Advertisement.

EnchantedLearning.com is a user-supported site.
As a bonus, site members have access to a banner-ad-free version of the site, with print-friendly pages.
Click here to learn more.

ad
(Already a member? Click here.)

ZoomDinosaurs.com
DINOSAUR ANATOMY AND BEHAVIOR
General Anatomy Size Teeth Herds, Packs Offense Defense Reproduction, Nests & Eggs Blood Pressure
Skeleton Tails Brains Male or Female? Skin Diet Locomotion Life Span Hot or Cold Blooded?

HOT-BLOODED OR COLD-BLOODED?

The debate about whether dinosaurs were hot- or cold-blooded is quite controversial. It used to be assumed that dinosaurs were cold-blooded like their reptile ancestors. Some paleontologists have recently argued that at least some dinosaurs were fast, active, competed against hot-blooded mammals, lived in cool areas, were related to birds, and therefore were endothermic (generating their own body heat, or hot-blooded).

Definitions:
  • Hot-blooded animals (homeotherms) generate heat internally and maintain a relatively constant body temperature (higher than the average temperature of the environment). Examples include the mammals (including people) and birds. A related term is endothermy, meaning that an organism generates their own heat to maintain body temperatures.
  • Cold-blooded animals (poikilotherms) have a body temperature that changes with external conditions. Examples include reptiles, who need to sun themselves in the morning to warm up, and then protect themselves in the midday heat. A related term is ectothermy, meaning that an organism uses external heat sources (and heat sinks) to regulate its body temperature.

Dinosaurs evolved from cold-blooded animals (the reptiles) and evolved into warm-blooded animals (the birds). All dinosaurs, however, were not the same, and perhaps their physiologies differed also. The huge dinosaurs and the tiny dinosaurs might have used different heat-regulation strategies, just as they used different strategies for other aspect of living. A good argument for this is found among modern mammals. Although warm-blooded, there are some mammals (monotremes, the egg-laying mammals like the duck-billed platypus) whose metabolisms are close to being cold-blooded.

Scipionyx, a Cold-Blooded Theropod?
Scipionyx samniticus was a Cretaceous period theropod (from about 113 million years ago), perhaps a maniraptor. It is known from a single, extremely detailed specimen of a hatchling that includes fossilized soft tissues, including muscles and internal organs. It was 9.5 inches (24 cm) long and had a very large head.

John A. Ruben, a vertebrate paleobiologist from Oregon State University, used an 80-watt ultraviolet (UV) lamp to help reveal outlines of Scipionyx's fossilized internal organs. Ruben found that the position of Scipionyx's colon (intestines) and liver were similar to that of modern crocodilians (which are cold-blooded), and unlike that of birds (which are warm-blooded). The position of the liver also gives information about the lungs, since a muscle that runs by the liver helps the lungs to expand and contract in crocodilians. Scipionyx probably had reptilian-style lungs (and not highly efficient bird lungs).

Although Ruben's work is not absolutely conclusive, it looks like the small theropod Scipionyx may be cold-blooded. For more information on Ruben's work, see the January 22; 283: 514-516 (1999) issue of the magazine Science.

A Fossilized Dinosaur Heart Found
ThescelosaurusRecently, a fossilized dinosaur heart was discovered. This powerful, four-chambered pump belonged to Thescelosuarus, a lated Cretaceous Period ornithopod (a plant-eater). This 66 million year old heart has recently been analyzed -- it may have four chambers and a single aorta, which is quite different from existing reptiles, but is similar to modern warm-blooded animals. However, Tim Rowe, Earl McBride and Paul Sereno think that the "heart" is an ironstone concretion.

If true, the discovery of a four-cha,bered heart suggests not only that Thescelosaurus may have been warm-blooded, but that many other dinosaurs may have been warm-blooded as well. This is because we now perhaps have evidence of warm-bloodedness in both Ornithischia and Saurischia (the two major groups of dinosaurs, which diverged early in the Mesozoic Era). Thescelosaurus was an ornithischian; birds, which are known to be warm-blooded, are saurischians.

Heat-Regulating Devices: Some dinosaurs seem to have had heat regulating structures on their bodies. For example, Spinosaurus and Ouranosaurus had large sails on their backs, and Stegosaurus had numerous plates. These devices were probably used for the collection and dispersion of heat. This suggests that they needed these structures to regulate their body heat and that they were cold-blooded.

Basically, it's difficult to answer this question with today's knowledge. There are a lot of people thinking about this, and we'll be hearing a lot more about it soon.

ZoomDinosaurs.com
DINOSAUR ANATOMY AND BEHAVIOR
General Anatomy Size Teeth Herds, Packs Offense Defense Reproduction, Nests & Eggs Blood Pressure
Skeleton Tails Brains Male or Female? Skin Diet Locomotion Life Span Hot or Cold Blooded?


Enchanted Learning®
Over 35,000 Web Pages
Sample Pages for Prospective Subscribers, or click below

Overview of Site
What's New
Enchanted Learning Home
Monthly Activity Calendar
Books to Print
Site Index

K-3
Crafts
K-3 Themes
Little Explorers
Picture dictionary
PreK/K Activities
Rebus Rhymes
Stories
Writing
Cloze Activities
Essay Topics
Newspaper
Writing Activities
Parts of Speech

Fiction
The Test of Time
iPhone app
TapQuiz Maps - free iPhone Geography Game

Biology
Animal Printouts
Biology Label Printouts
Biomes
Birds
Butterflies
Dinosaurs
Food Chain
Human Anatomy
Mammals
Plants
Rainforests
Sharks
Whales
Physical Sciences: K-12
Astronomy
The Earth
Geology
Hurricanes
Landforms
Oceans
Tsunami
Volcano
Languages
Dutch
French
German
Italian
Japanese (Romaji)
Portuguese
Spanish
Swedish
Geography/History
Explorers
Flags
Geography
Inventors
US History

Other Topics
Art and Artists
Calendars
College Finder
Crafts
Graphic Organizers
Label Me! Printouts
Math
Music
Word Wheels

Click to read our Privacy Policy

E-mail


Enchanted Learning Search

Search the Enchanted Learning website for:



Advertisement.



Advertisement.



Advertisement.


Copyright ©1997 EnchantedLearning.com ------ How to cite a web page