Tuesday, 22 February 2011

The 'babbler's top 10!

Those who know my palaeontological interests tend to know that I have a major passion within palaeontology and there is a particular fossil group which I adore more than any other. They are of course the Ediacaran fossils and I have written about them at length many a time. Just click on the search labels and see, or click here and here  for the same effect. And if you want to know how I got interested in them, see here.  This list, believe it or not, is not going to include Ediacarans. They are my number one, so the list would be too predictable if I included them. This list will not be static, instead it reflects what gets my attention at the moment. I am hoping that those who know me well will find at least one or two surprises.

Before I count down I want to mention those groups which narrowly missed out on making the list. The fauna of the Zechstein sea, particularly fossils found in South Yorkshire, interest me a lot as they are my local fossils. I have blogged about them a few times and hope to do something more academic with them too. I also briefly considered adding crocodiles to the list, as their past threw up many interesting variations which look nothing like our modern crocs, but I know little about them (I would say that if you want to be a vertebrate palaeontologist then crocodiles may be a great area to study). I also considered adding jawless, armoured fish from the Silurian, as I had a lecture on them today and found them very interesting, but they just missed out to some groups which I have liked for longer. So, onto the list...

10: Crinoids 
A crinoid fossil from Doncaster Museum.
This one might surprise a few people, as many find crinoids to be quite dull. I also often mock crinoids and call them flowers, but that doesn't mean that I don't like them, I genuinely do. I've even written about them a few times, see here (though I should add that I have written more than just those, but sometimes I get lazy with the labels). Crinoids are often beautifully preserved, are very impressive fossils (when articulated) and are thankfully rather common. They are also still alive, with a fossil record going back all the way to the Ordovician. This makes them a good group to study, yet they have not gotten much attention. They should be used as textbook examples of things like evolutionary responses to predation, so one can hope for that in the future. I got interested in them during my first year of my uni course as I had to make a poster with a course-mate. I paired up with James, whose main interest is crinoids, which we combined with my main interest (at the time) of evolution, producing a poster about crinoid adaptive strategies. I thoroughly enjoyed the research and recognised them as a group with a lot of beauty and potential. Certainly worthy of my top ten and I would not be opposed to dabbling in them some more in future if opportunity knocks.

9: The Dinosaur to Bird Transition
It is well established now that birds evolved from dinosaurs, which is testament to the hard work of many palaeontologists. Laboriously comparing traits on fragmented fossils, they had to rely completely on a few rare transitional fossils to come to their conclusions. No genetic testing was available, only comparison of fossils. If we had no Archaeopteryx then our understanding might have been rather different. We are fortunate now to have quite a range of fossils spanning this transition, with feathered dinosaurs on one side, primitive birds on the other, and a spectrum in between, where individual traits can be seen to gradually change. It also allows me to include a group I like but have not included in this list - dromaeosaurs. Those swift, vicious hunters were closely related to the ancestor of birds, possessing many key skeletal precursors and covered in many feathers. This group of fossils speaks of my childhood love of dinosaurs (which still exists in a non-academic sense, enough to get a tattoo of one) and of my love of evolution. I do not intend to study them academically, though I would not turn down a good look at Archaeopteryx and will undoubtedly write about them in future.

8: Thyreophora
These are the armoured dinosaurs. This group includes the stegosaurs of the Jurassic and the ankylosaurs of the Cretaceous, along with the nodosaurs which tend to get less attention (though thyreophorans as a whole tend to get overlooked, except perhaps Stegosaurus itself). The stegosaurs were a favourite of mine as a child, with Tuojiangosaurus being an obscure preference. These have leapt into my list because I attended a lecture about the thyreophora just last week, by a friend of mine, and was reminded how fascinating they can be. I also have an ankylosaur-obsessed friend, so I hear about them a lot. They might have been slow and stupid, but it worked! They were incredible beasts and deserve more attention. I think if I were fortunate enough to have the skeleton of just one dinosaur  on display, it would have to be some sort of stegosaur.

