I should clarify: dinosaurs were not exclusively endothermic in the way that some mammals are, but most dinos were almost certainly endothermic. Fossils suggest several things about many/most (though not all) dinosaurs: bones suggest high capillary density (like in mammals) and the presence of heat exchangers (like in mammals and birds). The large size of many dinos relative to modern day animals also supports endothermy (due to surface area:volume ratio). Unlike birds and mammals, however, dinosaurs did not appear to have nasal maxilloturbinals to reclaim water from exhaled air (a trait present in higher endotherms, eg mammals and birds), though these
were present in later dinosaurs.
Dinosaurs also had 4-chambered hearts (first discovered fossilized heart found in 1993, see link). 4-chambered hearts are found in mammals and birds and are most definitely characteristic of endotherms; among modern day reptiles, only the crocodile has a 4-chambered heart. The separation of oxygenated and deoxygenated blood allows for much higher metabolic rates, characteristic of endotherms.
Endotherms also have a much higher blood pressure in general than ectotherms. Considering the large size and volume of dinosaurs, they would have needed powerful hearts capable of producing such pressures (especially in dinosaurs that were very tall, eg brachiosaurs, ultrasaurs, apatosaurs, etc). The growth rates of dinosaurs were also similar to mammals and birds and required a high metabolic rate.
http://news.bbc.co.uk/2/hi/science/nature/720871.stm
http://www-tech.mit.edu/V120/N21/Dinosaur_21.21w.html
http://www.bbc.co.uk/dna/h2g2/plain/A590294
http://www.sciencemag.org/cgi/content/abstract/288/5465/503
http://www.nature.com/nature/journal/v412/n6845/full/412405a0.html
Sherwood, Klandorf, Yancey.
Animal Physiology. Belmont: Thomson, 2005.
Not sure why you’re trying to refute this one so much. Crocs are ectothermic, definitely, but they have a 4-chambered heart, very much a trait of endotherms. The extinct ancestors of crocs were also most likely endothermic.
Additionally, the isochores in the genes of endotherms (homeotherms) are generally very rich in GC-base pairs; very similar homeothermic isochores were found in crocodiles and turtles, as well as some species of alligator.
http://mbe.oxfordjournals.org/cgi/reprint/16/11/1521.pdf
http://www.springerlink.com/content/d31m7qn07176562m/
http://dml.cmnh.org/2005Apr/msg00204.html
This is incorrect. Camels don’t sweat as much as other mammals. There’s a big difference in the thermoregulatory physiology of camels vs other mammals.
Let’s take humans, for example. In humans, the normal core body temperature is 98.2 F. If the temperature falls below that, the body will warm it up back to 98.2 F. If the temperature goes above that, the body will sweat and increase vasodilation to cool back down to 98.2 F. In fact, in humans and most mammals, just going a degree or 2 above this temperature can cause serious illness (ever had a bad fever and been stuck in bed?).
Not so in camels. Camels use their fur, sweating, and inactivity (note that inactivity is an ectothermic trait) to stay cool. Even then, on a normal day, a camel’s core body temperature will rise
at least 2 degrees and it will not become ill. On a dehydrated day, a camel’s core body temperature can rise
6 degrees or more and it will still not become ill like a human; such large temperature ranges would kill humans and most other mammals. The camel has adapted to withstand these higher temperatures.
It is most definitely an ectothermic trait.
http://encarta.msn.com/encyclopedia_761553331_2/camel.html
http://www.jstor.org/pss/35544
http://en.wikipedia.org/wiki/Camel
Sherwood, Klandorf, Yancey.
Animal Physiology. Belmont: Thomson, 2005.
I think you’re confusing a lot of “endothermic” and “ectothermic” traits. A lot of things that endothermic mammals do, including us, are ‘ectothermic’. Examples include moving to warmer/colder areas (ie, going in the sun vs staying in the shade), vasoconstriction/vasodilation, and movement.
Endothermic attributes include the production of metabolic heat through
aerobic locomotory muscles (whereas many ectotherms are capable of short bursts of
anaerobic heat production), anatomic insulation, larger body size, countercurrent rete exchangers, maxilloturbinals, increased internal heat production through several mechanisms: decoupling movement from ATP production as seen in brown adipose tissue (
BAT), shivering, muscular activity, and perspiration.
Even the leatherback, which you mentioned, is not “completely endothermic”. It relies on many of those (including ectothermic mechanisms) to maintain its higher body temperature. Other turtles do this as well.
http://www.bio.davidson.edu/people/...s/2005/Fitzpatrick/An Endothermic Reptile.htm
Anyway, the reason I mentioned other animals (‘oranges’ when we were discussing ‘apples’) was to show that most animals are a combination of the two; they are heterothermic to some degree.
You seem to have quite an interest in biology, what level of study are you at? I enjoy discussing medicine and biology, and I pride myself on knowing a lot about it (or at the least, knowing where to look for answers).