For our overview of Eutherian orders, we will use the phylogeny proposed by Murphy et al. (2001).

Basal split = Afrotheria and all other orders

Afrotheria is composed of

All these lineages have African origins, but some have expanded their ranges beyond Africa.

The phylogenetic relationships of these lineages have been confusing, and at some point each of these orders was considered closely related to a taxa that we now know are only distantly related.

  1. Order Afrosoricida - African shrews and tenrecs
    1. Until very recently, this order was part of the large (>400 species) order called Insectivora. Several recent phylogenies have indicated that the group we knew as Insectivora was polyphyletic and was composed of 2 or 3 phylogenitically distinct lineages.
    2. General characteristics (include many retained ancestral traits)
      • Most (but not all) eat insects and small invertebrates
      • Small body size
      • Most are terrestrial, but some are fossorial, semi-aquatic or arboreal
      • Pellage consists of only one type of hair + vibrissae
      • Simple, triangular, pointy teeth
      • Limbs are unspecialized, feet are plantigrade
    3. Example: Tenrec
      1. Native to Madagascar
      2. Mouse- to rabbit-sized
      3. Long snout
      4. Small eyes
      5. Large pinnae
      6. Some have spines, others only have sparse, course guard hairs
      7. Can roll into a ball when threatened

  1. Order Macroscelidea - Elephant shrews
    1. General characteristics
      1. Rat- to mouse-sized
      2. Large eyes, large ears
      3. Long, mobile snout (hence the common name)
      4. Resemble other insectivorous mammals (previously and incorrectly lumped with them taxonomically in to the order Insectivora)
      5. Important anatomical differences between elephant shrews and the other species in this polyphyletic group

        1. Have auditory bullae
        2. Have zygomatic arches
        3. Olfactory lobes (in the brain) are small - more reliance on vision rather than smell
        4. Has a cecum

  1. Order Tubulidentata - Aardvark

    Now recognized as being part of the Afrotherian lineages, but in the past they were often lumped into a group that we now recognize as polyphyletic, called the edentates (contained anteaters, sloths, armadillos, and pangolins). This was because of shared adaptations for digging and eating ants/termites.

    1. General characteristics

      1. Skull is elongated
      2. Teeth

        1. No incisors or canines
        2. 5 cheek teeth top and bottom
        3. Cheek teeth are oval or figure-8 shaped
        4. Teeth have numerous tubular pulp cavities running vertically through each tooth (gives the order its name)

      3. Pig-like snout
      4. Long tongues
      5. Big ears
      6. Long, gradually-tapering tail with thick base
      7. Thick skin with bristles
      8. Digits have strong, hoof-like claws
      9. Roughened pyloric portion of stomach

    1. Ecology and behavior

      1. Eats termites, ants, other insects

    2. Picture of baby aardvark

The next three orders are often referred to as Subungulates, because they were thought to be closely related phylogenetically to the orders Artiodactyla and Perissodactyla (the even-toed and odd-toed ungulates). According to Murphy et al. (2001) and others, this is probably not correct...

  1. Order Hyracoidea - Hyrax

    1. General characteristics

      1. Rabbit-sized, resemble rodents
      2. Have enlarged, rootless incisors
      3. Incisors separated from cheek teeth by a diastema
      4. Weird feet for an animal in their niche

        1. Shortish toes
        2. Moist, glandular adhesive pads on feet
        3. Muscle in footpad that creates suction
        4. Flat nails that resemble hooves

  1. Order Proboscidea - Elephants

    1. General characteristics

      1. Teeth

        1. Top incisors are enlarged into tusks
        2. Tusks are rootless
        3. No canines
        4. Cheek teeth (6) are shed from the front as they are worn and replaced from the back

      1. Limbs

        1. Thick and straight
        2. Five digits on each foot
        3. Digitigrade - foot bones rest on a fat pad
        4. Most digits have a hoof-like nail

      1. Trunk

        1. Fusion and elongation of upper lip and nose
        2. Prehensile
        3. Nostrils are at the end

  1. Order Sirenia - Manatees and sea cows

    1. General characteristics

      1. Shows multiple anatomical specializations associated with marine lifestyle
      2. Limbs

        1. lack hind limbs
        2. forelimbs modified as flippers

      1. Tail modified into fluke (dorsoventrally flattened)
      2. Small eyes
      3. No pinnae
      4. External nares are high on the skull (on the upper surface of the snout), nasal bones are reduced or absent
        Photo of nares closed when submerged
      5. Teeth

        1. Canines and sometimes incisors are absent
        2. Cheek teeth are lost from the front and replaced from the rear

      1. Lips are large and mobile
      2. Vibrissae on upper lip and body (otherwise hairless)