7: Fossils of the Hunsrück-Schiefer
A beautiful pyrite-preserved brittle star Ophinurina lymani. 
This is a  lagerstätte from the Devonian, found in Germany, also known as the Hunsrück slate. This diverse array of fossils has soft tissue preservation, with many fossils being exceptionally beautiful as they are preserved in pyrite. Various echinoderms are found, including crinoids (more than 60 species), alongside trilobites, brachiopods, jawless fish, even jellyfish. The fossils found at this site are some of the most beautiful in the world in my opinion. I am thoroughly jealous of the person who owns the fossil pictured. I may write about them at length soon, as I intend to do an essay about them as an assignment.

6: The Fish to Amphibian Transition
Another fascinating evolutionary transition which is documented well by the fossils, yet manages to keep astonishing us. The "fishibian" Tiktaalik is becoming one of the main transitional forms mentioned, though it would need a lot more publicity to surpass Archaeopteryx in fame. One of the reasons this group of fossils makes my list is because Neil Shubin's book Your Inner Fish had a big impact on me, informing my understanding of evolution and helping reignite my passion for palaeontology. A good portion of the book is dedicated to Tiktaalik, which the author was instrumental in finding.

5: Eurypterids
These are the mighty sea scorpions, scourges of the Silurian seas. Some of them grew enormous, up to around eight feet long, yet recent studies sadly suggest that they were not the vicious sea monsters we would love them to be. They most likely spent a lot of time lurking, waiting for prey to come into close proximity, before they attacked. They did not have incredible strength, so likely went for weak and small prey in the sea. Even so, they are still impressive and their fossil remains are often beautiful and not too difficult to recognise. I managed to get a good look at quite a few eurypterid fossils last summer at the museum, Pterygotus and Slimonia, which gave me an interest in them. I enjoyed having to closely inspect them and try to work out how many segments each had, while attempting to learn the names of each part. I would love to see the giant sea scorpion up close some day. And for the record, they are not ancestors of terrestrial scorpions.

4: The Transition from Reptiles to Mammals
This is arguably the most beautiful transition in the fossil record. We are exceptionally lucky to have numerous well-preserved fossils documenting this pivotal change in our history. It is most famous for the fact that we can see the changes from the reptilian jaw, which contains around seven bones, to the mammalian condition where there is one main jaw bone. What is incredible about this is that the fossils show the other jaw bones becoming reduced and migrating to the ear, where they have become the inner ear bones of all mammals. There are even some fossils with double hinges on their jaws, caught in the act in a way. The changes in the jaw and ear are alongside changes from reptilian motion (side to side) to the up-down undulation of mammalian movement; changes in dentition and the development of a secondary palate, allowing them to chew; the development of fur and warm blood, and a whole host of other changes which are intimately linked (usually metabolism and consumption) and documented by the fossils. Astonishing!

3: The Cambrian "Explosion" Fauna
The fossils of the Cambrian are undoubtedly some of the most important, as we find the earliest examples of most of the modern phyla during a time of exceptional evolutionary creativity. Not only are there the familiar groups, such as trilobites and even members of our own phylum, but there are a host of oddballs which defy classification, such as Opabinia. My favourites during this period are the unusual arthropods, such as Anomalocaris, and lobopod worms such as Hallucigenia (pictured). There are a few famous sites of exceptional preservation during the Cambrian diversification event, giving us amazing windows to peer into the ancient world. Stephen Jay Gould made the Cambrian fossils of the Burgess Shale the stars of the show in his book Wonderful Life which I thoroughly recommend. This is likely a very predictable group for my list, as our understanding of Ediacara impacts on our interpretations of what was going on during the Cambrian. There are always new ideas popping up trying to explain the Cambrian explosion and it has been a constant source of fascination for palaeontologists for a while now.

2: Trilobites
I would be very surprised if trilobites did not make the list of the vast majority of palaeontologists, if they were asked to make such lists. Anyone interested in palaeontology should read Richard Fortey's Trilobite and marvel at the myriad forms and uses of this important fossil group. Trilobites are iconic, fascinating and are often beautifully preserved fossils. They exploited pretty much every marine niche possible and had stunning diversity, before their demise at the end of the Permian. They are justifiably one of the most studied groups, better known than some extant groups! They are not just wonders to gaze at, but are also heavily used in biostratigraphy, biogeography, palaeoecology and more. I have done a few blogs on trilobites, so this should have come as no surprise. I have sadly not been anywhere to find any yet, but that will be remedied soon. I'd love to work on them too.

