Seeing the Forest for the Trees

Reconstruction of Permian Forest from Inner Mongolia (Jun Wang et al. 2012)

OK I'm back after a long hiatus due to extensive travel (yay) and work (boo) commitments. There have been a few things to cover over the next few weeks, but in the meantime, something a little, . . . umm . . . younger than we're used to here on Ediacaran - but there is a link.

Working out how fossil organisms interacted is very difficult as they are usually found singularly or in small groups. Certain things, such as predation for example, can be worked out using single of small groups of fossils, but community interactions require large scale preservation. Such ecological-scale preservation is rare, but some do exist, for example Cretaceous dinosaur footprints, and Devonian fish. A new find from China has added to this small list.

In the earliest part of the Permian, around 298 million years ago, a large volcanic eruption in what is now northern China, resulted in a swampy region being covered by an approximately 100cm thick volcanic tuff. Just like in the more famous example of Pompeii, the tuff trapped and preserved everything beneath it. The ash fall buried and choked the plants, braking off twigs and leaves, felling trees, and preserved the forest remains in place.

Now part of a coal field 8km west of Wuda, Inner Mongolia, the Taiyuan Formation has revealed a wealth of exceptional preservation, but also a wealth of ecological information. The site has allowed approx. 1000 square meters of Permian swamp to be uncovered and systematically investigated. It has allowed the reconstruction of Permian plants, and has also provided information on the relationships between the plants growing at the time.

At the site, six groups of plants make up the vegetation, and an examination of the relationships shows several areas of distinctly different plant occurrences, as well as a number of patterns of co-occurrence. These allow for detailed reconstructions of the original forest, one of which is the photo at the start of this entry.

Some of the exceptional preservation is shown below.

Sphenopsids and lycopsids fossils from the Taiyuan Formation: (A) Asterophyllites longifolius, and (B) associated Paleostachya type strobili; (C) Sphenophyllum oblongifolius, and (D) associated
strobili; (E) Sigillaria cf. ichthyolepis leaf, (F) stem, (G) strobilus. (Scale bars, 2 cm in A, C, D, F, and G; 1 cm in B and E.)

So, what has this Permian deposit to do with the Ediacaran?

Well, this ecologically-focussed investigation has also been undertaken for the Ediacaran fauna. There are a couple of examples of such eco-related investigations.

The first is from the Ediacaran of Newfoundland. At Mistaken Point, the beds outcropping along the coast dip at shallow angles, which means that tennis court-sized areas of old sea floor are exposed along the cliff. Abundant Ediacaran fossils have been found on these surfaces . These fossils include spindle forms as well as the more familiar Charnodiscus disc-shaped forms. The relatively large expanse of uncovered old sea floor allows some interrelationships to be looked at.

Interestingly (and in another link to the Permian find above), preservation here is different to that in South Australia. Here, fossils are found on the top surface of the bed. This is because the organisms and sea floor was covered by an ash falls from volcanic eruptions some time around 565 million years ago. As in the Permian example, ash covered everything and subsequently preserved a snapshot of life at the time.

Ediacaran fossils from Mistaken Point, and the ash layer which has preserved them (photo credit)

The second example comes from South Australia. In the Flinders Ranges, several Ediacaran locations occur in low-lying hills with gentle slopes. As the beds erode out of the soil, they move down slope. As the area is remote, there is little disturbance, and so it is possible to roam the slope picking up pieces of distinctive layers and reconstructing the Ediacaran sea floor.

Reconstructing Ediacaran sea floors from South Australia, both in the field, and at the South Australian Museum (photo credit 1, 2)

The difference here is that the fossils are found on the underside of the bed, not on the top surface, which is normally contains ripple marks caused by current and wave action (as seen in the photo from the South Australian Museum above).

The ability to look at whole communities, rather than individuals provides a much better understanding of what was going on in the past which makes sites where you can actually do that very important.



