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7.2.2C: Post-Cambrian Evolution and Mass Extinctions - Biology

7.2.2C: Post-Cambrian Evolution and Mass Extinctions - Biology



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The post-Cambrian era was characterized by animal evolution and diversity where mass extinctions were followed by adaptive radiations.

Learning Objectives

  • Differentiate among the causes of mass extinctions and their effects on animal life

Key Points

  • During the Ordovician period, plant life first appeared on land, which allowed aquatic animals to move on to land.
  • Periods of mass extinction caused by cataclysmic events like volcanic eruptions and meteor strikes have erased many genetic lines and created room for new species.
  • The largest mass extinction event in earth’s history, which occurred at the end of the Permian period, resulted in a loss of roughly 95 percent of the existing species at that time.
  • The disappearance of some dominant species of Permian reptiles and the warm and stable climate that followed made it possible for the dinosaurs to emerge and diversify.
  • Another mass extinction event caused by a meteor strike and volcanic ash eruption occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end and pushing dinosaurs into extinction.
  • The disappearance of dinosaurs led to the dominance of plants, which created new niches for birds, insects, and mammals; animal diversity was also brought on by the creation of continents, islands, and mountains.

Key Terms

  • Cenozoic: a geologic era about between 65 million years ago to the present when the continents moved to their current position and modern plants and animals evolved
  • mass extinction: a sharp decrease in the total number of species in a relatively short period of time
  • Cretaceous: the last geologic period within the Mesozoic era from about 146 to 65 million years ago; ended with a large mass extinction

Post-Cambrian Evolution and Mass Extinctions

The periods that followed the Cambrian during the Paleozoic Era were marked by further animal evolution and the emergence of many new orders, families, and species. As animal phyla continued to diversify, new species adapted to new ecological niches. During the Ordovician period, which followed the Cambrian period, plant life first appeared on land. This change allowed formerly-aquatic animal species to invade land, feeding directly on plants or decaying vegetation. Continual changes in temperature and moisture throughout the remainder of the Paleozoic Era due to continental plate movements encouraged the development of new adaptations to terrestrial existence in animals, such as limbs in amphibians and epidermal scales in reptiles.

Changes in the environment often create new niches (living spaces) that contribute to rapid speciation and increased diversity. On the other hand, cataclysmic events, such as volcanic eruptions and meteor strikes that obliterate life, can result in devastating losses of diversity. Such periods of mass extinction have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind. The end of the Permian period (and the Paleozoic Era) was marked by the largest mass extinction event in Earth’s history, a loss of roughly 95 percent of the extant species at that time. Some of the dominant phyla in the world’s oceans, such as the trilobites, disappeared completely. On land, the disappearance of some dominant species of Permian reptiles made it possible for a new line of reptiles to emerge: the dinosaurs. The warm and stable climatic conditions of the ensuing Mesozoic Era promoted an explosive diversification of dinosaurs into every conceivable niche in land, air, and water. Plants, too, radiated into new landscapes and empty niches, creating complex communities of producers and consumers, some of which became extremely large on the abundant food available.

Another mass extinction event occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end. Skies darkened and temperatures fell as a large meteor impact expelled tons of volcanic ash, blocking incoming sunlight. Plants died, herbivores and carnivores starved, and the mostly cold-blooded dinosaurs ceded their dominance of the landscape to more warm-blooded mammals. In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs. Birds, the warm-blooded offshoots of one line of the ruling reptiles, became aerial specialists. The appearance and dominance of flowering plants in the Cenozoic Era created new niches for insects, as well as for birds and mammals. Changes in animal species diversity during the late Cretaceous and early Cenozoic were also promoted by a dramatic shift in earth’s geography, as continental plates slid over the crust into their current positions, leaving some animal groups isolated on islands and continents or separated by mountain ranges or inland seas from other competitors. Early in the Cenozoic, new ecosystems appeared, with the evolution of grasses and coral reefs. Late in the Cenozoic, further extinctions followed by speciation occurred during ice ages that covered high latitudes with ice and then retreated, leaving new open spaces for colonization.


Demons Dance Alone

So, this blog has a loooooong backlog of stuff I wanted to talk about but I didn’t. Old stuff, like, one year old or more. Alas, I cannot hope to make a complete post on all that, but I don’t want to let it rot. Let’s do a bit of quick catching up:

  • Bird blood on our hands. In 2019 a couple of papers pointed directly the fingers at humans for the extinction of the great auk and the Carolina parakeet, two once-widespread, iconic species of birds that went extinct in the XIX century. Both papers analyzed paleogenomes (is it right to use the ‘paleo’ prefix when it’s a couple centuries ago?) and found out that both species populations had a vibrant genetic diversity until their numbers fell abruptly to zero. Which means: no, they weren’t already fragile, declining species that we gently pushed off a cliff they would have met anyway. We systematically exterminated two robust, healthy bird species in the space of a few decades or centuries. Not exactly unexpected, but now there’s more proof.

