Which of the following promoted the success of the primates at the end of the tertiary period?

Question

A. The first primates were large, nocturnal animals.
B. Primates were diurnal.
C. Primates were insectivores.
D. Primates only lived in trees.
E. The first primates were marsupials and protected their offspring in pouches.

Answer 1

Tricky one. I think D is correct here.

I discount A and B because looking at the protosimians there are nocturnal AND diurnal species

I discount C because the arboreal theory suggests that early primates lived initially on fruits and leaves and insectivore primates developed later

E is patently wrong as primates are not marsupials

I dislike D because it uses the phrase "only lived in trees" but it is the one I think is most correct.

"The arboreal theory claims that primates became primates by adapting to arboreal life" - wikipedia

This theory suggests that arboreal life is responsible for primates developing many of their current day traits: keen vision, depth perception, hands (and feet) equipped for grasping (and subsequent tool use)...

Answer 2

Probably "D" because ...

Primates evolved directly from the most primitive placental mammals, the insectivores. In fact the most primitive primates are called "tree shrews" and are essentially arboreal insectivores. Insectivores themselves are amoungst the smallest of mammals and tree "shrews" are only squirrel sized.

Insectivores are nocturnal mammals. The first primates moved into a new environmental niche as day living, mammal insectivores. This was not an empty niche however, because the birds had been occupying this niche for millions of years. Primates were not able to effectively compete with birds in this manner because the birds were more highly evolved daytime insectivores. During the evening, any nocturnal primate species had to compete with nightime insectivores, the bats. Competition as an insectivore was not a major factor in primate evolution.

Insectivores are placental mammals, not marsupials. Therefore, their ancestors the primates were also placental. Marsupials themselves appear to be an evolutionary adaptation which has been largly abandoned amoungst the mammals. Marsupial eggs don't attach to the uterine wall and the young are actually born as embryos. This allowed the mother to remain fully active during her pregnancy and if suddenly attacked, she could suddenly abort a pouchfull of nursing young far better than a heavily pregnant placental mammal could. Kangaroos use this technique to escape preditors if they are carrying a large baby.

The major advantage of living in trees was that it allowed the primates to escape carnivores living on the ground. In the trees, the birds might have gotten the major share of the food, but it was much better for the primates to eat than to be eaten. As time passed, some carnivores followed the primates into the trees. This is particularly true of the cats. Their claws were as useful in climbing as they were as a means of catching prey. However, the primates were better adapted to tree living. Primates evolved hands which could grasp branches, something the cats could never do. This allowed primates to be far more mobile in a tree than any cat ever was. As reguards the birds, carnivorous birds tend to eat other birds, because it is very difficult to actually fly amoungst branches. Preditors found that any successful primate kill involved a sneak attack because pursuing prey in trees was a waste of energy. This probably started the evolution of the primate brain in an effort to out think clever preditors. By the time monkeys had evolved, the primates were conciderably more intelligent than mammal carnivores. Around 6 million years ago, apes had begun to live on the ground. These primates were intelligent enough to use tools as weapons and this meant they could even compete with ground based carnivores. The fact that apes are the largest of primates also helped them. A new competition started when these giant primates began competing with themselves, and weapons made this competition especially deadly. The rise of modern human intelligence can be seen as an intellectual "arms race". It also seems to explain the extremely xenophobic nature of humans, although our chimp relatives exhibit this behaviour too Therefore, it is concievable that humans were already killing each other long before they were recognizably human.