The Rise of Animals

30 05 2011

This talk will take us through the origin and initial diversifications of animal life.

It will be chronological, from the latest Neoproterozoic to the end of the Palaeozoic. Wikipedia has a timeline for you to orient yourself.

One theme that will be very prominent throughout is that of Konservat Lagerstätten, or sites of exceptional fossil preservation. Whereas 99% of the fossil record consists of bones, shells, teeth and other hard parts, these localities preserve soft parts, such as muscle and tissue. We will see just how important this is in general for palaeontology, but also in the study of this particular topic of the origin of animals.

We left off the previous talk with oxygen levels at ~10% PAL. Another rash oxidation event happened at ~700 Ma which led to the atmosphere reaching a similar oxygen level to today. This is correlated with the break-up of the supercontinent Rodinia.

This break-up caused, or played into, several severe changes happening in the geosphere at the time. The Earth was coming off the grips of a Snowball Earth period. So advanced was the glaciation that it was initially thought that the Earth was frozen right up to the Equator; now it is thought to be more of a “slushball Earth”. With the increasing temperatures and melting glaciers, the sea levels rose.

Accompanying this is the presence of drastic geochemical anomalies; the diagram above shows carbon isotope anomalies, but the same patterns can be seen with other geochemical elements, including sulphur.

As of the last glaciation, we have the earliest fossil record of animals. A pertinent question is whether these anomalies were the cause of the origin of animals, or whether the origin of animals caused the geochemical anomalies, or to which degree they influenced each other.

Diagram Source: Marshall, C. R. 2006. Explaining the Cambrian “Explosion” of Animals. Annual Review of Earth and Planetary Sciences 34, 355-384.

As I mentioned, Konservat Lagertätten are important when discussing this topic, and here you can see why: there are a lot of them in this period of time. We will see why later. The ones in bold are the ones we will look at specifically.

Bitter Springs preserves cells in 3D, and I include it here as it is 800 Ma, but contains no animals.

Dengying contains the earliest true Ediacarans (see later).

Uratanna is the original Ediacaran Fauna formation, where they were first discovered.

Finally, another thing to round off the introduction is the question of the sister group to the animal, in other words with who they share their last common ancestor.

It is thought that their sister group is the choanoflagellates, a group of flagellated unicellular eukaryotes. As the picture above shows, they can clump together to form multicellular colonies, and it is imagined that this is how the first animals (characterised by multicellularity) could have joined together from their unicellular precursors.

So now we can start looking at the first confirmed animals: the Ediacaran Fauna.

The diagram above shows their temporal distribution. The earliest fossils are small, from 635 Ma localities. These were interrupted by a last glacial period, after which the Ediacaran faunas radiated.

Diagram Source: Xiao,S. & Laflamme, M. 2009. On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota. Trends in Ecology & Evolution 24, 31-40.

The Twitya Formation in Canada records the first true animal life, from before the Ediacaran radiation. As you can see, there’s nothing really spectacular here.

Picture Source: Hofmann, H. J., Narbonne, G. M. & Aitken, J. D. 1990. <a href=”http://dx.doi.org/10.1130/0091-7613(1990)0182.3.CO;2″>Ediacaran remains from intertillite beds in northwestern Canada. Geology 18, 1199-1202.

It was only after the Gaskiers Glaciation that the familiar Ediacarans appeared. The above shows the most famous ones.

Charniodiscus, Charnia and Rangea are referred to as problematics, i.e. we don’t know what they are. They bear a superficial resemblance to sea pens, but they have nothing to do with them systematically, or with any other taxon known. As such, we place them as separate phyla in their own right.

Tribrachidium is similarly problematic, however some authors place it among the medusoids (jellyfish).

The others are at the focal point of a lot of research, as they are thought to be stem-group representatives of the phyla that radiated in the Cambrian Radiation, i.e. of the animals besides sponges and cnidarians. Kimberella is thought to be a stem-group mollusc, Parvancorina a stem-group arthropod, Dickinsonia a stem-group mollusc or annelid, and Spriggina a stem-group annelid. These are all very tentative, though, and a full discussion would require a talk of its own.

So, to summarise, what we have among the Ediacaran biota are sponges, cnidarians (jellyfish and corals) and the stem-group of animals.

In the past, a popular hypothesis pushed by Adolf Seilacher gained prominence: the Vendobiont hypothesis. Adolf Seilacher is a pioneer and revolutionary of trace-fossil palaeontology, and he postulated that the Ediacarans were something like colonies of unicellular organisms forming layers separated by air, like air-mattress organisms. This is now discounted even by Seilacher, as there is significant evidence that the Ediacaran faunas were animals, not just aggregated unicellular organisms.

Another hypothesis states that some of the fossils are actually algal or lichen trace fossils. This may sound outlandish, but experiments in algal and lichen taphonomy (grow them in similar mud and see what trace they leave behind) shows that their death trace bears an uncanny resemblance to some of the Ediacaran fossils, particularly Dickinsonia and the “compressed jellyfish”.

