Why Did Life in the Oceans Get So Big?

Written by on January 28, 2014 in Marine Life

Composed of nearly 3,000 individual reefs, the Great Barrier Reef is the largest living structure on the planet. Growing to an estimated length of over 50 feet (16 meters) megalodon, a prehistoric shark, would absolutely dwarf modern-day great whites, which are still considered pretty huge. The blue whale (Balaenoptera musculus) is the largest organism ever to have lived on our planet, reaching up t3 100 feet (30 meters), it exceeded the size of even the biggest dinosaurs.

So how did life in the oceans get so big? A new study by University of California, Los Angeles (UCLA) biologists helps answer this question. But they’re not talking about giant whales or ancient sharks, they’re going way back to the early oceans, about 580 million years ago, to look at rangeomorphs.

Charnia masoni, a rangeomorph.

Charnia masoni, a rangeomorph. Photo credit: Smith609 at en.wikipedia.

Rangeomorphs look like ferns and they dominate the earliest (579–565 million years ago) fossil communities of large eukaryotes (organisms whose cells contain a nucleus). Around Mistaken Point in Newfoundland, Canada, there are hundreds of rangeomorph fossils on rock surfaces exposed along the coast. The fossils range from several millimeters to tens of centimeters in height.

Rangeomorphs are made up of small units called frondlets which repeat themselves in branching patterns that resulted in many different shapes and sizes. Based on the rocks on which the fossils are found, researchers know that they lived in communities on the sea floor below the photic (light) zone. This means that they couldn’t use photosynthesis so they must have used another method for obtaining energy.

The branching patterns of the frondlets suggest that they absorbed dissolved nutrients directly from the water in the same way that bacteria do. This raised the question of how rangeomorphs competed with bacteria. Discovering what that advantage was will provide scientists with better insight into what drove the evolution of large life forms.

By growing up into the water column, the rangeomorphs were exposed to more water flow, which increased their nutrient uptake and gave them a competitive advantage over bacteria. Height also has an impact on the properties of water flow. A group of organisms extending into the water column can create a canopy layer. Above the layer, the water flows normally and below the layer, the water flow slows way down. The changing properties of water flow promotes further upward growth.

Understanding more about water flow, rangeomorphs, and the way they absorbed nutrients may help scientists understand other processes that affect ocean life today.

You can read the full paper here: Canopy Flow Analysis Reveals the Advantage of Size in the Oldest Communities of Multicellular Eukaryotes.

Copyright © 2014 by Marine Science Today, a publication of Marine Science Today LLC.

About the Author

About the Author: Emily Tripp is the Publisher and Editor of MarineScienceToday.com. She holds marine science and biology degrees from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and a Master of Advanced Studies degree in Marine Biodiversity and Conservation from Scripps Institution of Oceanography. When she's not writing about marine science, she's probably running around outside or playing with her dog. .

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