howting so as we previously discussed dinosaurs were likely mesotherms and were quite active animals creating much of their own body heat through their metabolism we saw evidence for this High metabolic rate in the micro structure of their bones and the size of the blood vessels preserved in those bones however being so large actually put dinosaurs at risk of overheating and some of the strange features we use to identify different types of dinosaurs might actually be adaptations for dealing with this unique issue so how big were dinosaurs really in the last segment you thought about the linear dimensions of dinosaurs as linear Dimensions increase the volume and mass of the organism increases even faster animals with large mass tend to have higher metabolic rates and thus have different physiological needs more massive animals also tend to live longer and more massive Birds tend to have larger egg clutches sizes thus understanding the size of an extinct animal can tell us a lot about its ecology lifespan and reproductive biology so you can imagine that paleontologists are quite eager to determine the various masses of dinosaurs to understand more about their biology the earliest ways of making estimates of dinosaur Mass actually use dinosaur towin models the models approximated the three-dimensional shape of the dinosaur and so determining the volume of those models and and then scaling up to actual size could give you an idea of the total volume of a dinosaur then one must estimate the relative amount of bone muscle and other tissues the animal would have had in life and use the average density of those materials to calculate the mass today we do something similar but instead of burying a toy in the sand to determine its volume we use digitally reconstructed skeletons and fill in the soft tissues using geometric solids to estimate volume this method however is best applied to a complete skeleton and many of our largest dinosaurs are represented by very few bones making it very challenging to reconstruct their body mass in this way there is also uncertainty in the amount of the different types of soft tissue a dinosaur should have and different estimates will yield different masses another way we estimate mass is by looking at the size of the Lim bones like the humorous and the femur and then calculating what the mass would be based upon analogy to living organisms in this diagram the light gray X's are data from living mammals and from living diapsids and shows the relationship between limb bone circumferences and total body mass on a log scale we can then use that scaling relationship represented by the black line to estimate the total mass of a dinosaur based upon measurements made on its limb bones as you might have expected the most massive dinosaurs are our sorop pods and the smaller dinosaurs are often therapods this method requires less knowledge of the overall shape of the dinosaur and relies on comparison to Modern animals however relying on a single bone can also lead to error particularly if that bone is more robust than needed to support the weight of the animal or in cases where the limbs are adapted to functions that extend beyond simple weight support given this uncertainty we will often calculate the mass in multiple ways to achieve a range of possible masses comparing the methods is important for testing our assumptions about how dinosaurs looked and behaved regardless of our method of estimation however it is clear that some dinosaurs were very large and this posed some physiological challenges particularly because the the bodies of animals tend to heat up much faster than they can cool down a lot of the metabolic energy produced by an organism goes to generating Heat and the surface area relative to the volume of an animal regulates how readily it can exchange heat with the environment small mammals like mice and rabbits have very high surface area to volume ratios and they lose heat very rapidly thus small dinosaurs wouldn't have had an overheating problem instead they have had the issue of losing heat too fast to meet metabolic demands large dinosaurs on the other hand had very low surface area to volume ratios and had difficulty releasing heat to the environment with a large mass that could absorb and retain heat but could not shed it quickly arterial blood temperatures could rise high enough to damage sensitive brain tissue under the assumption that dinosaurs did not have a cooling system to low lower their blood temperature mathematical models of dinosaur body temperatures suggest their core temperatures could have risen as high as 48° C for context your body temperature is just under 37° C and we'd say you were ill with a fever at 38° and you'd be having a medical emergency at 40° in today's Birds body temperatures of 37° c are lethal except in some species specifically adapted to hot environments alligators and some lizards can survive body temperatures up to 39° but that is still lower than the 48° that the size and mass of a dinosaur suggests their bodies could have risen to either dinosaurs were able to tolerate much higher body temperatures than modern animals or they had a system to cool their blood appendages that stick out from in the body and have high surface area to volume ratios are often good heat exchange surfaces and so rows of plates on dinosaurs like stegosaurus and large fan-like sails made of elongated neural spines are often hypothesized to play a role in thermo regulation and they most certainly did play some role in dissipating heat however the question is more whether they were adaptations under selective pressure to serve a thermm regulatory function or if they were under selective pressures for a different function and just happen to facilitate some heat exchange also if extra extensions of the body were adapted for heat exchange we might expect them to have enhanced blood flow and to be highly vascularized so as to move