkeys, apes and humans.

They are diurnal.

Larger size.

Larger brain.

Non snouty noses.

Most are non leaping.

b)

Closure of eye orbits is by eyelids.

Its important to maintain wetness of cornea and conjunctiva with even spreading of tears. Opened eyes for long can result in exposure keratitis and ulceration.

Reflex closure eye is another protective mechanism to save eye from injury.

Considering post orbital closure or orbital bar allowed in evolution to place eye ball in a cup. This gave more freedom of eye movement and fine attachment of muscles. The eye movement became more smoother. This made a complete separation from temporal region.

Fusion of mandibular symphysis is an evolutionary trait. Evolutionary significance is related to food habit. That is to produce more shearing force.

Now in comparison with post orbital closure, mandibular symphysis allows better functioning of oral muscles as in lateral, medial movements. This bacame more efficient. Similarly the oculomotor functions became better with post orbital bar.

When comparing eyelid closure of orbit and mandibular symphysis, both allows for better closure and to protect structures they contain.