Mammalia: General Characteristics and Classification | Zoology Optional Notes for UPSC PDF Download

Diversity of Mammals

1. Adaptations for Varied Environments

• Terrestrial Quadrupeds: The fundamental body type of mammals is the terrestrial quadruped, but intriguingly, some have evolved to thrive in different environments.
• Specialized Habitats: Mammals have adapted for life in the sea, air, trees, underground, and even on two legs.

2. Reproduction and Size Range

• Placental Mammals: The largest group of mammals, known as placental mammals, possesses a placenta. This feature contributes to the remarkable size range observed among them.
• Live Birth: With the exception of monotremes, all modern mammals give birth to live young.

3. Major Orders of Mammals

• Placental Dominance: The majority of mammals, particularly in the six most species-rich orders, fall under the placental group.
• Key Orders: Noteworthy orders include Rodentia, Chiroptera, and Soricomorpha, each with its unique characteristics and species.

4. Mammalian Terminology and Classification

• Origin of Term: The term "mammal" originates from the Latin word "mamma," meaning teat or pap. Carl Linnaeus coined the scientific name Mammalia in 1758.
• Nursing Young: All female mammals nurse their young with milk secreted from mammary glands.

5. Diversity in Classification

• Species Count: According to the Mammalian Species of the World, 5,416 species were known in 2006, categorized into various genera, families, and orders.
• Conservation Assessment: The IUCN Red List, in 2008, reported 5,488 species after a comprehensive Global Mammal Assessment.

6. Classifying Extant Mammals

• Subclasses: Some classifications divide extant mammals into two subclasses: Prototheria (Monotremata) and Theria (Metatheria and Eutheria).
• Crown Groups: Marsupials represent the crown group of Metatheria, while placentals are the crown group of Eutheria.

7. Evolutionary Dynamics

• Family-Level Stability: Mammal classification at the family level has remained relatively stable, but debates persist at higher taxonomic levels, including subclass, infraclass, and order.

In summary, the world of mammals is marked by incredible diversity, adaptation to various environments, and ongoing debates in taxonomy, showcasing the complex nature of their evolutionary history.

Characteristics of Class Mammalia

1. Warm-Blooded and Endothermic

• Warm-Blooded Nature: Mammals are warm-blooded, maintaining a constant internal temperature.
• Endothermic Metabolism: They are endothermic, utilizing the majority of heat energy to sustain high body temperatures.

2. Hair and Insulation

• Keratinous Hair: Possess hair made of keratin, providing insulation.
• Independent Evolution: The evolution of mammalian keratin is independent of reptilian keratin.

3. Cardiovascular System and Respiration

• Four-Chambered Heart: Mammals have a four-chambered heart for efficient circulation.
• Diaphragm Presence: The diaphragm separates the thoracic and abdominal cavities, aiding in respiration.

4. Reproduction and Parental Care

• Mammary Glands: Females have mammary glands producing milk for nourishing young.
• Viviparous Nature: Most mammals are viviparous, with some exceptions like monotremes.
• Extended Gestation: Placental mammals commonly undergo extended gestation for uterine development.
• Parental Care: Mammals exhibit well-developed parental care.

5. Skeletal and Dental Features

• Seven Cervical Vertebrae: Most mammals have seven cervical vertebrae in the neck.
• Heterodontic Teeth: Mammals are heterodontic, meaning their teeth have different shapes.
• Jaw Movement: Lateral movement of the jaw occurs during mastication.

6. Evolutionary History and Brain Development

• Therapsid Ancestry: Mammals evolved from therapsid ancestors during the Triassic period.
• Well-Developed Brain: Mammals possess a well-developed brain, contributing to their intelligence.

7. Sensory Characteristics

• Buccal Cavity and Nostrils: The buccal cavity has a false palate, and nostrils do not lead directly into the mouth.
• Sensory Organs: Acute smell (except in whales and higher apes), typical amniote eyes, and well-developed touch senses through vibrissae.
• Auditory and Visual Reflexes: Tectum reduced to corpora quadrigemina, functioning mainly as a relay center for auditory information and controlling visual reflexes.
• Corpus Callosum: Eutherians have a corpus callosum for additional communication.

8. Thermoregulation and Metabolic Heat

• Constant Body Temperature: Mammals maintain a constant body temperature.
• Heat Generation: They generate heat metabolically and have special cooling mechanisms.

