The Ocean Turnover These are brachiopods, a type of filter-feeding organism that first evolved in th

The Ocean TurnoverThese are brachiopods, a type of filter-feeding organism that first evolved in the Cambrian era oceans. Although they look a lot like modern-day bivalves (clams), they are a very different organism, found in a totally different phylum. They can readily be distinguished by their shell shapes; brachiopods have sort of a “kink” in their shells whereas bivalves have more rounded shapes. Clams are molluscs, while brachiopods come from the phylum brachiopoda. These two types of filter-feeding organisms have an interesting interplay in the geologic record; if you pick up a limestone from the Paleozoic it is likely to be dominated by brachiopods, while Mesozoic and Cenozoic bivalve shells dominate limestones.The change between these two filter feeding organisms occurred at the end-Permian, the largest mass extinction recorded since life developed hard parts. Prior to that time, brachiopods owned the ocean floor, with thousands of different species existing over time. That extinction devastated both types of organisms, but brachiopods barely recovered, with only a few hundred species existing today compared with thousands of bivalves.Exactly why brachiopods performed so much worse after the Permian remains a matter debated by geoscientists. Bivalves may have been mostly outcompeted by brachiopods before the Permian and forced to evolve other methods to find food, such as techniques for burrowing and for sucking in and ejecting water, which may have allowed them to survive the climate after the extinction more easily. Bivalves also are much larger, with much more muscle tissue, which may have enabled them to more quickly open and close their shells (this extra mass is why you might have tried eating clams but not brachiopods, the latter have almost no meat).Geologists continue working to understand exactly how abundant each phylum was before the extinction as buried in this change is some record of the environment during the planet’s toughest times for life.-JBBImage credit: http://bit.ly/1SvhfBqFossilFridayReferences:http://stanford.io/1UA0R8Chttp://bit.ly/1N3KNEthttp://www.fossils-facts-and-finds.com/brachiopods.htmlhttp://bit.ly/1PO5AM8 -- source link

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