Lecture 10: Origin of Mammals

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Lecture 10 Origin of Mammals
Reading Chapter 33 593-595 Chapter 49
868-872
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• Introduction
• Mammals Defined
• Mammalian Diversity

Origin of Mammals
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Introduction

• Monophyletic
• 4100 mammal species vs 20,000 fish species
• Diversity of habitats-very successful
• Large size range e.g largest animal that ever
  lived- mammal (blue whale), smallest mammals
  (shrew )

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Defining Mammals

• Mammary glands
• Modified sweat glands
• All provide milk from
• m. gland of female
• Monotremes-no nipples,
• milk released onto surface
• and lapped up

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Defining mammals
Hair
Not homologous with epidermal scales different
origin as tactile organ, later role
insulation other functions vibrissae (cat),
protective coloration, warning coloration
Fig. 45.7
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Defining mammals
New jaw joint -dentary squamosal articulation,
single lower jaw bone
 Middle ear with 3 bones-evolved from lower jaw
bones of reptiles
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Defining mammals
 Endothermy 4 chambered heart aorta bends
to left
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Defining mammals
Diaphragm sheet of muscle separating lung
cavity from abdominal cavity Ventilation in
mammals (tidal-exhalation inhalation) vs. fish
birds (flow through- single direction)
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Defining mammals
 more complex teeth- heterodont vs. homodont
teeth polyphyodont to diphyodont (monphyodont
)
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Defining mammals
Endothermic-produce own body heat
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Major Groups of Living Mammals1. Montremata
(platypus echidna)2. Theria (marsupials and
placentals
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Mammal Phylogeny
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Monotremata
Platypus
Echidna (spiny anteater)
egg laying-- Why isnt this an apomorphy?
restricted to Australia and New Guinea
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Theria Marsupialia
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Theria Placentalia
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Convergent Evolution Marsupials Placentals
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Mammal Diversity
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Mammal Diversity
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Mammal Diversity
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Mammal Diversity
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Mammal-like reptile-Therapsid (synapsid)
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Mammal Origins
evolved 200 mya but didnt diversify until 65
mya earliest mammals small, noctural and
insectivorous