9. Classification of Mammalia

• Phylum Chordate: Mammalia belongs to the phylum Chordate.
• Evolutionary Perspectives: Various classification systems exist, with cladistic thinking emphasizing monophyletic groups.
• Simpson's Contribution: George Gaylord Simpson's 1945 classification, while outdated, was influential until the late 20th century.
• Recent Developments: Molecular phylogenetics and cladistics have influenced recent modifications in mammalian taxonomy.

Conclusion
The class Mammalia is characterized by a multitude of features, from warm-bloodedness and unique hair composition to reproductive strategies, complex sensory organs, and evolutionary origins. The classification of mammals has evolved over time, reflecting advancements in understanding their relationships and genetic underpinnings.

Classification of Mammalia: A Comprehensive Overview

Subclass 1: Prototheria

1. Order 1: Monotremata
   • Family Tachyglossidae: Echidnas
   • Family Ornithorhynchidae: Platypuses

Subclass 2: Theria

Infraclass Metatheria

2. Order Didelphimorphia
   • Family Didelphidae: Opossums, etc.
3. Order Paucituberculata
   • Family Caenolestidae: Shrew opossums
4. Order Microbiotheria
   • Family Microbiotheriidae: Monito del montes
5. Order Dasyuromorphia
   • Family Thylacinidae: Tasmanian tigers
   • Family Myrmecobiidae: Numbats
   • Family Dasyuridae: Tasmanian devils, quolls, dunnarts, planigale, etc.
6. Order Peramelemorphia
   • Family Peramelidae & Family Peroryctidae: Bandicoots, bilbies, etc.
7. Order Notoryctemorphia
   • Family Notoryctidae: Marsupial moles
8. Order Diprotodontia
   • Family Phascolarctidae: Koalas
   • Family Vombatidae: Wombats
   • Family Phalangeridae: Brushtail possums, cuscuses

Infraclass Eutheria

9. Order Xenarthra
   • Family Bradypodidae, Megalonychidae, Dasypodidae, Myrmecophagidae: Pangolins and relatives
10. Order Insectivora

• Various families including Solenodontidae, Nesophontidae, Tenrecidae, Chrysochloridae, Erinaceidae, Soricidae, Talpidae

11. Order Scandentia

• Family Tupaiidae: Tree shrews

12. Order Dermoptera

• Family Cynocephalidae: Colugos

13. Order Chiroptera

• Various families including Pteropodidae, Emballonuridae, Craseonycteridae, Rhinopomatidae, Nycteridae, Megadermatidae, Rhinolophidae

14. Order Primates

• Various families including Daubentoniidae, Lemuridae, Lepilemuridae, Galagidae, Lorisidae, Cheirogaleidae

Subclass Prototheria

15. Order Platypoda

• Family Ornithorhynchidae: Platypuses

16. Order Tachyglossa

• Family Tachyglossidae: Echidnas (Spiny anteaters)

Subclass Theriiformes

• Infraclass Allotheria

17. Order Multituberculata

• Family Plagiaulacidae: Multituberculates

18. Super legion Kuehneotheria

• Family Kuehneotheriidae, Woutersiidae: Kuehneotheres

19. Super legion Trechnotheria

• Legion Symmetrodonta
  • Order Amphidontoidea
    • Family Amphidontidae: Amphidonts
  • Order Spalacotherioidea
    • Family Tinodontidae: Tinodonts

20. Legion Cladotheria

• Sublegion Dryolestoidea
  • Order Dryolestida
    • Family Austrotriconodontidae, Dryolestidae: Dryolestids
• Order Amphitheriida
  • Family Amphitheriidae: Amphitheriids
• Sublegion Zatheria
  • Family Arguitheriidae: Arguitheriids
• Infralegion Peramura
  • Family Peramuridae: Peramurids
• Infralegion Tribosphenida
  • Family Necrolestidae: Necrolestids
• Supercohort Aegialodontia
  • Family Aegialodontidae: Aegialodonts
• Supercohort Theria

21. Order Yalkaparidontia

• Family Yalkaparidontidae: Yalkaparidonts

22. Order Notoryctemorphia

• Family Notoryctidae: Marsupial moles

23. Order Peramelia

• Family Peramelidae, Peroryctidae: Bandicoots

24. Order Diprotodontia

• Family Palorchestidae: Palorchestids

25. Order Didelphimorphia

• Family Didelphidae: Opossums

26. Order Paucituberculata

• Family Sternbergiidae: Sternbergiids

27. Order Sparassodonta

• Family Mayulestidae: Mayulestids

28. Order Cingulata

• Family Dasypodidae: Armadillos

29. Order Pilosa

• Family Entelopidae: Entelopids
• Family Myrmecophagidae: Giant anteaters and relatives

