Thursday, 27 January 2011

Awww poor America.

Sadly American education on evolution is still not doing well, see here. I don't have much to say about this, though I think it is such a poorly taught subject in the UK as well. Shame.

Tuesday, 25 January 2011

Why Ediacarans?

As may be obvious, I am obsessed with the Ediacaran biota, which are organisms from the end of the Precambrian that are puzzling to palaeontologists, both in their relationship to living organisms and in how they lived. They have often been referred to as the Rorschach test of palaeontology - every palaeontologist sees something different. To the average viewer they probably look dull,; a friend of mine recently referred to Dickinsonia as the fart of a jelly slime and my girlfriend tends to refer to Ediacarans as "animal plants" or something similar, clearly thinking of Charnia. So why Ediacarans?
The jelly-slime-fart...errrm.... I mean Dickinsonia.
As a child, the Ediacarans would have bored me to tears. I was obsessed with dinosaurs and nothing else. Not even pterosaurs or ichthyosaurs. Even the massive mammals from earlier in the Cenozoic could not distract me from the dinosaurs. However, I do think part of my love for dinosaurs went on to later influence me, and not just because they involve fossils. Dinosaurs are weird, yet familiar. I think the weirdness and mystery appealed to a small extent, but those features are bland in dinosaurs when compared to some of the weird wonders of the ancient invertebrate world. Still, thinking about extinct lineages does have its appeal when it comes to imagination.

When I later returned to palaeontology it was due to a passion for evolutionary biology. It brought the fossils back to life for me again and I wanted to be a vertebrate palaeontologist, getting paid to research transitional forms and to write books about the ins and outs of evolutionary theory. Neil Shubin's work appealed to me a lot as it tied in genetics, which I also find fascinating. At this point the Ediacarans might have come to my attention, but even then they were an odd little esoteric detail. They were covered for no more than a page of a book really, which tended to amount to little more than mentioning that they are enigmatic and may have been a failed evolutionary experiment. I learnt about them at this point solely to inform me about the goings on of the Cambrian "explosion".

My favourite proposed evolutionary sequence (and ontogenetic)
from the Ediacaran, going from Parvancorina to an arthropod.
Before I started my course I read Trilobite by Richard Fortey and found it enthralling. At some point during my first year I asked myself if I would be interested in invertebrate palaeontology as opposed to vertebrate palaeontology and I instantly imagined studying trilobites. My answer was yes, with the addition that although I still wanted to study evolution, I could study all sorts of other things too. This potentially opened things wide as I was no longer far removed from the Ediacaran, but my subject of interest went back at least to the Cambrian. I was possibly also swayed whilst I was working with a friend on a poster presentation about crinoids. Crinoids are stalked echinoderms, which also often get mistaken for plants. We did the poster on a comparison of adaptive strategies, enabling me to engage with evolution and my friend (or should that be colleague?) to study crinoids. I thoroughly enjoyed the challenge of researching a group I knew little about and realised that I would not be opposed to doing it for a living (studying areas I had not yet considered, such as invertebrates). University is supposed to make one specialise, yet there I was broadening my possibilities. 

The poster presentation was done as a little competition too, from which I won a book. It was Wonderful Life by Stephen Jay Gould and as should be well known, it is about the Cambrian explosion. I found myself exposed to many of the weird beasties from the Cambrian and finding them fascinating. Vertebrates were certainly out of my mind by that point, yet evolution could still remain at the forefront. Gould briefly covered life just before the Cambrian explosion and I started to take notice, though at this point it was the Small Shelly Fossils (or Fauna) which intrigued me. They are such mysterious creatures, considering for most of them we just have microscopic bits of shell. The picture I use for this blog is Microdictyon; a SSF which was originally known by only its sclerites, until soft-bodied fossils were found, revealing it to be a lobopod worm. 

The Cambrian oddball Opabinia. 

So by this point my interest was in SSFs and the Cambrian diversification, still obsessed with evolution, having forgotten about vertebrates and embraced invertebrates. It did not take long for my obsession to switch, but I don't know how. I think I desired to see the link from Ediacarans to SSFs then through to the Cambrian diversification. It is so difficult to link these times together, I needed to know more. The Ediacarans are by far the most mysterious of the lot and the more I learn about them the more I find I do not know. There is a surprise round every corner, or in the case of palaeontology with every fossil found (and in my case with every paper or book I read). I still like the SSFs and the Cambrian diversification, but the Ediacaran has managed to enthral me with its mystique, yet like the dinosaurs of my youth they are tangible in a way. The fossils range in size, but many are large enough to make out without having to get too close. There is also a good diversity, contrary to what most books show. Your average book which mentions them, including textbooks, will show typical forms like Spriggina, Dickinsonia and Charnia. Yet I fell in love with Parvancorina and Kimberella. 

