Comparative Anatomy Mammalian Evolution

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Comparative AnatomyMammalian Evolution
Kardong Chapter 3 Part 6
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Mammals

• Mammals arose in mid-Triassic Period
• Cenozoic Age of Mammals
• Quaternary and Tertiary
• Synapsid lineage began with pelycosaurs, which
  therapsids succeeded
• Therapsids gave rise to mammals

Figure 6.1.
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Therapsids

• Synapsid skulls
• Possess hair and mandible
• Heterodont dentition
• Two lower jaw bones (2 dentarys)

Figure 6.2. (Book fig. 3.44, p. 122).
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Evolution of Reptilian Jaw

• 1. Reduction in
• number of bones
• 2. Fusion of bones
• In reptiles, articular bone articulates with
  quadrate
• In mammals, dentary articulates with squamosal

Figure. 6.3. Mandible evolution.
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Mammalian Jaw

• Articular of lower jaw and quadrate of upper
  jaw become middle ear bones malleus, incus and
  stapes (stapes evolved from hyomandibula of hyoid
  arch)

Figure 6.4. Evolution of the jaw and middle ear
bones.
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Middle Ear Bones
Figure 6.5. Origin of middle ear bones adult
(left) and embryo (right).

• Articular and quadrate evolved from 1st visceral
  arch
• Stapes evolved from hyomandibular of 2nd arch (
  hyoid)
• Eustachian tube from 1st pharyngeal pouch

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Figure 6.6. Skeletal derivatives of pharyngeal
arches (see Table 7.2, p. 246).
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Phylogeny of Mammals

• Oviparous- egg layers
• Therapsids and all birds
• Viviparous- give birth to live young
• Most mammals
• Ovoviviparous- retain eggs in body and give birth
  to live young
• Many fish and reptiles

Figure 6.7. Major categories of living mammals
(book figure 4.31).
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Characteristics of Mammals

• Hair
• Single dentary bone
• Fused to form mandible
• Sebaceous glands
• Sweat glands (some lack these glands)
• Mammary glands
• Homeothermic
• Enucleated RBC

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Placental Types

• Therians diverged into the metatheria
  (marsupials) and eutheria (placental mammals)
  orders
• Metatheria- yolk sac placenta
• Eutheria- true placenta
• chorioallantoic placenta

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Selected Orders in Class Mammalia

• Infraclass Ornithodelphia
• Monotremata- egg layers
• Infraclass Metatheria
• Marsupialia- marsupium present
• Infraclass Mammalia
• Artiodactyla- Even-toed ungulates
• Perissodactyla- Odd-toed ungulates
• Rodentia- Largest groups of mammals
• Primates- catarrhine (Old World monkeys and
  humans) and platyrrhine (New World monkeys)

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Living Mammals
Figure 6.8 . (p. 125).
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Figure 6.9. Eutheria (placenta mammals)
phylogeny.
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• Suborder Anthropoidea
• -Infraorder Platyrrhine
• -Infraorder Catarrhine
• Two infraorders distinguished
• by nose form
• Platyrrhine
• Nostrils flare to sides
• Flat nose
• Wide septum
• Catarrhine
• Nostrils point straight down
• Narrow septum

(a)
(b)
Figure 6.10. Platyrrhine (a) and catarrhine (b).