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Relative advantages and disadvantages of endothermyand
ectothermy depend on climate and food supply
Ectotherms can only be active at higher temperatures. However,
they onlyneed to consume about 10% of the calories needed to
maintain an endothermof the same size.
Endotherms can be active at lower temperatures and atnight, but
have an energetically expensive lifestyle. Theymust eat a lot to
maintain their body temperature. In manycases, they must feed their
young high calorie food and keepthem warm in nests or burrows.
Many adaptations that we seein birds and mammals are inresponse
to endothermy.
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But might dinosaurs have been endothermic?(see the essay in
Kardong, p. 115)
Bone Structure. Present day ectotherms show annual growthrings
in skeletal structures. Endothermic animals do not, nor do
dinosaurs.
Geographic Distribution. Reptiles are not found in the north
today, particularly large reptiles. Dinosaurs were, even to
thelatitude of perpetual darkness in winter. Fossil Ecology. Modern
ectothermic animals have a higher
predator to prey ratio than endotherms. Predatory dinosaurswere
rare relative to herbivores.
Dinosaur Anatomy. Dinosaurs resemble modern, active,running
animals in limb anatomy.
Some small dinosaurs had feathers, but were not able to fly.
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Evidence to the contrary
no living reptile is endothermic (unless birdsare considered to
be reptiles).
dinosaurs did not have the elaborate nasal bones that allow
mammals to conserve heatand moisture when breathing.
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Reptiles were incredibly diverse in theMesozoic (250 mybp to 65
mybp)
Note that this chartdoes not include theaquatic reptiles
andflying reptiles, or the Parareptilia, just
the Ornithischia andSaurischia.
KK 3.37
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Reptiles were largely replaced by a radiation of birds and
mammals since 65 mybp
KK 3.41
The boundary betweenthe Mesozoic andCenozoic Eras, or Cretaceous
and Tertiary
periods, marks a major period of change in theearths flora and
fauna. Itis now widely believedthis marks the time whenan asteroid
struck the
earth.
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Features of Class Aves
endothermy feathers bipedal, wings
short tail keel-shaped sternum crop, gizzard no teeth (bill made
of keratin) unique lungs, air sacs, hollow bones
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Are birds dinosaurs? Kardong, being a cladist, would say so
because birds share a
common ancestor with reptiles. More conventionally we callAves a
class of its own, making Reptilia paraphyletic.
KK Fig. 3.42
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Class AvesBirds go back about 200 mybp, Archaeopteryx
Different from modern birds
-fingers on wings
-teeth
-long tail
-no keel on sternum
-solid bonesKK Fig. 1.32
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Modern Birds or Neornithes Paleognathae , large
flightless birds
Neognathae
Emu
Blue Jay
Neognathae radiated starting 65 mybp.
There are now about 30 ordersof Neornithes.
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Synapsida - early forms
Synapsids are usuallyconsidered a subclassof reptiles.
ButKardong, again being
a purist, follows therules and keeps themseparate.
KK Fig 3.43
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Class Mammalia - 200 mybp
Mammalian Characteristics-endothermy
-hair
-mammary glands
-posture (legs under body,rather than sprawling)
-dentition (differentiatedteeth)
-skull (malleus rather thanarticular bone)
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Subclass Monotremes (Prototheria)Egg-laying mammals with
rudimentary mammary glands.
Extant examples are found in Australia only.
Platypus
Echidna
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Kangaroo neonate
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Infraclass Eutheria or placental mammals underwent a great
expansion 65 mybp, as did
metatheria to a lesser extent (why?) ancestral order has long
thought to be the Insectivora
(presently moles, shrews and hedgehogs), but recentevidence
suggests the Edentata (anteaters, sloths,
armadillos). largest order is the Rodentia . includes an order
of flying mammals ( Chiroptera , or
bats), two orders of entirely aquatic mammals(Sirenia, Cetacea
), and ourselves ( Primates ).
other orders we will mention in the course includeCarnivora,
Proboscidea, Perissodactyla, Artiodactyla.
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