<div class="tree_txt_unlinked"><p>Prosimii
exhibit the most primitive primate morphology of all primates. Fossil
evidence suggests they evolved about 55 Ma, shortly after the first
appearance of primates, though their specific origin remains debated.
Prosimian features include an unfused mandibular symphysis and frontal
bone, a postorbital bar, and a relatively small brain size. Prosimians
rely more on smell than sight as indicated by a longer snout, well
developed rhinarium, and large olfactory bulbs in the brain. Prosimians
have relatively large eyes and a tapetum lucidum in the eye indicating
current or ancestral nocturnalism. Most prosimians have a dental
formula of 2.1.3.3., procumbent incisors, reduced canines, and a tooth
comb.</p>
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