One Day in the Western Interior Sea...... Copyright © 2000-2009 by Mike Everhart Last updated 08/02/2009         Used with permission of Dan Varner; Copyright © Dan Varner

The female mosasaur swam slowly through the calm, warm water of the Inland Sea. Three of her week-old young swam cautiously on either side and slightly above her rear flippers. A fourth baby, the smallest of the litter, had not been able to keep up with the steady pace of the mother. When it dropped behind two days ago, it had been quickly eaten by a large fish. The others were instinctively alert to any signs of predators and kept as close as possible to their mother’s scaly side. They also stayed well behind her head and out of the reach of her toothy jaws. Even though she was their mother, her feeding instinct was very strong. A mistake in recognition of her own offspring could be instantly fatal.

For the last several days, the mother mosasaur had guided her young through areas of the ocean that teemed with schools of small, soft bodied prey. The young mosasaurs had been accomplished hunters almost from the moment of birth, and had easily caught enough of the squid to keep their bellies full. If they were to survive, it was essential that they eat as much and as often as they could. They were growing quickly but still would be vulnerable to attacks by the other predators in the ocean for many months to come.

The mother mosasaur paused briefly in the water to rest and floated motionless in the calm sea. Her young slithered part up way on her back to take advantage of relative safety of her large body. Few other animals in the ocean, except mosasaurs of her own species, could match her 30 foot length.

For her young, it was a rare chance to absorb warmth from the sun that shined hotly in the clear, blue-white sky. While the mother mosasaur rested with her eyes and nose barely above water, her predatory senses were very active. Hunger gnawed at her belly. She was used to eating often and well, and her recent pregnancy had all but depleted her body’s energy reserves.

Dimly aware that she couldn't hunt her usual prey without endangering her offspring, she had curbed her urge to stalk the schools of large fish that she sensed were nearby. She had eaten only twice in the last three days; first the bloated carcass of a small shark and then a large, swimming bird that had blundered across her path.

As she watched and waited, her senses detected the commotion caused by several large fish feeding on a school of smaller fish. She could 'feel' the vibrations that carried through the water as the smaller fish leaped into the air to avoid the jaws of their attackers.

For a few moments, she didn’t move, but the urge was too great. With a powerful flick of her long, sinuous tail, she started her large body moving in the direction of the feeding frenzy. Startled by her sudden movement, her young splashed awkwardly into the water and then swam swiftly to her side. Her movements were efficient and silent, swimming just below the surface. Experience had taught her that hunting was more successful when her prey was unaware of her presence until it was too late to get away. The noise created by the smaller fish in their panic to escape would conceal her approach from the larger fish. They were her intended prey. One would fill her belly and satisfy her hunger for a day or so.

As she got closer to the commotion, she sensed rather than saw the larger fish darting into the turbulence caused by the panic of their smaller prey. Moments later, a long, silver torpedo emerged from a cloud of bubbles and almost ran into her open mouth. Too late, the fish recognized the danger and tried to turn away. With a swift lunge, the mosasaur’s jaws snapped closed just behind the head of the fish. The water turned red with blood and a shower of scales glittered in the sun lit water as the fish struggled briefly and then went limp.

Waiting a moment to make certain that the fish was dead, the mosasaur then opened and closed her jaws in rapid movements to position her victim headfirst to be swallowed. Once the fish’s head was inside the mosasaur’s mouth, two rows of sharp teeth on the roof of the mouth helped hold the fish in place as the lower jaw flexed and pulled it deeper inside. Once the fish was securely started down the mosasaur’s throat, she raised her head out of the water and used gravity to help her swallow her large meal. When the fish’s large bony tail was the only part remaining, she closed her mouth, and shook her head sharply. With an audible snap, the tail broke off at the base and skipped across the water.

Again, the mosasaur was almost motionless in the water as she finished swallowing the large fish. Her young milled nervously around her flanks, uncertain what to do in all the confusion. She had almost forgotten about them in her drive to satisfy her hunger.

The feeding frenzy had attracted other predators to the area. A large shark moved swiftly into the fray, sensing the same signals that the mosasaur had reacted to. As it got closer, the shark detected the faint traces of blood in the water. Seeing three small objects that struggled at the side of the larger stationary one, it raced upward from the depths.

The mother mosasaur and her young sensed the pressure wave generated by the approaching shark but it was too late to react. As the babies turned to flee, the shark’s jaws closed viciously across the muzzle and neck of the largest one. The sharp, blade like teeth of the shark sliced easily through the small animal’s skull and cervical vertebrae, killing it instantly.

With the body of the young mosasaur in its mouth, the momentum of the shark carried it into the side of the mother mosasaur. The shark was less than half the length of the mosasaur and no match for the larger animal in a fight. As the mosasaur turned almost double on itself, slashing with open jaws at the flank of the shark, the shark flicked its tail and swam swiftly away with the little mosasaur held securely in its mouth. The mother mosasaur pursued the shark for a short distance, and then slowed so that her two remaining young could catch up.

Swimming quickly out of danger, the shark wolfed down the carcass of the little mosasaur. Hours later, it would regurgitate the some of the indigestible skull bones.

Lower and upper views of a partially digested muzzle of a small mosasaur from the Smoky Hill Chalk, Gove County, Kansas, as found by Tom Caggiano on May 3, 1997. The cut ends of the premaxillary and both maxillaries show erosion by stomach acid. All the teeth have been dissolved away.