Mammals {mammal} evolved from therapsids.
types
Mammals (Eutheria) are extinct multituberculates, monotremes like platypus, marsupials like kangaroo, and placental mammals (Placentalia).
evolution
Eutheria evolved from Theria. Early mammals included 30-gram Megazostrodon [-220000000] and Triconodon.
behavior
Early mammals hunted alone, signaled, and had territoriality. Voluntary muscles allowed rapid locomotion and good control.
body temperature
More food and oxygen allowed higher metabolic rate, more muscle action, and warm-bloodedness {homoiothermic, mammal}. Body temperature was higher than surroundings but lower than humans have now. Homeostasis allowed wider territory ranges and longer maturation times. Because early mammals were nocturnal, they only needed heating. Panting and sweating to cool body came later.
body temperature: hair
Mammals have hair, rather than scales, plates, or feathers, covering skin, to aid thermoregulation and insulation. They have sweat glands.
respiration
Diaphragm, bony palate, and turbinals allowed more oxygen and better respiration. Specialized red-blood-cell erythrocytes carry heme to provided better energy and oxygen management. Only warm-blooded animals can have erythrocytes.
reproduction
Reproductive-tract and digestive-tract openings became separate, allowing better and more reproduction and childcare varieties. Early mammals had birth rituals, courtship rituals, and sexual intercourse.
reproduction: mammaries
Sweat glands evolved into mammary glands, which provided balanced nutrition to young. Only warm-blooded animals can make milk. Milk redefined mother and father roles relative to children and allowed longer maturation and more brain growth. Mothers cared for babies until weaning.
teeth
Mammals have three teeth types: incisor, canine, and molar. They have two teeth sets, baby and adult, instead of continuous replacement, allowing head to be greater size in early life. Deciduous baby teeth and permanent adult teeth, rather than having continual replacement, allowed more teeth variety and more chewing. Head can be greater size in early life.
nervous system
Hippocampus and archicortex replaced some thalamus functions. Larger cerebellum allowed more sensorimotor coordination.
nervous system: involuntary muscle
Automatic circuits in ganglia and paleocortex control involuntary muscles, as in reptiles and birds. In lower mammals, archicortex and mesocortex or paleocortex add a supragranular layer to lower-animal granular and subgranular layers. In middle mammals, both supragranular and granular layers thicken, but subgranular layer stays the same.
nervous system: neocortex
In higher mammals, neocortex thickens, cellular complexity increases, newborn unmyelinated areas increase, and brain has more fissures. Paleocortex extension above ganglia forms neocortex to control voluntary muscles. All mammals have four lobes and three fissures in neocortex. Neocortex had four layers with minicolumns and interconnected specialized modules, to make maps for more complex local processing and more integration. Larger cerebrum allowed more spatial and temporal integration.
Higher mammals try alternate strategies to reach goals and identify object and event categories, such as individuals, selves, space, and time. Some mammals learn abstract symbols and categories. Some mammals generalize from specifics and specify objects from general categories. Some mammals learn relationships but cannot use analogies, metaphors, similes, parables, and mental models. Mammals have pleasant and unpleasant dreams. Mammals are curious, sentient, and know object categories, not just specific objects.
senses
Animals evolved new sensation abilities [Dawkins, 1987] [Griffin, 1974] [Griffin, 2001] [Griffin and Speck, 2004] [Haugeland, 1997].
senses: smell
Smell sense developed first, in amygdala and forebrain paleocortex.
senses: vision
At first, small eyes bulged out, as in tree shrews. Optic tectum allowed better object localization and size detection. Mammals typically have no or limited color vision, except for primates.
senses: hearing
Maleus evolved from cynodont articular jawbone, and incus evolved from cynodont quadrate jawbone, to work with stapes. Stapedius muscle controlled stiffness. Outer hair cells paralleled inner hair cells. These allowed hearing frequencies above 10000 Hertz and so high-frequency insect noises and baby cries. Outer hair cells can also change shape quickly, changing frequencies to which inner hair cells respond best. Early mammals had ear pinnae.
Biological Sciences>Zoology>Kinds>Mammal
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Date Modified: 2022.0224