    Butterflies that we will never know. In Singapore, 46% of the butterfly species disappeared (locally) in a mere 160 years, according to a paper of February 2020. Interestingly enough, the study accounts for extirpations of undetected species, using a model. I’m in no position to comment on the math, but the very idea is intriguing and melancholic: about a hundred of species would have gone extinct before we ever discovered them. Of these, some could have well been endemic species: ghosts, of which now we have nothing else than numbers in a statistical analysis. 󈫾.9% of the species discovered before 1900 also were extirpated before 1900. These high early observed extirpation rates, during a period where many species remained to be discovered, suggest that a high number of species were never detected before they were extirpated”

  • Innocent volcano. In January 2020, Pincelli Hull and coworkers put another nail in the coffin of the volcanic hypothesis for the K/T extinction. The K/T event has the distinction of having two competing or possibly synergic explanations: the well known Chicxulub asteroid impact, and the Deccan traps, a major volcanic event. For decades scientists have fought on what of these events was most important, and even if the impact seemed more and more clearly the culprit, the Deccan enthusiasts didn’t lose their grip. However, if the study is correct, it seems that 1)Deccan outgassing isn’t chronologically correlated to the extinction, but the impact is, and 2)the Deccan volcanism simply wasn’t generating enough gas to trigger an extinction, since similar events didn’t alter the biosphere so much. Another paper a few months later even argued that, if the Deccan volcanism had any effect, it was mitigating the extinction effects.

The continent that died

Antarctica is now the closest thing on Earth we have to another world: a barren continent almost entirely covered in miles-thick ice, with temperatures going below -80° and practically devoid of macroscopic life once you go beyond the coast.

Yesterday night I was reading the a bit outdated but still amazing The Origin and Evolution of Mammals by T.S.Kemp and my jaw dropped to the floor when I stumbled on the following sentence:

Needless to say” but oh dear, that’s when the obvious slaps you in the face, and it needs to be said. For tens or hundreds of millions of years Antarctica was a living, flourishing continent like the others, covered in forests, teeming with life. Right before the ice came, Antarctica looked like this:

Picture from Reguero et al. “Antarctic Peninsula and South America (Patagonia) Paleogene terrestrial faunas and environments: biogeographic relationships” Palaeogeography, Palaeoclimatology, Palaeoecology 179:3-4 (2002) https://doi.org/10.1016/S0031-0182(01)00417-5

I will have to dig deeper into this subject, that I suspect deserving a book (if one isn’t already there), and now I have no time to detail why and how it happened. But just let that sink in: The death of Antarctica is one of the main tragedies of the biosphere in the last 66 million years. Imagine if tomorrow Europe or South America, with all their life forms, their forests, their rivers, the singing of birds and the buzzing of bees, if all of that simply disappeared. That is what happened between 45 and 34 millions of years ago. Ice started to build up in the middle Eocene, and by the end of the period it was a frozen desert.

Imagine the slow death: a cap of ice every year slowly crawling from the core of the continent towards the coasts, animals and plants pushed to the edges, the winters every year more freezing, the summers every year shorter, until the ice reached the sea and there isn’t anywhere else to go. The penguins are basically the only survivors of this tragedy, relicts of a rich ecosystem.

What happened to Antarctica was an extinction of major proportions, but confined to a specific continent. Was it a mass extinction? Perhaps we need more categories, we need to start a taxonomy of extinction events. I will think about it. But for now, just remember: every time you see the beautiful glaciers and icebergs of Antarctica, you are witnessing the grim burial of an entire continent full of life, that was and now is gone.


“Let Us Prepare the Earth”: Natural Selection in the Scriptures

You’ve probably heard of Charles Darwin. He’s kind of famous in the scientific community infamous in some other communities. But do you know why everybody knows him? It’s because he came up with evolution, right?… Well, not exactly.

Charles Darwin isn’t famous for thinking that animals evolved, but for coming up for a way that explained how they evolved–a mechanism that drove evolution and caused it to occur (3). He called that mechanism “natural selection”, where changes in the earth produce changes in living things (4). This is what made Darwin’s theory so captivating, because he described how nature created the animals. For many people (perhaps even Darwin included), this removed the need for any Creator (5). And this–not the idea of evolution happening–is the root of the conflict between evolution and religion.

But of course on this blog, we’re believers of both God AND evolution, so there has to be a way that a Creator could use nature to make things (see Introduction post). If natural selection is true, then it would have been super nice if God had given us some kind of clue that He utilized it to create life on earth. I mean, just a little hint would’ve been really great.

But wait… Did He give us some kind of clue about it? Did He hint that changing the earth was how He created stuff? In this post, I claim that He actually did. Even though nature did the creating, God was behind it all, and I think there’s good evidence in the Pearl of Great Price to support that. Of all the accounts of creation, this method of creation by changing the environment is found in only two of them: the rocks and the Book of Abraham.

Yes, you read correctly. The idea of natural selection came from Charles Darwin in 1859, but it’s been in the Book of Abraham since 1842, right under our noses. And with some incredible science-anticipating foresight, the Book of Abraham came from Joseph Smith. Sounds like something a prophet would do.

What Is Natural Selection, Again?