The Ediacaran period is one of the most important times in evolution. Animals were evolving at this point, but exactly when we do not know. Finding the unequivocal ancestors of extant phyla is fraught with difficulty. Understanding the evolution within the Ediacaran biota is tricky, with potential relationships found all over the place. It has been included in disparate interpretations of the metaphysics of evolution. Gould supported Seilacher's Vendobiont interpretation as it expresses the contingency and happen-stance of evolution, rendering humans as mere accidents. Whereas McMenamin looked at the same interpretation and believed that some of them showed potential signs of cephalisation, which he extended to mean that they could have evolved sentience had they not met their demise! McMenamin thought that the Vendobiont hypothesis supported convergent evolution as ubiquitous and directional, whereas Simon Conway Morris, a champion of convergent evolution, saw fit to want to get rid of the Vendobiont interpretation, believing that fewer lineages meant a more directed evolution. But I have digressed a tad.

Those beautiful Ediacarans...

What next? I doubt that my Ediacaran fondness will wane. I feel like I have found an area which I am sufficiently passionate about to study to a high level, perhaps dedicating my life to it. Other interests pop up now and again. I am interested in my local palaeobiology, enjoying studying the Permian fossils of the Zechstein Sea and their palaeoecology, but that it a side interest as it connects my home to my studies. I found trace fossils very interesting when we studied them, so fortunately there are Ediacaran trace fossils. I also really enjoyed examining the eurypterids at my local museum last summer, though I don't see that as a career prospect. I currently intend to try to find a doctorate position studying Ediacarans when I finish my degree in a year and a half's time. Watch this space. 

Monday, 24 January 2011

Charnia - About Time!

One of the most important fossils ever discovered, especially when you are interested in the Ediacaran period as I am, is Charnia masoni, yet I have never blogged about it. I barely ever mention this iconic find. On top of its importance it can be found in Britain and I have looked at casts of it, yet still no mention. Until now...

The original Charnia masoni fossil. 
The discovery of Charnia is a very well known one within palaeontology. In the past year it has been discussed on Bang Goes the Theory by the lovely Liz Bonnin, and more recently by Sir David Attenborough in his First Life documentary. The absence of fossils before the Cambrian had baffled Darwin, causing him much embarrassment which creationists sadly still think is a problem. In the 1950s fossils were found in Australia, but due to circular reasoning were not recognised internationally as they should have been. As Precambrian rocks were devoid of fossils, so the logic went, the fossiliferous rocks must have been Cambrian. It wasn't until a budding young geologist in Leicestershire's Charnwood Forest discovered a frondose fossil in unequivocally Precambrian rocks.

Modern sea pens.
Like all Ediacaran fossils good old Charnia is difficult to classify and its life habits have remained mysterious. It was first classified as algae (in the journal of the Yorkshire Geological Society believe it or not) before being reinterpreted as a sea pen (pennatulacean cnidarians), an interpretation which stuck for quite some time and resulted in many Ediacaran forms being shoe-horned into modern phyla.

This interpretation was first challenged when Dolf Seilacher presented his Vendozoa classification, suggesting that the Ediacaran forms were an evolutionary experiment in multicellularity which left no descendants. The nature of what are now referred to as Vendobionts has changed a lot since Seilacher's ingenious proposal. Originally they were a separate, metacellular, kingdom, before later becoming an extinct phylum which diverged before true animals evolved. Eventually Seilacher settled on the idea that Vendobionts were large, quilted protists.

Seilacher's view of a separate phylum is widely accepted, though his classification of the Ediacaran Vendobionts as protists is less well accepted. Charnia is classified as a Rangeomorph - a taxon containing the frondose fossils of the Ediacaran, believed to potentially be a monophyletic clade (meaning they are not from separate groups but have similar morphologies because they are closely related) morphospace data appears to bear this out.

Charnia's connection to the sea pens was not completely thrown out, particularly because the classification of Charnia is hugely important. If it can be connected to modern forms then the Garden of Ediacara was not so bizarre after all, perhaps evolution is actually quite predictable. If, however, it was a failed experiment, then the Ediacaran remains ridiculously enigmatic, positively alien to us. The connection to sea pens was made through a Cambrian frond-like fossil called Thaumaptilon, which I elucidated here. At the time I did not want to comment on a potential relationship with Charnia, but now I know that they were unlikely to have been related. One simple reason I will give is that Charnia has no stalk running down the centre, yet Thaumaptilon does, though a much better case can be made. Charnia's potential connection to the sea pens took its heaviest blow when it was shown that it grew in a very different way to sea pens. Ontogeny is important in connecting disparate fossil forms as it can be inferred from fossil data and is often quite evolutionarily rigid. Sea pens grow by adding extra polyps to the bottom, whereas Charnia did the opposite and added to the tip.