heat from internal to the body to the surface the most important thing to keep cool is the brain and in large mammals today we see adaptations for reducing temperature temperes in the head for example elephants have large heavily vascularized ears to help cool the animal and the faces of giraffes are also sites of enhanced heat exchange some diapsids have regions in the mouth nose and around the eyes to help cool the blood before it gets to the brain some paleontologists have hypothesized that the long necks of sorap PODS were adaptations for Thermo regulation the long thin neck would give blood time to cool before reaching the head neck surface area increases with increasing metabolic rate in sorop pods which might imply that one of the advantages of a long neck was its function as a radiator having a long neck Works uniquely in sorop pods because they have such a small head that there isn't much weight on the end of the neck that needs support in dinosaur bones we can also see traces of veins on on their surfaces and infer how vast realized portions of the body were here this computed Tom tomographic scan of a dinosaur skull shows the canals in the bone where blood vessels used to be allowing us to estimate the amount of blood flow and determine its pathway through the head in this reconstruction of a depicus head we see oral and nasal blood vessels that pass through the nose and mouth where the blood can cool before it reaches the brain this means that even though the Torso of dioicus could reach very high temperatures the head would stay cool enough to function thus sorop pods may have had two strategies for keeping the brain cool a long neck that allowed some heat to dissipate from the blood before reaching the head and blood vessels within the head that led the blood on a path through the head that allowed it to cool even further large therapods had yet another strategy in the head these have highly enlarged an orbital finestra that are hypothesized to contain large vascularized air sacks that helped cool the blood head shields in large ceratopsians may have also played a role in thermo regulation and were highly vascularized as shown by the blood vessel grooves across the frill we can determine the temperatures of different parts of the dinosaur body using oxygen isotopic compositions of the bone the relative proportion of different isotopes of oxygen incorporated into biomineralized bones and dinosaurs varies with temperature thus by measuring the chemistry of the bones we can estimate the temperature of different parts of the body despite being an extremity portions of the frill were as warm as the rest of the body suggesting that warm blood was circulated to the area where it would have then lost heat across the large surface area this heat dissipation is supported by oxygen isotope measurements across the shield the edges of the frill had lower temperatures than the center showing that the blood did cool as it circulated across the shield this illustration also highlights the large regions around the nerys that likely contained a vast relized air sack used to cool the blood on the way to the brain like in the earlier therapod example the plates on stegosaurus have also been implicated as therm regulatory adaptations these plates were large flat and thin making them ideal heat exchange surfaces in addition vascular grooves and pitting on the scoots suggests they had a high amount of blood flow so some folks imagine these plates function much like elephant ears do to dissipate heat others have examined the vascular pits and realized that they don't actually line up with the external grooves on the plates meaning the blood vessels were not actually running on the external surfaces of the bones the external grooves instead reflect the way bones grew and the vascular Plumbing to the scoots were important for supporting blood growth and remodeling the authors reason that while the plates may have helped dissipate heat given their large surface area that their morphology was not adapted for this purpose thus the plates instead were likely important as a social display and to identify members of the species similarly alternative hypotheses have been put forth for ceratops in head Shields including functions in defense and an interspecific display in Triceratops the size of the horns and head Shield change with ontogeny and are very small in baby dinosaur but are proportionally much larger in adults perhaps the ontogenetic changes we see in the head shield in ceratopsians were not only useful for identifying adults of the species but also served to add cooling capacity to the head as the body grew larger and needed more surface area for thermal regulation as we saw in previous segments dinosaur size changed a lot through ontogeny and the core body temperatures of the dinosaurs would thus also have changed thyy driving different metabolic and anatomical needs to maintain a constant body temperature through the dinosaur's lifetime many aspects of dinosaur morphology were certainly multifunctional and the relative importance of features like the Triceratops frill to therm regulation intraspecific display to find mates protection during combat or muscle attachment is difficult to determine efficiency in any or all all of these functions would have enhanced reproductive Fitness and sometimes a feature that is acted upon by natural selection due to its role in one function can serve other functions as well thus when interpreting the Adaptive purpose of dinosaur features we must be cautious and remember that a given feature can serve many functions finding support that something like a catopian frill played a role in thermal regulation does not mean that it could not have served other important functions as well big dinosaurs had lots of physiological problems to solve and their Anatomy reflects many layers of adaptations that allow them to pass their genes to the Next Generation