Were Dinosaurs warm blooded?
Or
Were they cold blooded?
Does it really matter?
Thermoregulation
Thermoregulation
Poikilothermy - temp directly controlled by environment
Robert Bakker is one of the
strongest proponents that all
dinosaurs were warmblooded.
Homeothermy - Body temp. remains relatively constant
Endothermic = internal heat source = “warm-blooded”
Ectothermic = external heat source = “cold-blooded”
We will discuss a few of his
ideas and some of the “pros
and cons”
Thermoregulation
1. Erect Gate and built for speed
- Birds and mammals have fully erect posture, and
they are warm blooded.
- To achieve high speed, a vertebrate would need
to be warm blooded.
Smaller bipedal ~ 40-60 km/hr (25-37 mph).
Larger forms ~ 10-20 km/hr (6-12 mph).
Thermoregulation
1. Erect Gate and built for speed
* Can breathe and run at the same
time.
* Why would a cold-blooded
animal be built for speed?
* Not all dinosaurs were built for
speed.
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Thermoregulation
2. Haemodynamics
Sauropods would have needed a four chambered
heart to pump blood to their head.
- Birds and mammals have four chambered hearts
= Dinosaurs must have been endothermic
Thermoregulation
2. Haemodynamics
* Crocodiles have a 4 chambered heart as well…?
Thermoregulation
3. Paleoclimate and distribution
Arctic dinos must have been endothermic to survive.
* Climatic evidence doesn’t support this conclusion.
* Dinosaurs may have migrated during the cold periods.
Thescelosaurus
Late Cretaceous
Thermoregulation
4. Predator-Prey ratios
Warm-blooded animals need more per each
individual ~ need more prey to support warm-blooded
carnivores than cold-blooded carnivores.
In general the ratio is:
Endothermic ~ 5%
Ectothermic ~ 30-50%
Thermoregulation
4. Predator-Prey ratios
Early Permian = 50-60%
Late Permian = 10%
Triassic- Cretaceous dinosaur faunas = 2-3%
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Thermoregulation
4. Predator-Prey ratios
* Ratios for large ectothermic predators approach
those of endotherms.
* Ratios are influenced by the size of the animal.
* The fossil record is incomplete.
Thermoregulation
5. Bone histology
A. Early work showed that
dinosaurs have highly vascular bone similar to that of mammals, but unlike
that of cold blooded reptiles.
* Haversian canals have been found in
some ectotherms, and some small
mammals and birds have been shown to
lack Haversian canals.
Section lengthwise of mammal bone
Thermoregulation
5. Bone histology
B. Fibrolamellar bone - type of compact bone that
grows quickly without the formation of growth rings found in large fast growing mammals and some large
birds.
* Dinosaurs grew fast… does not necessarily
mean that they were warm-blooded.
Section perpendicular to
long axis
Thermoregulation
Thin sectioned tibia of the
tyrannosaur Albertosaurus
lancensis (LACM 23845)
exhibiting a line of arrested
growth (arrow) between
zones of highly
vascularized fibrolamellar
bone. Scale = 1 mm.
Thermoregulation
5. Bone histology
C. Modern reptiles have lamellar-zonal bone
which grows slowly and will exhibit growth lines
(rings) that correspond to periods of low growth (low
food, or bad climate).
* Is seen in some dinosaurs.
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Thermoregulation
6. Brain size
Thermoregulation
6. Brain size
Ornithomimids, Troodontids, and
Dromaeosaurids all have large brains (like mammals
and birds).
* There is no direct correlation between brain size
and thermoregulation.
* Likely corresponds to the advance eyesight,
balance and hand to eye coordination that these groups
possess(ed).
Thermoregulation
8. Nose Turbinates
Modern warm blooded birds and mammals have
complex folds of bone and cartilage within their nasal
passages that serve to moisten and warm the air that is
brought in through the nose.
Also help to recover heat and moisture from air
that leaves the body through the nose = prevents heat
loss (endothermic traits).
Thermoregulation
7. Oxygen isotopes
Barrick and Showers (1994) looked at the O18/O16 ratio of
core (central body) vs. peripheral (extremities) bone
apatite (within T. rex) to see if there was evidence of
thermoregulation.
Noted a 4°C difference between the core and the
peripheral elements ~ interpreted as proof of endothermy.
* Inertial homeotherms also would show such
differences.
Thermoregulation
8. Nose Turbinates
* Dinosaurs lack turbinates = ectothermic
* Maybe the dinosaurs could be warm-blooded
without turbinates because of the warmer climate.
* Maybe turbinates are a novelty that is beneficial
to warm-blooded animals, but not essential.
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Thermoregulation
9. Inertial Homeothermy
Large animal = smaller surface area to mass ratio.
~ Large animals do not lose heat as fast as small
animals.
~ Large dinosaurs could (would) have maintained
a fairly stable body temp. by retaining most of the heat
produced by everyday activities.
