Synapsids

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Synapsids
-The Synapsids diverged early from the rest of
the amniotes, and actually diversified quite
extensively during the Permian period a time of
relatively cool and dry temperatures.
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Synapsids
-Some of the earliest synapsids showed
adaptations for temperature regulation, albeit
ectothermally. The sails on these animals (and
they are NOT dinosaurs, or even reptiles! They
are synapsids called Pelycosaurs) may have acted
as heat-exchange organs. Members of this lineage
of synapsids were the predominant large animals
on land during the early Permian.
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Synapsids
-One group of synapsids, the Therapsids showed
greater mobility, and signs of endothermy. They
diversified later in the Permian, and during
their time were the predominant large land
animals.
-Therapsids like this wolf-like animal had legs
tucked beneath them, like mammals showing high
mobility -They also had turbinate bones thin,
flat bones behind the nose that help to
condense water on exhalation. This may be a sign
of endothermy, because these bones help to
conserve water in heavy breathers.
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Synapsids
-Therapsids showed increasingly mammal-like
characteristics. These smaller therapsids had
smaller ribs in their lumbar region, like
mammals. This may have indicated the presence of
a diaphragm providing greater ventilation than
ribs alone.
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Synapsids
-Despite their increasingly mammal-like
characteristics, the larger therapsids went
extinct near the end of the Permian period
perhaps victims of a major mass extinction.
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Synapsids
-During the Triassic period, when the dinosaurs
appeared and began to diversify, the remaining
therapsids were small animals. Many appeared to
be nocturnal.
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Mammals
-Mammals appeared in the Triassic period, as part
of a lineage of small, nocturnal therapsids. The
feature distinguishing them was the
transformation of the the quadrate and articular
bones to the incus and malleus.
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Mammals
-Mammalian characteristics acquired before
transition to true mammals -Endothermy? (as
indicated by turbinate bones) -Mammalian gait
(limbs tucked under body) -Mammalian
characteristics that could have appeared before
the transition to mammals -Hair (as insulation
for endothermy, and for sensation by touch at
night) -Lactation (signs of lips in some
pre-mammalian therapsids supply of high-energy
food for endothermic young) -Increase in size
of cerebral cortex (associated with olfaction in
nocturnal animals) -Appearing after the
transition -Viviparity
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Mammals
-While mammals persisted throughout the Mesozic
era (the Age of Reptiles), they were not the
dominant large land animals. Some of the major
lineages of mammals appeared during this time.
-Monotremes are egg-laying mammals, but they
produce milk in a slit. Young lap
milk. -Marsupials are viviparous, but young are
born poorly-developed, and depend on lacatation
for nourishment as they develop. The young suck
milk.
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Mammals
-While mammals persisted throughout the Mesozic
era (the Age of Reptiles), they were not the
dominant large land animals. Some of the major
lineages of mammals appeared during this time.
-Eutherian mammals have placentae (singular,
placenta), which provides direct nourishment for
young until they are born at a relatively large
size. A greater proportion of nourishment comes
before birth than in marsupials.
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Mammals
-Our lucky stars. Strong evidence for a large
extraterrestrial impact on earth 65 million years
ago, marking the end of the Cretaceous
period. -Probably the cause of mass extinctions
at this time, including the dinosaurs (except
birds) -This may have allowed the diversification
of mammals as the predominant large land animals.
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Mammals
-In another apparent conflict between molecular
clocks and fossil evidence, it is not clear
whether the main lineages of Eutherian mammals
began to diversify even before the end of the
Cretaceous. Nevertheless, these groups did
become predominant afterwards, along with the
modern orders of birds.
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Mammals vs. Birds
-Some parallels (and some not) between birds and
mammals
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Mammals vs. Birds
-Four-chambered heart
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Mammals vs. Birds
-Some parallels (and some not) between birds and
mammals
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Mammals vs. Birds
-Ventilation of lungs -Air sacs of birds provide
nearly constant flow of air through air tubes,
where there is counter-current flow of air and
blood. -Mammals have a diaphragm, but air still
sits in alveoli, with passive exchange. Gases
only equilibrate.
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Mammals vs. Birds
-Some parallels (and some not) between birds and
mammals