As kids, we all liked to imagine scenes where big dinosaurs squared off against each other for gigantic battles - if you're young, imagination is like a Transformers movie, but without $100 million for special effects.  

Those battles rarely happened, if at all, goes a new hypothesis.    Dinosaurs became chickens in evolution (well, maybe) but they were already chickens at heart, say paleontologists at Ludwig-Maximilians-Universität (LMU) in Munich.

Dr. Oliver Rauhut and Dr. David Hone instead surmise that giant carnivores like Tyrannosaurus Rex preyed mainly on juvenile dinosaurs. "Unlike their adult and well-armed relatives these young animals hardly posed any risk to the predators," says Rauhut. "And their tender bones would have added important minerals to a theropod's diet. Now we hope for more fossils to be found that add new evidence to our hypothesis."

The 21st century has been a real disappointment for Tyrannosaurus Rex,  by far the most famous dinosaur. Not even recent finds of slightly bigger, and maybe even more terrifying,  species like Giganotosaurus could dent the aura of "T-Rex".

But if 'The King' turns out to be just a baby killer the party may be over.

There is extremely sparse direct evidence for the diet of predatory dinosaurs – stomach contents and coprolites – and the data show that juveniles or much smaller prey species were ingested and the latter were swallowed whole. Rauhut and Hone, who is now at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, therefore propose as a hypothesis that large predatory dinosaurs only as an exception attacked other large dinosaurs, but mainly fed on juveniles.

"Even modern predators prefer old and sick animals or unexperienced young individuals," states Hone. "These are an easy prey to bring down and the risk of injury for the predator is much lower. This strategy was probably the same in dinosaurs."

Another look at recent predators reveals an additional benefit of young prey: Crocodiles, the closest living relatives of dinosaurs, have extremely strong acids in their stomachs. They can completely dissolve the poorly ossified bones of young animals which adds important nutrients to the reptiles' diet. The fossil finds of juvenile dinosaurs that have been swallowed whole by theropods support the idea that dinosaurs might have profited from this as well.

Missing fossils, though, lend even more plausibility. "Finds of dinosaur nesting sites indicate that they contained large numbers of eggs which should have resulted in a high number of offspring," says Rauhut. "But little of this is reflected in the fossil record: Juvenile dinosaurs are surprisingly rare – maybe because many of them have been eaten by predators. Hopefully there will soon be more evidence to help us really understand the theropods' hunting behavior."

Article:  David W. E. Hone and Oliver W. M. Rauhut, "Feeding behaviour and bone utilization by theropod dinosaurs", Lethaia online, 3 August 2009