Mammalia: Primates | Zoology Optional Notes for UPSC PDF Download

Characteristics of Primates: An Overview

1. Arboreal Adaptations:

1. Rotating Shoulder Joint:

   • Secure ball joints and strong clavicles enable effective arm usage for climbing trees.

2. Thumb and Big Toe Separation:

   • Primates, excluding spider monkeys, exhibit pentadactylism with opposable thumbs and big toes, facilitating grasping and manipulation.

3. Stereoscopic Vision:

   • Two overlapping fields of vision result in stereoscopic vision, enhancing depth perception. Fifty percent of the cerebral cortex in primates is involved in visual processing.

2. General Characteristics:

1. Brain Size:

   • Primates boast larger brains, with a higher brain/body ratio than similar-sized non-primates, emphasizing manual dexterity, hand-eye coordination, and enhanced visual capabilities.

2. Nail Modification:

   • Claws transformed into flattened nails, aiding in precision gripping and manipulation.

3. Reproductive Traits:

   • Typically, primates have only one offspring per pregnancy, and gestational periods are longer relative to animal size.

4. Posture and Bipedalism:

   • Most primates exhibit an erect upper body and occasional bipedalism. Humans and gorillas are notable exceptions.

5. Olfactory Reduction:

   • Reduced nose size and corresponding olfactory areas, except in lemurs.

6. Social Behavior:

   • Primates are highly social animals, engaging in complex social structures and behaviors.

3. Division of Order Primates:

1. Prosimians:

   • Nocturnal, including bush babies, pottos, lemurs, and lorises.
   • Smaller brain/body ratio compared to anthropoids.

2. Anthropoids:

   • Diurnal and include monkeys, apes, and humans.
   • Greater brain/body ratio, diurnal lifestyle, and advanced social structures.

4. Additional Features:

1. Bipedalism:

   • While most primates are arboreal, humans consistently exhibit bipedalism.

2. Grooming:

   • Advanced primates, including humans, engage in the pleasurable activity of grooming, reinforcing social bonds.

Diversity Within the Order Primates

1. Extremes within Primate Diversity:

• Size Range:

  • From small prosimians comparable to squirrels to large primates like Man and Gorilla, the size spectrum in the order Primates is vast.

• Structural and Behavioral Disparities:

  • Differences in structure, behavior, and intelligence between prosimians and anthropoids are unparalleled within any other order of animals.

2. Definition Challenges:

• Anthropologists hesitate to define Primates definitively due to the considerable differences among its members.

3. Historical Definitions:

• The first significant definition by Mivert focused on several key characteristics:
  • Placental mammals
  • Presence of clavicles (collar bones)
  • Orbital bone encirclement
  • Specific dental patterns
  • Brain features like a posterior lobe and calcarine fissure
  • Opposable thumbs
  • Specific features related to reproductive organs

4. Mix of Characteristics:

• Mivert's definition comprises a mix of general mammalian traits and specialized primate features.

5. Specialized Characters of Primates:

1. General Mammalian Characters:

   • Shared by all mammals, including primates.

2. Specialized Characters:

   • Specific to primates, evolving at different levels (suborder, genera, species).
   • Examples include the posterior lobe of the brain and opposability of the thumb.

6. Suborders and Infraorders:

• The order Primates is classified into two suborders: Prosomii and Anthropodia.
  • Prosomii: Further divided into four infraorders, including Tupaiiformes, Lemuriformes, Lorisiformes, and Tarsiformes.

7. Characteristics of Prosomii:

• Locomotion Adaptations:

  • Varied adaptations for arboreal life, ranging from long legs in Tarsius to short forelimbs in lemurs.

• Manual Adaptations:

  • Lack of separate mobility of fingers, precision grip challenges, claws instead of nails.

• Visual and Olfactory Features:

  • Laterally placed eyes, mobile ears, developed olfaction.

• Dental Characteristics:

  • Clawed digits for cleaning, dental formula typically 2:1:3:3.

• Brain and Posture:

  • Smaller cerebrum, backward-placed Foramen Magnum, and arboreal and nocturnal habits.

8. Evolutionary Perspective:

• Prosomii, considered lower primates, showcase more similarities to other mammals, while higher primates (Anthropoids) exhibit advanced and evolved primate traits.

Evolutionary Advancements in Anthropoids

Characteristics of Anthropoids:

1. Cranial Features:

   • Large, comparatively round cranium.

2. Facial Changes:

   • Reduction in prognathism and nasal cavity size.
   • Face aligns more directly under the frontal lobe of the brain.

