How Seals Migrated to Living in the Ocean

A variety of seals inhabit the oceans today, such as leopard seals from the Antarctic seas and rare Hawaiian monk seals hanging on the shorelines. However, seals were not always calling the ocean their natural habitat. In fact, paleontologists have found that the ancient ancestors of seals lived and walked on land more than 30 million years ago. So what exactly helped these mammals pull the plunge and take on a new permanent territory into the seas? That is a story that researchers have recently begun piecing together.

According to the Journal of Vertebrate Paleontology, two researchers studied the fossils of prehistoric seals and the remains of the modern species and reported in March that contemporary seals use similar techniques in attacking their prey as their ancestors did millions of years ago. The abstract states that “[true seals] use multiple feeding strategies—biting, filter, and suction feeding—to capture and consume prey” and those methods have been studied and deduced from “cranial, mandibular, and dental adaptations.”

The cranial and mandibular framework for the extinct species were then studied to compare with those from current day seals, and it shows that “biting was a common and important feeding strategy for early phocids.” These multiple methods for attacking and feeding among prey paved the way for animals to move into various different areas, which may have likely contributed to their evolutionary transition from living on land to living on sea biomes.

Led by comparative biologist Sarah Kienle from the University of California, Santa Cruz, the research highlights the evolution of seals from living on land to being dependent on the oceans. University of Wisconsin paleontologist Morgan Churchill, who did not partake in this study, calls this research on seals as “the first comprehensive analysis that’s looked at the skulls and mandibles of living species that also incorporates fossils.”

Kienle also reports from studies that although seals inhabit the oceans unanimously among various areas in the world, they harbor various different styles of eating, such as the leopard seal that catches the penguin by biting it, shaking it until the penguin breaks into pieces, then finally swallowing the pieces. Other seals use others methods in eating. Some seals will suck food from the water, such as fish, whereas others will take a gulp of crustaceans then let the water seep out from their mouths—similar to baleen whales. Through extensive study, each species of seal can be distinguished based on their unique skull and mandibular shape which would classify their eating technique.

Kienle and her colleague Annalisa Berta of San Diego State University attempt to match the bones of fossil seals with samples of every modern seal known to man, that way to help determine the eating styles of the ancestors of these seals. Kienle’s research team developed digital maps to use illustrations of bones from precisely 234 modern seals and 15 extinct seals. The maps collected specific markers on the images of the bones where the researchers categorized the origin of seals that used to feed by biting, sucking or filter-feeding.

Then, the team compared the images from modern seals with the images from extinct seals, discovering that the seals in the past were more frequently distinguished as biters. This suggestion would pave way to assume that a bite would be received from land-dwelling ancestors. If this theory is correct, then the ancient seals who first transitioned to the seas may have most likely been biting instead of the current three methods of biting, sucking or filter-feeding.

Kienele stands firmly upon her study that seals “evolved from terrestrial carnivores” and that they were able to take a feeding strategy that they were doing on land and successfully translate that to the water environment. While it is true that they were successfully able to transition their methods to better suit the lifestyle of marine animals, it leaves people to wonder if they were very successful during their first move to the oceans when they were unaware of what to expect beneath the seas. Were they ready to attack, bite and prey upon smaller animals on their first try? Did it take years or decades for them to master their eating techniques now? One would assume it did take them a longer-than-usual time due to the transition having taken place more than 30 million years ago.

Although there may be still remain many questions on the exact cause of what drove seals to transfer into the waters from the lands, it is still fascinating to see the versatility of these animals and their willingness to change their entire identity by associating their habitat with the oceans as opposed to land. This change in technique has transferred seals into marine animals and given them the chance to expand their skills into a number of different habitats today.