The illustration shows a Spinosaurus dinosaur in a wading heron-like hunting position, on top, and a swimming, aquatic predator position, on the bottom. Illustration by David Hone, et al./Palaeontologia Electronica
Jan. 26 (UPI) -- The giant dinosaur Spinosaurus, also known as the spine lizard, wasn't able to chase down fish or pursue marine reptiles.
Instead, a new analysis -- published Tuesday in the journal Palaeontologia Electronica -- suggests the enormous dinosaur hunted from the shoreline and shallows, like a heron, picking off unsuspecting prey.
There are only two known Spinosaurus species, each represented by only a few fossil specimens -- all of which have been unearthed from Late Cretaceous deposits in Africa.
The remains suggest Spinosaurus dinosaurs were nearly as large as the biggest theropods, challenging for the title of longest and largest predator to ever walk the Earth.
Since the genus' discovery in 1915, scientists have debated the dinosaur's modus operandi.
Many paleontologists have suggested the predator looked and behaved like a giant crocodile, but some have argued the massive dinosaur regularly swam and chased down aquatic prey.
"The biology and ecology of Spinosaurus has been troubling palaeontologists for decades," lead study author David Hone said in a news release.
"Some recent studies have suggested that it was actively chasing fish in water but while they could swim, they would not have been fast or efficient enough to do this effectively," said Hone, a senior lecturer at Queen Mary University of London.
To figure out what a day in the life of a Spinosaurus dinosaur might have looked like, researchers developed a sophisticated model to compare the genus' anatomical characteristics to those of a pair of predator prototypes -- an aquatic pursuit predator concept and a wading heron-like model.
While their analysis showed Spinosaurus could swim and certainly spent time in the water, it's skeletal characteristics contradicted the prototypical design of an aquatic pursuit predator in several important ways.
The model showed the giant dinosaur was best equipped for a wading heron-like lifestyle. Spinosaurus, the analysis showed, likely hung out in the shallows and along shorelines, waiting for fish and small marine prey to venture too close.
"Spinosaurus was a bizarre animal even by dinosaur standards, and unlike anything alive today, so trying to understand its ecology will always be difficult," said co-author Tom Holtz.
"We sought to use what evidence we have to best approximate its way of life. And what we found did not match the attributes one would expect in an aquatic pursuit predator in the manner of an otter, sea lion, or short-necked plesiosaur," said Holtz, a principal lecturer in vertebrae paleontology at the University of Maryland.
But while crocodiles are perfectly comfortable in the water, they aren't pursuit predators -- they ambush their prey, they don't chase them down. Crocs can out-swim most other land animals, but they can't swim nearly as well as species that spend all of their time in the water.
According to the study's authors, Spinosaurus dinosaurs were similar to crocs -- capable but not great swimmers. The giant predators had a proportionally shorter tail than crocodiles, likely inhibiting their swimming prowess.
"If Spinosaurus had fewer muscles on the tail, less efficiency and more drag, then it's hard to see how these dinosaurs could be chasing fish in a way that crocodiles cannot," Hone said.
While the latest research confirms the predator's affinity for the water, the research has offered a more nuanced portrait of the dinosaur's hunting strategy.
But the fossil record of the Spinosaurus genus remains sparse.
"Whilst our study provides us with a clearer picture of the ecology and behavior of Spinosaurus, there are still many outstanding questions and details to examine for future study and we must continue to review our ideas as we accumulate further evidence and data on these unique dinosaurs," Holtz said.
"This won't be the last word on the biology of these amazing animals," Holtz said.