Jun Wang, Hermann W. Pfefferkorn, Yi Zhangc, and Zhuo Feng. (2012) Permian vegetational Pompeii from Inner Mongolia and its implications for landscape paleoecology and paleobiogeography of Cathaysia. Proceedings of the National Academy of Science of the United States of America, Published online before print, doi: 10.1073/pnas.1115076109

Palaeoporn 24

Tribrachidium heraldicum

Ediacaran goes back to its roots with this Palaeoporn, with probably the most enigmatic of a group of enigmatics, Tribrachidium heraldicum.

Tribrachidium (photo credit)

Tribrachidium is a disc-shaped organism which is characterised by having three 'arms' which spiral out from the centre. Tribrachidium always occurs in negative hyporelief (pressing up into the bottom surface of the sandstone bed) indicating that it had a rigid body that pressed upwards into the overlying sand. The photo above is actually of a cast taken from a fossil so that the original body relief is shown - i.e. this is positive relief. The actual fossil is at right.

The tripartite body plan of Tribrachidium is quite unusual as most metazoans are either bilaterally or radially symmetrical.

So what is it? Well Tribrachidium is a cnidarian. Umm no, actually it's a lophophore (related to brachiopods), umm, or it could be an echinoderm, umm, no, it's an ecdysozoan (a group characterised by organisms that shed their external covering), no actually it's a sponge . . . possibly. Alternatively it could belong to a whole new phylum, the Phylum Trilobozoa. Umm, maybe Class Trilobozoa, well, clade trilobozoa anyway.

So its been a question of, "Look! Up in the sky! Is it a lophophore? Is it a cnidarian? No it's . . . , umm . . . , it's . . . , well . . . , it's a Trilobozoan! Yeah . . . , that's what it is, a Trilobozoan.

[voice from the crowd] It's a what?

Trilobozoan.

[voice from the crowd] What's a Trilobozoan?

Glad you asked.

The Trilobozoa are predominately an Ediacaran group who's members have a tripartite or tri-radial body plan, typified by Tribrachidium.

A triumvirate of Trilobozoa. Albumares Brunsae (x4) (left), Anfesta stankovski (x1) (top right) (Photo credit). Rugoconites enigmaticus (x1) (Photo credit)

The group is a bit of a grab-bag with Albumares and Anfesta from Russia and maybe Rugoconites, as well as some others. The tripartite body plan is almost unique with modern examples confined to teratological (developmental defects) causes. Like Tribrachidium, other trilobozoans are usually found in negative hyporelief and, importantly, although not common, where they do occur in groups they do not overlap, indicating that they are not 'strandings' or simply groups of free swimming forms washed together (otherwise they would overlap).

Tribrachidium, the most common and hence most studied, can also be found in size range of 3 to 30 mm indicating a growth pattern of organisms recruited to the sea floor and growing there, rather than a free swimming form where the sizes would be similar due to current activity. Trilobozans are thought, then, to have been sessile filter feeders, attached to the microbial mats, normally by a bulb-like structure, throughout adult life.

It appears as though the tripartite body plan, or derivatives of it, were quite common in the Ediacaran. Finds such as Ventogyrus are being reinterpreted as a stalked trilobozoan, but placed within the Phylum Cnidaria. Another form, Eoandromeda octobrachiata, though to be related to comb jellyfish (a group of vicious killer jellyfish), is also though to share a number of features in common with Tribrachidium.

So evidence is growing that trilobozoans may well be Cnidarian.

Vicious killer jellyfish, trilobed body plans! The Cnidaria have a lot to answer for!

Trilobozoan Cnidarians? Reconstructed. Tribrachidium stamp (left). Ventogyrus (photo credit)

3.4 Billion Year Old Microfossils? . . . Umm Yes (Probably)

Sshhh, be vewy vewy quiet. We’re hunting Awchean pwokawyotes.

There is good carbon and sulphur isotope geochemical evidence that life has existed on Earth from the early Archean. This life is thought to consist of small prokaryote cells with a penchant for sulphur instead of oxygen.

However, identifying actual fossil evidence is very tricky for a number of reasons. One of the major ones being, that given the 3.5 billion year time span and plate tectonics, few rocks from this period of Earth history remain on the surface. Of those that do, most either were unsuitable to preserve life in the first place (e.g. volcanic rocks) or have been metamorphosed until any possible organic trace has been cooked to oblivion.

