Submitted by Xerrostron t3_xtuh86 in askscience
ResponsibleAd2541 t1_iqtz78j wrote
Reply to comment by regular_modern_girl in How much does the size of an animal impact whether it is cold or warm Blooded? by Xerrostron
Wouldn’t a larger body mass mean that you cooled off more slowly and in principle I don’t know if it would be much of a problem if you were a dinosaur to maintain a reasonable body temperature.
regular_modern_girl t1_iqub47l wrote
I think it depends on a lot of factors. In general, I believe that adipose tissue (fat) retains heat better than a lot of other tissues, so I think it depends somewhat on an organism’s bodily composition. For ectotherms, they do need circulation to distribute warmth around to all their tissues, and a bigger body means that process naturally is going to take somewhat longer. This is part of why crocodiles (which in many cases are really big animals) are all in aquatic sit-and-wait predatory niches in their surviving forms, as they can be huge but still relatively sluggish and spend a lot of time basking, because they just need enough energy to strike out hard when the moment is right, they don’t need to pursue prey, etc. There used to be fully-terrestrial predatory lineages of crocodilians, but they were in general not quite as big and were built very differently, being generally lean and long-legged for pursuing land-based prey (they were probably a lot like big monitor lizards like Komodo dragons in terms of the niche they occupied and how they hunted, and they were probably similarly limited to being diurnal hunters in hot climates).
Like I know that, at least for big predatory dinosaurs, the assumption that they were ectothermic like living reptiles was long a source of confusion, to the point where (prior to the theory that dinosaurs were probably mostly or entirely warm-blooded) a number of paleontologists forwarded the idea that dinosaurs like T. rex were more likely scavengers than active hunters, because it was just too hard to imagine them being able to relentlessly pursue prey with that kind of bulk if they were cold-blooded.
Clearly, it isn’t a complete barrier against getting really big, as plenty of very large presumably cold-blooded creatures have existed over time (like I believe that most Mesozoic marine reptiles like ichthyosaurs and mosasaurs are assumed to have been ectotherms, since they came from older diapsid lineages that hadn’t evolved endothermy—in fact, mosasaurs seem to have literally been gigantic marine lizards, related to monitors—and they were still able to get pretty massive in some cases, although still not quite as big as the largest whales), but I also think it probably indicates something that the very biggest of animals to ever live all seem to have been warm-blooded, and that’s definitely not that endothermy itself is a barrier to great size, quite the opposite in fact.
Moonduderyan t1_iqup6kk wrote
Endotherms rely on circulation as well, that's the whole way they distribute heat across the body. Our heat moves across the body all the time. It's why our hands and feet get cold, because our body moved the heat to the vital organ when outside temperatures are relatively colder. Adipose tissue is only reliable so long as you can actually get heat to the tissue.
Also weren't there terristrial crocodiles which were active chase predators such as boverisuchus?
Where did you the info that marine reptiles didn't regulate their body temperature? I just found a paper stating the marine reptiles probably controlled their body temperature.
regular_modern_girl t1_isd3ydw wrote
There were terrestrial predatory crocodiles, but they weren’t anywhere near the size of large predatory dinosaurs (nor even present day saltwater crocodiles, let alone the even larger aquatic crocodiles that existed in the Mesozoic).
Last I’d heard, most marine reptiles from the Mesozoic were not assumed to be warm-blooded because non-archosaur diapsids like that simply weren’t assumed to have evolved endothermy, but I haven’t really kept up on speculation about that, so it’s possible the consensus has shifted with at least some of them (as obviously dinosaurs themselves have only been widely-assumed to be endothermic relatively recently).
Viewing a single comment thread. View all comments