However, it is undeniable that animals were present amid the Ediacaran biota. The proof of this comes courtesy of the first of the very significant Konservat Lagerstätten, the Doushantuo Formation, China. Fossils from Doushantuo are all microfossils: nothing above a certain size gets preserved. However, these microfossils are impeccable, preserved in 3D and preserving cellular detail. Among them, we have found these microfossils pictures above.

These are embryos, which I sorted by cleavage stage. The only organisms that produce embryos like this are animals.

However, there is no extant animal taxon that has this cleavage pattern, so these embryos are not sortable systematically.

2012 update:  many of these have been shown not to be embryos, but clustered single-cells organisms!

Pictures Source: Xiao, S., Zhang, Y. & Knoll, A. H. 1998. Three-dimensional preservation of algae and animal embryos in a Neoproterozoic phosphorite. Nature 391, 553-558.

More impressive pictures can be seen at DOIs 10.1073/pnas.0904805106 and 10.1038/nature04890. Geological information on Doushantuo at DOI 10.1016/j.gr.2011.01.006.

The Ediacaran fauna went extinct at 545.5 Ma, coincident with the Cambrian Radiation.

From now we will look at the Cambrian Radiation of animals, starting with the three classic localities documenting it, before reviewing the causes.

The earliest of these localities is the Chengjiang outcrop of China. On the palaeogeographical map, it would be on the ocean floor on the outskirts of Gondwana, near where it says “South China”, whereas the Burgess Shale would be near Laurentia (where it says “Alaska”).

The fact that they are so wide apart, but are still so similar (as we will see) makes it reasonable to conclude that what is observed there are representative of the situations around the globe.

Map source: Scotese Palaeomap Project

Chengjiang and the Burgess Shale are very similar in every way, as seen in the diagram on the right with faunal compositions. 65% of the fossils there are arthropods – and almost all of them are non-mineralised, i.e. they are all soft parts.

Among them we can count all the main ecological guilds, from deposit feeders to carnivores.

Besides arthropods, we also find sponges, brachiopods and various “wormy” taxa. Also, the earliest chordate, Haikouella, is found in Chengjiang.

By far the most abundant Chengjiang fossils are these small, bivalved crustacean-like organisms called bradoriids. These can be imagined as swimming in swarms, like the krill of today, and probably served as the main food source for predators.

Picture Source: Hou, X., Williams, M., Siveter, D. J., Siveter, D. J., Aldridge, R. J. & Sansom, R. S. 2010. Soft-part anatomy of the Early Cambrian bivalved arthropods Kunyangella and Kunmingella: significance for the phylogenetic relationships of Bradoriida. Proceedings of the Royal Society B 277, 1835-1841.

The chronologically next Lagerstätte is the Sirius Passet of Northeast Greenland.

Sirius Passet is most well-known for its small shelly fauna. These include fragments of larger organisms, as well as whole organisms. As the name suggests though, they are all below a certain size and are essentially microscopic.

Sirius Passet also has its own share of macrofossils too, the more interesting ones being the problematics, two of which are pictured above.

Kerygmachela is a stem-group arthropod.

Halkieria is thought to be a mollusc, but could also be an annelid. It has two shells (‘as’ = anterior shell, ‘ps’ = posterior shell), and the soft body is slug-like between them. The body is surrounded by sclerites (‘sc’).

For the brachiopodologists, Sirius Passet is of special interest as it records the earliest divergences of brachiopod subphyla.

One particularly common group of enigmatic microfossils are the mobergellans. They are little shells with 9 muscle scars on them; no such arrangement is known from other taxa, fossil or recent.

And now we come to what is the granddaddy of Konservat Lagerstätten, the 505 Ma Burgess Shale, found in the Canadian Rocky Mountains.

Some history on the place: it was discovered by Charles Doolittle Walcott, an American invertebrate palaeontologist, in 1901. He was out looking for trilobites when he stumbled on peculiar fossils. He later got permission to dig out a quarry there and by 1916 had accumulated and described hundreds of specimens, and left thousands more in the Smithsonian Institution of which he was the Secretary.

Through no fault of his own, the fossils were inadequately described – phylogenetic thought was not known or popular at the time. In the 1970s, Harry Whittington and his two students Derek Briggs and Simon Conway Morris started redescribing all these specimens in a brand new way: not as “weird animals”, but as stem-group representatives of modern phyla.

This is, of course, the correct approach (although some disagreed, notably Stephen J. Gould), and it was this reinvestigation, which is still ongoing with a new generation of students, that led to the discovery that there was indeed a Cambrian radiation of animals. Keep in mind that this was the first Cambrian Konservat Lagerstätte to be discovered, the rest came later.

As with Chengjiang, the Burgess Shale preserves an entire community. The taphonomical story shows why it is so reliable.

