A gallery of prehistoric seaweeds

fossils of noncalcified marine macroalgae

from 700 to 400 million years ago


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Classification and Preservation

Ediacaran Gallery

Cambrian Gallery

Ordovician Gallery

Silurian Gallery

Credits

Macroalgae Present and past

 

Noncalcified marine macroalgae, commonly known as “seaweeds,” are the most abundant plants in the sea large enough to be seen with the naked eye. As such, they comprise a fundamentally important component of the modern Earth system. With growth habits ranging from dense turfs to spectacular kelp forests towering 40 meters above the seafloor, the rate at which these photosynthetic primary producers generate organic carbon, per unit mass, can exceed that of phytoplankton1,2 by an order of magnitude, and they partition the shallow marine environment into an enormous array of habitats for animals.

 

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An undersea forest of giant kelp.

A seafloor carpet of the green alga Caulerpa

 

The importance of macroalgae to marine animals made a particularly strong impression on a young Charles Darwin3 when the Beagle encountered kelp beds off the coast of South America, prompting him to comment: “I can only compare these great aquatic forests of the southern hemisphere with the terrestrial ones in the intertropical regions. Yet if in any country a forest was destroyed, I do not believe nearly so many species of animals would perish as would here, from the destruction of the kelp.” Beyond the biosphere, macroalgae influence sediment accumulation and organic content in shallow shelf settings, and they produce prodigious amounts of atmospheric oxygen. In an even broader Earth system context, they play a key role in the dynamics of the global carbon cycle.

 

As important as they are today it is likely that macroalgae played an even larger role in biosphere and Earth system dynamics during a critical interval of Earth history spanning from 700 to 400 million years ago, a timeframe which encompasses the last part of the Proterozoic Eon and the early part of the Paleozoic Era of the Phanerozoic Eon. That this is so emerges from the confluence of three factors. First, inland (epeiric) seas covered most of the continental masses during this interval. As a consequence, macroalgal habitat for much of that time exceeded that of today by approximately an order of magnitude.

 

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North America during the Silurian Period. Note the vast areas of

shallow marine habitat provided by extensive inland (epeiric) seas.

(from Ron Blakey, NAU Geology)

 

Second, macroalgae were the only marine plants of this time, apart from microbial mats. Although seagrasses are important marine plants today, they would not originate until the Mesozoic4. To put this combination of factors in perspective, consider that macroalgae in the modern Earth system account for approximately 6% of net primary productivity (NPP) in the ocean2 and perhaps as much as 12% of marine organic carbon burial because of their much greater burial potential relative to phytoplankton (particularly picoplankton). By comparison, during the early Paleozoic macroalgae could have accounted for as much as 25% of marine NPP and an even greater percentage of organic carbon burial based on the expanded habitable area and the lack of competition from other macrophytes. Finally, this timeframe includes the great animal radiations known as the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE). These truly game-changing evolutionary events played out in shallow marine settings, so that macroalgae comprised a substantial part of the “stage” on which these “dramas” unfolded. Indeed, two substantive hypotheses have implicated macroalgae as “triggers” for the first of these radiations5,6 and it is conceivable that they were important factors during the second as well. Only recently, however, has a picture of ancient macroalgae emerged from the fossil record with a resolution sufficient to test these hypotheses and to glimpse the basic structure of seaweed communities from this ancient time. This website is designed to provide a detailed overview of macroalgae from this pivotal chapter in the history of the Earth system, including many newly discovered species.

 

Within the website, the various species of fossil macroalgae are grouped into “Galleries” according to the Period in which they lived: Ediacaran, Cambrian, Ordovician, and Silurian. Notably, because the conditions required for preservation of macroalgae as fossils were narrowly defined within each Period (see Preservation and Classification page), the assemblage of species presented on each Gallery page can be thought of, for the most part, as portraying the structure of an entire algal community from that time. Clicking on a picture within a Gallery will open a new page that provides detailed information about that species. In some cases the pictures are rather crude, but these will be updated as better photographs become available for the specimens, many of which are from remote parts of the planet.

 

References

1. Bunt, J. S. (1975). Primary productivity of marine ecosystems. In H. Lieth & R. H. Whittaker (Eds.), Primary productivity of the biosphere (pp. 169–183). New York: Springer.

2. Valiela, I. (1984). Marine ecological processes. New York: Springer-Verlag.

3. Darwin, C. (1871).  Journal of researches into the natural history and geology of the countries visited during the voyage of H. M. S. Beagle round the world, under the command of Capt. Fitz Roy, R.N. New York: D. Appleton and Company.

4. Aires T., Marba, N., Cunha, R. L., Kendrick, G. A., & Walker, D. I. (2011). Evolutionary history of the seagrass genus Posidonia. Marine Ecology Progress Series, 42, 117–130. doi:10.3354/meps08879

5. Schopf, J. W., Haugh, B. N., Molnar, R. E., & Satterthwaite, D. F. (1973). On the development of metaphytes and metazoans. Journal of Paleontology, 47, 1–9.

6. Stanley, S. (1973). An ecological theory for the sudden origin of multicellular life in the late Precambrian. Proceedings of the National Academy of Sciences, USA, 70, 1486–1489.