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Were Dinosaurs warm blooded?Or

Were they cold blooded?

Does it really matter?

Thermoregulation

Poikilothermy - temp directly controlled by environment

Homeothermy - Body temp. remains relatively constantEndothermic = internal heat source = “warm-blooded”Ectothermic = external heat source = “cold-blooded”

Thermoregulation

Robert Bakker is one of the strongest proponents that all

dinosaurs were warm-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. HaemodynamicsSauropods 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

* Crocodiles have a 4 chambered heart as well…?

Thermoregulation

2. Haemodynamics

ThescelosaurusLate Cretaceous

Thermoregulation

3. Paleoclimate and distributionArctic dinos must have been endothermic to survive.

* Climatic evidence doesn’t support this conclusion. * Dinosaurs may have migrated during the cold periods.

Thermoregulation

4. Predator-Prey ratiosWarm-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 ratiosEarly 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 histologyA. 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

Section perpendicular to long axis

Thermoregulation

5. Bone histologyB. 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.

Thermoregulation

Thin sectioned tibia of the tyrannosaur Albertosaurus lancensis (LACM 23845) exhibiting a line of arrested growth (arrow) between zones of highlyvascularized fibrolamellarbone. Scale = 1 mm.

Thermoregulation

5. Bone histologyC. 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 sizeOrnithomimids, 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

7. Oxygen isotopesBarrick and Showers (1994) looked at the O18/O16 ratio of core (central body) vs. peripheral (extremities) boneapatite (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 TurbinatesModern 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

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 HomeothermyLarge 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

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

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!!The feathered dinosaur fossils that made international headlinesin 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)

Feathers! (Sinosauropteryx prima) Sinosauropteryx prima“first Chinese dragon (lizard) feather”

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Sinosauropteryx primaEarly Cretaceous (Barremian)

1.3 meters long (30 cm tall)

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!

Sinosauropteryxprima

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”

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“tail feathers”

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

Caudipteryx

Sinornithosaurus“Chinese bird lizard”

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Sinornithosaurus“Chinese bird lizard”

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

Sinornithosaurus

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Microraptor “small thief”

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

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!

Dromaeosaur? or bird?

Unenlagia“half bird”

Late Cretaceous of Argentina

2-3 meters long

Partial postcranium

No known feathers, but wing like forelimbs

“Bent back” pubis

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Shuvuuia – similar to Mononychus“bird”

Late Cretaceous of Mongolia

1 meters long

2 skulls and partial postcranium

Seems to have had feather like structures

Archaeopteryx“ancient wing/feather”

Archaeopteryx“ancient wing/feather”

Archaeopteryx

ArchaeopteryxThermoregulation

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?