One can imagine the Burgess Shale as being a somewhat deeper water environment, with all the organisms either in, on or swimming above the ocean floor. The habitat was right beneath a cliff. At some point, this cliff got dislodged, perhaps due to an earthquake, leading to an underwater mudslide which buried the entire habitat.

The main organism group we find there are arthropods, especially this one, Marrella.

Also among the significant organisms are the first cephalochordates (Pikaia) and early echinoderms (sea stars, brittlestars, sea urchins, sea cucumbers and sea lillies are the five classes still alive; there were 42 classes in their history, many of which had very strange morphologies, e.g. the helicoplacoid above).

Also well represented in the Burgess Shale are ecological associations, examples listed above. This hints at a fully-functioning ecosystem, unlike what we see in the Ediacaran.

Picture Source: Skovsted, C. B., Brock, G. A., Lindström, A., Peel, J. S., Paterson, J. R. & Fuller, M. K. 2007. Early Cambrian record of failed durophagy and shell repair in an epibenthic mollusc. Biology Letters 3, 314-317.
This is also obvious from the number of ecological guilds preserved, which span the entire possible spectrum.

The fossils of the Burgess Shale are very well-known for their weirdness [Note: yellow rocks above are Chengjiang ones]. It is a veritable freakshow. What will now follow is a simple showcase of the more famous fossils.

Anomalocaris is the poster child of the Cambrian Radiation, a large and probably vicious predator with two large eyes, an enormous toothy appendage and a characteristic pineapply mouth,

Originally, it was described as two animals, the appendage being one animal and the pineapple mouth another. It wasn’t until the Whittington et al. reinvestigations that it was discovered to be one single animal.

Anomalocaris is the original, but many more relatives have been found with very different morphologies. Only three have body fossils: Anomalocaris (top left), Hurdia (top right) and Laggania (bottom left). The rest are known from isolated appendages.

As a sidenote – going into the stem-group arthropod fossil record and systematics is impossible in this space – this appendage is called the great appendage, but it evolved in other taxa independently, although they are erroneously lumped together as “great appendage arthropods“.

Hallucigenia, as the name suggests, is a very strange animal. Originally, it was described upside down, but then was flipped over. It is a stem-group velvet worm (Onychophora) with spikes on its back, presumably for defence.

Sanctacaris is another strange arthropod, thought to be on the stem line to the Chelicerata (spiders, scorpions et al.)

Opabinia is the classic freak of the Cambrian Radiation – when its reconstruction was first unveiled at a scientific conference, the auditorium reportedly burst out laughing. And it’s not hard to see why, with its five stalked eyes and that ridiculous proboscis ending in a grasping appendage.

To move away from the arthropods, we also have Wiwaxia. It’s an animal whose body is entirely covered by sclerites, and it also possesses those elongated spines. There is no fossil available yet to shows us what lay beneath all the armour. It is assumed to be either a stem-group mollusc or annelid.

And for a brand new reconstruction, here’s a reinterpretation of Nectocaris pteryx as a cephalopod.

It also has a varied history, first described an an anomalocarid, then as an arrow worm, before ending up as a cephalopod. This is a testament to the difficulty of getting the interpretations of these ancient fossils right.

So basically, when you see a picture like this, the only thing that is fictional are the colours. No matter how strange the organisms in a Cambrian reconstruction look like, they are most likely to be real.

So now that we know what was around, it’s time to dig into why this is such a significant event in the history of life. What makes the Cambrian Radiation so special?

It was the first appearance of bilaterian animals in the fossil record. The Bilateria is the node numbered 573 above – all animals excluding Cnidaria (jellyfish) and Porifera (sponges). Before the Cambrian, what was present was the stem-group of all these phyla. But it was only in the Cambrian that the crown groups started appearing.

For a more graphical perspective, here is another picture, to put a face to all the perhaps unknown names.

Source: Barton, N. H., Briggs, D. E. G., Eisen, J. A., Goldstein, D. B. & Patel, N. H. 2007. Evolution. CSHL Press. [See http://evolution-textbook.org/]

In the talk, these arrow-fests were brought gradually by clicking, but here you can take your time and examine them carefully.

The Cambrian Radiation is the result of a new innovation in developmental biology: triploblasty, i.e. a third germ layer. In sponges, there is only one germ layer, the endoderm, which builds the digestive system and epithelial linings (and lungs, in those animals who have those). Cnidarians go one step further and have an ectoderm, out of which arises the nervous system.

Bilaterians all have three germ layers with the addition of the mesoderm. This allows some very significant changes in morphology to happen, as the skeleton, the coelom and the circulatory system arise from it.

In abstract terms, what these lead to is an expansion of the possible morphospace. In practical terms, there is more support available for differing morphologies: with muscles come new ways of moving, circulatory systems allow larger body sizes, coeloms provide structural support.

There were two major changes in the nature of the fossil record in the Cambrian. The first is the appearance of massive biomineralisation – the building of shells and carapaces.