“My eyes are constantly wide open to the extraordinary fact of existence. Not just human existence but the existence of life and how this breathtakingly powerful process, which is natural selection, has managed to take the very simple facts of physics and chemistry and build them up to redwood trees and humans. That’s never far from my thoughts, that sense of amazement.”– Richard Dawkins (6)

On earth, things change, a lot. All the time. And when things change, the animals and plants have to change too. They either adapt, or die. I guess you could say, they get pressured to change with the earth—kind of like peer pressure, but from the planet. Planet pressure, if you will. Populations will experience selective or evolutionary pressures which force nature to select for certain traits over others (see How Evolution Works). Climates change, continents split apart and change, habitats change, ecosystems change—and all of this change helps groups of living things to change as well. Those who survive these changes will pass on their good attributes and will continue to reproduce and evolve and those who don’t survive the changes (i.e. don’t have those good attributes that help them survive) will eventually die out, leaving no descendants. That’s natural selection, and that’s how it drives evolution (8).

The big thing that natural selection tells us is that nature created the stunning diversity of life on earth–which, if you think about it, is completely amazing! Everything around you was created by natural processes. It was nature that created the precious, cuddly-looking fur of the panda (9) it was nature that created the terrifying, bone-crushing bite of the Tyrannosaurus rex (10) and it was nature that created the irresistible, life-altering taste of the açaí berry (11). Nature, obviously, is pretty darn awesome at making things.

But even with the undeniable coolness of nature, is there still room for a loving, imaginative God to be a part of the creation process?… Absolutely.

God Does Not Micromanage the Universe

“[T]he universe keeps proving itself to be more creative than we give it credit for.”- Pamela Gay (12)

As we begin to delve into how God uses natural selection to create, we need to first understand that He doesn’t micromanage the universe. He lets it do its own thing.

The Book of Abraham teaches us that, like ourselves, the universe and all living things in it are free to act for themselves. During the creation account, the Gods “order” or command the waters, land, earth, beasts, whatever, and they wait until those things obey Them: “And the Gods saw that they were obeyed” (Abraham 4:10,12). “And the Gods watched those things which they had ordered until they obeyed” (Abraham 4:18). “And the Gods saw that they would be obeyed, and that their plan was good” (Abraham 4:21). “[A]nd the Gods saw they would obey” (Abraham 4:25). “And the Gods said: We will do everything that we have said, and organize them and behold, they shall be very obedient” (Abraham 4:31).

The universe doesn’t necessarily have to obey, so the Gods watched it until it did.

This is an important principle to understand. God doesn’t have to keep his hand in everything all at once. He just has to organize things, then watch them obey. Yes, the scriptures do say that God upholds the heavens and keeps the planets in orbit (see D&C 88:41-47 Hebrews 1:3 Colossians 1:17), but that doesn’t mean that if He loses concentration, the entire fabric of reality would crumble to pieces. If He were to focus on something other than the cosmos for a moment, electrons won’t proceed to fall off their atoms and the moon won’t come crashing down on us. He doesn’t have to sit there and control everything. The fact that the Gods have to wait to see if the universe and the living things within it will obey them speaks volumes. VOLUMES. And as we have already discussed on the blog, all living things have freedom of choice, to essentially do and live as they please (see The Four Beasts and Organization of Intelligences). They don’t have to obey if they don’t want to.

We know that there are fundamental laws of nature, such as those contained in physics, chemistry, biology, etc. It was through these laws, according to scientists, that stars, planets, and life were formed and evolved to what we know today. Was it “the God of nature” who established these laws before our universe existed (1 Nephi 19:12)? Were the things we see and are part of now ingeniously coded into the initial conditions of the Big Bang? And was setting the universe in motion and waiting for it obey and create all that God had to do?

Things Appear “Naturally”

“God has set many signs on the earth, as well as in the heavens, for instance the oak of the forest, the fruit of the tree, the herb of the field all bear a sign that seed hath been planted there for it is a decree of the Lord that every tree, plant, and herb, bearing seed, should bring forth of its kind, and cannot come forth after any other law, or principle.”– Joseph Smith (14)

The Book of Moses teaches us that all living things appeared on our planet “naturally” (Moses 3:5). This is a big deal. And how do living things appear naturally?… Why, they are born of course! That’s how all plants, animals, and humans are created. They have to be born! Why would it be any different at the beginning of the world? Why would the creation process described in the scriptures, which is said to have happened “naturally”, be any different? (Ahem… does “natural selection” ring a bell?)

All organisms, whether it be your pet chinchilla, the apple tree in your grandma’s backyard, or the fossilized plesiosaur in the museum, had to be born (or hatched or something along those lines), and had to have parents that gave them life. “Where was there ever a son without a father?” reasoned Joseph Smith, “And where was there ever a father without first being a son? Whenever did a tree or anything spring into existence without a progenitor? And everything comes in this way” (16). Everything must be born. Everything must come forth naturally, and that’s the rule. God, the Creator of all things, has to follow this rule, even from the very beginning of Creation.

This brings us to the principle that the creation, including the creation of animals, was not out of nothing. The idea that God created things out of nothing, or ex nihilo, is a “sectarian notion” that Joseph forcefully preached against (17). It’s just not how the Lord works. You say that God created you, and you are correct–He totally did! But He didn’t fashion you out of clay, or wave His hand to make you magically appear out of thin air. You had to be born, naturally, as a baby with a mom and a dad, with moms and dads for each of them too. You had to have a long line of “progenitors” all the way back to the beginning, as did all living things that ever existed on earth. And this has never changed, no matter how far back in time you go. Apparently, Joseph Smith had no problem with this idea.