So, if you want to go hunting Archean microbes you need to look in an area with rocks that have been relatively unmolested for some 3.5 billion years or so.

Presenting the Pilbura Craton, Western Australia. The Craton consists of (relatively) unaltered 3.7-2.6 billion year old rocks formed of a granite–greenstone terrane consisting of a series of dome shaped granitoid bodies, overlain by an extensive sequence of Archaean and later metasediments. Within the Craton, the East Pilbara Terrane contains a suite of approx. 3.4 billion year old sedimentary rocks which occur sandwiched between two suites of volcanic rocks.

This is the Strelley Pool Formation and is thought to be between 3426-3340 million years old. At the base of Formation, sitting unconformably on underlying 3515 million year old basalts, is a remarkably well preserved sandstone. (The ridge in the header image above. The red dots mark the position of the unconformity between the underlying basalts and the Strelley Pool Formation. Image (sans Elmer) from Wacey et al. 2011. Supplementary Information)

The sandstone is dark coloured at the base, due to it being carbonaceous- and pyrite-rich, where it sometimes fills channels eroded into the underlying basalt. Above this, the sandstone becomes lighter as the carbonaceous matter and pyrite disappear, before passing into overlying limestones - which contain possible stromatolites - and cherts.

Thin section photomicrograph showing multiple generations of carbonaceous material and silica cements within the Strelley Pool sandstone. DQ, detrital quartz grains. C1, carbon material, interpreted as a biolfilm, covering quartz grains. S1, first silica cement layer, up to c. 30 μm partially filling the void space between the detrital quartz grains. C2, A second carbon biofilm covering the surface of the S1 silica layer. S2, a second generation of silica cement precipitated in the larger pore spaces. C3, a third generation of carbon biofilm. (Wacey et al. 2011. Supplementary Information).

This fantastic thin section photomicrograph provides a wealth of information that allows us to reconstruct how the sandstone was formed. The grains are well rounded detrital quartz. Grains of detrital pyrite are also present. The grains are covered with a thin film of carbonaceous matter, and show a number of silica cementation events, some of which show a dripstone texture.

A second film of carbonaceous matter covers the primary silica cement layers. The central spaces between grains not occupied by the silica layers and carbon films, is filled with chert.

From this we can say that the well-rounded, large quatrz and pyrite grains suggest the sandstone was deposited in a high energy environment, such as a beach or estuary. The sandstone is also very clean - there is no fine material such as silt or clay - also supporting a high energy environment of deposition which would have washed out all the fine-grained material such as silt and clay.

The several episodes of silica cementation suggests cyclic inundation of silica-rich fluids into porous, clean sands.

Thin section showing b, Rounded quartz grain separated from a carbon-rich chert infilling by a dripstone cement (white arrow). c, Rounded grain of detrital pyrite (black grain) with a dripstone chert cement and carbon coating (red arrow). (Wacey et al. 2011).

The dripstone cements are exactly that, they appear as 'drips' of cement on the bottom on grains. This is because they form when the grains are exposed to air and trapped fluid flows to the bottom of the grains. This supports a beach-type environment which was influenced by valdose conditions - where non-marine groundwater is retained by adhesion to grains or by capillary action.

The evidence suggests then, that the sandstone was deposited in a nearshore beach-type environment which helped smooth out the quatrz and pyrite grains, and removed any fine material. During this time the first layer of carbonaceous material was formed around the grains (C1 above). Periodically, the highly porous sand came under the influence of valdose conditions, allowing the precipitation of silica cement around the grains (S1 above), trapping the carbonaceous layer, but maintaining the porous nature of the sand. Subsequently a second layer of carbonaceous material (C2 above) was formed over the S1 cement, possibly suggestive of a reversion to marine influences. A second round of valdose conditions produced a second cementation layer (S2 above). Followed by another return to marine influences and a third carbonaceous layer (C3 above). Finally, after the sands were buried, subsequent chert deposition provided the source for the last event, the filling of the remaining pore space with chert.

Before we look at the carbonaceous material in more detail there is the question of the link between the detrital pyrite grains and the carbonaceous matter.