This not only plays into the support-for-morphologies aspect (and other aspects, as we will see), but is also a fundamental change for the fossil record, as it is the beginning of ‘regular’ fossilisation.

Obviously, biomineralisation started out small. There are isolated examples from the Ediacaran fauna, but mineralisation first became popular with the rise of the small shellies in the Tommotian stage of the Early Cambrian.

For some background, biomineralisation is not simply a process by which a lump of hard material is thrown on an organism’s back – although it may have started that way. It’s a tightly-regulated process. Even in snails and bivalves, the shelled molluscs, the shells do not consist solely of minerals, but the minerals are integrated into a complex cocktail of proteins. In arthropods such as shrimp, biomineralisation is also present in the head shield, where trace amounts of carbonates are embedded in the chitin matrix. Vertebrate bones are the same: they are not clumps of calcium phosphate, they are living tissue.

Anyway, the appearance of biomineralisation can easily be linked to the geological changes of the time. With the break-up of Rodinia, more nutrients were leeched into the oceans and they became saturated. Combined with the warming of the climate, crystallisation was favoured. This was incorporated and controlled by the organisms because biomineralisation is very useful for shells and for weapons, as we will see.

The other major change is in the trace fossil record. The picture shows Trichophycus pedum, a trace fossil whose earliest presence at 535.5 Ma is the accepted boundary between the Proterozoic and the Cambrian periods.

Note that it has now been found at earlier times, but the generalisations in the next page are still valid.

Trichophycus is a deep and very sculpted trace, something typical of a burrowing animal. Traces like these are only found from the Cambrian onwards – Ediacaran trace fossils are mere scratches on the surface.

Such an advance in a trace fossil can only be brought about by advances in morphology – this is the effect of triploblasty and the development of muscles and active movement.

In turn, this leads to what is referred to as the “Cambrian substrate revolution”. Animals could now invade a new, up to now unexplored territory: the sediment. They could anchor themselves or dig tunnels. In essence, the increase in trace fossil complexity heralds the start of regular marine ecology, and it can all be traced back to the development of triploblasty.

The above picture summarises what we see as the Cambrian Radiation: a drastic radiation of animals, concurrent with an increase in biomineralisation and the complexity of trace fossils.

So now we can begin exploring some of the more general aspects of the Cambrian Radiation and write a basic synthesis. Written in red are key rules of thumb that should always be kept in mind.

We already went through the Ediacarans, but just as a reminder: it was not a “garden”, as it is sometimes called in popular articles. It contained animals.

What triggered the radiation of the animals was the environmental changes of the time – the rise in temperatures allowed a general increase in biological activity (heat = energy, after all).

The deglaciations caused flooding and a great increase in the space available for animals to live in. At the start, these were colonised by the Ediacaran faunas, which formed what is called a permissive ecology, i.e. one in which even inefficient organisms like the Ediacarans could survive.

However, their reign was ended due to the rise of oxygen. Oxygen was the key to taking advantage of triploblasty: it allowed circulatory systems to develop and body size to increase, by allowing the biosynthesis of many types of tissues and fibers, most notably collagen. These, combined together, allowed the triploblasts to rise to dominance.

Another aspect to keep in mind is the evo-devo (evolution of development/evolutionary developmental biology) one. It is well-known that many, if not most, genes, especially developmental ones, are conserved across all animal taxa. The early evolution of animals proceeded largely by cooption of existing genetic pathways, and a few select duplications.

This, combined with the environmental chaos, led to a whole load of experimentation, producing such weird freaks of nature as the vetulicolians, pictured above.

With natural selection, the successful “body plans” (I use that term loosely for the sake of pedagogy!) were kept and development was “canalised”, i.e. focused along narrower and narrower paths. In abstract terms, the few fitness peaks on the morphospace were gradually being discovered and climbed.

This plays into a larger issue in palaeontology and evolutionary research, namely how genetic changes result in morphological ones. This is another issue which would require a specific lecture (series) to deal with properly, so it is summarised in red: you cannot simply correlate genetic change to morphological change.

This may seem like an irrelevant quip to make for this topic, but whether the Cambrian Radiation is a real event is actually a controversial subject. Molecular phylogeneticists employ a molecular clock in order to measure divergence dates. This molecular clock is not at all as foolproof as is made out to be and is faulty more often than it is correct (for reasons that would require their own talk to explain!).

Earlier molecular clock studies had outrageous dates for the origin of animals (cf. above example). Nowadays, they are closer to the fossil record, but still have an (expected) gap, mostly placing the origin of animals between 700 and 600 Ma.

This has led to talk of the Cambrian Radiation being merely an illusion, brought about by a gappy fossil record. This is complete poppycock: you cannot wish for a better fossil record than that in the Cambrian. It is the molecular clocks that are wonky, not the fossil record.

Very basically, the molecular clock finds out when genetic intermixing stopped – i.e. the point of speciation. However, because genetic changes are not directly measurable in morphology, this is impossible to see in the fossil record.

