Comparative Anatomy
Mammalian Evolution
Kardong
Chapter 3
Part 6
Mammals
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Mammals arose in mid-Triassic Period
Cenozoic – “Age of Mammals”
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Quaternary and Tertiary
Synapsid lineage began with pelycosaurs,
which therapsids succeeded
Therapsids gave rise to mammals
Figure 6.1.
Therapsids
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Synapsid skulls
Possess hair and mandible
Heterodont dentition
Two lower jaw bones (2 dentarys)
Figure 6.2. (Book fig. 3.44, p. 122).
Evolution of Reptilian Jaw
1. Reduction in
number of bones
2. Fusion of bones
Figure. 6.3. Mandible evolution.
In reptiles, articular bone articulates with quadrate
In mammals, dentary articulates with squamosal
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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.
Middle Ear Bones
Figure 6.5. Origin of middle ear bones; adult (left) and embryo (right).
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Articular and quadrate evolved from 1st visceral arch
Stapes evolved from hyomandibular of 2nd arch (= hyoid)
Eustachian tube from 1st pharyngeal pouch
Figure 6.6. Skeletal derivatives of pharyngeal arches (see Table 7.2, p. 246).
Phylogeny of Mammals
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Oviparous- egg layers
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Viviparous- give birth to
live young
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Therapsids and all birds
Most mammals
Ovoviviparous- retain
eggs in body and give
birth to live young
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Many fish and reptiles
Figure 6.7. Major categories of living
mammals (book figure 4.31).
Characteristics of Mammals
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Hair
Single dentary bone
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Sebaceous glands
Sweat glands (some lack these glands)
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Fused to form mandible
Mammary glands
Homeothermic
Enucleated RBC
Placental Types
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Therians diverged into the metatheria (marsupials)
and eutheria (placental mammals) orders
Metatheria- yolk sac placenta
Eutheria- true placenta
 chorioallantoic placenta
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)
Living Mammals
Figure 6.8 .
(p. 125).
Figure 6.9. Eutheria (placenta mammals) phylogeny.
Suborder Anthropoidea
-Infraorder Platyrrhine
-Infraorder Catarrhine
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Two infraorders distinguished
by nose form
Platyrrhine
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(a)
Nostrils flare to sides
Flat nose
Wide septum
Catarrhine
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Nostrils point straight down
Narrow septum
(b)
Figure 6.10. Platyrrhine (a)
and catarrhine (b).