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A mesotherm (from
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
μέσος ''mesos'' "intermediate" and ''thermē'' "heat") is a type of animal with a thermoregulatory strategy intermediate to cold-blooded
ectotherm An ectotherm (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...
s and warm-blooded
endotherm An endotherm (from Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions inste ...
s.


Definition

Mesotherms have two basic characteristics: # Elevation of body temperature via metabolic production of
heat In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these ...

heat
. # Weak or absent metabolic control of a particular
body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a sy ...
. The first trait distinguishes mesotherms from
ectotherm An ectotherm (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...
s, the second from endotherms. For instance, endotherms, when cold, will generally resort to
shivering Shivering (also called shuddering) is a bodily function in response to cold and extreme fear Fear is an intensely unpleasant emotion Emotions are mental state, psychological states brought on by neurophysiology, neurophysiological change ...
or metabolizing
brown fat Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue White adipose tissue (WAT) or white fat is one of the two types of adipose tissue Adipose tissue, body fat, or simply fat is a loose connective ...
to maintain a constant body temperature, leading to higher
metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cell ...
s. A mesotherm, however, will experience lower body temperatures and lower metabolic rates as
ambient temperature Ambient or Ambiance or Ambience may refer to: Music and sound * Ambience (sound recording)In filmmaking, ambience (also known as atmosphere, atmos, or background) consists of the sounds of a given location or space. It is the opposite of "silence" ...
drop. In addition, mesotherm body temperatures tend to rise as body size increases (a
phenomenon A phenomenon (; plural phenomena) is an observable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies ma ...
known as gigantothermy), unlike endotherms. This reflects the lower
surface area to volume ratio The surface-area-to-volume ratio, also called the surface-to-volume ratio and variously denoted sa/vol or SA:V, is the amount of surface area of radius has surface area . The surface area of a Solid geometry, solid object is a measure of the t ...
in large
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s, which reduces rates of heat loss. While
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
mesotherms are relatively rare, good examples include
tuna A tuna is a saltwater fish that belongs to the Tribe (biology), tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet ...

tuna
, lamnid sharks (e.g., the
great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of shark ...

great white shark
), the
leatherback sea turtle The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtle Turtles are an of s known as Testudines, characterized by a developed ma ...
, some species of
bee Bees are flying insects closely related to wasps and ants, known for their role in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyly, monophyletic lineage within the ...

bee
,
naked mole rat The naked mole-rat (''Heterocephalus glaber''), also known as the sand puppy, is a burrowing rodent native to parts of East Africa East Africa or Eastern Africa is the eastern subregion of the Africa Africa is the world's second-lar ...

naked mole rat
s, the
hyrax Hyraxes (from grc, ὕραξ, translit=hýrax, "shrew Shrews ( family Soricidae) are small mole-like mammals Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Ind ...

hyrax
, and the various monotremes. Historically, the same term was used by
Alphonse Pyramus de Candolle Alphonse Louis Pierre Pyramus (or Pyrame) de Candolle (28 October 18064 April 1893) was a French-Swiss botanist, the son of the Swiss botanist Augustin Pyramus de Candolle Augustin Pyramus (or Pyrame) de Candolle (, , ; 4 February 17789 Sept ...
to describe
plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel ...

plant
s that require a moderate degree of heat for successful growth. In his scheme, a mesotherm plant grew in regions where the warmest month had a mean temperature greater than and the coldest month had a mean temperature of at least .


Dinosaur thermoregulation

The
thermoregulatory Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
status of
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
s has long been debated, and is still an active area of research. The term 'mesothermy' was originally coined to advocate for an intermediate status of
non-avian dinosaur Dinosaurs are a diverse group of reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge ...
thermoregulation, between endotherms and ectotherms. A more technical definition was provided by Grady ''et al'', who argued for dinosaur mesothermy on the basis of their intermediate growth rates, and the empirical relationship between growth, metabolism and thermoregulation in extant
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
s. This viewpoint was challenged by D'Emic, who argued that because growth rates are sensitive to seasonal variation in resources, dinosaur maximum growth rates were underestimated by Grady ''et al''. Adjusting dinosaur rates upwards by a factor of two, D'Emic found dinosaurs to grow similarly to
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s, and thus were likely endothermic. However, sensitivity to seasonal variation in resources should be true for all vertebrates. If all vertebrate
taxa In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
were similarly adjusted, the relative differences in rates does not change. Dinosaurs remain intermediate growers and good candidates for mesothermy. Nonetheless, the dinosaur mesothermy hypothesis requires further support to be confirmed.
Fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

Fossil
oxygen isotope There are three known stable isotopes of oxygen (8O): oxygen-16, 16O, Oxygen-17, 17O, and Oxygen-18, 18O. Radioactive isotopes ranging from 11O to 26O have also been characterized, all short-lived. The longest-lived radioisotope is 15O with a hal ...
s, which can reveal an organism's body temperature, should be particularly informative. Recently, a study of
theropod Theropoda ( from Ancient Greek, Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three-toed limbs. Theropods are generally classed as a group of saurischian d ...
and
sauropod Sauropoda (), whose members are known as sauropods (; from ''sauro- This is a list of common affixes used when scientific name, scientifically naming species, particularly extinct species for whom only their scientific names are used, along wi ...

sauropod
isotopes offered some support for dinosaur mesothermy. Feathered theropods are probably the best candidates for dinosaur endothermy, yet the examined theropods had relatively low body temperatures . Large sauropods had higher body temperatures , which may be reflective of mesothermic gigantothermy. Future isotopic analysis of small, juvenile dinosaurs will better resolve this question.


See also

*
Heterothermy Heterothermy or heterothermia (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...
* Gigantothermy *
Poikilotherm A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
* Argentine black and white tegu#Warm-bloodedness


References

{{Reflist, 2 Thermoregulation