Thin sections from scutes, taken from a fossil individual that had reached about 80 percent of its estimated adult size, show around 40 growth rings. This may mean that the animals took 50 to 60 years to reach their full size, says the Science study team.
This surprising longevity for a crocodilian suggests that Sarcosuchus attained its mammoth proportions by extending the duration of its growing time, rather than speeding up its rate of growth like most dinosaurs, says Sereno.
The new Sarcosuchus skulls have long snouts, comprising about 75 percent of total skull length, that are relatively broad compared to the needle nose of the living gharial (a modern crocodilian from India) and other ancient, narrow-snouted crocodilians like Pholidosaurus and Terminonaris.
Features in the skull and jaw link Sarcosuchus with Pholidosaurus and Terminonaris on the reptile family tree, according to the Science report. Yet unlike Pholidosaurus and Terminonaris, found in marine deposits, Sarcosuchus fossils come from river deposits, located about 100 miles from any ancient coastline.
These two crocodilian cousins were also specialized fish-eaters, while Sarcosuchus' anatomy points to a more generalized diet. Sarcosuchus had a substantial overbite, with its upper jaw overhanging the front teeth of the lower jaw. All the teeth of the lower jaw fit inside the upper tooth rows during a bite, rather than interlocking like the teeth of an exclusively fish-feeding jaw. Many of Sarcosuchus' teeth themselves are stout, smooth, and rounded, more suited for puncturing and crushing, says Sereno, who believes the giant may have included dinosau
Contact: Lisa Onaga
American Association for the Advancement of Science