UNIT 8 CLASSIFICATION AND CHARACTERSTICS OF LIVING PRIMATES REVISION NOTES

 Introduction to Primates

Definition and Classification

• Primates: A group of mammals including lemurs, lorises, tarsiers, monkeys, apes, and humans.
• Characteristics:
  • Nails instead of claws.
  • Presence of clavicle.
  • Bony ring encircling the orbits.
  • Males with hanging penis and scrotal testes.
  • Females with mammary glands on the chest.
  • Well-developed caecum.
  • Calcarine fissure in brain.
  • Opposable thumb or big toe.

Diversity and Classification

• Diversity: Primates comprise over 300 species, making them the third most diverse order of mammals after rodents (Rodentia) and bats (Chiroptera).
• Anatomical Unity: Despite variations, primates share anatomical and functional characteristics reflecting common ancestry.
• Behavioral Differences: Behavioral differences are more discriminant among primate taxa compared to morphological variations.
• Success Criteria: The most successful primates in terms of population numbers and territorial spread are those closest to the ancestral behavioral pattern.

Taxonomy and Classification

Definition and Purpose

• Taxonomy: Branch of biology concerned with classification and naming of organisms.
• Etymology: Derived from Greek roots:
  • Taxis (arrangement)
  • Nomia (method)
• Objective: Organize organisms into groups demonstrating evolutionary relationships based on common biological features.

Relationship with Systematics

• Systematics: Includes taxonomy but extends to study of evolution and biodiversity.

Species Concepts

• Evolutionary Species Concept:

  • Defines species as lineages evolving separately with distinct evolutionary roles.
  • Emphasizes separate evolutionary trajectories (Simpson, 1961).

• Biological Species Concept:

  • Defines species as populations capable of interbreeding and producing fertile offspring.
  • Emphasizes reproductive isolation (Mayr, 1963).

• Phylogenetic Species Concept:

  • Defines species as groups sharing a unique combination of characters derived from common ancestry.
  • Focuses on diagnosable clusters of organisms (Christoffersen, 1995).

• Genetic Species Concept:

  • Defines species based on genetic compatibility and isolation from other groups.
  • Emphasizes genetic distinctiveness (Baker and Bradley, 2006).

Importance in Understanding Primate Taxonomy

• Primate Taxonomy: Classification of primates based on shared biological features.
• Basic Units: Species are fundamental to taxonomy and serve as units for classification.
• Application: Understanding species concepts aids in classifying and studying primate diversity and evolution. 

Who are Primates?

Definition and Classification

• Definition: Primates are eutherian mammals belonging to the order Primates.
• Taxonomy: Primates are classified within the class Mammalia, under the subclass Eutheria or Placentalia, which is the most diverse branch of extant mammals.

Evolutionary Origins

• Ancient Group: Primates originated approximately 65 million years ago from a primitive mammalian stock.
• Evolution: Likely evolved from insectivorous mammals in the late Cretaceous period.

Diversity and Adaptations

• Variety: Primates have evolved into a diverse range of forms from tiny shrew-like creatures to large-bodied species.
• Specializations: Display a wide range of morphological and behavioral adaptations.

Size Variation

• Size Range: Primates vary greatly in size:
  • Smallest: Pygmy mouse lemur (weighs around 30 grams).
  • Largest: Male eastern lowland gorilla (may weigh over 200 kilograms).

Study of Primates

• Primatology: The study of primates, encompassing their evolution, behavior, morphology, and ecology.

Geographic Distribution

• Habitat: Primates are primarily found in tropical and subtropical regions across:

  • South and Central America
  • Africa
  • Asia
  • Islands of Indonesia

• Historical Distribution: Fossils of primates have been discovered in non-tropical regions such as:

  • British Isles
  • Northern United States
  • Tip of South America

Note

• Human Exception: Humans are a part of the primate order but have a global distribution unlike other non-human primates.

Primate Origin

Overview

• Diversity: Primate group consists of about 400 living species, most diverse in lowland tropical rainforests.
• Phylogeny: Understanding primate evolution and origin is still debated with various theories.

Earliest Primate Forms

• Timing: Earliest primates likely evolved in late Cretaceous or early Paleocene (~65-55 million years ago).
• Plesiadapiformes: Purgatorius ceratops is one of the earliest recognized primate-like species, considered primitive.
• Controversies: Debate over the basal primate—Altanius from Eocene Mongolia or Altiatlasius from Late Paleocene Morocco.

Geographic Origins Debate

• Locations: The debate on where primates originated spans continents:
  • Asia: Supported by Fleagle and Gilbert (2006).
  • Africa/India: Favored by Rasmussen (2002).
  • North America: Argued by Bloch et al. (2007).
  • South America: Proposed by Arnason et al. (2008).
  • African Origin: Considered a leading hypothesis, also Indo-Madagascar (Heads, 2010).