3. Vision Adaptations:

   • Eyes placed closer for front vision.
   • Developed facial muscles.

4. Digits and Nails:

   • Fingers and toes equipped with nails.
   • Third finger longer than or equal to the fourth.

5. Ear Characteristics:

   • Small and movable pinna.

6. Lachrymal Canal:

   • Opens into the orbital cavity.

7. Bipedal Locomotion:

   • Greater capacity for bipedalism.

8. Prehensile Hands:

   • Hands adapted for grasping.

Superfamilies and Groups:

• Anthropoids are classified into three superfamilies: Ceboidea, Cercopithecoidea, and Hominoidea.

Classification into Platyrrhini and Catarrhini:

• Anthropologists often categorize anthropoids into two natural groups: Platyrrhini (New World Monkeys) and Catarrhini (Old World Monkeys, including Cercopithecoidea and Hominoidea).

Characteristics of Platyrrhini (New World Monkeys):

1. Brain Complexity:

   • More developed than Prosomii but less than Hominoids.

2. Dental Formula:

   • Typically 2,1,3,3 or 2,1,3,2.

3. Tooth Structure:

   • Molars and premolars usually squarish.

4. Zygomatic-Temporal Fossa:

   • Larger in size.

5. Buccal Pouch and Ischia Callosities:

   • Lack of buccal pouch.
   • Lack of ischia callosities.

6. Thumb Characteristics:

   • Thumb not opposable and usually small or absent.

7. Toe Structure:

   • Long big toe, strong, and distantly placed from fingers.

8. Tail Adaptations:

   • Long and prehensile tail.

Anthropoids, representing an advanced evolutionary stage within Primates, exhibit distinctive characteristics setting them apart from prosimians. The suborder is further classified into superfamilies, and the Platyrrhini and Catarrhini distinction helps delineate New World Monkeys from Old World Monkeys and apes. These evolutionary advancements emphasize the diversity and complexity within the order Primates.

Hominoidea: The Intelligent Primate Group

From an anthropological perspective, Hominoidea stands out as the most intriguing group within the living primate world. Members of this group are widely recognized as the most intelligent beings in the animal kingdom. Hominoidea comprises three families: Hylobatidae, Pongidae, and Hominidae, with Gibbons belonging to Hylobatidae, and Chimpanzees, Gorillas, and Orangutans belonging to Pongidae. The family Hominidae includes humans.

Key Characteristics of Hominoidea:

1. Size and Facial Bones:

   • Increase in overall size with a decrease in the size of facial bones.

2. Dental Arch:

   • Transition from a V-shaped to a U-shaped dental arch.

3. Molars:

   • Molars exhibit signs of increase in size.

4. Lower Third Molar:

   • Characteristic Dryopithecus Y-5 cusp pattern in the lower third molar.

5. Foramen Magnum and Occipital Condyle:

   • Indications of forward movement in the foramen magnum and occipital condyle.

6. Body Proportions:

   • Long neck and forelimbs.
   • Broad shoulders and iliac bone.

7. Limbs Development:

   • More developed use of forelimbs, while hind limbs are comparatively less developed.

8. Tail Absence:

   • Lack of an externally visible tail.

Similarities Between Higher Apes and Humans:

• Higher apes and humans share various interesting similarities, including similar blood proteins, living in small groups, and susceptibility to diseases like flu and syphilis.

Differences Between Humans and Apes:

1. Bipedalism:

   • Humans exhibit bipedalism and orthograde posture, while apes typically display knuckle walking, quadrupedalism, and pronograde posture.

2. Great Toe Development:

   • The human hallux (great toe) is more developed and not opposable.

3. Foot Structure:

   • Human feet have curves to distribute body weight effectively.

4. Foramen Magnum and Occipital Condyle Placement:

   • In humans, the foramen magnum and occipital condyle are positioned lower and forward, indicating adaptations for bipedalism.

5. Stereoscopic Vision:

   • Both humans and higher apes possess stereoscopic vision.

6. Mastoid Process:

   • Well-developed mastoid process in humans.

7. Facial Morphology:

   • Reduction in the length of the face and mandible, resulting in an orthognathous or slightly prognathous face.

Conclusion:

Hominoidea presents a fascinating array of characteristics, showcasing evolutionary adaptations that have led to the development of highly intelligent primates. While humans share some similarities with higher apes, distinct differences, especially in locomotion and facial morphology, underscore the unique evolutionary path that has led to the emergence of Homo sapiens.