Mesotherm

Animals manage their body heat in different ways. Most animals are either ectotherms or endotherms. Ectotherms are often called cold-blooded. They do not produce much internal heat. Endotherms are often called warm-blooded. They produce heat to keep a constant temperature. Mesotherms represent a middle ground between these two strategies. A mesotherm is an animal with an intermediate thermoregulatory strategy. This means they fall between the two common ways of managing heat.

Mesotherms possess two specific biological characteristics. First, they elevate their body temperature through metabolic heat production. This metabolic production of heat distinguishes them from ectotherms. Second, they have weak or absent metabolic control over a specific temperature. This lack of control distinguishes them from endotherms. For example, endotherms can shiver to stay warm. They can also metabolize brown fat to maintain a constant temperature. This keeps their metabolic rates high even when it is cold.

In contrast, mesotherms react differently to the environment. When the ambient temperature drops, a mesotherm's body temperature will also decrease. Their metabolic rates drop along with the temperature. This is a major difference from endotherms. Mesotherms also exhibit a phenomenon known as gigantothermy. In these animals, body temperature tends to rise as body size increases. This happens because large animals have a lower surface area to volume ratio. This ratio reduces the rate at which they lose heat to the world.

We can see several examples of mesotherms in the world today. Many are found in the ocean, such as tuna and lamnid sharks. The great white shark is a well-known lamnid shark. The leatherback sea turtle is another example of a marine mesotherm. Some species of bees also use this strategy. On land, we find naked mole rats and hyraxes. The echidna is another living example of a mesotherm.

The term "mesotherm" has a different history in botany. A person named de Candolle used the word to describe plants. He referred to plants that require a moderate degree of heat. These plants grow in specific climate regions. They need a warmest month with a mean temperature above a certain point. They also require a coldest month with a specific mean temperature. This shows the word has been used to describe intermediate needs in different fields.

Scientists are currently debating the thermoregulatory status of dinosaurs. The term "mesothermy" was originally coined for this purpose. Researchers wanted to suggest that non-avian dinosaurs were intermediate. Grady and his team argued for dinosaur mesothermy. They based this on intermediate growth rates. They looked at the relationship between growth, metabolism, and thermoregulation. However, this idea was challenged by a scientist named D'Emic.

D'Emic argued that dinosaur growth rates were underestimated. He believed growth rates change based on seasonal resources. If you adjust dinosaur growth rates upward by a factor of two, they look like mammals. This would mean dinosaurs were likely endothermic. Yet, other scientists argue that all vertebrates are sensitive to seasonal resources. Even with these adjustments, dinosaurs still appear to be intermediate growers. This makes them strong candidates for mesothermy.

To solve this mystery, scientists use fossil oxygen isotopes. These isotopes can reveal the body temperature of an organism. Recent studies of theropod and sauropod isotopes provide some support for mesothermy. Feathered theropods are often thought to be endothermic. However, studied theropods showed relatively low body temperatures. Large sauropods had higher body temperatures. This might be caused by mesothermic gigantothermy. Future analysis of small, juvenile dinosaurs may finally resolve the question.