Cold Blooded Dinosaurs: A Literature Review
Grady et al (2014) not only looked at growth rings in fossils, but also sought to estimate their metabolic rates by looking at changes in body size as animals grew from birth to adults.
The researchers compiled an unprecedented dataset on growth and metabolism from studies of hundreds of animals encompassing both extinct and living species, including cold- and warm-blooded creatures, as well as dinosaurs. In general, warm-blooded mammals, that grow about 10 times faster than cold-blooded reptiles, also metabolize about 10 times faster.
When the researchers examined how fast dinosaurs grew, they found that the animals resembled neither mammals nor modern reptiles, and were neither ectotherms nor endotherms. Instead, the researchers coined the …show more content…
term "mesothermic," to explain this intermediate metabolism. Echidna, tuna, and leatherbacks sea turtle are all mesotherms. Body size may play a role in mesothermy, because larger animals can conserve heat more easily.
Mesotherms have adaptations to conserve heat, but they do not boost their metabolic rate to stay warm.
"Gigantotherms like crocodiles rely on basking to heat up, so they are not mesotherms,"
Grady said to LiveScience. "Gigantotherms are slower to heat up and cool down, but if they rely on external heat sources like the sun, then they are not mesotherms. In general, mesotherms produce more heat than gigantotherms, and have different mechanisms for conserving it."
Mesothermy would have permitted dinosaurs to move, grow and reproduce faster than their cold-blooded reptilian relatives, making the dinosaurs more dangerous predators, and more elusive prey.
At the same time, dinosaurs' lower metabolic rates compared to mammals allowed them to get by on less food. This may have permitted the enormous bulk that many dinosaur species attained.
All in all, Grady suspected that where direct competition occurs, warm-blooded endotherms suppress mesotherms, mesotherms suppress active but cold-blooded ectotherms, and active ectotherms suppress more lethergic sit-and-wait ectotherms.
When D'Emic (2015) reanalyzed the Grady et al data using different techniques, he concentrated on two different aspects. First, the previous study had scaled yearly growth rates to daily ones as a way of standardizing comparisons; however the growth rates were especially underestimated for larger animals and animals that live in very stressful or seasonal environments.
Thus, doubling dinosaur growth rates, to help them standardize comparisons among animals that are actually not growing for about half the year, on average, and, second, adding birds
(which are known to be warm-blooded and are descendants of dinosaurs) into the calculations, the dinosaurs ended up with growth rates that lends more support that they
were warm-blooded, not occupants of a special, intermediate metabolic category; they fit right within the understanding of what it means to be a 'warm-blooded' animal.
It's possible that their large size made them warm just from the heat of their metabolism, the so-called ̳gigantotherm‘ theory. Calculations based on size indicate that if they were gigantotherms, the dinosaurs should be running even warmer than their teeth indicate — up to 113 °F (45 °C). Researchers believe that the dinosaurs probably had some behavioural or bodily mechanisms to regulate their body temperatures, when they reached adult size.
Regulating their body temperature could be one of the key factors in the massive success that dinosaurs enjoyed for more than 160 million years. Achieving such a level of energy utilization allowed dinosaurs to maintain activity for a longer time, while its sensory support led to complication and diversification of their behavioural repertoire (as well as that of birds and mammals later) facilitating the conquest of almost entire part of the biosphere that was suitable for living, even at high latitudes, places where cold-blooded creatures, like reptiles, aren‘t likely to be.
The researchers compiled an unprecedented dataset on growth and metabolism from studies of hundreds of animals encompassing both extinct and living species, including cold- and warm-blooded creatures, as well as dinosaurs. In general, warm-blooded mammals, that grow about 10 times faster than cold-blooded reptiles, also metabolize about 10 times faster.
When the researchers examined how fast dinosaurs grew, they found that the animals resembled neither mammals nor modern reptiles, and were neither ectotherms nor endotherms. Instead, the researchers coined the …show more content…
term "mesothermic," to explain this intermediate metabolism. Echidna, tuna, and leatherbacks sea turtle are all mesotherms. Body size may play a role in mesothermy, because larger animals can conserve heat more easily.
Mesotherms have adaptations to conserve heat, but they do not boost their metabolic rate to stay warm.
"Gigantotherms like crocodiles rely on basking to heat up, so they are not mesotherms,"
Grady said to LiveScience. "Gigantotherms are slower to heat up and cool down, but if they rely on external heat sources like the sun, then they are not mesotherms. In general, mesotherms produce more heat than gigantotherms, and have different mechanisms for conserving it."
Mesothermy would have permitted dinosaurs to move, grow and reproduce faster than their cold-blooded reptilian relatives, making the dinosaurs more dangerous predators, and more elusive prey.
At the same time, dinosaurs' lower metabolic rates compared to mammals allowed them to get by on less food. This may have permitted the enormous bulk that many dinosaur species attained.
All in all, Grady suspected that where direct competition occurs, warm-blooded endotherms suppress mesotherms, mesotherms suppress active but cold-blooded ectotherms, and active ectotherms suppress more lethergic sit-and-wait ectotherms.
When D'Emic (2015) reanalyzed the Grady et al data using different techniques, he concentrated on two different aspects. First, the previous study had scaled yearly growth rates to daily ones as a way of standardizing comparisons; however the growth rates were especially underestimated for larger animals and animals that live in very stressful or seasonal environments.
Thus, doubling dinosaur growth rates, to help them standardize comparisons among animals that are actually not growing for about half the year, on average, and, second, adding birds
(which are known to be warm-blooded and are descendants of dinosaurs) into the calculations, the dinosaurs ended up with growth rates that lends more support that they
were warm-blooded, not occupants of a special, intermediate metabolic category; they fit right within the understanding of what it means to be a 'warm-blooded' animal.
It's possible that their large size made them warm just from the heat of their metabolism, the so-called ̳gigantotherm‘ theory. Calculations based on size indicate that if they were gigantotherms, the dinosaurs should be running even warmer than their teeth indicate — up to 113 °F (45 °C). Researchers believe that the dinosaurs probably had some behavioural or bodily mechanisms to regulate their body temperatures, when they reached adult size.
Regulating their body temperature could be one of the key factors in the massive success that dinosaurs enjoyed for more than 160 million years. Achieving such a level of energy utilization allowed dinosaurs to maintain activity for a longer time, while its sensory support led to complication and diversification of their behavioural repertoire (as well as that of birds and mammals later) facilitating the conquest of almost entire part of the biosphere that was suitable for living, even at high latitudes, places where cold-blooded creatures, like reptiles, aren‘t likely to be.