Note that I am oversimplifying the matter to the point of perhaps being false. If wanted, contact me for more detailed info on the difference between molecules and morphology, and molecular clocks and the fossil record.

So by now we have our diverse animals that can move around in whole new ways. The driver of the Cambrian Radiation was how the animals employed their new abilities both in dealing with their environment and among themselves.

The Cambrian substrate revolution is the main novelty in the former, but it should not be forgotten that active swimming and movement was also a novelty.

However, the real star of the show is the latter: how animals started influencing each other. I mentioned the preservation of organismal interactions in the Burgess Shale. These can all be led back to a single selective pressure: predation.

Biomineralisation was selected for because hard shells offer protection. In response, predators took advantage of the same effect to make weapons. In response to those, animals lower on the food chain reinforced their shells. And so on. This pattern is called a coevolutionary arms race and it is most evident in the Cambrian Radiation.

Predation explains why we have animals such as Opabinia with five eyes, or anomalocarids with huge eyes: they were predators and needed to see their prey. The main use of shells is for defence, and they needed to be in top shape at all times, as evidenced by this particular picture with the shell damaged by predation. Even the Cambrian substrate revolution played into the predation aspect: burrows are great hiding spots.

In a nutshell, environmental changes triggered the radiation, developmental biology and geochemistry allowed animals to diversify, and the radiation was made all the more spectacular by all-new types of ecological interactions, most importantly predation.

To move on from the Cambrian Radiation, we can look at the next striking Konservat Lagerstätte: the Orsten. Initially, it referred to a single locality from the Late Cambrian of Sweden, but it is now known as a special taphonomic window (i.e. a place that preserved specific things) from all over the world.

It preserves small animals in small nodules with extremely fine detail and in 3D, as seen above. The majority of these are arthropodan larvae.

For more info: Maas, A., Braun, A., Dong, X.-P., Donoghue, P. C. J., Müller, K. J., Olempska, E., Repetski, J. E., Siveter, D. J., Stein, M., Waloszek, D. 2006. The ‘Orsten’—More than a Cambrian Konservat-Lagerstätte yielding exceptional preservation. Palaeoworld 15, 266-282.

For pictures and updates: http://www.core-orsten-research.de/

As an example of how spectacular these fossils are, here’s Cambropycnogon, the first instar larva of a pycnogonid (sea spider).

Even more informative, we have larvae of stem-group crustaceans, which provides us with a lot of info and data on the systematics and evolutionary history of the crustaceans that is otherwise unobtainable.

So by the end of the Cambrian, this is what the sea-floor looked like: it was by and large arthropod-dominated, with trilobites being the most diverse group, some competing with the hyoliths (those conical animals with the handlebars). A couple of epibenthic bivalves were also common.

Picture source: Harper, D. A. T. 2006. The Ordovician biodiversification: Setting an agenda for marine life. Palaeo3 232, 148-166.

The Cambrian had a unique type of fauna, with low species diversity. With the beginning of the Ordovician, though, this changed as one of the largest radiations in the history of life on Earth took place.

It should be clarified that the Cambrian Radiation did not lead to such a huge increase in diversity, but was a diversification of “higher levels of systematics” (of phyla and form). However, it was in the Ordovician that the lower levels (orders, classes) known from the fossil record and today originated, as seen in the diagram above.

This radiation is explained by more environmental changes. In the Ordovician, the oceans rose more and huge epicontinental seas developed, leading to more colonisation space for the opportunistic organisms to take advantage of quickly.

These included the brachiopods, who managed to diversify into many forms (now extinct).

Picture source: Zhan, R.-B., Jin, J. & Rong, J.-Y. 2006. β-diversity fluctuations in Early–Mid Ordovician brachiopod communities of South China. Geological Journal 41, 271-288.
Another group that radiated in the Ordovician were the trilobites, reaching high taxonomic, morphological and ecological diversity.

The echinoderms reached their highest diversity in the Ordovician, with most classes (including the ones still living today) originating in this radiation.

For more on echinoderm palaeodiversity: Smith, A. B. 2005. The pre-radial history of echinoderms. Geological Journal 40, 255-280.

What all these radiations led to was a drastic shift in the way marine benthic ecosystems are structured. The Cambrian seafloor was crawling with very mobile species; in the Ordovician, these were replaced by many mostly-sessile organisms such as sea lillies (crinoids) and bivalves. Brachiopods were at their peak, and molluscs were beginning to rise to dominance.

However, it is from this point that we start getting the effect of the Cambrian Radiation on the fossil record. The animals that radiated in the Ordovician all have hard parts and are preserved in any case.

Soft part preservation depends on anoxic, undisturbed deposition. With the advent of burrowing in the Cambrian Radiation, such depositional enbironments were hard to come by: any carcass that gets buried will just be fed on by an organism living in the sediment.

What this means is that this radiation of shelly- and skeletonised organisms, while it did definitely take place, may also have been accompanied by diversifications in non-shelly taxa, such as most arthropods (besides trilobites).

