The T.rex and other huge predatory dinosaurs were the masters of ‘energy-efficient walking’ at lower speeds, giving them an edge over faster prey species, study finds.
Researchers from Mount Marty College, South Dakota used data on limb proportions, body mass and the gait of 70 species of therapod dinosaurs.
They found that for small to mid-sized creatures longer legs helped them move faster but for the giants like T.rex longer legs helped them preserve energy.
Running is important for hunters, but they generally spend much more time roaming around in search of food – so don’t need to move as fast as smaller species.
Researchers from Mount Marty College, South Dakota used data on limb proportions, body mass and the gait of 70 species of therapod dinosaurs
The researchers applied a variety of methods to estimate each dinosaur’s top speed as well as how much energy they expended while moving around at a slower pace.
They found that evolution of legs in therapods wasn’t dictated by any one strategy, but appears to have evolved in different ways for large and small species.
Among smaller to medium-sized dinosaurs, longer legs appear to be an adaptation for faster running – beneficial for prey species.
For the real titans weighing over a tonne, top running speed is limited by body size, so longer legs instead are linked with low-energy walking.
The team found that the longer legs, when moving at lower speeds, significantly saved on the cost of daily foraging in terms of energy expenditure.
‘These savings, up to several tones of meat per year per individual, would dramatically reduce the need to engage in the costly, dangerous and time-consuming act of hunting,’ the authors wrote.
The authors suggest that speed was a major advantage for dinosaurs who needed to hunt prey and also escape predators.
Among giant theropods, the champions were tyrannosaurs like T. rex, whose long legs were well-adapted for reduced energy expenditure over time.
‘Size matters. Smaller theropods were both hunter and the hunted, so their lives were lived at high speed,’ the authors wrote.
‘For giants like T. rex, a top predator with no natural enemies, life was a marathon not a sprint.’
The team say the legs of a T.rex were disproportionately long compared to their arms and this could have been an evolutionary trait linked to greater foraging and hunting ability brought on by the extra height and efficiency in movement.
The researchers say the differences in speed and energy efficiency of limb size is also found in modern mammals.
‘In the largest mammalian land animal of today, white rhinos and elephants, top recorded speeds are much lower than those of smaller animals with shorter absolute limb lengths,’ they wrote.
The team say the legs of a T.rex were disproportionately long compared to their arms and this could have been an evolutionary trait linked to greater foraging and hunting ability brought on by the extra height and efficiency in movement
‘Their limbs are suspected to be adapted more for reducing locomotive costs at these sizes than fast running.’
They say it would still be possible for the giant species to run, but they were more efficient at walking than other species.
White rhinos have been recorded running at speeds over 24 miles per hour – similar to speeds scientists predict T.rex may have been able to move when running.
However, the authors say their biggest advantage was energy efficiency gained from walking at slower speeds using their long, powerful hindlimbs.
The authors say tyrannosaurids were on occasion living in groups and their primary prey was on average relatively small and elusive.
‘This paints a picture where efficiency would be a major evolutionary advantage,’ the authors wrote.
‘Beyond being the apex predator of the latest Cretaceous Laurasian ecosystems, the tyrannosaurids were amongst the most accomplished hunters amongst large bodied theropods.
‘We find that their anatomy, at once efficient and elegant, yet also capable of burst of incredible violence and brute force, lives up to their monikers as the tyrant kings and queens, of the dinosaurs.’
The research has been published in the journal Plos One.