The world’s oceans contain the largest animals that the Earth has ever seen. According to a recent analysis of body sizes of animals that lived over a period spanning 542 million years, marine life has been slowly getting bigger and bigger since the Cambrian Period. The key statistic is that modern marine animals are around 150 times larger on average than they were during the Cambrian period.
Commenting on the research, lead scientist Noel Heim told BBC Science: “The degrees of increase in both mean and maximum body size just aren’t well explained by neutral drift.” The paleontologist went on to add: “It appears that you actually need some active evolutionary process that promotes larger sizes.” Heim and his colleagues measured animals across more than 17,000 genera, including extinct plesiosaurs, trilobites, clams, and whales.
The scientists suggest that many selective pressures may have driven ocean animals to get so big (as an example, whales are by far the largest animals to ever live). As an example, at 30 meters (98 feet) in length and 190 tonnes or more in weight, the blue whale is the largest existing animal and the heaviest that has ever existed.
In addition, an important difference between mammals in the water compared with those that live in the land is the way that they breathe. The extra oxygen that comes with breathing air, rather than water, allows animals to sustain bigger bodies in aqueous environments.
The findings have been published in the journal Science. The research paper is titled “Cope’s rule in the evolution of marine animals.” (Cope’s rule proposes that animal lineages evolve toward larger body size over time.)
