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Brachiopod education needed


minnbuckeye

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I am currently providing fossils for a  project involving an advanced earth science class. In talking with the instructors, a few questions came up that I could not answer.

    1. What caused brachiopods to crash and then pelecypods  to flourish? 

    2. Are present day scallops pelecypods even though they look more like brachiopods?

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1. The Permian-Triassic extinction event hit both brachiopods and bivalves hard, but may have hit the former much harder, having an impact on their diversity. With that being the case, the brachiopods had fallen a bit behind in terms of diversification, but both of them continued to diversify until the modern day. For a statistical analysis of that trend, see: 

 

Gould, S.J; Calloway, C.B (1980). "Clams and Brachiopods - Ships that Pass in the Night". Paleobiology. Paleontological Society. 6 (4): 383–396.

 

2. Scallops are bivalves, so, yep, pelecypods! :) 

 

 

...How to Philosophize with a Hammer

 

 

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It is not mentioned much in the literature but occasionally in a brachiopod paper you will read where the evolution of barnacles and irregular echinoids negatively impacted brachiopods. Most articulate brachiopods needs a hard substrate to attach to in order to grow. During much of the Paleozoic and into the Mesozoic, brachiopods could attach to pebbles and shells and rocky outcrops in shallow water without too much competition for space. Acorn barnacles became abundant in the Cenozoic and competed with brachiopods for attachment space on rocky outcrops and larger shells and pebbles. Brachiopods could also attach to small pebbles but when irregular echinoids diversified, many became infaunal and would plow through the sediment disturbing small pebbles and shells that brachiopods attached to. Today brachiopods are still fairly abundant in deeper water where there are rocky outcrops that lack barnacles.

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Hope its ok to join this thread with my own agenda. I have begun a project to put together a talk and display for the Maryland Natural History Society(I'm a volunteer) on Brachiopods and Bivalves. Brachiopods are not well known. I would appreciate recommendations from TFF about unusual and attention getting brachiopods and bivalves that would interest the general public. For instance, in working on this I have learned about Rudists -only have collected in the east. I was not familiar with them. Interested in trading or reasonable purchasing  examples for this project. Thanks in advance for your suggestions. Mainly interested in US fossils but open to interesting examples from elsewhere.

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3 hours ago, minnbuckeye said:

 2. Are present day scallops pelecypods even though they look more like brachiopods?

Scallops only appear to have lateral symmetry. If you look at the ears or wings of a scallop or similar bivalve they are always different.  There are definitely some bivalves that come pretty close to having a similar symmetry to brachiopods. But you will never see a brachiopod that doesn't have the distinct side to side symmetry.

 

But more importantly the animal that made the shell is quite different. In the phylum Mollusca versus Brachiopoda. Very different critters indeed.

 

One other note would be that the term Pelecypoda is some what outdated. Most modern work on these animals uses the term Bivalvia. And you will be hard-pressed to find two systems of classification for bivalvia that agree with each other. Maybe look to the most recent volumes of the Treatise on Invertebrate Paleontology for a common guide.

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I recall seeing an article once that proposed the loss of Brachiopod diversity was related to the fact that they make their shells from Calcite while Pelecypods make their shells from Aragonite. In essence, both are the same mineral, CaCO3, but they crystallize differently. The relative abundance of Calcite vs. Aragonite in seawater varies over time and can be tracked. The lesser amounts of Calcite available in seawater may have been a factor in the decline of the brachs as well.

 

I found a Wikipedia article which is much better at explaining it than me. :)  https://en.wikipedia.org/wiki/Calcite_sea

-Dave

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9 hours ago, fossilnut said:

Hope its ok to join this thread with my own agenda. I have begun a project to put together a talk and display for the Maryland Natural History Society(I'm a volunteer) on Brachiopods and Bivalves. Brachiopods are not well known. I would appreciate recommendations from TFF about unusual and attention getting brachiopods and bivalves that would interest the general public. For instance, in working on this I have learned about Rudists -only have collected in the east. I was not familiar with them. Interested in trading or reasonable purchasing  examples for this project. Thanks in advance for your suggestions. Mainly interested in US fossils but open to interesting examples from elsewhere.

 

The most morphologically unusual brachiopods that I know of (and brachiopods aren't really my main area of interest) would be the productids(http://palaeos.com/metazoa/brachiopoda/productida.html). However, someone with more knowledge of the topic should chime in, there's very likely several minor clades that most people haven't heard of and that are unusual in one way or the other.

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Thanks Hapchazzard for the reference I found it very informative especially the ones that mimic coral. Also hope to get an example with spines attached.

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