Magnorder Epitheria: Epitheres

30. Superorder Leptictida

• Family Gypsonictopidae, Kulbeckiidae: Gypsonictops, Kulbeckiids

31. Superorder Preptotheria
32. Grandorder Anagalida

• Family Zambdalestidae: Zambdalestids

33. Mirorder Macroscelidea

• Family Macroscelididae: Elephant shrews

34. Mirorder Duplicidentata
35. Order Mixodontia

• Family Eurymylidae: Eurymylids

36. Order Rodentia

• Various families including Alagomyidae, Thryonomyidae, Sciuridae, Castoridae, Geomyidae, Heteromyidae, Dipodidae, Muridae, Anomaluridae, Pedetidae, Ctenodactylidae, Myoxidae, Bathyergidae

37. Order Lagomorpha

• Family Ochotonidae: Pikas

38. Mirorder Simplicidentata

• Order Mimotonida
  • Family Mimotonidae: Mimotonids

39. Order Lagomorpha

• Family Ochotonidae: Pikas

40. Mirorder Simplicidentata

• Order Mixodontia
  • Family Eurymylidae: Eurymylids

41. Order Rodentia

• Various families including Alagomyidae, Thryonomyidae, Sciuridae, Castoridae, Geomyidae, Heteromyidae, Dipodidae, Muridae, Anomaluridae, Pedetidae, Ctenodactylidae, Myoxidae, Bathyergidae

42. Order Lagomorpha

• Family Ochotonidae: Pikas

43. Mirorder Simplicidentata

• Order Mimotonida
  • Family Mimotonidae: Mimotonids

44. Order Lagomorpha

• Family Ochotonidae: Pikas

45. Mirorder Simplicidentata

• Order Mixodontia
  • Family Eurymylidae: Eurymylids

46. Order Rodentia

• Various families including Alagomyidae, Thryonomyidae, Sciuridae, Castoridae, Geomyidae, Heteromyidae, Dipodidae, Muridae, Anomaluridae, Pedetidae, Ctenodactylidae, Myoxidae, Bathyergidae

Grandorder Ferae

47. Order Cimolesta

• Various families including Palaeoryctidae, Cimolestidae, Apatemyidae

48. Order Creodonta

• Various families including Hyaenodontidae, Oxyaenidae

49. Order Carnivora

• Various families including Viverravidae, Nimravidae, Procyonidae, Felidae, Viverridae, Herpestidae, Hyaenidae, Canidae, Ursidae

50. Order Chrysochloridea

• Family Chrysochloridae: Golden moles

51. Order Erinaceomorpha

• Various families including Sespedectidae, Amphilemuridae

52. Order Soricomorpha

• Various families including Otlestidae, Geolabididae

53. Order Chiroptera

• Various families including Pteropodidae, Archaeonycteridae

54. Order Primates

• Various families including Purgatoriidae, Microsyopidae

55. Order Scandentia

• Family Tupaiidae: Tree shrews

Grandorder Ungulata: Ungulates

56. Order Tubulidentata

• Family Orycteropodidae: Aardvark

57. Order Dinocerata

• Family Uintatheriidae: Uintatheres

Mirorder Eparctocyona

58. Order Procreodi

• Family Oxyclaenidae, Arctocyonidae: Oxyclaenids, Arctocyonids

59. Order Condylarthra
60. Order Arctostylopida

• Family Arctostylopidae: Arctostylopids

61. Order Cete

• Various families including Triisodontidae, Mesonychidae

62. Order Artiodactyla

• Various families including Raoellidae, Hippopotamidae, Camelidae, Tragulidae, Giraffidae

Mirorder Altungulata

63. Order Perissodactyla

• Various families including Equidae, Palaeotheriidae

64. Order Uranotheria

• Various families including Pliohyracidae, Procaviidae

The classification of mammals is a complex system, reflecting their diverse evolutionary history and adaptations. This overview provides a detailed breakdown of major orders, families, and species within the class Mammalia, highlighting the rich biodiversity and evolutionary relationships among mammals.