Within the reptilian world, many of these cold-blooded creatures lack a physiological bodily feature known as thermoregulation. This is what allows living creatures to regulate their body temperatures on a homeostatic level. Because creatures like marine iguanas, or more scientifically known as Amblyrhynchus cristatus, lack thermoregulation, they are forced to maintain an internal temperature through other means. In the Galapagos Islands, these means are by basking in the sunlight to heat up whenever they are cold, or by bathing in the ocean water whenever they are too hot. Based on the behaviors that these creatures exhibit, a question that comes across is how often and for how long these creatures exhibit these behaviors.To get a clearer idea of how marine iguanas survive, we decided to understand their behavior mechanistically. We studied the behavior of marine iguanas in the Galapagos and how they react with the environment to regulate their body temperatures since they lack internal thermoregulation. The goal of our project is to model how marine iguanas use their environment to regulate their temperature and determine how long it takes to reach a new thermal steady-state at its ideal body temperature of 36°C after exiting the water. n order to achieve this goal, we decided to model a marine iguana after it has exited the ocean water and is then basking in the sun on a hot molten rock surface in order to heat up. Using results from already existing research combined with background information, we were able to support our analysis by validating the results of our model. Additionally, thorough pre-processing of the proper boundary conditions, governing equations, and estimations for our key variables were used in the model so that in processing, COMSOL was able to solve the heat transfer equations with the provided information. The main governing equation that was used was the heat equation, which is more explicitly defined later in the report. The boundary conditions used were that involving radiation, convection, and evaporation of water on the iguana’s surface as well as conduction of the molten rock through the iguana body. Through post-processing of the 3D heat exchange, the model will be able to provide us with insight as to how the temperature quickly rises in the core of the iguana, of which we defined as its large intestine. Through this analysis, we will be able to gain a better understanding of how external heat sources benefit creatures that lack internal thermoregulation in the natural world. The process being modeled involves an iguana heating itself from an initial temperature out of the water of about 26°C to its ideal body temperature at 36°C through means of external heat sources. Such sources come from heat conduction from the warm igneous rock beneath it, convection from the surrounding environment, and solar flux from the iguana’s sunbathing. The solar flux will take into account the changing sun angle and temperature with time as the process will last a few hours. The result will be an increase in temperature until a new steady-state is reached at the ideal body temperature of 35-37°C at the iguana’s core.