This highlights the importance of Konservat Lagerstätten, only one of which exists for the Ordovician: the Fezouata Formation in Morocco. What we find there, besides the shelly taxa, are remains of many soft-bodied arthropods, many of which can be linked back as relatives of the Cambrian freaks. For example, above you see Furca, a relative of Marrella, the most abundant arthropod of the Burgess Shale and most abundant arthropod of the Cambrian.

As a summary, here is what happened in the Ordovician Radiation. It is a classic case of shifting ecological dominance. The cause was the appearance of new and widespread shallow oceans, allowing the orthids (cephalopods, the straight-coned ancestors of the ammonites) and snails to radiate and push the previously dominant trilobite and early crinoid fauna into deeper waters. The same happened in the Late Ordovician, when bivalves took over and pushed those groups into mid-deep water.

However, this was rather short-lived, as at the end of the Ordovician, the second-largest extinction event of all time happened: the end-Ordovician mass extinction.

However, this was not as drastic as it may seem. Sure, biodiversity took a big hit, but the new ecological structure that was established in the Ordovician Radiation re-emerged unscathed, just with other taxa filling those ecological guilds.

The cause of it is simple. These new oceans that had formed were exceptional, in that they were the result of melted glaciers. As soon as a cold climate came back into play, these oceans disappeared quite suddenly, and the shallow-water organisms had no time to move or adapt to the deeper waters to survive.

To continue with our Konservat Lagertätten theme, we move on to the Silurian, where again, there is only one of note: the Hereforshire locality.

Here, organisms were buried in volcanic ash and preserved in 3D (like in Pompeii). However, there is one unique aspect: these organisms cannot be prepared out of their nodules. Instead, many very thin slices are made (on the several µm-scale), and all these slides are scanned and digitally stacked together to form a 3D model of the organism inside. An example of a slice can be seen on the left, middle.

Through the years, the technique has been improved, and we can now make such detailed pictures as the coloured ones above, showing 2 stem-group arthropods (left), a brachiopod with pedicle (middle) and a pycnogonid (right; modern analogue for comparison below).

Again, examination of the specimens in this locality provides data we would otherwise not have on diversity for many organisms, and in enough detail to make proper morphological analyses possible.

As a small case study for the importance of Konservat Lagerstätten, consider the anomalocarids. Select examples are pictured above. These are all from the Cambrian.

This is where Schinderhannes bartelsi comes in. It is an anomalocaridid from the Lower Devonian Hunsrück Slates, another Konservat Lagerstätte, and the only [at the time, see note] non-Cambrian anomalocaridid known. [Note added in press: just this week, an Ordovician anomalocaridid was published, from the Fezouata Formation, see above. Interestingly, I had predicted this during my talks, meaning that I have divine powers and thus you should send me money. Uhh, where was I? Right, reality...]

Without its finding, it would logically be assumed that the anomalocaridids died out at the end of the Cambrian. This is the true importance of the Konservat Lagerstätten.

And to round off the talk, some more about these Hunsrück Slates, since I’ve done some work in them myself (in the same team that described Schinderhannes, although I joined later than that). The locality is 405 Ma, from western Germany. The fossils come from three quarries, Simmern, Gemünden and Bundenbach; see the map above, prepared by Gabriele Kühl (Uni Bonn) based on Rothe (2005) and Mittmeyer (1980).

Mittmeyer HG. 1980. Zur Geologie des Hunsrückschiefers. In: Stürmer W, Schaarschmidt J & Mittmeyer HG (eds.). Versteinertes Leben im Röntgenlicht. Kleine Senckenberg-Reihe 11, 34-39.

As you can see, the quarry is now left alone and collectors can just walk in and pick up slabs of slate. However, be warned that the fossils are very, very rare, especially the spectacular ones. The picture above is by Alexandra Bergmann (Uni Bonn).

On the deposition, the Hunsrück Slates are the result of turbidites (underwater mud flows). They swept through from shallow waters to deeper waters, carrying organisms and habitats with them, before depositing them in an anoxic basin. The anoxia was caused by bacteria who fed on the carcasses. Importantly, these bacteria caused the muscles to be replaced by pyrite – the ocean waters were saturated with iron and sulphur. This is what causes the soft-past preservation: pyrite is a hardy mineral.

The Hunsrück Slate fossils are pyritised. Pyrite is a radiodense material, meaning X-Rays cannot pass through them. This means we can X-Ray them, and in fact, the first fossils to have been studied by X-Ray were Hunsrück Slate ones, just a couple of years after the discovery of X-Rays.

In recent years, the advent of computer tomography has made it possible to X-Ray them in 3D, as shown above. This can potentially provide more information, or make it easier to interpret enigmatic structures.

Basically, what I want to say is that palaeontologists are not hole diggers and stamp collectors, and we also need and use technology to get the most out of our materials.

