The Miocene marks a period in geologic time in which massive changes were occurring to Earth. Major landmasses came close to their present-day positions, and the closing of the Tethys Ocean ended the circumglobal circulation of warm waters. Modern patterns of ocean and atmospheric circulation developed, as gyres formed in the northern and southern hemispheres, bringing warm water to the poles and cold water towards the equator. A cold transarctic ocean current isolated the waters around Antarctica, permanently freezing the continent.
The cooling of Antarctica and the consequent cooling of the deep waters of the oceans triggered episodes of upwelling, which brings dense, nutrient-rich, cooler waters towards the oceanʼs surface. These episodes of upwelling were likely critical in the evolution of kelp forests, which appeared for the first time, bringing with them sea otters and other species unique to these environments. The changes in ocean circulation, the cooling of the planet, and the availability of nutrients all encouraged the evolution and spread of a high diversity of marine vertebrates.
Many Miocene fossil species have close relatives alive today. Almost all modern groups of whales were present, as well as early seals, sea lions and walruses. During this time, marine mammals greatly diversified, with baleen and toothed whales being particularly diverse. They inhabited the oceans with sea cows, sharks, corals, turtles, fish, and a variety of invertebrates.
Recently, paleontologists discovered one of the biggest predators that ever lived- a whale called Leviathan melvillei, “Leviathan” meaning sea monster, and “melvillei” referring to Herman Melville, the author of Moby Dick.
Two years ago, while working with the Royal Belgian Institute of Natural Sciences in the Pisco-Ica desert of Peru, Dr. Olivier Lambert and his colleagues found the skull and mandible from a sperm whale that lived 12 to 13 million years ago during the Middle Miocene, when the desert was underwater.
Leviathan wasnʼt like the modern day sperm whale, with its tiny teeth that are adapted to sucking squid into their mouths– it was a raptorial feeder, similar to the modern killer whale. “These are probably the largest teeth that I have ever seen,” says Lambert. “The maximum length of some of the teeth is 36 centimeters.”
The skull of Leviathan was about 9 feet long and up to 7 feet wide, and a full-grown man could have easily fit inside Leviathanʼs mouth. The upper and lower teeth interlocked when the mouth closed — good for securing prey and tearing large pieces of flesh from the body of the victim, as performed on a smaller scale by todayʼs killer whale.
At about 60 feet in length, Leviathan adults were probably free from predation themselves, and it is believed that they preyed upon medium-sized baleen whales, and would have been in competition with the giant shark Megalodon. Along with Megalodon, Leviathan probably had a profound impact on the structuring of Miocene marine communities and food webs. Other Miocene hotspots worldwide indicate that raptorial sperm whales occupied a top predator position in various marine regions during the Miocene, a role now mostly taken by the killer whale.
The extinction of both Leviathan and Megalodon is one of scienceʼs great mysteries. “Clearly they were feeding on the same kind of prey, so they could have suffered the same problems,” says Lambert. Although more is known about Megalodon through an extensive fossil record, Leviathan is still so new that scientists can only begin to hypothesize about itʼs life and demise. “It is possible that such an animal went extinct with a decrease in the diversity of baleen whales in the Late Miocene, and we think that could have played a role in the extinction of this large predator,” says Lambert. “There was a major cooling in the oceans during the Late Miocene, and this other parameter could have also played a role in the extinction of such an animal.”
Much about the oceanʼs past can only be speculated, as clues are still needed in order to tell a more complete story. The parts of earthʼs history that are known come from data collected by scientists. By looking at benthic oxygen isotopes and the magnesium to calcium ratio in foraminifera, scientists have discovered that the Late Miocene experienced a dramatic temperature drop, an increase in ice volume, and rapid sea level changes. All of these factors could have contributed to the extinction of the two great predators of the Miocene oceans, by limiting the availability of food and suitable habitat. The relatively high foraminiferal values in the Miocene are also at least partially associated with higher open ocean productivity. This widespread increase in marine productivity has been dubbed the ʻbiogenic bloomʼ, and implies a change in global nutrient cycling. Analyses of Miocene deep sea cores reveal major paleo- oceanographic changes affecting the biological productivity in the ocean. Maps created from these analyses revealed that four main episodes in the evolution of ocean circulation and paleoproductivity led to the establishment of present-day high productivity areas.
These events from long ago not only helped shape Earth today, but also provide insight into Earthʼs present, and future climate. By looking at the geologic record, scientists can try to figure out the causes and effects of what occurred, which provides a better understanding of how the same processes are working today and how they will work in the future.
Lambert, O., Bianucci, G., Post, K., de Muizon, C., Salas-Gismondi, R., Urbina, M., & Reumer, J. (2010). The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru Nature, 466 (7302), 105-108 DOI: 10.1038/nature09067