A graveyard of ancient crocodiles has revealed that the world was once home to a veritable menagerie of crocs of various sizes, shapes and fearsome forms. They ranged from a dog-like crocodile to a supercroc that was so big it dined on dinosaurs.
Palaeontologists have unearthed five new crocodile species that lived with the dinosaurs about 100 million years ago until they too became extinct about 64 million years ago.
Professor Paul Sereno of Chicago University and his colleagues discovered the dinosaurs while excavating remote sites in the Sahara desert, which was once part of the ancient southern continent of Gondwana and enjoyed a warm, moist climate similar to present-day Florida.
The finds show that these large reptiles once consisted of a far more diverse range of species than can be seen from today's crocodiles and alligators. They included a crocodile with dagger-like teeth that stuck out like the tusks of a boar and another with a snout shaped like a duck's bill.
Professor Sereno said that many of the fossilised jawbones and skulls were found on the surface of remote, windswept stretches of rock and dunes in the deserts of Niger and Morocco – a far cry from the lush plains and river valleys that had existed there when the dinosaurs ruled the land.
"These species open a window on a croc world completely foreign to what was living on northern continents," said Professor Sereno, whose discoveries were filmed for a documentary to be shown tomorrow night on the National Geographic Channel.
In 2001, Professor Sereno led an expedition to the same area that uncovered fossilised bones belonging to the largest crocodile ever discovered, an eight-tonne, 40ft giant called Sarchosuchus imperator – "flesh crocodile emperor" – which was said to be so large that it not only walked with dinosaurs, it ate them.
The finds show that crocodilians exhibited a fascinating array of forms and may even have walked "upright" with their legs below their bodies and their bellies off the ground, rather than their limbs jutting out to the side like present-day crocs and alligators.
"My African crocs appeared to have had both upright, agile legs for bounding overland and a versatile tail for paddling in water. Their amphibious talents in the past may be the key to understanding how they flourished in and ultimately survived the dinosaur era," Professor Sereno said.
One of the most surprising elements of the discovery turned out to be the immense diversity of the crocodiles that once lived in what is now the Sahara desert. Along with the boarcroc, duckcroc and dogcroc, the scientists found a 3ft long ratcroc with a pair of buckteeth in the lower jaw, and a fish-eating crocodile with an immense, pancake-flat skull filled with spiked teeth.
"We were surprised to find so many species from the same time in the same place. Each of the crocs apparently had different diets, different behaviours. It appears they had divided up the ecosystem, each species taking advantage of it in is own way," said Professor Hans Larsson of McGill University in Montreal.
The scientists carried out CT scans of the skulls to create digital and physical casts of their brains. The results suggest that dogcroc and duckcrock had broad, spade-shaped forebrains that are different to the brains of present-day crocodiles.
"They may have had slightly more sophisticated brain function than living crocs because active hunting on land usually requires more brain power than merely waiting for prey to show up," Professor Larsson said.
Ancient crocodiles first evolved abut 240 million years ago but modern crocodiles first appeared 80 million years ago. Only 23 species of crocs, alligators and caimans survive today, and many of them are endangered.