Brachiopods Vs. Pelecypods

[mosasaur]

A question poped into my mind today... after the Permo-Triassic border extinction, brachiopods (so dominant through Paleozoic times) did not make much of a recovery; instead, the pelecypods filled what seems to be the same ecological niche. The question is, why? Were the brachs that much less efficient at food gathering than the pelecypods?

From my viewpoint, it seems the decline started in the Pennsylvanian, but that may be due to a bias on where I have collected. Certainly the Capitan Reef area in Texas had a diverse assemblly of brachs!

Kenneth Quinn

[Guest Cris]

I did some reading and found some theories on why some think most of the abundant brachiopods died off (95% of species) while the pelecypods prospered so well. I read that pelecypods use an energetically-efficient ligament-muscle system for opening valves, and thus require less food to subsist. Since brachiopods didn't use such a method, they may have starved from declining organic matter in the water. It makes sense that during the end-Permian extinction, there was less life out there.. (It was an "extinction", after all) the less organic life, the less organic matter in the water. (a.k.a. brachiopods/pelecypods food)

Another theory which may have influenced this is that Predation played a role. Marine reptiles with 'tooth pavements' appeared, mollusk-crushing fish, sharks, rays, etc. This theory doesn't sound as solid as the other to me. It just wouldn't make sense that predation would kill off 95% of the brachiopod species alone.

What's your theory, Kenneth? (or anyone else, for that matter) If you've given it thought, you must have a theory.

[geofossil]

A question poped into my mind today... after the Permo-Triassic border extinction, brachiopods (so dominant through Paleozoic times) did not make much of a recovery; instead, the pelecypods filled what seems to be the same ecological niche. The question is, why? Were the brachs that much less efficient at food gathering than the pelecypods?

From my viewpoint, it seems the decline started in the Pennsylvanian, but that may be due to a bias on where I have collected. Certainly the Capitan Reef area in Texas had a diverse assemblly of brachs!

Kenneth Quinn

Interesting question.

Actually I'll modify it a bit. There was a decline of orders of brachs at the end of the Pemian but not necessarily a lack brach dominanace. The big decline in the individuals begins in late Jurasic deposits and ever since. Rich marine deposits in France, etc. with continuous stratigraphy have complex and rich brachiopod fauna. I've collected about 150 species fom those areas (along with principally ammonites but few pelecypods). I'd also modify the question of brachs vs pelecypods to brachs vs other filter feeders (including pelecypods). We're down to 300 or so species of brachs today. The phylum that has largely displaced brachs in warmer waters are corals and not mollusca....mollusca have largely displaced brachs in many temperate and cold waters but brachs still flourish in many cool and cold waters.

One explanation put forth sometimes is brach specialization. The 'generalist' forms still exist (lingula since the Cambrian). Other brach orders went off on tangents that made them less able to adapt to competition, climate, food sources, etc. Another thought is that the biochemistry of the phylum is unable to adapt to freshwater cnditions and it has been confined to oceans and never evolved to freshwater and back to saltwater, etc. over the last few hundreds of millions of years. Regional global areas of brachs are wiped out due to continental drift..the closing of water flows, currents, etc. If not certin levels of saltwater then no brachs,...accumulated over hundreds of millions of years this chips away globally. The same thought may be why cephaloods such as ammonites are extinct (same phylum as pelecypod). Ammonites are also a non-freshwater class. Classes of mollusca (pelecypods, gastropods) are much more adaptable (in geologic time) to changing conditions if they have bridged freshwater/saltwater adaptation or at least adpted to inter-tidal, terrestrial living.

[jkfoam]

This is an interesting q1uestion. I have always been facinated with the Permian- Triassic boundary extinction. Who survived, who didn't, etc.

I'm not sure when the Brachiopod decline started but there is no denying the brachiopod extinctions and decreases in populations of surviving suborders at the end of the Permian. Two suborders did recover nicely through the Triassic and Jurassic while others disappeared completely.

I never thought about the pelecypods filling the niche of the Brachiopods at the end of the Permian but I can see how it could be conferred. The number of suborders/families of pelecypods did increase after the Permian.

I'm not sure if the decline of the brachs and rise of the clams was simply due to food gathering effeciency or other factors such as selective predation of the larval life forms or the adult forms. All brachs were sessile while some clams have mobility (probably not enough had mobility to matter that much in the larger scheme of things). All brachs were marine while some clams are non-marine. Again, I'm not sure this had any influence in their success. Many clams are very tollerant of water turbidity. I don't know about a brachs tollerance for turbidity.

I hope someone can contribute a definitive answere to this question.

Can someone recommend a good book that discusses the major geological extinction, especially the Permian-Triassic extinction.

JKFoam

[mosasaur]

Another theory which may have influenced this is that Predation played a role. Marine reptiles with 'tooth pavements' appeared, mollusk-crushing fish, sharks, rays, etc. This theory doesn't sound as solid as the other to me. It just wouldn't make sense that predation would kill off 95% of the brachiopod species alone.