The detrital pyrite grains are large, much larger than the possible cells in the carbonaceous matter, and are rounded. This suggests that the pyrite is not a product of possible organic activity. There is some pyrite within the carbonaceous matter, but this pyrite is much smaller and angular in shape - as expected if they have been precipitated as a result of organic activity. The detrital pyrite grains are also covered by the silica cement layers. The evidence suggests that the pyrite is primary - that is it was present as an original constituent of the sand - rather then being a product of organic activity. As the pyrite only occurs in the base of the sandstone, primarily in erosive channels in the underlying volcanics, it seems likely that the pyrite grains were formed from the erosion of underlying rocks and have been left behind as a lag deposit as pyrite grains are much heavier that similar sized grains formed from other materials like quartz. The renewed influx of sediment resulted in the pyrite grains mixing with the quartz grains to form a pyrite-rich basal sand. Subsequent deposts of sand did not have the pyrite grains and so were deposited free of pyrite and carbonaceous matter. Remember also that the 3.4 Bya atmosphere has precious little in the way of free oxygen, so the pyrite would be quite stable under surface conditions.

Since the detrital pyrite and carbonaceous matter are absent from the sandstone above the basal layer, there does appear to be a connection between the detrital pyrite and the carbonaceous matter. It appears that the carbonaceous matter is present because of the pyrite.

To answer why the carbonaceous matter should be linked to the pyrite, we first need to know what the carbonaceous matter is and what it contains.

Wacey et al. have found a number of elements (at right) in the carbonaceous film that look like prokaryote cells (or at least what prokaryote cells would look like after 3.4 billion years). So the question is, are we dealing with 3.4 billion year old microfossils?

Ramen spectroscopy (it's to do with lasers and nothing to do with Arthur C. Clarke) supports a disordered structure. This is important because organic matter is disordered, inorganic carbonaceous matter is ordered - abiotic graphite, for example, is found in rocks of this age but shows a well ordered internal structure. So that's a tick for organic. Also, an analysis of the structures indicates the presence of carbon, nitrogen and sulphur in the possible cell wall structures. Again a tick for organic as these are essential for organically formed structures, but not for inorganic ones.. Finally analysis of the carbon in the possible cell walls shows a 26-39 parts per thousand enrichment in ¹²C compared with atmospheric CO2. This also support the structures being organic as only organic activity can partition light ¹²C from the 'heavier' ¹³C to such an extent.

So the evidence suggests that the structures are organic, but are they microfossils?

Well, the shapes are round and tube-shaped. So, as prokaryotes tend to be round and tube-shaped, this is a good thing. However, a number of inorganic processes can produce round and tube shapes. So, by itself, this doesn’t tell us much. The specimens do show some evidence of folding, which organic shapes would do that inorganically produced shapes wouldn’t. So shape is a point in favour of them being microfossils, but not conclusive.

Size is an interesting one. Prokaryotes come in a range of sizes, but modern forms are generally around the 10 μm mark. The forms found range in size from 5-25 μm, with an average size of around 10 μm, not a bad comparison with modern forms.

Size distributions of microfossils from the Strelley Pool Sandstone compared to those from three younger biological microfossil assemblages and one abiotic spherulite assemblage. (Wacey et al. 2011).

Also the distribution of sizes is similar to that of other accepted fossil forms in the 1.9 billion year old Gunflint Chert of Ontario and the 0.8 billion year old Bitter Springs formation of Central Australia. These latter fossils are considered to be Prokaryote fossils. However, this does not represent the total distribution.

80 μm giant from Wacey et al. 2011

As Wacey et al. state, and PZ has discussed, there are larger specimens, if rare, up to 80 μm in size (see left), which is much larger that normal. However, prokaryotes do exhibit larger size ranges, so it is not implausible that cells could range up to this size.

Another explanation could be that these large ‘cells’ represent a cluster of cells in which only the outer cell walls in contact with pore fluids have been preserved, while the internal walls dividing individual cells are not preserved. Certainly the structures arrowd in the large specimen could represent the boundaries between cells as much as they could represent folding. The presence of silica micro-crystals in cell walls does suggest that silica-rich pore fluids played a part in the preservation process. So the larger specimens could be the remains of clumps of cells, or possibly a different group of organisms from the smaller ones.