~ It also seems logical that a very large animal
would have easily overheated had it been warm-blooded
(elephants).
Thermoregulation
Thermoregulation
9. Inertial Homeothermy
~ Small dinosaurs could not have used inertial
homeothermy to maintain body temperatures because of
their high surface area to mass ratio. They would lose
too much heat (more likely to have been warm
blooded).
~ Really small dinosaurs may have been unable
to be warm-blooded without some sort of insulation.
(Ratio would be too high) - Is this why feathers
evolved??
Thermoregulation
Gigantothermy – an object of a large enough size will
maintain a relatively constant temperature simply due to its
large size.
Gigantothermy??
Even if a whale were not
warm blooded, it would
still maintain a fairly high
body temp because of its
size.
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Thermoregulation
Feathers!
There are multiple dinosaur genera (recently
described) that exhibit feathers. It seems likely that the
initial selection of feathers would have been for
insulation. Only later would have selection acted to
produce flight feathers and/or sexual plumage.
* Insulation is important if you are endothermic,
but not if you are ectothermic.
* These taxa most certainly were endothermic.
Feathered Dinosaurs!!
Feathers! (Sinosauropteryx prima)
The feathered dinosaur fossils that made international headlines
in 1998 were preserved in rock layers deposited in a lake that
existed 120 million years ago in Liaoning Province in
northeastern China.
Feathers! (Sinosauropteryx prima)
Sinosauropteryx prima
“first Chinese dragon (lizard) feather”
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Sinosauropteryx prima
Early Cretaceous (Barremian)
1.3 meters long (30 cm tall)
Sinosauropteryx
prima
Exhibits “fur-like” filiments
Further from birds than many
other dinosaur groups, so suggests
that other groups may have had
feathers.
At least 4 complete skeletons with
soft tissue
Very long tail! – 64 vert!
Protoarchaeopteryx
“early ancient wing”
Protoarchaeopteryx
“early ancient wing”
Early Cretaceous (Barremian)
1 meter tall (~ big turkey)
Exhibits feathers that are symmetric (non-flight feathers)
At least 2 skeletons with preserved feathers
Short tail (most of length is feathers)
Protoarchaeopteryx
“early ancient wing”
Beipiaosaurus
“Beipiao lizard”
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Beipiaosaurus
“Beipiao lizard”
Caudipteryx
“tail feathers”
Early Cretaceous (Barremian)
Partial skeleton with integument
impressions
2.2 meters long
Filaments (“fur”) are longer than
Sinosauropteryx – up to 7 cm long
4 functional toes – derived relative to the
primitive 3-toe condition
Caudipteryx
“tail feathers”
Caudipteryx
Early Cretaceous (Barremian)
70-90 cm long
Half a dozen nearly complete skeletons
with preserved integument and
gastroliths
Feathers are symmetric
Preserved pigment from the feathers?
Caudipteryx
Sinornithosaurus
“Chinese bird lizard”
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Sinornithosaurus
“Chinese bird lizard”
Sinornithosaurus
Early Cretaceous (Barremian)
1 meter long
Nearly complete specimen with integument impressions
Small down-like feathers – central shaft with branching filaments
Seems to be a primitive Dromaeosaur – suggests that more
advanced forms may be secondarily flightless!
Sinornithosaurus
Sinornithosaurus
Sinornithosaurus
Sinornithosaurus
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Microraptor “small thief”
Microraptor
Early Cretaceous (Barremian)
Placed within the Dromaeosauridae (Xu, at el, 2003)
Only 40-50 cm long!! (smaller than Archaeopteryx)
Has fuzzy “fur” or “down”
Scansorial? Glider?
Heterodont teeth (front teeth are recurved, laterally compressed,
and lack serrations = more bird-like than posterior teeth)
One species has four wings!!
Some controversy over the name = Archaeoraptor?
Microraptor
(Dromaeosaur)
Glider?
Rahonavis
“menace bird”
Madagascar
Late Cretaceous
Raven-sized
No feathers preserved,
but has anchor points on
some of the bones
Has sickle claw!
Unenlagia
“half bird”
Late Cretaceous of
Argentina
2-3 meters long
Partial postcranium
No known feathers, but
wing like forelimbs
“Bent back” pubis
Dromaeosaur? or bird?
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Shuvuuia – similar to Mononychus
“bird”
Archaeopteryx
“ancient wing/feather”
Late Cretaceous of
Mongolia
1 meters long
2 skulls and partial
postcranium
Seems to have had
feather like structures
Archaeopteryx
“ancient wing/feather”
Archaeopteryx
Archaeopteryx
Thermoregulation
At least some dinosaurs were
endothermic.
(Small feathered dinos and perhaps some of the
med-sided taxa)
But, it is certain that some were not.
(The large taxa – sauropods, etc.)
Dinosaurs as a whole were so diverse
and unique, is it really that surprising
that some were warm-blooded and
some were not?
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