I don't buy this argument either - I have seen (and collected) shark teeth from the Mississippian that were not pavement teeth but looked as though they were shell-crushers anyway.

And no, I have no theory and no real hypotheses.

Hmm, as I wrote this a though occured to me. When limestomes from the Capitan Reef were dissolved to yield the enclosed (silicified?) productid brachiopods, they were very heavily spined. Was this an adaptation to a predator or a way to hold themselves about the sea bottom? The second idea sounds more likely to me.

Kenneth

[mosasaur]

Can someone recommend a good book that discusses the major geological extinction, especially the Permian-Triassic extinction.

JKFoam

Peter Ward, who seems to be trying to become the Carl Sagan of paleontology. has written a book called "Gorgon" about his field work in South Africa. What gets me is that the first 90% of the book he seems to support one possible explanation for the end-Permian extinction, then suddenly changes his tune! But he does point out a lot of evidence toward a gradually increasing strain on the world ecosystem and possibly a catastrophic, sudden event. AFAIK the evidence seems to point toward a conglomeration of events. The formation of one supercontinentment that there was a huge decrease in the amount shallow seas, which host so much diversity of marine life. A barren, arid interior made things rough on land life. There was an episode of flood basalts in Siberia, causing (possibly) very acid rain and other air pollution. The evidence for meteor impact is pretty shaky. Finally, there may have been a sudden and catastrophic release of methane from the seabed, which resultedin a very rapid and significant episode of global warming - methane is very much a greenhouse gas!! Another book - I do not have the exact title but I think it is "When Life Nearly Ended". I will do some research and in a little while I will post the exact title and the author.

[mosasaur]

The book is "When Life Nearly Died: The Greatest Mass Extinction" by M. J. Barton.

Kenneth

[jkfoam]

Yes, most of the Productid brachs in the Permian were heavily spined. Howerver most of the other Order/Suborders of brachs were not heavily spined if spined at all. I don't know what the manifestation of spines mean. Was it functional or ornimental. If it was functional what was the function that it provided or inhanced. The spines must not have provided much of an advantage since the Productids did not survive past the permian. Or the spines could not protect against the extinction environment.

JKFoam

[ebrocklds]

Yes, most of the Productid brachs in the Permian were heavily spined. Howerver most of the other Order/Suborders of brachs were not heavily spined if spined at all. I don't know what the manifestation of spines mean. Was it functional or ornimental. If it was functional what was the function that it provided or inhanced. The spines must not have provided much of an advantage since the Productids did not survive past the permian. Or the spines could not protect against the extinction environment.

JKFoam

from my understaning, the spines on productid brachs serve two purposes depending on the brach. the standard free standing long spines are an anchor to keep the animal in the soft bottom sediments. ( hence the spines are almost always on the larger pedicle valve) these makes the brachiopod mostly bured with just its feeding apparatus and brachial valve exposed.

the other is a similar use but for a rocky environment. brachs from glass mountain texas are perfect examples. they have developed long erratic spines that essentially entangle and sometime cement them to there surroundings.

ornementation was doubtful (at least in my opionion) as the decoraive valve is usually buried.

brock

[Guest solius symbiosus]

from my understaning, the spines on productid brachs serve two purposes depending on the brach. the standard free standing long spines are an anchor to keep the animal in the soft bottom sediments. ( hence the spines are almost always on the larger pedicle valve) these makes the brachiopod mostly bured with just its feeding apparatus and brachial valve exposed.

the other is a similar use but for a rocky environment. brachs from glass mountain texas are perfect examples. they have developed long erratic spines that essentially entangle and sometime cement them to there surroundings.

ornementation was doubtful (at least in my opionion) as the decoraive valve is usually buried.

brock

That is what we were taught in paleo years ago. There is no need for ornamentation; Brachiopods have no eyes.

The Paleo/Meso extintions were a subject that too intrigue me. I have seen a few explanations for this event; the best being Himalayian outgassing during the creation of those Mnts raising global temps ... until recently.

There is some speculation, of late, that attributes Gamma Ray Burst or a similar extra-terrestrial explanation for this, and other, extinctions. There is some solid research out there supporting this hypothesis.

[ashcraft]

The thing about mass extinctions is that they level the playing field. Brachiopods may not have been as adapted to the environment as pelycopods, but because they were here first, they filled up the niches and suppressed the speciation of the pelycopods. The mass extinction would have opened up many niches by extinction. Adaptive radiation would have begun from whatever survivors there were, and the best and luckiest would have filled the niches, excluding others from that niche. I think bats and birds are a prime example. Are birds so superior to bats? Or do they dominate the day skies because they were here first, and the bats can't get a foothold? It will (would) be interesting to see the masters of the sky after the next mass extinction.

My simplistic view,

Brent Ashcraft

[ebrocklds]

i totally agree. it has happened many times. look at reptiles (dinosaurs, if you classify them as such) and mammals. the main predator niches were already filled by the dinosauria, suppressing the mammals, that is untill after the extinction. same thing with birds and pterosaurs... ?

Brock