How did baby dinosaurs get enough nutrients to grow into giant beasts? Dinosaur "milk." At least that's the idea put forth in a new paper by Dr. Paul Else, a professor of health sciences at Australia's University of Wollongong.
The "milk" wouldn't have been the same as the white stuff mammals make. It would have been similar to what some birds produce and mouth-feed to their young.
“Pigeons, emperor penguins and flamingos all produce ‘milk-like’ substances from crop glands or glands of the oesophagus that they feed to their young through their mouths,” Dr. Else said in a written statement. “Since birds and dinosaurs share much in common I proposed that some dinosaurs likely used this feeding strategy.”
Dr. Else suggests that the so-called milk might have been full of antibodies, antioxidants, and growth hormone for the baby dinos. Similar nutrients have been found in "pigeon milk," which is essential for the growth and development of squab.
As Discover magazine notes, pigeon milk researchers "compared levels of gene expression between 'lactating' and non-milk-producing cells, finding a high level of activation in genes involved with antioxidant synthesis and cell growth. This helps explain why their 'milk' has high levels of antioxidants."
If Dr. Else is right, the milk-like substance would have formed in the dino's upper digestive tract, which is similar to birds' crop glands and different from mammals' mammary glands.
“Although I work at the molecular level, I’m basically a comparative physiologist," Dr. Else said in the statement, "and one thing that always struck me as unresolved about dinosaurs was how a dinosaur parent of several tonnes could feed young of only a few kilograms. It seemed obvious, a form of lactation, similar to that present in birds."
Specifically, Dr. Else turned to the plant-eating duck-billed hadrosaurs as his muse.
“Hadrosaurs were herd, site breeders with nest bound young fed by parents," he said. "The proposal is that rather than regurgitating partially fermented plant matter these dinosaur parents initially used lactation then progressed to plant regurgitation."
Have scientists uncovered any hard evidence for dino milk? Not exactly. The parts of the dinosaur responsible for secreting the "milk" would have been soft tissue, which wasn't preserved in the fossil record.
"I think, in my opinion, it will remain an idea," University of Sydney biologist Dr. Frank Seebacher told Australian Geographic, "but that's what science is made out of."
Dr. Else's paper was published Feb. 1, 2013 in The Journal of Experimental Biology.