Jump to: The Origin of Life and of the Atmosphere, Terrestrialisation, Mesozoic Vertebrates, Coevolution of Flowers and Insects, The Tertiary

Research Blogging necessities :)

Marshall, C. (2006). EXPLAINING THE CAMBRIAN “EXPLOSION” OF ANIMALS Annual Review of Earth and Planetary Sciences, 34 (1), 355-384 DOI: 10.1146/annurev.earth.33.031504.103001

Xiao, S., & Laflamme, M. (2009). On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota Trends in Ecology & Evolution, 24 (1), 31-40 DOI: 10.1016/j.tree.2008.07.015

HARPER, D. (2006). The Ordovician biodiversification: Setting an agenda for marine life Palaeogeography, Palaeoclimatology, Palaeoecology, 232 (2-4), 148-166 DOI: 10.1016/j.palaeo.2005.07.010


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38 responses

30 06 2011
inquilinekea

Hey Marc – what do you think of this paper though? http://www.sciencemag.org/content/282/5386/80.full . It actually says that we have the first animal fossils from 1 billion years ago!

30 06 2011
Marc

Ah, I just realised I axed the slides where I mentioned this paper, because I cracked way too many jokes at poor old Seilacher’s expense ^^ These traces turned out to be nothing – I can’t remember the citation for the rebuttal and disproof though, sorry! The oldest putative animal fossils are ~660 Ma sponges :) Citation for those is pretty new: http://dx.doi.org/10.1038/NGEO934 .

30 06 2011
inquilinekea

Aw – damn it. :( I was hoping that these traces were something! And I even mentioned it to people in the earth/planetary sciences! Something definitely has to be done to link up articles with possible criticisms/refutations of them, especially ones in Science/Nature

Now I just googled his name – is http://www.sciencemag.org/content/284/5418/1235.1.full.pdf the paper?

30 06 2011
inquilinekea
30 06 2011
Marc

That paper is a commentary, but it is outdated as well >.< Here is the latest paper on these things: http://www.pnas.org/content/106/19/7729.full, by Bengtson et al (2009). They are fossils, but they have nothing to do with animals :) Quick summary: They're algae and cyanobacteria. Still exciting for uncovering the evolution of multicellularity, but not for animals.

And yes, I agree about having some sort of follow-up system, especially for those who don't keep up with a particular field. Scholar is acceptable, but you have to separate papers that just mention it offhand and those that actually comment on the paper, so it's a bit of a hassle :P But better than nothing.

30 06 2011
inquilinekea

Hahaha – I see – thanks for the paper!

Yup – good points about Scholar! (I had that issue when browsing through them). What follow-up systems generally exist in people who do keep up within a particular field?

30 06 2011
Marc

The best way is to sign up to be alerted to the Table of Contents of your favourite journals. The Big 3 (Nature, Science and PNAS) are a must, at least. If you’re a biologist, the Proc. R. Soc. B is also a must. And then it depends on what your speciality is – you get to learn the journals eventually (I can tell you the good ones for the various bio fields, if you’re interested, dunno for physicists and chemists). The various Annual Reviews series are excellent all around.

Most publishers (except, inexplicably, Nature!) offer a citation alert service for each paper (“E-mail me when this article is cited” or something similar). Sign up for that and you’ll get alerted whenever your fave papers get cited.

Those are the two main ways. The rest is word of mouth from colleagues. I tried to have weekly updates of new exciting papers (see the “Research Blogging” tab from the main page), but I just don’t have the time for that anymore, at least not with writing short texts summarising the new papers :) Maybe I’ll resurrect the section and just link to the new papers instead of writing anything about them.

30 06 2011
inquilinekea

Oh thanks – I see! Yup – I read Nature and Science every week – PNAS doesn’t have the short readable articles on the top though. I love the Annual Reviews as well.

Oh cool – what are the good journals for ecology and zoology? (animal behavior/intelligence is actually my favorite of the fields – I’ve RSS-subscribed to a few of the journals, but it’s hard [from my side] to tell which ones are the most well-regarded)

30 06 2011
Marc

Journal of Animal Ecology, Behavioral Ecology, Behavioral Ecology and Sociobiology, Animal Behaviour, and Journal of Ethology are the main ones in animal behaviour.

In ecology, most journals are either “case studies” journals or they’re theoretical ecology that nobody except ecologists cares about/undderstands. For pure zoology, there’s the Journal of Morphology that publishes excellent papers on all taxa, but that’s an exception, most journals are specialised :)

1 07 2011
inquilinekea

Haha I see – thanks very much for the examples! Which ones of these are biggest about animal intelligence?

Interesting points about ecology: yeah – there seems to be a split between the mathematical ecologists and the more practical ecologists (I wonder what the relative proportion between the two is).

