Mesozoic Lifestyles

Mesozoic Lifestyles

Prehistoric remains often tell amazing stories of how an animal lived and died. Among the more interesting are those that help to interpret the lifestyles of the many dinosaur species and their associates that lived from 250 million to 65 million years ago during the Mesozoic Era.

Crocodiles lived side by side with dinosaurs that played a large part in the daily crocodilian menu, as shown by the following tale re—created from their remains. During the early 1960s two 30—foot crocodile skeletons of the genus Parasuchus were found in an ancient floodplain deposit in central India. The remains were less than a meter apart and lying at such an angle that the crocodiles appeared to be in communication when they died. One may have been complaining to the other of the excruciating stomachache it was having, and the other, experiencing the same agony, understood completely. Their discomfort could have been related to the fact that within the rib cages of both skeletons of Parasuchus were the skeletons of the four—foot dinosaur Malerisaurus. Both of the Malerisaurus appeared to have been gobbled up at the same time.

From the evidence of the skeletons and the surrounding sediments, the scientists were able to reconstruct what had happened. The two dinosaurs were drinking side by side at the edge of a stream, unaware of the crocodiles lying submerged and preparing to strike. The predators grabbed the victims simultaneously, pulling them into the water, where they drowned. Four—foot dinosaurs were tidbits to the crocodiles, and they were swallowed whole almost immediately.

The most probable explanation for the simultaneous deaths of the crocodiles is that the skin of their victims was poisonous. Their Malerisaurus meals were followed by some agonizing moments for the Parasuchus. They writhed in torment briefly, twisting and turning, possibly even snapping at each other until the relentless pain was quieted by their death. They gradually sank into the soft bottom muds. Here the victims lay in close proximity, as if each were describing and comparing its demise the way it happened nearly 180 million years ago.

The most popular members of the dinosaur clan have always been the sauropods. No child's treatment of these ancient creatures would be complete without the lovable Brontosaurus (Apatosaurus), an almost generic dinosaur. The sauropods were by far the largest animals ever to walk the earth. As one paleontologist observed, "Sauropods were beasts of the size of whales, on legs of elephants, with tails of lizards, necks of giraffes, heads of horses and nostrils of tapirs." They were among the most successful of any dinosaur group.

The dentition of the sauropod dinosaurs indicates that their diet consisted largely of marsh plants, although the largest ones undoubtedly browsed on leaves they nipped off of large trees with their blunt teeth. To swallow they probably had to raise their heads and let gravity help the neck muscles. How strange it would have been to watch a herd of feeding sauropods! Rhythmically raising and lowering their heads, they must have resembled a battery of dredges.

The most remarkable characteristic of the sauropod dinosaurs is their size. A recent contender for the largest known sauropod species was discovered in New Mexico in 1985 and is currently being excavated. It appears to have been, from the tip of its tail to the nose, about 140 feet long and weighed anywhere from 60 to 90 tons. Scientists named it Seismosaurus because the ground must have shook when this great beast walked. A footprint of a Seismosaurus, or a near relative, was found in the area of the Paluxy River in Texas during excavations over 50 years ago. A famous photo of the find shows a boy about six years old taking a bath in the fossil footprint. It was almost bathtub size because when completely filled it held over 18 gallons of water.

Scientists have contemplated, with difficulty, just how much vegetation a full—grown adult Seismosaurus would eat. The dinosaur must have fed almost constantly, its long neck serving as a funnel that led to the huge body reservoir. The undersized head was like a rake, ceaselessly scooping and swallowing whatever vegetation was within reach. It did not chew its food; instead the Seismosaurus swallowed enormous numbers of plum—sized stomach stones (gastroliths) that served as teeth and ground up the food as it passed into the primary stomach. In the rib cage of the skeleton being excavated in New Mexico, over 230 of these stomach stones were found, all quite similar in size. Near the rib cage, however, was a stone the size of a large grapefruit. Scientists studying the specimen believe this could have been a death rock. Seismosaurus may have deliberately swallowed an oversized rock to add some vigor to its collection of internal "teeth."

This rock seems to have been too large and lodged in the throat of the beast, causing it to choke to death. A perfect case for the Heimlich maneuver, which unfortunately for this dinosaur would not be in use for another 154 million years!

Tyrannosaurus rex, king of the tyrant lizards, is among the best known of the carnivorous dinosaurs. It stood 16 to 20 feet tall, was nearly 50 feet long, and weighed well over six tons. Its jaws, at least three feet in length, were armed with numerous serrated teeth six to seven inches long. Although bipedal (two—footed), with its body held in a horizontal position it ran very fast. Toothy jaws agape, roaring in anticipation, it must have been a living nightmare for its prey. Encounters would have been, in most cases, short lived, and T. rex would feed.

Tyrannosaurus rex, although the largest carnivore to have walked on the globe, was not guaranteed an easy life. Far from it. In August 1990 the largest, most complete skeleton of T. rex was found in South Dakota. The bones indicate that it was a female, so she became Sue.

During her lifetime Sue suffered a number of major injuries. She must have engaged in a deadly fight with another tyrannosaur because one rib harbors the point of a tooth within an abnormal growth of bone, showing that the bone had healed after the bite wound. A hole in the skull and a lump on the lower jaw also represent healed wounds, possibly from the same fight.

Both legs were broken during her violence—prone life. The two fibulae must have been fractured on separate occasions, because she couldn't have survived two broken legs at once. One can easily theorize how the breaks occurred. Scientists know that a charging Tyrannosaurus rex could reach speeds rivaling those of a modern racehorse. As Sue bore down on her prey she unwittingly stepped into a depression or a hidden hole in the ground and was pitched headlong on her face, with a leg dangling from the sudden break. She managed to survive this type of mishap twice! It was noted that several of Sue's tail vertebrae were fused together. Because this was a common injury among large female dinosaurs, it most likely occurred during the mating process.

Just before Sue died she appears to have dined on the plant—eating dinosaur Edmontosaurus as several bones of this dinosaur were identified in her rib cage and were etched as if by stomach acid.

Sue met her death in a fight with another tyrannosaur. The left side of her skull shows definite injury from a heavy bite, and there is no sign of recovery. Sue's antagonist doubtless succumbed along with her, for her skeleton shows no major signs of any chewing on the bones. Her opponent probably staggered off some distance before it too lay down for the last time, about 75 million years ago.

Although incomplete, the sad tale of Therizinosaurus (scythe reptile) is worthy of note here. A few years younger than Sue, Therizinosaurus passed away about 70 million years ago when it went to a lake to drink. This dinosaur may have resembled a present—day anteater, for it had enormous claws that would have been useful for ripping apart insect nests.

Because it had no way of knowing that a large carnivore lay in ambush near the watering spot, this specimen of Therizinosaurus never finished its drink of water. Instead it fell prey to the carnivore and was almost completely consumed. Its few remains include parts of the forelimbs and hind limbs, flattened ribs, a tooth, and several enormous claws. Scientists have been able to speculate very little about this dinosaur, but they agree that it must have been gigantic. One of its foreclaws, preserved in the Museum of Paleontology in Moscow, measures a staggering 28 inches along the outside curve.

From the book: 
Petrified Lightning