1: Small Shelly Fauna
Often referred to as SSFs these may seem like an odd group to have at number one. The informed or observant reader might have predicted this though. The blog icon is Microdictyon, a lobopod worm and SSF which is related to the aforementioned Hallucigenia. SSFs are microscopic mineralised parts which are largely enigmatic, though some are recognisable. They are found during the earliest stages of the Cambrian, right before the Cambrian explosion and right after the Ediacaran fossils. They herald the arrival of mineralised parts (not quite true, as there are a couple of genera at the end of the Ediacaran with hard parts) but we do not know what many of them are. Some fortunate soft tissue preservation has shown some of them to be parts of bigger organisms; the tiny, net-like sclerites of Microdictyon for example. There are cap-like shells which are micromolluscs, but many of them remain incredibly mysterious, though they are useful in biostratigraphy and overlap with trilobite zones which occur a bit later. I liked this group before I started getting really into Ediacarans, though I don't know too much about them. They are currently my favourite topic of research as I am considering doing a major project on them, which I am really looking forward to.

So there you go, my top ten. While I was writing it I felt like swapping around the order, but this list is meant to be transient, so I thought I would stick to it how I originally order it rather than constantly shuffling them around. I can possibly guess what you are currently thinking and I bet the words "nerd" or "geek" pop up at least once.

Saturday, 19 February 2011

Deciphering Dickinsonia...

The Ediacaran organism Dickinsonia  is one I have often avoided writing about and the first time I did I stated that I would like to do a blog about the different interpretations of Dickinsonia which have been offered, though I thought it would be futile (see here, where I mentioned the comparison with the polychaete Spinther). Since then I have done only one blog about this puzzling fossil, which was a joke post where I pretended that a live one had been found. I had also been avoiding writing about Charnia, which is one of the icons of Ediacara alongside Dickinsonia, though I finally got my backside into gear and wrote at length about it around a month ago, see here.  Just like with Charnia this is an iconic and enigmatic fossil, which I have looked at casts of (though not the real thing) and have finally found the impetus to write at length about it. While researching for my final year project, which I have to start this summer, I started reading a paper about Dickinsonia  which was exceptionally informative and is the source of the information I present here (though simplified and opinionated as many blogs do). My project will sadly not be on Ediacarans, as that is just not viable for an undergrad project in the UK, but I still ended up getting enthralled by the paper on Dickinsonia. So what is it?

Photograph by Phoebe Cohen
When Dickinsonia was first found, by Reg Sprigg in Australia, 1947, it was thought to be a Cambrian fossil, as everyone "knew" that Precambrian rocks did not contain macrofossils. The first interpretation came from Harrington and Moore in 1956 (still believing it as Cambrian) who classified it as a cnidarian (a jellyfish) and saw evidence of simple tentacles. Since then the evidence of tentacles has been reinterpreted as contraction marks, though as late as 1992 Valentine was comparing it to a cnidarian, this time the coral Fungia. I personally like this comparison, but only really because Fungia corals are rather beautiful (the isomer arrangement is not like that of Dickinsonia). In 2006 Dickinsonia was even linked with the ctenophores (comb jellies).

A Fungia coral, resembling Dickinsonia. 
In 1966, Glaessner and Wade interpreted it as a polychaete worm, though lacking the characteristic parapodial claws (though interestingly Wade interpreted the morphologically similar Chondroplon as a type of cnidarian). The main comparison for Dickinsonia became the modern polychaete Spinther, which I still find hard to locate pictures of online. I've found beautiful images in books dedicated to polychaetes, which I recommend doing as the resemblance is interesting (though considered incorrect). So far what has been outlined is what has sometimes been termed the "Australian School" of thought concerning Ediacaran affinities (due to the main proponents working in Australia). This line of thought sees them as bilateral and although they are seen as not being modern examples of a particular phylum, they are seen as stem groups of modern phyla, which branched long ago and went extinct but were still part of the groups we know and love today. This view went unchallenged until the 70s and 80s, when new ideas emerged in Europe. The 'Australian school' is still going strong, though are less forthright in their proclamations than before.