Time of Origin

• Paleocene Epoch: Begins approximately 65 million years ago with Plesiadapiformes in Europe and North America.
• Eocene Epoch: Marks appearance of true primates (~55 to 37.5 million years ago), euprimates with modern aspects.

Challenges in Evolutionary History

• Fossil Record: Fragmentary and incomplete nature complicates understanding of primate evolution.
• Interpretation: Varies among researchers, influencing phylogenetic reconstructions.

Taxonomy of Living Primates

Traditional vs. Modern Classification

• Traditional Classification:

  • Prosimii: Includes lemurs, lorises, and tarsiers (considered more primitive).
  • Anthropoidea: Includes monkeys, apes, and humans (considered more advanced).

• Modern Classification:

  • Strepsirrhines: Includes lemurs and lorises.
    • Distinguished by wet nostrils and presence of tapetum.
  • Haplorrhines: Includes tarsiers, monkeys, apes, and humans.
    • Distinguished by dry nostrils and absence of tapetum.

Tarsiers and Anthropoids

• Revised Placement: Tarsiers moved from Prosimii to Anthropoidea based on genetic and anatomical studies.
• Common Features: Dry nostrils and lack of tapetum shared between tarsiers and anthropoids.

Apes and Humans Relationship

• Traditional View: Grouped under superfamily Hominoidea, with great apes in family Pongidae and humans in Hominidae.
• Recent Evidence: Molecular studies suggest closer relation of African apes (gorillas, chimpanzees) to humans than to Asian orangutans.

Suborder Strepsirrhini (earlier Prosimii)

Characteristics of Strepsirrhines:

• Nostrils (Rhinarium): Moist and bare, similar to a dog's.
• Tapetum Lucidum: Reflective layer behind the retina, enhances night vision.
• Activity: Mostly nocturnal.
• Sensory Adaptations: Developed sense of smell; prominent whiskers, large mobile ears, and large eyes adapted for night vision.
• Mouth and Teeth: Upper lip divided and attached to gums by membrane; protruding snout (rostrum); tooth comb formed by lower incisors and canines.
• Digits: Grooming claw on second digit of foot; flat nails elsewhere.

Infraorder: Lemuriformes

• Distribution: Found exclusively on Madagascar and neighboring Comoros Islands.
• Size Range: From the pygmy lemur (~30 grams) to the Indri (~10 kilograms).
• Adaptations: Diverse dietary and locomotor adaptations.
  • Some species leap using long hindlimbs (e.g., sifakas).
  • Others are arboreal quadrupeds or spend time on the ground.
• Superfamilies:
• Daubentonoidea
• Lemuroidea

Superfamily Daubentonoidea

Family: Daubentonidae

• Genus: Daubentonia
• Species: Aye-aye (Daubentonia madagascariensis)
• Characteristics:
  • Moderately sized, black animal with large ears.
  • Extreme specializations yet retains basic features of Lemuriformes.

Superfamily Lemuroidea

Family: Chirogaleidae

• Genera: Chirogaleus
• Characteristics:
  • Most primitive and smallest of the Lemuroidea.

Family: Indriidae

• Genera: Indri, Propithecus, Avahi
• Characteristics:
  • Includes genera with various adaptations within Madagascar.

Family: Lepilemuridae

• Genera: Lepilemur
• Characteristics:
  • Characterized by specific adaptations within their habitat.

Family: Lemuridae

• Genera: Lemur, Hapalemur, Prolemur, Eulemur, Varecia
• Characteristics:
• Diverse genera with varying adaptations and behaviors.

Infraorder Lorisiformes

Characteristics of Lorisiformes:

• Activity: Nocturnal, inhabits forest regions of Africa and Asia.
• Diet: Primarily fruits, gums/exudates, and insects.
• Special Features:
  • Tooth comb and grooming claw on second digit.
  • Tympanic ring fused to lateral wall rather than suspended in bulla as in lemurs.

Families within Lorisiformes:

• Family: Lorisidae

  • Characteristics: Includes various genera with specific adaptations.

• Family: Galagidae

• Characteristics: Primarily known for specific adaptations within their habitat.

Suborder: Haplorrhini (Semiorder in some classifications)

Characteristics of Haplorrhini:

• Definition: Considered the "higher" primates.
• Includes: Tarsiers, monkeys, apes, and humans.
• Appearance: First appeared in the Eocene around 50 million years ago.

Infraorder: Tarsiiformes

Family: Tarsiidae

• Genera:
  • Carlito (Philippines)
  • Cephalopachus (Borneo and Sumatra)
  • Tarsius (Sulawesi islands)
• Characteristics:
  • Found in Southeast Asia.
  • Mix of prosimian and anthropoid traits.
  • Primitive features such as high cusped molars, unfused mandibular symphysis, multiple nipples, and grooming claws on second digit.
  • Unique features include large eyes (larger than the brain), very long legs and ankles.