Now, contrast this with what many Creationists believe. They subscribe to the “sectarian notion” that the creation was done specially that it happened supernaturally, from nothing–as opposed to naturally, from something (i.e. from previously-existing ancestors)(18). Also, contrast this with Heber C. Kimball’s idea that earth’s animals were transplanted here from other worlds (see Church Leaders and Evolution)(19). There’s nothing natural about either of these methods of creation. Yes, they would certainly get the creatures here physically, but it wouldn’t do the job “naturally,” as Moses 3:5 so elegantly requires (20). Since the beginning of time, all organisms had to be born, for they “cannot,” as Joseph Smith would say, “come forth after any other law, or principle.”

In this view, Joseph did not differ much from Darwin, who wrote, “When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before … , they seem to me to become ennobled” (21). There is nothing dishonorable or blasphemous about life always appearing on earth through natural birth and lines of descent. Charles Darwin knew that, and so did Joseph Smith.

Once again folks, it’s the Pearl of Great Price that helps us to understand that life always comes about “naturally” by natural processes (i.e. birth), and that science is well in line with the revealed word of God on this fundamental fact.

The Earth, Not God, Does the Bringing Forth

“And there stood one among them that was like unto God, and he said unto those who were with him: We will go down, for there is space there, and we will take of these materials, and we will make an earth whereon these may dwell And we will prove them herewith, to see if they will do all things whatsoever the Lord their God shall command them.” (Abraham 3:24-25)

The books of Genesis, Moses, and Abraham all teach us that during the creation of plants and animals, it’s not God that’s creating them, but the earth that is. The Gods want “the earth” and “the waters” on the earth “to bring forth” the various living creatures (Abraham 4:11-12, 20-21, 24-25). “Let the earth bring forth [living things]” (Genesis 1:11-12, 24 Moses 2:11-12, 24), and “Let the waters bring forth [other living things]” (Genesis 1:20 Moses 2:20), they say. This is super important because it’s not the Gods that are doing the bringing forth, it’s the earth itself. And the earth brings forth the animals and plants naturally, remember? None of this special, supernatural creation stuff– and that’s according to the creation accounts in the scriptures themselves.

However, the Genesis and Moses creation accounts aren’t completely consistent all the way through that it’s the sole responsibility of the earth to do all the bringing forth—yet (unsurprisingly) Abraham still is. Even when Genesis and Moses seem to slip up a couple times and say that “God created [the whales and stuff],” and “God made the beasts of the earth” (Genesis 1:21, 25 Moses 2:21, 25) Abraham fixes it and says instead, “the Gods prepared the waters that they might bring forth [the whales and stuff]” and “the Gods organized the earth to bring forth the beasts” (Abraham 4:21, 25)(23). By doing this, Abraham is essentially saying, “Whoa! Wait, guys. I’ll take it from here. It’s not God who made the beasts, but the earth that did.” Abraham, as the last scriptural creation account Joseph Smith gave us, is the ONLY one that keeps the bringing forth coming exclusively from the earth, as it should be (24). It takes all semblances of a special creation out and makes it 100% compatible with natural selection. More points to the Book of Abraham for that one! Abraham knew what was up.

The scriptures declaring that the earth brings forth the diversity of plant and animal life is completely consistent with what we know about natural history and evolution: that all the species on earth now and in the past were created by the earth. Their histories and lineages stretch far, far back–even 3.8 billion years or so back when the earth was just coming out of a cooling, recently-molten baby phase (25). And the reason each species came to be what they are is because of the earth, and the changes that have happened in it. That’s what natural selection is. Nature, or the earth, selected certain species to live or die, to reproduce and diversify or leave no descendants. Therefore, to use the language of the scriptures, it was the earth that brought them forth.

Is it any wonder, then, why the earth in Enoch’s vision refers to herself as “the mother of men”, and by extension, the mother of all living things (Moses 7:48)? Whether it be the scriptures or the rocks, the message is the same: The earth is what brings living things forth, and we’re all here because of that liveable/loveable planet.

The Gods Changed The Earth To Bring Forth Diversity

“As geology plainly proclaims that each land has undergone great physical changes, we might have expected that organic beings would have varied under nature, in the same way as they generally have varied under the changed conditions of domestication. And if there be any variability under nature, it would be an unaccountable fact if natural selection had not come into play.”–Charles Darwin (26)

So, if it’s the earth that brings things forth, and all things must be born or created naturally, then what role did God play in the creation? Well, my friends, we have to look to the Book of Abraham to find the answer. This is my all-time favorite thing about this particular book because this is where we see natural selection in the scriptural creation account.

The Book of Abraham describes the Gods making plans to “prepare” and “organize” the earth and waters to bring forth different species of plants and animals (Abraham 4:11,12,20,21,24,25). They didn’t just order or command the earth to make birds, whales, or cows they prepared it so that it would produce those things. “Let us prepare the earth to bring forth grass”, herbs, trees, and fruit (Abraham 4:11-12). “Let us prepare the waters to bring forth … the moving creatures that have life”, the fowl, and great whales (Abraham 4:20-21). “Let us prepare the earth to bring forth the living creature,” cattle, creeping things, and the beasts of the earth (Abraham 4:24-25). Apparently, the Gods were making (or planning to make) certain changes in the earth such that the earth would bring forth different living things “abundantly”, in breathtaking variety (Abraham 4:20-21)(28).

