This lifeform is found widely in the New World tropics. This lifeform is common in suitable environments.

Common Squirrel Monkey (Saimiri scircus to Saimiri sciureus) is one of the smallest New World monkeys. They are widely distributed in the virgin forests of both Central and South America. They consume fruit and occasionally various insects.

New World Monkeys (Platyrrhines) are found from southern Central America, south through most of tropical South America. They are characterized by having their nostrils far apart and by the fact that they spend most of their lives in trees. Most species are small mammals with very long tails. Marmosets and squirrel monkeys are included herein. This family can be divided into New World monkeys (Atelidae) with eighty-two species, and the tamarins and marmosets (Callitrichidae) with forty-three species.

Lemurs, Monkeys, Apes, and Man are combined into the single order of Primates. This order contains over 390 different species.

Mammals (Class Mammalia), together with the birds, are among the youngest of the classes of animals. In species count, mammals number about fifty-one hundred, trailing reptiles (approximately fifty-five hundred), fish (approximately eighteen thousand), and birds (approximately eighty-six hundred).

There are three sub-types of mammals:

   monotremes, the most primitive:
      Develop in reptilian-like eggs and suckle milk emerging
      (i.e., spiny anteater, duckbilled platypus)

   marsupials
      Newborn emerges very underdeveloped and continue to
      mature in a pouch on its mother's abdomen (i.e., opossums,
      koala, kangaroo)

   placental  
      Embryo develops within the uterus of the female and is
      dependent on a placenta for nutrition and waste removal
      (i.e., humans, lions, monkeys)  

About sixty-five million years ago, the Tertiary era produced thirty-five orders of mammals. Of this number, eighteen have survived to represent Earth's most diversified as well as its most highly developed classification of animals.

Extinction of mammals is fast becoming a serious issue. Duff and Lawson present a list of forty-one extinct species that reached extinction prior to 1800. These forty-one species are not acknowledged in the counts of the various families. Duff and Lawson also present a list of forty-six species including three gazelles, one zebra, one seal, one deer, and one wolf that have probably gone extinct since 1800. These forty-six species are included in the family counts. Science is adding about forty to fifty new species a year to the list. Many of these are the result of divisions of prior species; some are recent discoveries.

Mammals owe their survival to adaptive capabilities that include the ability to exploit whatever sources of food are available to them, as well as their ability to adjust to various climes. Food specialization influenced evolution to such a great extent that the teeth structure can and has been used to provide extensive information on the food needs and various lifestyles of extinct species.

Despite the vast diversity among mammals in terms of size, habitats and adaptations, they share without exception many characteristics such as:  

    a. body hair
    b. mammary glands
    c. certain skull characteristics
    d. four limbs that permit speed
    e. parallel not perpendicular limbs
    f. compartmentalized internal organs
    g. a four-chambered heart and pulmonary circulation

Backboned Animals (Phylum Chordata) are the most advanced group of animals on earth. These animals are characterized by having a spinal cord or backbone. Most members have a clearly defined brain that controls the organism through a spinal cord. Fish, amphibians, reptiles, birds, and mammals are in this phylum.

Currently, some taxonomists believe that the fish should be divided into two groups (sharks and regular fishes) and that there are some other primitive groups in the phylum such as hagfish or lampreys.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.