Enter the "European School". The antipodean researchers tended to compare differences in Ediacarans, whilst also comparing perceived similarities with modern invertebrates, causing them to see primitive forms of modern taxa. Contrary to this, the 'European School' favoured the idea that the Ediacaran biota were more closely related to each other than to modern organisms. They looked instead to similarities in the fossils as potential homologies. This view began with Pflug in 1970, when he looked at Ernietta  and erected his own group Petalonamae. One of the key features here is that the body segments on each side of Dickinsonia and many other Ediacarans is offset slightly - what is known as 'glide symmetry'. Some have seen this as a variation of bilateral symmetry, whereas others see it as excluding them from true bilateria and being a unifying feature of many Ediacaran forms. Pflug saw the Petalonamae as colonial bodies, with segments either side of the centre.

Fedonkin, in 1983, was the first to show that Dickinsonia had glide symmetry, arguing that it was not bilateral. He placed these organisms in his own phylum Proarticulata, which was considered to be an extinct metazoan group, though he did suggest that it might be ancestral to true bilaterians, even linking them to chordates.

The epitome of 'European School' thought is that of Seilacher. He used the shared characters of Ediacaran forms and differences from modern phyla to suggest an extinct kingdom. Over time he reduced it to a phylum and it has been known as Vendozoa, though now more commonly Vendobionta.  Seilacher's argument revolved around morphology and taphonomy. He pointed out similarities in structure, including the glide symmetry, but also the 'quilted pneu' structure of the fossils, filled with fluid, unlike any of the organisms they had normally been compared to. Oddly enough though, he reconstructed Dickinsonia as bilateral. The quilt-like structure, he argued, prevented Vendobionts from functioning like modern organisms with which they had been compared. He also claimed that they had a tough, leathery skin, which was integral in their unusual preservation. In one fell swoop Seilacher had steered the study of Ediacarans in new directions (pardon the mixed metaphors). The period became weirder than we had ever imagined and the shoe-horning interpretations of his Australian colleagues did not seem tenable.

How Seilacher organised his Vendobionts.
A 20cm xenophyophore. 
In 2003 Seilacher's views began to change, classifying the Vendobionts as giant protozoans, though that interpretation was first offered by Zhuralev in 1993. Seilacher had opened the door for a wide variety of interpretations, challenging perceived orthodoxy. Xenophyophores are large protists which do occasionally resembled Ediacarans and the foraminifera are amoeboid protists which were occasionally very large. 

McMenamin envisioned Ediacaran times to be peaceful, with no predation, labelling it the Garden of Ediacara. He also suggested that these large protists (as he also saw them) were symbiotic, containing a large number of smaller protists and bacteria, possibly allowing them to photosynthesise and chemosynthesise.

A heavily contested interpretation of Dickinsonia is that it is connected to fungi and lichens, and the chordate connection resurfaced in 2003. In 2004 Brasier and Antcliffe brought ideas which are, in my eyes, the most sensible suggestion. They appear to be connected to true metazoa, but of a simple grade of organisation, comparable to that of what is informally known as a coelenterate (these have only 2 layers of cells, simply organised, with a hollow body cavity). They also suggested that similar forms (based on lack of clear internal subdivisions), labelled dickinsoniomorphs, may be different variations of the same species, whether it be due to ontogeny, environment or taphonomy. With this interpretation we can see them as connected to modern life in some way, but still an evolutionary experiment which largely failed; we can happily state that we don't know what they are, but have ideas of how to classify them and further our understanding.

