I don't write often enough so I'll be the first to admit this is pretty unpolished, probably filled with holes.  But I was inspired last night and had to get something down (second draft)...

A herd gathered at the mountain lake, gratefully lapping at the edge of the water in the high grass. Some of the younger males had walked a little farther in and were play-fighting in the shallows. The largest, at 12 meters long, stood proudly on a rock watching his herd. In another age they would be given the name of "hadrosaur". They were hardy and adaptable, gentle and intelligent. Farther in the lake was a gigantic beast who lived in the water. Harmless but curious, it stretched its huge neck high above the water to observe the visitors. Everything seemed idyllic. A faint rumble, quite unnoticeable, sent a small ripple through the water. The long-necked host sunk down and disappeared in the depths of the lake.

At a rising along the top of the low valley, one of the hadrosaurs was keeping look-out. This one was the first to feel the rumble and thought a storm was coming. There was a second shake, and a third. As the pounding gathered speed it was accompanied by a deep sound. The look-out sounded a warning trumpet. The family began gathering itself to run. A mother rounded up her babies. Young and old escaped to the shelter of the trees.

But the adolescent males had been distracted by their play. One finally looked up and saw that they were alone. It was too late. The giant was near and would dine generously today. Now it advanced up and over the surrounding hillside, and pounded down to its prey. The ground shook feverishly. Batum. Batum. Batum. Batum.

Next, an excerpt from a master, with just a slight amendment. 

No doubt I now grew very pale; --but I talked more fluently, and with a heightened voice. Yet the sound increased --and what could I do? It was a low, dull, quick sound --much such a sound as a watch makes when enveloped in cotton. I gasped for breath --and yet the officers heard it not. I talked more quickly --more vehemently; but the noise steadily increased. I arose and argued about trifles, in a high key and with violent gesticulations; but the noise steadily increased. Why would they not be gone? I paced the floor to and fro with heavy strides, as if excited to fury by the observations of the men --but the noise steadily increased. Oh God! what could I do? I foamed --I raved --I swore! I swung the chair upon which I had been sitting, and grated it upon the boards, but the noise arose over all and continually increased. It grew louder --louder --louder! And still the men chatted pleasantly, and smiled. Was it possible they heard not? Almighty God! --no, no! They heard! --they suspected! --they knew! --they were making a mockery of my horror!-this I thought, and this I think. But anything was better than this agony! Anything was more tolerable than this derision! I could bear those hypocritical smiles no longer! I felt that I must scream or die! and now --again! --hark! louder! louder! louder! louder!

"Villains!" I shrieked, "dissemble no more! I admit the deed! --tear up the planks! here, here! --It is the beating of his hideous heart!"  Batum. Batum. Batum. Batum.