And their plan worked. “And the Gods saw that they would be obeyed, and that their plan was good.” (Abraham 4:21) Their plan was good because it was working! The preparations, organizations, or alterations they made in the earth were causing different forms of life to appear, or–dare we say–evolve. They didn’t just speak and cause a whale to magically appear, they prepared earth’s waters just right so that they would bring forth whales. They didn’t just snap their fingers and make a cow out of dirt and water, they organized the earth in such a way so that it would produce cattle–presumably (as with the whales) over a very long period of time. Same for the birds and for every living thing: the earth was prepared in a specific way so that these groups would eventually appear. And as these different organisms and families appeared, the Gods would “cause them to be fruitful and multiply” (Abraham 4:22)(29). They would make such changes to the planet so that these animals could reproduce and be successful on their own, so that they could survive and pass their genes on to their offspring. Later in this blog, we’ll see how the Gods “caused” humans to be successful too, and eventually to take over the world (Abraham 4:28).

Now, doesn’t that sound like natural selection to you? Isn’t making or exploiting changes in the earth to cause different species to appear exactly what natural selection claims to do? Remember, it’s the earth that brings things forth and different environments, climates, and pressures on said earth that drive the evolution of species. And if God doesn’t micromanage the universe, but can perhaps make or cause or “plan” little adjustments here and there when needed, then it wouldn’t necessarily be Him that’s doing the creating, but natural selection that is (see Abraham 4:21, 5:1). I mean, if God can create animals and a world for them to live on, then He could certainly arrange the right changes to occur in that world so that the world itself would make the animals. The planet just needs to be “prepared” right, and then nature will do the rest.

The idea of “preparing the earth” is an extremely important principle to understand. It fully complies with what we know about natural selection and how evolution works. The earth was formed. Life arose somehow. The earth changed a lot. Life changed a lot too. That’s how it works! That’s natural selection, and it’s all in our Book of Abraham. So, if you’ve been looking for evolution in the scriptures, here it is, nestled snugly in the pages of the Pearl of Great Price for over 175 years.

How To Prepare An Earth

“Boys, there is some meaning to this. God is in this storm!”- Joseph Smith, at Zion’s Camp, 1834 (30)

How would one go about preparing the earth for different species to emerge?

Our scriptures and Church history contain stories of God using natural phenomena to further His work. Around 34 A.D., a furious mix of natural disasters caused fatal destruction in the Americas following the death of Christ (see 3 Nephi 8-10)(32). In 1815, a massive volcano erupted in Indonesia, drastically altering climates all over the world, which effectually forced the Joseph and Lucy Mack Smith family to relocate from Vermont to Palmyra, New York–close to where Moroni deposited the gold plates (33). In 1834, a powerful rain and hailstorm caused a flash flooding of the Fishing River in Missouri, protecting the Zion’s Camp from an angry, militant mob (34). And we could go on and on, but you get the idea. Natural things happen God works in mysterious ways and His will is ultimately executed.

Now, I’m not saying that God necessarily commanded a deadly volcano to erupt so that Joseph Smith would eventually find the gold plates and translate the Book of Mormon. But He does have really good timing, and seems to make the most out of any situation. I definitely think He knew that the volcano would explode long before it did, and He knew how it would affect His children on earth–for good and bad (see 1 Nephi 9:6). I believe He can use natural events to realize His plans, and that He does so all the time.

But let’s take that principle in the context of natural history, natural selection, and evolution. What kinds of changes were made in the earth to bring forth the glorious array of different species we have today and have had in the ancient past? What changes to the planet can cause evolution to occur? What kinds of changes caused us and every other organism to appear?… Well, you’ve got earth’s axial tilt, earth’s wobble, gamma ray bursts, solar radiation, solar flares, sunspots, supernovae, hypernovae, sea level drop and rise, glaciation, climate change, asteroid impacts, vulcanism, continental drift, carbon dioxide, oxygen, ocean currents, Milankovitch cycles, ecological niches, magnetic field strength and reversals, the moon, storms, trophic cascades, co-evolution, mass extinctions,… and many, many more (35).

There are SO MANY factors that could cause evolution that we couldn’t possibly name them all. Everything on earth is connected, and one change here can cause another change there. In fact, every boundary in the geologic time scale actually marks a significant shift or change in the earth’s conditions that brought about new environments and new types of organisms (36). How these shifts occurred, how they influenced life, and what the earth looked like throughout each period are questions that make up a large portion of what geologists and paleontologists are continually studying.

Although we can’t know all of the big or little changes that have shaped our planet over the eons, somehow they all worked together to give us the staggering array of species we see today, including us. It’s truly astounding to think about the sheer amount of stuff that had to go down in the past just to make it possible for you to be here. You are pretty special, and God definitely loves you. I hope you are reminded of that as you contemplate the fossil record, because it’s basically a meticulous journal detailing how the Lord created you.

