Robert T. Bakker
Theories
Theories
--------

[thumb\|Mounted *[Gorgosaurus](/wiki/Gorgosaurus "Gorgosaurus")* skeleton with several bone injuries, from the "Dinosaur Mummy: CSI" exhibit at the [HMNS](/wiki/HMNS "HMNS"), Bakker on the right](/wiki/File:Dr._Bob_Bakker_with_Dino.jpg "Dr. Bob Bakker with Dino.jpg")
In his 1986 work *[The Dinosaur Heresies](/wiki/The_Dinosaur_Heresies "The Dinosaur Heresies")*, Bakker puts forth the theory that dinosaurs were [warm\-blooded](/wiki/Warm-blooded "Warm-blooded"). His evidence for this includes:
* Almost all modern animals that [walk upright](/wiki/Walk_upright "Walk upright") are warm\-blooded, and dinosaurs walked upright.
* The [hearts](/wiki/Heart "Heart") of warm\-blooded animals can pump much more effectively than the hearts of [cold\-blooded](/wiki/Ectotherm "Ectotherm") animals. Therefore, the giant *[Brachiosaurus](/wiki/Brachiosaurus "Brachiosaurus")* must have had the type of heart associated with warm\-blooded animals in order to pump blood up to its head.
* Dinosaurs such as *[Deinonychus](/wiki/Deinonychus "Deinonychus")* led a very active life, behavior which is much more compatible with a warm\-blooded animal.
* Some dinosaurs lived in northern [latitudes](/wiki/Latitudes "Latitudes") where it would have been impossible for cold\-blooded dinosaurs to maintain their body temperature.
* The rapid rate of [speciation](/wiki/Speciation "Speciation") and [evolution](/wiki/Evolution "Evolution") found in dinosaurs is typical of warm\-blooded animals and atypical of cold\-blooded animals.
* The hypothesized population ratios of predatory dinosaurs to their prey is a signature trait of warm\-blooded predators rather than cold\-blooded ones.
* Birds are warm\-blooded and evolved from dinosaurs; therefore, a change to a warm\-blooded metabolism must have taken place at some point. There is far more change between dinosaurs and their ancestors (basal [archosaurs](/wiki/Archosaur "Archosaur")) than between non\-avian dinosaurs and birds.
* A warm\-blooded metabolism is an evolutionary advantage for [top predators](/wiki/Top_predators "Top predators") and large [herbivores](/wiki/Herbivores "Herbivores"); if dinosaurs had not been warm\-blooded there should be fossil evidence of warm\-blooded animals evolving to fill these ecological niches. No such evidence exists; in fact, by the end of the [Cretaceous](/wiki/Cretaceous "Cretaceous"), mammals had become much smaller than their [stem\-mammal](/wiki/Synapsid "Synapsid") ancestors.
* Dinosaurs grew rapidly, evidence for which can be found by observing cross\-sections of their bones. Warm\-blooded animals grow at a similar rate.

Bakker is also a proponent of the idea that [flowering plants evolved](/wiki/Evolutionary_history_of_plants%23Flowers "Evolutionary history of plants#Flowers") because of their interactions with dinosaurs. He also believes the principal cause of extinction for all non\-avian dinosaurs was in fact a plague caused by invasive species crossing land bridges, retorting that, had the comet been large enough to kill off every non\-avian dinosaur, it would have also wiped out the various taxa known to have survived the K\-T extinction event.


What physical characteristics would confirm or deny that dinosaurs were warm-blooded?