Prehistoric Wild: Life in the Mesozoic

Dive of Peril (226 MYA)

Hosselkus Limestone, California, 226 million years ago

In the western regions of the United States lies the Sierra Nevada. This landscape is dominated by rugged limestone cliffs, stretching over 400 miles long. Beneath these jagged peaks, pine forests and vast lakes like Tahoe create one of North America's most serene environments. Although this mountain range doesn't reach as far as the Appalachian or Rocky Mountains, its tallest summit, Mount Whitney, towers above all others in the continent at over 14,500 feet high.

In the Late Triassic, this great Californian mountain range lies submerged at the bottom of moderately deep waters. Above where the summits would hit their peak, fading daylight shines off of gentle waves. This change also means that the great lakes and conifer forests of Yosemite are absent as well.

At this time in Earth's history, the continents as we know them are still conjoined in a single landmass. This arrangement birthed a massive superocean, nearly spanning the entire globe. Just as Pangea is "all land," Panthalassa aptly means "all sea."

As it tends to be this far from land, the ocean waters are fairly quiet. Sea birds have yet to evolve, so their familiar calls are absent. All there is for sound is a soft breeze and the smooth flow of waves.

Below the surface is where it appears most vacant. Where bits of land can be seen fading into the horizon above, what lies in the underwater distance is shrouded by dark blue. It's closer to the surface where the area is most visible, the light above making the waters appear a clearer azure as it peers through. With night approaching, this clarity is slowly being consumed by the encroaching darkness of the deeper depths.

With land being distant, these high seas are largely barren, the ocean equivalent of a desert. Despite this, marine life does thrive here in abundance. The most common just so happens to be its smallest.

As is the case in our modern oceans, plankton can be found in nearly every part of this ancient marine world. They're incredibly small to the human eye, appearing only as tiny particles without the aid of a microscope. Unable to actively propel themselves, they instead drift wherever the current takes them. To nourish themselves, they rely on a technique known as photosynthesis, wherein they absorb sunlight and convert it into nutrients. This same method is used by plants, just added with the soaking up of water.

Naturally, they gravitate closer to the sunlit surface where the light is most abundant, leaving the deeper water behind. In doing so, they kickstart a vital feeding chain for the ocean's residents. It all starts with a familiar type of marine life.

Fish, the oldest groups of backboned animals, having been fully aquatic since the dawn of life on Earth. In this long time, they've evolved and diversified into several forms well into our modern day. Some, like these anchovy-sized species, have developed the ability to filter-feed, using specialized gills to strain plankton from the water. This feasting benefits both the fish and the ecosystem, preventing the buildup of these microorganisms from triggering toxic algal blooms.

In their feast, the fish gather in the millions, forming dense, shimmering clouds that swirl and shift in perfect sync. Out in the sea, however, these filter-feeders are themselves food. Another species hunts them in mass, slicing through the water to snatch mouthfuls of their plentiful prey. The liquid blue comes alive with its bubbling rushes and splashes as they spring through the surface.

These hunters' roots lie not in the ocean, but on land. Called Californosaurus, they belong to the ichthyosaur order of marine reptiles. As with many of their relatives, their 10-foot-long bodies are sleek and streamlined like dolphins. They even have a layer of blubber underneath their smooth skin. Four flippers grow from these bodies, the front half being nearly double the length of the rear ones. They also have a single dorsal fin and two caudal fins that form a crescent-like shape. Large expressive eyes rest in front of long, narrow snouts filled with sharp, conical teeth. Across the midsection of their bodies, their smooth scaleless skin is a deep, slate-gray with a solid white underbelly. Meanwhile, the skin on their limbs, snouts, and around their eyes is a dark gray.