The numerous lines of evidence tends to support the identification of these structures as organic ans potentially prokaryote cells, making them the oldest life forms so far identified.

So why the attraction to sulphur? Well, in the absence of oxygen, SO₄^2- makes a good terminal electron acceptor. Larry Moran has the details.

Given the age, it will probably be impossible to get absolute evidence that any particular set of structures represent Archaen prokaryotes, but the evidence Wacey et al. 2011 present is probably as close as we could reasonably expect to come.

So with these Archaen prokaryotes, and the Ediacaran fauna, when it comes to Precambrian life, AUSTRALIA ROCKS!

Wacey, D., Kilburn1, M.R., Saunders, M., Cliff, J. and Brasier, M.D (2011) Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia. Nature Geoscience. Published online Aug. 21. DOI: 10.1038/NGEO1238

Palaeoporn 23

Indiana Nedin and the Temple of Kaili

OK, I'm back, after several months of work and travel, which included losing the top of the Eiffel Tower, and finding it again, avoiding an Ebola E-coli outbreak in Hamburg, and retracing the route of The Italian Job in Torino, it's about time I got back to some real work and started posting on the blog again!

Continuing the tradition of famous fossil sites wot I have visited, the photo above (taken a few years ago now) is of me doing my Indiana Jones impression on a hilltop at the site of the Kaili Formation in Guizhou province, southwest China, some 550 kilometres ENE of Kunming and the Changjiang fauna.

The Kaili formation is basal Middle Cambrian in age (see figure at right) and contains the Kaili Biota, a Changjiang/Burgess Shale type lagerstätte. Given it's age, the biota sits midway in age between the Lower Cambrian Changjiang fauna and the Middle Cambrian Burgess Shale fauna.

As would be expected, the Kaili biota shows significant overlap with both the Chengjiang and Burgess faunas in terms on genera in common. Wikipedia, suggests that of the (quite diverse) 110 genera occurring in the Kaili biota, 30 are shared with the Chengjiang fauna, and 40 are shared with the Burgess fauna.

The Kaili biota is thought to represent an outer-shelf environment and contains large numbers of planktonic trilobites, and eocrinoids, along with a range of soft bodied forms such as neroiids, Wiwaxia and Marrella

However, that's not what I want to talk about. See the village to my right in the photo above (click on the photo to enlarge)? That was our way down from the site. That's what I want to talk about because when we entered the village we were greeted with this:

We had entered a village of the Mountain Miao Minority Peoples of Guizhou, and they laid on a traditional welcome ceremony for us. This started with two local girls in full traditional costume offering food and drink to each person as they entered. The traditional dress included amazing jewelry in solid silver! On this occasion we were offered fish and some lethal alcoholic local brew from a ceremonial horn.

Once inside we were treated to a series of traditional dances, again performed by the girls of the village complete with elaborate gorgeous silver jewelry.

We were not informed that this was going to happen so it was a complete surprise. It was an amazing experience, and was the perfect end to the day.


Further Reading

ZHAO Yuanlong, ZHU Maoyan, Loren E. BABCOCK, YUAN Jinliang, Ronald L. PARSLEY, PENG Jin1, YANG Xinglian1, WANG Yue1 (2005) Kaili Biota: A Taphonomic Window on Diversification of Metazoans from the Basal Middle Cambrian: Guizhou, China. Acta Geologica Sinica; 79(6) 751–765. DOI: 10.1111/j.1755-6724.2005.tb00928.x

Paris June 2011

Good news. The bit of the Eiffel Tower that was missing in February is now back.

Hamburg

Things have been a bit quiet recently because inexplicably, the people who pay me actually want me to do stuff!

Part of that stuff will have me at a loose end in Hamburg on the weekend of 11th and 12th June. So if anyone has any suggestions about things to do in Hamburg, I'd be grateful for some tips.