Now, I don’t think that God sits there and throws asteroids at our planet when He needs to make an adjustment but I do think He’s behind it in some way. All the physics of moving things in the universe–all the asteroids, planets, comets, star formations and star demises–all of it was basically predetermined by the initial conditions at the Big Bang, and then physics has run its course since then (37). Like I said above, God may have planned His creations, mass extinctions, and other factors to influence natural selection long before this universe even existed. That would allow for Him to be both the Creator AND the non-micromanager of the universe. Perhaps, as the theory of natural selection implies to some, there appears to be no divine Creator simply because He has already done His part of the creating or “planning” (Abraham 4:21) long before the atoms that make up our bodies were even formed. This, in my opinion, is way more impressive than a supernatural creation. God, as He complies with the laws of the universe, is “able to show forth great power, which looks small unto the understanding of men,” yet is more than enough to craft the various species of this world from cosmic scratch (Ether 3:5).

“Let Us Prepare the Earth [With Mass Extinctions]”

“[A]ll things shall work together for your good.” (D&C 90:24)

I don’t want to sound morbid, but my favorite evolution-influencing factor has got to be mass extinction. Mass extinction events are just what they sound like: they are bad (for most) and make a lot of cool (and scary) things go extinct. Mass extinctions are like pruning the tree of life, snipping off a branch here and another branch there. The spaces left in the tree after the pruning session are eventually filled by new branches–a.k.a. new species. When groups disappear, or go extinct, it leaves niches open for other groups to fill and diversify in (39). For example, it was a gnarly mass extinction that allowed the dinosaurs to take over the world and it was another gnarly mass extinction that killed them off. Mass extinctions sound horrific–and they are–but they go both ways, and you’re only alive (and can even have a favorite dinosaur at all) because of a whole specific slew of them.

So, for you to get an idea of how the earth is constantly changing and experiencing extinction events, and how life is trying to survive it all, here’s a table showing some of the known mass extinctions in earth’s history. Somehow, miraculously, your ancestors survived every single one of them, allowing you to be born:

When I read the words “Let us prepare the earth” in Abraham 4, I imagine erupting volcanoes, falling space debris, and rising sea levels. I imagine retreating glaciers, shifting continents, and global temperature spikes. I imagine mass extinctions and the wonderful creations that followed them. When I think of mass extinctions, I see “God moving in his majesty and power” (D&C 88:47).

Conclusion

“But a seer can know of things which are past, and also of things which are to come, and by them shall all things be revealed, or, rather, shall secret things be made manifest, and hidden things shall come to light, and things which are not known shall be made known by them, and also things shall be made known by them which otherwise could not be known.” (Mosiah 8:17)

In 1859, Charles Darwin gave us his theory of natural selection, delineating the way that nature itself creates the diverse and abundant forms of life on earth. Between 1830 and 1842, Joseph Smith gave us the books of Moses and Abraham, which opened the door for us to accept natural selection, a good chunk of time before the theory had even been published. This Pearl of Great Price, which came from Joseph, tells us that the Creator is hands-off in the universe, and must wait for it to obey that life must and always has appeared naturally, even at the dawn of creation that it’s not a Deity who directly brings forth life on our planet, but the earth itself and that the earth had to be organized and prepared so that it would bring forth the various different species and families, of both creatures and vegetation.

If you look in the fossil record, you will find evidence of the many ways in which the world has been prepared to bring things forth. You’ll find the factors with which the earth was organized so that certain groups would evolve and flourish, or languish and die. Mass extinctions are very important in paleontology and the study of the evolutionary history of our planet, and have prepared it just right for us. We owe a lot to those devastating asteroids, volcanoes, and other natural, physics-obeying killers. And we owe a lot to that God who prepared the earth for us. Who’s to say that it wasn’t He who planned everything out before the world was? Who’s to say that He’s not the God of natural selection?

If you look in the fossil record, you’ll find how God prepared the earth. In the Pearl of Great Price, you will find the same. It’s not as detailed or as filled with scientific evidence, but it’s the same. The Lord loves us, along with all other living things, and He organized and prepared this earth for us all (see Abraham 3:24-25). He is the Creator of every person, plant, and creature and He used natural selection to do it.

Joseph Smith prophesied of many things in his sermons, conversations, and in the scriptures he produced. That’s what prophets do. He foretold of things from when the Second Coming would not happen to the American Civil War (see D&C 130:12-17, D&C 87)(42). Much has been written about his predictions and their fulfilments (see Matthew 7:15-20)(43)… Should we add the theory of natural selection to the list?


The Dragon's Tales

Scientists have known for some time that most major groups of complex animals appeared in the fossils record during the Cambrian Explosion, a seemingly rapid evolutionary event that occurred 542 million years ago. Now Virginia Tech paleontologists, using rigorous analytical methods, have identified another explosive evolutionary event that occurred about 33 million years earlier among macroscopic life forms unrelated to the Cambrian animals. They dubbed this earlier event the "Avalon Explosion."

The discovery, reported in the January 4 issue of Science, suggests that more than one explosive evolutionary event may have taken place during the early evolution of animals.