Much current controversy revolves around trace fossils found of dickinsoniomorphs. The most well known are those of Yorgia, where resting traces were found next to a preserved print of the causative organism (they are clearly the same organism and are preserved in opposite relief to Yorgia). This was seen as clear evidence of motility in Dickinsonia and its kin. If they had been skip trails then they would have been better aligned than they are, though there are reasons not to take it as evidence of the organism moving on its own. The organism was not heavy enough to cause traces of such depth, which has led many to suggest that they were made through feeding on the underside through absorption of the biomat, possibly using pseudopodia (which led to the suggestion that they were a stem group of the Placozoa as these feed that way and are also seen as a link between protozoa and metazoa, though this comparison is ill-justified). The direction of movement suggests that the organism glided over the surface after it finished feeding, which lacks intentionality and is not the sort of movement associated with metazoa.

Yorgia resting traces. Beautiful!
So what is Dickinsonia? Well, I have no idea. I take the European view that it is more closely related to other Ediacaran forms than to modern groups and is not a stem group of any phylum. I prefer Seilacher's old view to his newer ones (though they were more flexible than his leathery reconstruction, but had rigidity due to turgor of the liquids inside) and do not believe that they were protists, or fungi as others suggested. Far more study needs to be done into dickinsoniomorphs to determine relationships and we must avoid seeing what we want to see. I expect that they will be argued over for a long time and for now I am particularly liking the views of Antcliffe and Brasier.

I have mentioned a lot of research within this blog, but due to the hour I am posting and the fact that the paper was very informative, I shall only reference one paper, which is essential reading if you are interested in Dickinsonia:

Brasier, M.D., Antcliffe J.B., 2008. Dickinsonia from Ediacara: A new look at morphology and body construction. Palaeogeography, Palaeoclimatology, Palaeoecology 270, 311–323.

Monday, 7 February 2011

In the tooooown where I was born...

I've mentioned my home village a couple of times in relation to palaeontology as I have spent the last year attempting to collect fossils there. I spent my whole life not knowing that I could find them, but that is not surprising considering how small they are and their rarity. My village does not have much to offer palaeontologists, but that does not mean it is a dull place to live. The village is Conisbrough, which is almost a small town, sitting on the outskirts of Doncaster, along the river Don, in South Yorkshire, England. Conisbrough is one of those places which is quite built up, yet at the same time is surrounded by countryside, so one is able to live in both worlds in a way. I spent my youth wandering the streets at times, whilst also being able to wander off deep into the woods or through farmers' fields. We also combined the two when we roughed it in the woods sometimes, as we used to raid skips in the street for firewood instead of what was available there. Conisbrough has some great appeal, especially for me, as I have passing interests in castles, old churches and UFOs/aliens, all of which can be found in Conisbrough.

The main attraction of Conisbrough is the castle, standing proud even though its walls are mostly rubble. Built in the 12th century, it also has a round keep, making it rather special. It is well known as the inspiration for Sir Walter Scott's novel Ivanhoe, and many streets and schools in Conisbrough are named after characters in the book (Conisbrough also used to have a street called "Butt Hole Road" but sadly it changed to "Archers Way").  I have a soft spot for castles, they are such incredible buildings and speak of a lost age where warriors died by the sword and not by the bullet. Conisbrough Castle is well worth visiting and does not get the advertising it deserves. It is one of the most breathtaking buildings in South Yorkshire, if not the whole of Yorkshire. I've lived in Stafford and currently live in Portsmouth, both of which have castles, yet neither have compared to Conisbrough and that is not bias speaking.

Conisbrough also boasts the oldest building in South Yorkshire, as St Peter's Church dates back to the 8th century. It was greatly expanded in the 12th century, during a time when it was one of the most important churches in the area. Even though I have spent most of my life attending this church, crawling under pews as a kid, taking kids up on the roof as a youth group member, playing guitar in the worship group, I still don't know which part is from the original church. A couple of years ago some kids smashed a Medieval window in the church, among other things. It has also suffered from lead being stolen from the roof repeatedly, necessitating the expensive replacement of the roof recently. This is not just a place of worship, it is an icon of Conisbrough (along with the castle, the water tower and the viaduct) and a valuable piece of English history. It is such a shame when people take it for granted.

