National Geographic : 2009 Nov
SINCE THE 1990s, with my teams of researchers and students, I have combed the Sahara for evidence of creatures great and small that lived with the dinosaurs. My recent expeditions have revealed a treasure trove of crocs that populated Gondwana---the landmass that comprised today s southern continents---some 110 mil- lion years ago. Some were plant-eating dwarfs, others dinosaur-eating giants. Now their fossilized bones poke from parched Saharan landscapes, from windswept cli s in Morocco to barren dune elds in Niger. In some ways the fossils we have found remind me of the crocodilians alive today. All had textured skull bones and slow-growing body armor that absorbed heat while the animals basked in the sun. Some resemble mammals, with erect limbs for eet-footed pursuit of prey on land; teeth divided into incisors, canines, and postcanines; and forward-pointing eyes. Nicknames for the monstrous BoarCroc (le ) and the more diminutive three-foot-long RatCroc, DogCroc, and DuckCroc (right) capture those likenesses. So what were the lifestyles of these creatures? Were they landlubbers, or were they predominantly aquatic like their kin, the crocs that remain today? I found a clue on a trip to northern Australia. e freshwater crocs there run so fast they actually gallop. At full speed on land they move in a sinuous, up-and-down motion like a running mammal. At water s edge their tails sud- denly start to move side to side like a sh, propelling them underwater. I closed in on a new perspective. My African crocs appeared to have had both upright, agile legs for bound- ing overland and a versatile tail for paddling in water. Perhaps that lay at the crux of their evolution and drove the explosion of Cretaceous crocs across Gondwana that began some 145 million years ago. Under the noses of the dinosaurs, crocs evolved into ferocious predators and pint-size plant-eaters with a dual locomotor capability, best seen today in Australia s freshwater crocs. A distinctive survival strategy had emerged that even a monstrous asteroid could not completely erase. ---Paul Sereno STRANGE CROCS OF THE SAHARA RatCroc: A pair of buckteeth in the lower jaw may have allowed this croc to burrow in the ground for tubers. DogCroc: With differentiated teeth and a soft nose pointing forward, this omnivore may have escaped from predators on its lanky legs. DuckCroc: A broad, overhanging snout and hook-shaped teeth may have helped this croc catch small fish or worms in shallow water. WHEN CROCS ATE DINOSAURS Some 110 million years ago precursors of today's crocodiles ruled Earth. Explorer-in-Residence Paul Sereno brings a lost Cretaceous world to life on National Geographic Channel, November 21 at 9 p.m. in the U.S. Trace croc evolution with an interactive time line at ngm.com/crocs.