Bizarre Dinosaurs

AMARGASAURUS
X-FACTOR: Double row of spines on neck and back
WHEN: 130-125 million years ago
WHERE: Argentina
Like the tail fins on a 1959 Cadillac, a bizarre double row of spines extending from the vertebrae of Amargasaurus may have served little purpose other than to turn heads. Since the discovery of the sauropod was announced in 1991, paleontologists have pondered the function of the delicate bony rods, which would have offered limited defense at best against predators. Perhaps the bony rods were covered with skin, forming sails similar to those on some living lizards. If so, Amargasaurus might have flushed blood into the sails to help cool its body. But their likely function, says Smithsonian paleontologist Hans-Dieter Sues, was to attract mates or intimidate rivals. “In evolution nothing is really bizarre. Every structure makes perfectly good sense to the organism. In the case of extinct animals the challenge is to identify what the purpose might have been.”


CARNOTAURUS
X-FACTOR: Bull horns, tiny arms
WHEN: 82-67 million years ago
WHERE: Argentina
Consider the evolutionary hand dealt to Carnotaurus, or “meat-eating bull”: a big, bad, but seemingly underequipped predator, as if nature had set out to design a perfect killing machine but ran out of funding. Powerful jaws and long, agile legs suggest a highly mobile hunter prowling the lakeshores of what is now Patagonia. Its skull, constructed like a battering ram, features a stout pair of horns. Yet accompanying this formidable hardware are tiny arms (even more stunted than the famously puny arms of Tyrannosaurus rex) and surprisingly small teeth. Some scientists, like University of Chicago paleontologist Paul Sereno, envision Carnotaurus and its kin as dinosaurian hyenas—fleet of foot and short-snouted to track down and gnaw on carcasses. “Who needs arms for that?” he asks.


MASIAKASAURUS
X-FACTOR: Inscrutable teeth
WHEN: 70-65 million years ago
WHERE: Madagascar
The mouth of Masiakasaurus speaks to how this German shepherd-size meat-eater survived in the river basins of northwestern Madagascar, near the end of the dinosaurs’ reign. But what is it saying? Stony Brook University paleontologist David Krause led the team that found the remains, including part of the lower jaw. Masiakasaurus has long, conical front teeth with hooked tips that curl out of its mouth—unique among theropods—while its back teeth are more typically blade-like and serrated. So how did it use such a specialized mouth? “Our best guess is the teeth up front were used to stab small prey, perhaps mammals, lizards, and/or birds,” says team member Scott Sampson of the University of Utah, “and the teeth at the rear of the jaw were then used to tear up the kill.” Despite its formidable dentition, Masiakasaurus was likely prey itself for crocs and other large carnivores, like the 20-foot-long (6 meters) theropod Majungasaurus, with which it shared territory. Against such monsters, its best defenses would have been speed and agility.

-National Geographic-