Meanwhile, normal service will be resumed as soon as possible

Mopping up some Ediacaran Enigmatics

The most common form of preservation of Ediacaran fossils in the Flinders Ranges of South Australia is by sands covering objects on the sea floor and masking them. Much of the sea floor was covered with algal and bacterial mats, or films, that add an extra dimension to the structures preserved by the covering sands. We have to take this extra dimension into account if we are to successfully interpret what it is that has been preserved. Some organisms lived on the mats, some below, and some had elements below and elements above. Understanding the interactions between organism, mat and sand will allow us to better understand what was going on at the time and help separate out body fossils from trace fossils from non-biogenic traces.

A good example of this are "mops".

"Mops" are a series of abundant, distinct structures which look like the head of a mop - hence the name. "Mops" are always preserved in hyporelief, that is on the underside of the rock, unusually though, they can be either positive - standing up from the surface like a pimple, or negative - a depression in the surface like a dimple. Most Ediacaran fossils are usually either one or the other.

Tarhen et al. studied a series of "mops" which show a highly varied shape and structure, but found some consistent features.

Mop structures in hyporelief from the Ediacaran of South Australia.
Scale bar = 2cm. (Tarhan et al. 2010)

(1) "Mops" are always orientated within 10 degrees of the palaeocurrent as derived from a number lines of evidence.

(2) They have a distinct margin at one end - considered to be the distal or far end. This can be straight (arrowed in (A) above), curved (in (B)) or lumpy (in (C)).

(3) They have a series of roughly parallel lines running at around 90 degrees to the margin (arrowed in (B) above). These appear filament-like and can be either linear or wavy and tangled

These features can vary even within the same bed and between specimens in close proximity.

They do tend to appear in close association with the disc form Aspidella, which it though to represent the holdfast of a Charniodiscus-like organism or sea pen. But are they fossils or non-biogenic marks?

Well they appear biogenic. The association with Aspidella is too strong to be random. But are they body or trace fossil? Well, they are a little of both.

The association with Aspidella appears important. Aspidella is the holdfast of a sea pen-like organism, which had a large bulbous holdfast buried in the sediment, with a stalk and frond rising up into the water column. So the organism has some elements (the holdfast) below the bacterial mat, and some (the frond) above the mat.

In this configuration, the frond will be subject to water currents. What is though to have happened is that strong currents carrying the sand that will eventually overlay the organisms has hit the frond and basically dragged the whole organism including the holdfast, in the direction of the palaeocurrent. As the holdfast is under the mats, this dragging has uprooted the holdfast and dragged it through the microbially bound mat layer. The parallel lines represent torn-up bits of mat which were attached to the top of the holdfast. Lumpy margins of the 'mops' are probably caused by small lumps of sediment trapped next to the holdfast.

Formation of "mops". A: Normal conditions. B: Current drag. C: Current induced structures.
D: Sand deposition. E: Preservation. (Tarhan et al. 2010)

This explanation can explain a number of structures seen in Ediacaran rocks. One in particular is Pseudorhizostomites.

Pseudorhizostomites. Scale bar = 2 cm. (Tarhan et al. 2010).

Pseudorhizostomites has been interpreted as a rhizostomean medusa (a jellyfish without tentacles), and even a gas escape structure formed during the decay of an organism. But an interesting interpretation based on the 'mop' formation, is that they are Aspidella-like holdfasts that have been torn free by current action, but vertically rather than in a more horizontal direction. So they have been plucked out of the sediment rather than being dragged along.

Another structure that appears related is one associated with actual holdfasts.

Here the holdfast has remained intact and in place, but the stem has been flattened and the surface of the holdfast has been distorted by the sheer forces caused by the current pushing the frond and stem over.

Here is an annotated example that has been featured here before. The wrinkles (W) and the impression of the stem (S) are clearly visible and have been caused by the stem and frond being pushed over by a strong current which eventually deposited the overlying sand bed

The explanation of the "mop" structures is a neat use of the interplay between sedimentology and taphonomy, that ties together a number of structures.

Tarhan, L.G., Droser, M.L. and Gelhing, J.G (2010) Taphonomic Controls on Ediacaran Diversity: Uncovering the Holdfast Origin of Morphologically Variable Enigmatic Structures. Palaios V. 25, pp 823-830. DOI:10.2110/palo.2010.p10-074r

New Find Challenges Evolution

I've been a passionate supporter of evolution, but now . . .