Infraorder: Platyrrhini

Characteristics of Platyrrhini (New World Monkeys):

• Distribution: Central and South America.
• Nose Shape: Broad, flat, dry noses with outwardly directed nasal openings.
• Distinguishing Features:
  • Lack bony tube between eardrum and outer ear.
  • Tympanic ring fused to side of auditory bulla.
  • Three premolars (Old World monkeys typically have two).
  • Lack ischial callosities (bare skin patches on rump).
  • Mostly arboreal and diurnal.
  • Tail usually well-developed and prehensile in some genera.
  • Imperfect opposability of thumb, poorly developed finger grip.
  • Large and strongly opposable hallux.
  • Special scent glands in some species.

Families within Platyrrhini:

1. Family: Pitheciidae

   • Subfamilies: Callicebinae, Pitheciinae

2. Family: Atelidae

   • Subfamilies: Alouattinae, Atelinae

3. Family: Cebidae

• Subfamilies: Aotinae, Callitrichinae, Cebinae

Infraorder: Catarrhini

Characteristics of Catarrhini:

• Nose Shape: Narrow, close together, downward-facing nostrils.
• Dental Formula: Typically two premolars in each quadrant.
• Ear Structure: Bony tube between eardrum and outer ear.
• Activity: Mostly diurnal.
• Manual Dexterity: Well-developed grip, opposable thumb and big toe (except humans).

Superfamily: Cercopithecoidea (Old World Monkeys)

Family: Cercopithecidae

• Subfamily:
  • Cercopithecinae
  • Colobinae
• Distribution: Found in Africa, Asia, and some parts of Europe.
• Characteristics: Diverse and numerous among living catarrhines.

Superfamily: Hominoidea (Apes and Humans)

Family: Hylobatidae (Gibbons and Siamangs)

• Genera: Hylobates, Symphalangus, Hoolock.
• Distribution: Northeast India and tropical forests of Southeast Asia.
• Characteristics: Smallest and most numerous of the apes, known as lesser apes.

Family: Hominidae (Great Apes and Humans)

• Genera: Chimpanzees, orangutans, gorillas, bonobos, humans.
• Characteristics: Larger brain relative to body size, sexual dimorphism, relatively larger body size, semi-upright to upright posture.

Characteristics of Primates

1. Pentadactyle hands and feet

   • All primates except spider monkeys have five fingers on each hand and five toes on each foot.
   • Retained ancient mammalian trait of pentadactylism.

2. Increasing refinement of hands and feet for grasping

   • Evolutionary trend towards increasing manual dexterity.
   • Highly sensitive tactile pads at fingertips enhance grasping ability.

3. Presence of flat nails

   • Primates have flat nails instead of claws.
   • Nails protect fingertips and aid in fine manipulation.

4. Presence of opposable thumbs

   • Opposable thumbs allow for power grip and precision grip.
   • Important for grasping objects and manipulating tools.

5. Presence of clavicle and generalized limb structure

   • Retained primitive mammalian limb structure.
   • Strong clavicles and flexible shoulder joints facilitate climbing and brachiation.

6. Erect posture

   • Primates exhibit a marked tendency towards erectness in upper body posture.
   • Some species display bipedalism, especially humans.

7. Reduction in the sense of smell

   • Olfactory center of the brain (rhinencephalon) is reduced in size.
   • Facial features related to smell (snout length) are reduced, except in lemurs and baboons.

8. Increased dependence on visual sensation

   • Orbits are frontally placed, enhancing binocular vision and depth perception.
   • Stereoscopic vision is common among diurnal primates.
   • Most diurnal primates likely have some degree of color vision.

9. Relatively large brain

   • Primates have a relatively large brain compared to body size.
   • Continuous development and enlargement of cerebral cortex.
   • Enhances manual dexterity, hand-eye coordination, and cognitive abilities.

10. Reduction in number of teeth

    • Reduced dental formula compared to primitive mammals.
    • Generally two incisors, one canine, three premolars, and three molars per quadrant.

11. Presence of mammary glands

    • Most primates have one pair of mammary glands on the chest.

12. Trend towards smaller litter size and longer gestation

    • Longer gestation periods and smaller litter sizes compared to other mammals.
    • Offspring are born more mature and have a greater chance of survival.

13. Increase in natural life span

    • Primates generally have longer natural life spans compared to other mammals.
    • Ranges from several years in small prosimians to several decades in larger primates.

14. Complex social behavior

    • Primate social behaviors are diverse and complex.
    • Include vocalizations, visual displays, grooming, and specific social interactions like infant care.
    • Primates exhibit high levels of sociality compared to other mammals.