To test whether other major branches of life also evolved in an abrupt and explosive manner, Virginia Tech graduate students Bing Shen and Lin Dong, along with Xiao and Kowalewski, analyzed the Ediacara fossils: the oldest complex, multicellular organisms that had lived in oceans from 575 to 542 million years ago that is, before the Cambrian Explosion of animals. "These Ediacara organisms do not have an ancestor-descendant relationship with the Cambrian animals, and most of them went extinct before the Cambrian Explosion," said Shen. “And this group of organisms – most species – seems to be distinct from the Cambrian animals.”

Surprisingly, however, as shown by Shen and colleagues, these earliest Ediacara life forms already occupied a full morphological range of body plans that would ever be realized through the entire history of Ediacara organisms. "In other words, major types of Ediacara organisms appeared at the dawn of their history, during the Avalon Explosion," Dong said. "Subsequently, Ediacara organisms diversified in White Sea time and then declined in Nama time. But, despite this notable waxing and waning in the number of species, the morphological range of the Avalon organisms were never exceeded through the subsequent history of Ediacara."

Scientists are still unsure what were the driving forces behind the rapid morphological expansion during the Avalon explosion, and why the morphological range did not expand, shrink, or shift during the subsequent White Sea and Nama stages.

"But, one thing seems certain -- the evolution of earliest macroscopic and complex life also went through an explosive event before to the Cambrian Explosion,” Xiao said. “It now appears that at the dawn of the macroscopic life, between 575 and 520 million years ago, there was not one, but at least two major episodes of abrupt morphological expansion."

Really it ought to be called the Ediacaran, Avalon, or Vendian Explosion. It has little to do with the subsequent evolution of animal life as far as we can tell, but, still, it seems to have been an important stage if for no other reason than it tells an interesting tale in and of itself about life. And its extinction.


Contents

The base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. [15] The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult since the occurrence of very similar trace fossils belonging to the Treptichnids group are found well below the T. pedum in Namibia, Spain and Newfoundland, and possibly in the western USA. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. [16] [17]

Subdivisions Edit

The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period. The Cambrian is divided into four epochs (series) and ten ages (stages). Currently only three series and six stages are named and have a GSSP (an internationally agreed-upon stratigraphic reference point).

Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three series (epochs) with locally differing names – the Early Cambrian (Caerfai or Waucoban, 541 ± 1.0 to 509 ± 1.7 mya), Middle Cambrian (St Davids or Albertan, 509 ± 1.0 to 497 ± 1.7 mya) and Furongian ( 497 ± 1.0 to 485.4 ± 1.7 mya also known as Late Cambrian, Merioneth or Croixan). Trilobite zones allow biostratigraphic correlation in the Cambrian. Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.

Each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:

International Series Chinese North American Russian-Kazakhian Australian Regional
C
a
m
b
r
i
a
n
Furongian Ibexian (part) Ayusokkanian Datsonian Dolgellian (Trempealeauan, Fengshanian)
Payntonian
Sunwaptan Sakian Iverian Ffestiniogian (Franconian, Changshanian)
Steptoan Aksayan Idamean Maentwrogian (Dresbachian)
Marjuman Batyrbayan Mindyallan
Miaolingian Maozhangian Mayan Boomerangian
Zuzhuangian Delamaran Amgan Undillian
Zhungxian Florian
Templetonian
Dyeran Ordian
Cambrian Series 2 Longwangmioan Toyonian Lenian
Changlangpuan Montezuman Botomian
Qungzusian Atdabanian
Terreneuvian
Meishuchuan
Jinningian
Placentian Tommotian
Nemakit-Daldynian*
Cordubian
Precambrian Sinian Hadrynian Nemakit-Daldynian*
Sakharan
Adelaidean

*Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms. [18] [19] [20]

Dating the Cambrian Edit

The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago and ending at 485.4 million years ago .

The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier, led to calls for a more precisely defined base to the Cambrian period. [21]

Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum. [21] Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, and it is the T. pedum ichnofossil assemblage that is now formally used to correlate the base of the Cambrian. [21] [22]

This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, [21] though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise date using modern radiometric dating yield a date of 541 ± 0.3 million years ago . [23] The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils (Namacalathus, Cloudina). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 or 542 Ma, are more suitable. [21]

Plate reconstructions suggest a global supercontinent, Pannotia, was in the process of breaking up early in the period, [24] [25] with Laurentia (North America), Baltica, and Siberia having separated from the main supercontinent of Gondwana to form isolated land masses. [26] Most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. [26] Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian. [27]

With a lack of sea ice – the great glaciers of the Marinoan Snowball Earth were long melted [28] – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for sea life. The sea levels fluctuated somewhat, suggesting there were "ice ages", associated with pulses of expansion and contraction of a south polar ice cap. [29]

In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into an epicontinental sea. [30]

The Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. However, average temperatures were 7 degrees Celsius higher than today. There were likely polar ice caps and a series of glaciations, as the planet was still recovering from an earlier Snowball Earth. It became warmer towards the end of the period the glaciers receded and eventually disappeared, and sea levels rose dramatically. This trend would continue into the Ordovician period.