A recent find from the Flinders Ranges of South Australia will shake the theory of evolution to the core. But no-one knows about it.

Why?

I've tried to talk to palaeontologists about it, but the refuse to discuss it. Evolutionists I've known for years no longer reply to my emails. I've been ignored buy organising committees for conferences and symposiums in favour of other evolutionists when I have earth shattering evidence against their pet theory.

They may have frozen me out, but I will not be silenced.

From a Precambrian site deep in the Flinders Ranges, I was guides by something . . . or someone, and I found startling remains - reptile remains with clear preservation of skin. How could that be if the 'so called' (in my opinion now) theory of evolution is true? How can exceptionally preserved reptile remains be present at a Precambrian site?

It can't. But it is. So evolution must be false.

Click on the link below and spread the evidence the the evolutionists have tried to stop me from exposing.

Reptiles in the Precambrian disproves evolution

Paris Feb 2011

Something told me I'd picked the wrong day to check out the view from the top of the Eiffel Tower . . .

Palaeoporn 22

Treptichnus pedum

The type section for the Cambrian-Precambrian boundary is at Fortune Head, Burin Peninsula, Newfoundland, as is marked by the first appearance of the trace fossil Treptichnus pedum (the trace fossil formally known as Phycoides pedum).

Treptichnus pedum is a distinctive burrow pattern comprised of a series of lobes set along a central, sometimes curved burrow, thought to represent successive probes into the sediment searching for food. The traces are thought to represent an organism more complex that those of the Ediacaran, but that is not necessarily true, as no actual animal has been found is association with the burrows, so we don't know what made them (although modern priapulid worms make similar burrows).

However, we should not confuse the somewhat complicated pattern of Treptichnus pedum with the first occurrence of well-developed, fairly complex metazoan animals.

While the start of the Cambrian is marked by the first appearance of Treptichnus pedum, this is not the first appearance of trace fossils probably from metazoans. A number of trace fossil types exist in the preceding Ediacaran rocks. In fact they show a neat line in increasing complexity from simple traces early in the Ediacaran to traces as complex as T. pedum towards the end of the Ediacaran.

The earliest traces we have, and the most simple, is Planolites

This is a lowermost Cambrian specimen (picture from NCSE), but it shows you what they are like. The fossil is of simple, cylindrical, unbranched and unlined burrows. They are usually sinuous and undulatory, and often appear as small knobs or discontinuous segments on bedding planes. The small image below is what they typically look like in Ediacaran rocks

Further up in the Ediacaran, more traces appear. This is Helminthopsis

Helminthopsis are much more meandering burrows that appear to represent shallow feeding burrows. the distinctive whorls and loops are considered to represent a different feeding strategy to that of Planolites.

Towards the top of the Ediacaran, things get a bit more complex. As well as Planolites and Helminthopsis, we get the feeding traces of Kimberella.

Here, the feeding traces are marked "R" for radula, and the animal itself is marked "K". A Dickinsonia is also present. "K'" and "D'" mark the resting trace of Kimberella and Dickinsonia, which comprise, of course, another form of trace fossil.

Towards the top of the Ediacaran, things start to get crowded. Not only do we have all the previous traces, but they are joined by Mattaia miettensis.

This specimen comes from the Kessyusa Formation, from Khorbusuonka in northern Siberia. The trace is filled with two bands of sediment, raised on the sides and depressed in the middle, where the bands are separated by a vertical fissure filled with clay. A possible culprit is a pripulid worm such as the Burgess Shale form Louisella pedunculata.

So by the time you get to the Cambrian-Precambrian boundary there were quite a few traces around. Sure in the Cambrian the traces get much more diverse, but they don't start at the boundary, there is a steady increase in trace fossils through the Ediacaran.

---

Update
Aleksey Nagovitsyn has kindly informed me that the age range for Mattaia miettensis in Palaoeporn 22 is incorrect, and Mattaia miettensis is actually to be found in the Cambrian Tommotian Stage of the Cambrian.

So we need to remove Mattaia miettensis from the list of trace fossils found at the top of the Ediacaran.