Domain Eucarya
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Class Mammalia

Mammals evolved on land during the late Triassic period, but were not nearly as successful as the dinosaurs which evolved at the same time.

During the Cenozoic Era, mammals radiated into so many ecological niches that the Era is often called the "Age of Mammals".

Defining mammalian characteristics include:

  • Mammary glands from which females feed their newborn offspring
  • Three bones in the middle ear
  • Molar and premolar "cheek teeth" (where they have not evolved away)
  • Bodies covered in hair

  • Paleoryctoidae
  • Subclass Prototheria:

    • Infraclass Eotheria:
  • Infraclass Ornithodelphia:
  • Infraclass Allotheria:

  • Subclass Theria:
    • Infraclass Pantotheria:

  • Infraclass Metatheria (marsupials):

  • Infraclass Eutheria:


  • Mammals are a class of bony fishes that have evolved to live on land, and whose scales have attenuated into long, thin projections called "hair". A cladistic lineage of the mammals looks something like this1:


    Eukaryota - cells with nuclei
    Ophisthokonta
    Metazoa - animals
    Bilateria - triploblast embryos, bodies with bilateral symmetry
    Deuterostoma
    Chordata - vertebrates
    Craniata - vertebrates with skulls
    Vertebrata - vertebrates with backbones (i.e. instead of a cartaliginous notochord
    Gnathostomata - vertebrates with jaws
    Teleostomi - mouth at end, three ear bones
    Osteichthyes - bony fishes
    Sarcopterygii - lobed fins
    Tetrapoda - four limbs
    Stegocephalia - digits
    Amniota - young develop in amniotic egg
    Synapsida - ear hole in skull
    Anthracosauria
    Eupleycosauria
    Sphenacodontia
    Sphenacodontoidea
    Therapsida
    Theriodontia
    Cynodontia
    Mammalia


    University of Michigan Animal Diversity Web - Mammalia
    http://animaldiversity.ummz.umich.edu/chordata/mammalia.html

    Smithsonian Institution, National Museum of Natural History, MSW Scientific Names
    http://www.nmnh.si.edu/cgi-bin/wdb/msw/names/query/1

    The Ultimate Ungulate Page, your guide to the world's Hoofed Mammals]
    http://www.ultimateungulate.com/index.html

    Biognomen
    http://members.aol.com/bafiler/index.html

    1Tree of Life Web Project
    http://tolweb.org/tree/

    MAMMALS: A World Listing of Living and Extinct Species, Edited by John H. Burkitt, Tennessee Department of Agriculture, Nashville, Tennessee, Second Edition, 1995