2 07 2011
Marc

Hmm… for animal intelligence, there might be focused studies in Animal Behaviour or Journal of Ethology. But the syntheses and good essays ont hat kind of stuff would be found in more general journals – as I mentioned in the e-mail, animal intelligence per se is very understudied, or at least doesn’t focus exclusively on the intelligence aspect. I think BioEssays would be a good source for this kind of essay. Of course, now that I know you like this stuff, I’ll be sure to alert you whenever I come across something new ;)

No idea what the practical:maths ratio is. But you’re right about the gulf. I’m very much a field ecologist, but I could never do any of that theoretical maths stuff that the theoreticians do. Statistics, Bayesian analyses, whatever, okay. But I need my hard data, not these generalised model thingies :P

2 07 2011
inquilinekea

Oh cool I see. Thanks very much for all your responses! =)

12 07 2011
Quora

What explains the explosion of life during the Cambrian period?…

If I’m allowed some utterly shameless advertising, I explained it all in here: http://bioteaching.wordpress.com/2011/05/30/the-rise-of-animals/ (if short on time, just search for “The Cambrian Radiation is the result of” and read from there). In a n…

11 10 2011
belly12

This is a recommended article with the fossils that been presented and way too ice to be read.

31 10 2011
Quora

Is there a relationship between the last Snowball Earth event and the Cambrian Explosion?…

Yes. Whether it was really a Snowball Earth or a “Slushball Earth” is more or less irrelevant; it was definitelly really cold. And cold always restricts biology. So the Snowball events may have delayed the Cambrian Radiation in that respect. After th…

17 12 2011
Cool New Paper: Marine Fungi « Teaching Biology

[...] authors interpret several Ediacaran fossils as marine fungi (e.g. Peterson et al., 2003), but given that they don’t share any [...]

18 12 2011
Cool New Paper: Opabinia’s Limbs « Teaching Biology

[...] is one of the stranger members of the Cambrian freak show (see fossil above, from Hagadorn (2002)); far from the original Walcott reconstruction as a [...]

20 12 2011
Cool New Paper: Anomalocaris Eyes « Teaching Biology

[...] in great with the scheme of the Cambrian Radiation as being an ecological phenomenon, as I outlined here. While I hesitate to go into fantasy, as a palaeontologist my job involves having an active [...]

31 12 2011
2011: Summary « Teaching Biology

[...] The Rise of Animals. I’m very, very happy that this got such a high spot, if only because it’s my [...]

5 02 2012
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[...] it. It turns out that it impeccably preserves organisms at the microscale, kind of like small shelly fossils. Among these are cuticles of crustaceans, including the oldest representatives of extant [...]

30 06 2012
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[...] fossil below is pretty much the same story: the Ediacaran Kimberella. Current concensus places it as a bilaterian animal due to the bilateral symmetry of the [...]

30 06 2012
– The Scientific Method, Exemplified By Palaeontology

[...] fossil below is pretty much the same story: the Ediacaran Kimberella. Current concensus places it as a bilaterian animal due to the bilateral symmetry of the [...]

4 07 2012
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[...] times with specimens, and key events can have a panel dedicated to them (the mass extinctions, Cambrian Radiation, terrestrialisation, [...]

13 08 2012
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[...] “freaks” and of that time of animal evolution as a period of wacky experimentation (see here). This is overembellishment and is constantly being shown as not true. The view used to be [...]

6 05 2013
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6 06 2013
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[…] in the Eumetazoa is the presence of two body layers. I hinted at the importance of this in my Cambrian Radiation lecture. They arose due to the evolution of gastrulation: the blastula known all the way from the basal […]

7 06 2013
24h blogathon!: Tabulate corals | Teaching Biology

[…] their morphotypes by the mid-Ordovician, gaining a slight upper hand over the rugoses. However, the end-Ordovician extinction affected them more than the rugoses, and they had to rebuild their dominance, which was again […]

7 06 2013
24h blogathon!: Red algae | Teaching Biology

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14 06 2013
Best of Teaching Biology | Teaching Biology

[…] The Rise of Animals:  From the same series as the Origin of Life post, this is a heavily-butchered version of my undergrad Cambrian Radiation mini-course (20 minutes versus 6 hours), with additions  going all the way up to the Devonian. Despite the chopping up, it’s still a fairly thorough look at the initial diversifications of marine animals. […]

1 07 2013
Carnival of Evolution #61: Crustie Lovin’ Edition | Teaching Biology

[…] you want to read some more, I wrote a 30-minute distillation of my 6-hour Cambrian Radiation course here, as part of a broader public lecture on the origin and early evolution of animals (Snowball Earth […]

3 08 2013
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22 09 2013
The Eurypterida (Sea Scorpions) | Teaching Biology

[…] as in a classic coevolutionary “arms race” (Lamsdell & Braddy, 2010) that began in the Ordovician Radiation. The largest ever arthropod (as of time of writing) is the pterygotid Jaekelopterus rhenaniae from […]

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[…] fossil below is pretty much the same story: the Ediacaran Kimberella. Current concensus places it as a bilaterian animal due to the bilateral symmetry of the […]

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