Evolution of life in the ocean changed 170 million years ago


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The ocean as we understand it today was shaped by a global evolutionary regime shift around 170 million years ago, according to new research.

Until that point, the success of organisms living within the marine environment had been strongly controlled by non-biological factors, including ocean chemistry and climate.

However, from the middle of the Jurassic period onwards (some 170 million years ago), biological factors such as predator-prey relationships became increasingly important.

Writing in Nature Geoscience, scientists say this change coincided with the proliferation of calcium carbonate-secreting plankton and their subsequent deposition on the ocean floor.

They believe the rise of this plankton stabilised the chemical composition of the ocean and provided the conditions for one of the most prominent diversifications of marine life in Earth's history.
more at link......

the paper:


Jurassic shift from abiotic to biotic control on marine ecological success:

Environmental change and biotic interactions both govern the evolution of the biosphere, but the relative importance of these drivers over geological time remains largely unknown. Previous work suggests that, unlike environmental parameters, diversity dynamics differ profoundly between the Palaeozoic and post-Palaeozoic eras. Here we use the fossil record to test the hypothesis that the influence of ocean chemistry and climate on the ecological success of marine calcifiers decreased throughout the Phanerozoic eon. Marine calcifiers build skeletons of calcite or aragonite, and the precipitation of these calcium carbonate polymorphs is governed by the magnesium-to-calcium ratio and temperature in abiotic systems. We developed an environmental forcing model based on secular changes of ocean chemistry and temperature and assessed how well the model predicts the proliferation of skeletal taxa with respect to calcium carbonate polymorphs. Abiotic forcing governs the ecological success of aragonitic calcifiers from the Ordovician to the Middle Jurassic, but not thereafter. This regime shift coincides with the proliferation of calcareous plankton in the mid-Mesozoic. The deposition of biomineralizing plankton on the ocean floor buffers CO2excursions and stabilizes Earth’s biochemical cycle, and thus mitigates the evolutionary impact of environmental change on the marine biota.

Bizarre analogy:
Sounds like what we heard with the onset of "Web 2.o" or "the semantic Web".
Before the turn of the millennium, there was no such thing as social media. Content on the web was direct from provider to consumer. Web 2.0 came along when the penetration of users reached a threshold, where the very users that were consuming were also the ones being consumed.
The Phys Org article seems to mis-state what the Nature article is about. It is not about marine life in general but about "calcifiers" i.e, shell-secreting organisms, in particular.

It is obvious that other marine organisms (chordates such as fish, plesiosaurs etc), higher up the food chain, did not live lives in which evolutionary success was determined by ocean chemistry. It must have been determined by predation and food supply in the form of prey. There have been fish since the Cambrian.

Not only that but, going further back, I gather it is considered probable that the appearance of the "small shelly fossils" in the pre-Cambrian was a response to predation, which followed hard on the heels of the evolution of the mouth. So in pre-Cambrian times evolutionary success of calcifiers was seemingly driven by predation as well.

It seems to me the claims of this research are more modest and relate only to changes in the factors dominating the success of shell-secreting animals, after the end of the Palaezoic.
Predator-prey relationships predate the late pre-Cambrian appearance of multicellular organisms and even predate the appearance of Eukaryotes.

There are numerous predatory bacteria out there. (Many of them little studied.) They may have evolved from saprophytic bacteria that metabolized other dead bacteria. Some of these may have mutated such as to acquire the ability to chemically kill nearby living bacteria so as to make more dead ones that they could exploit and hence acquired an evolutionary advantage.


Jump forward to the fascinating "Cambrian explosion" in which most the current animal body types appeared seemingly all at once, already quite complex, suggesting a long evolutionary history, but with few traces of complex multicellular life previously (the enigmatic Edicaran fossils). That might be explained by the relatively sudden appearance of hard body parts that fossilize better than the soft body parts of whatever was ancestral to these things.



And I think that predation was obvious among the early Cambrian animals from the very beginning. For example the (then) ubiquitous trilobites, an early form of arthropod that's now extinct, but once more or less dominated the ocean floor. These too seem to have primarily been scavenger-predators. There's suggestions that some of them may have hunted things like worms.


If anyone else is interested in trilobites, as I am, check out Sam Gons' trilobite website. Everything you ever wanted to know about them, their taxonomy, their anatomy, their ecology, their larval development, their hypothesized evolutionary ancestry:

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Why should we struggle to stash items in out of the way places? Are we being charged for each thread that is started?
My issue is with threads that are simply news. No questions for discussion. This is a discussion board.
Pad aside, there are people who habitually use science forums as blogs.
Why should we struggle to stash items in out of the way places? Are we being charged for each thread that is started?
My last profile post has been sitting there, unmoved on the home page since Saturday at 10:37 AM (whatever time zone that's in) for four days.

I didn't discuss anything on a topic of: Alexa Calls Guy “Shithead” After He Cancelled Prime Subscription.

But, if anyone wanted to discuss, they were always at liberty to actually start a thread on it
Oh, did I forget to mention that one of the pitfalls of threads without questions is that they tend to rapidly wander off-topic into meta-discussion? :D
It would be a sad day when an interesting item of scientific news didn't provoke questions/comments. However, those don't have to be here.

And sharing such news is important. If Galileo was writing today he could have been read around the world, and the Church could go suck it.