The Cambrian flora was little different from the Ediacaran. The principle taxa were the marine macroalgae Fuxianospira, Sinocylindra, and Marpolia. No calcareous macroalgae are known from the period. [31]

No land plant (embryophyte) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya., [13] and microbes forming microbial Earth ecosystems, comparable with modern soil crust of desert regions, contributing to soil formation. [32] [33]

The Cambrian explosion was a period of rapid multicellular growth. Most animal life during the Cambrian was aquatic. Trilobites were once assumed to be the dominant life form at that time, [34] but this has proven to be incorrect. Arthropods were by far the most dominant animals in the ocean, but trilobites were only a minor part of the total arthropod diversity. What made them so apparently abundant was their heavy armor reinforced by calcium carbonate (CaCO3), which fossilized far more easily than the fragile chitinous exoskeletons of other arthropods, leaving numerous preserved remains. [35]

The period marked a steep change in the diversity and composition of Earth's biosphere. The Ediacaran biota suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches. [36] Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla except the Bryozoa, which appeared in the Lower Ordovician. [37] However, many of those phyla were represented only by stem-group forms and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla. [38]

While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 million years ago, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels. 500 million years ago, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events the stromatolites which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids became extinct. This declining trend did not change until the Great Ordovician Biodiversification Event. [40] [41]

Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the Protichnites. [42] Fossils of the track-maker of Climactichnites have not been found however, fossil trackways and resting traces suggest a large, slug-like mollusc. [43]

In contrast to later periods, the Cambrian fauna was somewhat restricted free-floating organisms were rare, with the majority living on or close to the sea floor [44] and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry. [44]

Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of Lagerstätten.

The United States Federal Geographic Data Committee uses a "barred capital C" ⟨Ꞓ⟩ character to represent the Cambrian Period. [45] The Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR . [46] [47]


7.2.2C: Post-Cambrian Evolution and Mass Extinctions - Biology

518 Ma) consists of mudstones about 8-met. more ABSTRACT The lower Cambrian Sirius Passet Lagerstätte (

518 Ma) consists of mudstones about 8-meter thick located in the Franklinian Basin of North Greenland. We analyzed major and trace elements plus the S, C, Cu, Fe, Zn, and Mo isotope compositions. Factor analysis allowed the lithology of the mudstone to be broken down into variable proportions of two inputs, a dry felsic component and a hydrous mafic component (smectite or chlorite). Zircons U-Pb ages indicate multiple sources, the local Proterozoic basement of Northern Greenland (1250-2400 Ma) and Pan-African felsic magmas (620-650 Ma) from across the Iapetus ocean. Diagenesis involved the reduction of Fe, S, and Mo from seawater and pyritization. The Sirius Passett Lagerstätte formed in oxygen-starved muds inhibiting degradation of organic matter underneath a well-ventilated water column. The chemistry of the samples, their very fine grain size, their apparent lack of graded bedding, and the age of zircons suggest that the Lagerstätte may represent wind-blown dust deposited on the continental slope.


7.2.2C: Post-Cambrian Evolution and Mass Extinctions - Biology

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FINALLY GOING ON TWITTER (from Nov 16, 2019) Follow @michael_s_y_lee for all our research news !
Evolutionary biology, phylogenetics, Bayesian inference, palaeontology, macroevolution, herpetology, lizards, snakes, reptiles, and of course Woody Allen.
Supervisors: Jennifer Clack FRS

Background: Palaeognathae is a basal clade within Aves and include the large and flightless rat. more Background:

Palaeognathae is a basal clade within Aves and include the large and flightless ratites and the smaller, volant tinamous. Although much research has been conducted on various aspects of palaeognath morphology, ecology, and evolutionary history, there are still areas which require investigation. This study aimed to fill gaps in our knowledge of the Southern Cassowary, Casuarius casuarius, for which information on the skeletal systems of the syrinx, hyoid and larynx is lacking-despite these structures having been recognised as performing key functional roles associated with vocalisation, respiration and feeding. Previous research into the syrinx and hyoid have also indicated these structures to be valuable for determining evolutionary relationships among neognath taxa, and thus suggest they would also be informative for palaeognath phylogenetic analyses, which still exhibits strong conflict between morphological and molecular trees.

The morphology of the syrinx, hyoid and larynx of C. casuarius is described from CT scans. The syrinx is of the simple tracheo-bronchial syrinx type, lacking specialised elements such as the pessulus the hyoid is relatively short with longer ceratobranchials compared to epibranchials and the larynx is comprised of entirely cartilaginous, standard avian anatomical elements including a concave, basin-like cricoid and fused cricoid wings. As in the larynx, both the syrinx and hyoid lack ossification and all three structures were most similar to Dromaius. We documented substantial variation across palaeognaths in the skeletal character states of the syrinx, hyoid, and larynx, using both the literature and novel observations (e.g. of C. casuarius). Notably, new synapomorphies linking Dinornithiformes and Tinamidae are identified, consistent with the molecular evidence for this clade. These shared morphological character traits include the ossification of the cricoid and arytenoid cartilages, and an additional cranial character, the articulation between the maxillary process of the nasal and the maxilla.

Syrinx, hyoid and larynx characters of palaeognaths display greater concordance with molecular trees than do other morphological traits. These structures might therefore be less prone to homoplasy related to flightlessness and gigantism, compared to typical morphological traits emphasised in previous phylogenetic studies.


Watch the video: What caused the Cambrian explosion? The Economist (August 2022).