I also mentioned that UFOs could be found in Conisbrough - I was not lying. In 1966 a schoolboy named Stephen Pratt (I went to school with his son) took this picture, which is widely considered to be legitimate. Any good book on UFO sightings will show it. The street happens to be very close to my nannan's house, where I also saw a UFO once. I was sitting in one of the bedrooms at my nan's, watching things out of the window, when suddenly I saw something zoom above the back gardens. It was roughly level with the window and looked like a rock, possibly about the size of my body, with a long tail of fire. I automatically thought it was a meteorite and my dad did not dismiss my claim. I still have no idea what it was, or whether I even really did see something. I don't for a second believe that I saw an alien craft, just that I saw something flying through the sky which I could not identify.

For the record, my views on aliens are that they may possibly exist in a form which we would identify as microbial. I don't rule out the possibility of microbial alien life existing in our solar system, though I don't see it as too likely. I also don't rule out the possibility of alien life having converged on different aspects of Earth-life. I like the idea of plants on other planets requiring different coloured chlorophyll due to different stars and atmospheres. Even sentience evolving more than once is not completely far-fetched, however, I do believe it would be so rare that it would either be too far away or will have gone extinct already. We will never make contact in my opinion. I wrote a bit more on a Facebook discussion a while ago. I also blogged about the possibility of Martian palaeontology, see here.

Conisbrough does have more to offer, though not too much. The Earth Centre was intended to be an eco-friendly theme park, built for the millennium, yet it bombed and closed in 2005. I personally only went there when it was free or when they had a skate park up. It may soon be used by universities teaching ecology or some such, though at the moment it reminds me of Jurassic Park in places. Conisbrough also spawned the singer Tony Christie and Top Gear's Jeremy Clarkson traced his family back to the village (which he labelled a shithole apparently). And then there is me...

Sunday, 6 February 2011

Confused by Charniodiscus

Within one of the university draws lie the casts of frondose Ediacaran fossils, famous for changing our understanding of Precambrian life. One such form is Charniodiscus, known for its large frond, prominent stalk and circular holdfast. Until recently I had not taken enough of an interest in either Charnia or Charniodiscus to be able to tell the difference between the two, however, I did recently blog on Charnia and got better acquainted with its morphology. I intend to go back in to the stores and compare the two forms in order to get a better feel for them both (the cast of Charniodiscus can be seen here, with me, in a rather rude pose).

I would also like to be able to compare Charniodiscus to the Cambrian frond Thaumaptilon. The latter had once been linked to Ediacaran frondose fossils, though more specifically Charnia, which has been shown to have grown differently to modern sea pens. Thaumaptilon was perceived as possible evidence that Ediacaran forms had extended into the Phanerozoic and could potentially be linked to Cnidarians. This link does not work with Charnia, however, Charniodiscus resembles Thaumaptilon more closely.  I'm not suggesting that I think they are closely related, just that the resemblance is worth investigating and so far I have done little to no research on this.

My source of confusion, however, is not due to phylogeny. I am open-minded about the phylogenetic position of Charniodiscus, whether it is closely related to Charnia and other rangeomorph Ediacarans, or whether it is some sort of primitive pennatulacean, though I do believe the morphospace data suggests close relationship to Charnia. My source of confusion is this image:

It depicts two types of Charniodiscus, but I have no idea what they are meant to be doing. The website can be seen here, though it is in Japanese and there is no clue as to what is going on or who the picture is by. Are they fighting? Kissing? Accidentally bumping one another? Is this an example of Precambrian violence? or porn? I'm baffled!


Antcliffe, J.B.; Brasier, M.D. (2007a). Charnia and sea pens are poles apart. Journal of Geological Society 164 (1): 49.

Antcliffe, J.B.; Brasier, M.D (2007b). Towards a morphospace for the Ediacara biota. 377–386. In VICKERS-RICH, P. and KOMAROWER, P. (eds). The rise and fall of the Ediacaran biota. Geological Society of London Special Publication 286, London, 456 pp

Shu, D.-G., Conway Morris, S. & Han, J. et al. 2006. Lower Cambrian vendobionts from China and early diploblast evolution. Science, 312, 731–734