You are in the temperate floodplains of North America, 98 million years ago.

The air in the early Cretaceous lake was thick, humid, and smelled of sulfur and cycads. Navigating through the conifer undergrowth, you froze when you hear a guttural bellow—a deep, resonating hum that seemed to rattle the very air. The noise can be heard from miles, travelling far and wide. It’s a vibrating, infrasonic resonance that rattles your ribs more than it hits your ears—a mating call of a dinosaur.

You follow the source of the calls, eventually reaching a clearing, the entire area filled with flowering plants. Standing in the middle, near the edge of a stream, was an ankylosaur.

It is a 20-foot, two-tonne "monstrous heavy one," a living tank covered in thick plates and shoulder spikes, moving slowly but with undeniable power. Its back was a fortress of bony plates, a mix of raised scutes and smaller ossicles, all casting a deep shade in the morning sun. As it turned, you saw the key feature of this nodosaurid: a pair of enormous, spikes projecting from its shoulders, far larger than the surrounding osteoderms. It didn't possess the tail club of later ankylosaurs, but looking at those spikes, it didn't need one.

As you continue to watch mesmerized, the nodosaur pauses, lowering its armored head to the damp ground. It doesn't open his mouth; instead, it inflates its throat, rubbing its scaly chin against the mud. Then, it lifts its armored head up and made the same low-frequency, throaty rumble that seemed to vibrate through the ground beneath your feet. It wasn't just bellowing; it was engaging in a slow, rhythmic display you realized. It’s a call for companionship.