Washington, April 24 : The discovery that birds lack a tissue which is specialized to generate heat has lead scientists to speculate on the possibility of dinosaurs disappearing form the face of the Earth due to the same lack of heat-generating tissue.
This particular hypothesis has been mentioned in a paper published in the online journal BMC Biology, written by Stuart A. Newman, professor of cell biology and anatomy, Nadejda Mezentseva from New York Medical College, and Jaliya Kumaratilake from University of Adelaide, Australia.
Humans, like all mammals, have two kinds of adipose tissue, white fat and brown fat. While white fat is used for storing energy-rich fuels, brown fat generates heat. ibernating bears have a lot of brown fat, as do human infants, who have much more than adults, relative to their body size. Infants' brown fat protects them from hypothermia.
In fact, clinicians would like to find ways of making adult white fat behave more like brown fat so that we could burn, rather than store, energy.
While most mammals have a key gene called UCP1, which is responsible for the heat-generation function of brown fat, birds do not.
The researchers found they could induce a specific type of stem cell in chicken embryos to produce differentiated cells that are structured and behave like brown fat. These chicken cells can even activate a UCP1 gene if presented with one from a mouse.
The ability to produce brown fat evolved in a common ancestor of birds and mammals, but the ability to generate heat was lost in the group that gave rise to birds and lizards after it separated from the mammalian lineage.
The researchers found the lizard genome similarly lacks a UCP1 gene.
This strongly implies that dinosaurs, which diverged from birds even later than lizards, also lacked brown fat.