In working out the evolutionary relationships of many Ediacaran forms, particularly rangeomorphs, it seems that working out their life cycle might be the key. Many have overlapping morphologies which may be different growth stages. With heterochronic evolution changes in developmental timing produces different adult-stage morphologies, allowing a juvenile form to reach sexual maturity for example. These overlapping forms may also be different variations of the same organism, but from different environmental conditions (ecophenotypic variation) much like the variation seen in people from different continents. Bradgatia is one such form, as it is like a bush of Charnia. Many fossils are spindle forms (e.g. Fractofusus) which resemble two Charnia stuck end to end, branching outwards. All have fractal branching frondlets.
Bradgatia from Charnwood Forest. Photograph by Tina Negus. 
How it lived is perhaps the biggest mystery. It is believed to have lived quite deep, so photosynthesis seems to have been out of the question (whether it was an autotroph or used symbionts). Filter feeding is a possibility, but it seems to have evolved ways of folding which were inefficient. We may never know how it lived and fed.

There are many other rangeomorph fossils which resemble Charnia. Unsurprisingly Charniodiscus is one such fossil, also found in Charnwood Forest, a cast of which is pictured to the right, upside down, with myself using it for a rather lewd pose. This specimen is small compared to the 2m long Charnia found in Newfoundland.

The mysterious ivesheadiomorphs, or "pizza-discs", have recently been interpreted as the decayed remains (taphomorphs) of Charnia and related taxa.

An ivesheadiomorph.
Now all I need to do is see Charnia up close. I intend to visit Charnwood Forest some time over the summer if possible, though the Charnia found in Newfoundland, Canada, do greatly appeal.

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

Brasier, M.D. & Antcliffe, J.B. 2004. Decoding the Ediacaran enigma. Science, 305, 1115–1117.

Ford, T.E. 1958. Precambrian fossils from Charnwood Forest. Proceedings of the Yorkshire Geological Society, 31, 211–217.

Liu, A. G.; McIlroy, D.; Antcliffe, J. B.; Brasier, M. D. (2011). Effaced preservation in the Ediacara biota and its implications for the early macrofossil record. Palaeontology: In press.

Seilacher, A. (2007) The nature of vendobionts. 387-397. 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

Dickinsonia, still alive?

Look, photographic evidence of the Ediacaran form Dickinsonia on the modern sea floor, taken using specialist cameras:

OK, so I lied... this is actually a picture of a Dickinsonia cast which I played around with for a bit. The photo was poor quality so I tried to improve it and ended up finding different settings which made it look like a possible modern photo. A much better job could be done in faking this (not that I am advocating that) as this was a mess around for a few minutes.

Though imagine the implications of finding this thing alive, having been absent from the fossil record for over 540 million years. So many questions would be answered by simply observing it. Does it move? This is constantly being debated as the trace fossils found accompanying some dickinsoniid fossils may not be trace fossils at all. Interpretations range from it being highly mobile, to it moving rarely, to not moving at all but producing the traces through being buffeted by currents. How does it feed? We'd be able to tell whether it sucked up nutrients from algal mats or whether it carried endosymbiotic organisms, or whether it used some completely different mode of feeding. A proper analysis of its morphology would be possible, giving much better insight into its habits, but most importantly its taxonomy. And of course, genetic testing would be possible, answering some of the fundamental questions which might potentially never be answered using fossil evidence alone. Ah, one can dream...

Sunday, 23 January 2011

A spot of news

I stopped blogging about various bits of palaeo news quite a while ago when I slipped way behind and couldn't be bothered to catch up. Well, now I can, so here are the stories which have been catching my eye recently:

Darwinopterus is sexy

As my university is involved in pterosaur research I do like to keep my eye out for new information on those flying beasts (occasionally being privy to info before it has been published). This particular story is exciting for several reasons: the pterosaur in question is Darwinopterus, which is the rather recently found intermediate form between the two major groups of pterosaurs; it provides insight which is usually difficult (or impossible) to glean from fossils; and it simply is a beautiful fossil to look at. "Mrs T" as the fossil has been dubbed, is a Darwinopterus fossil which has been found with an egg. The egg appears to have been expelled from the body, probably due to the usual build up of gas after she died. This find allows palaeontologists to sex pterosaurs accurately for the first time; before now trying to determine the males and the females was based on conjecture. Mrs T lacks a crest, showing that pterosaurs are sexually dimorphic and lending support to the idea that pterosaur crest evolution was driven by sexual selection. Amusingly, Attenborough's ambitious pterosaur documentary in 3D apparently shows two crested pterosaurs mating (I intend to review his documentary at some point, as palaeontologists attending the premier in London recently were heavily critical of it). The females also had larger pelvises than the males, which naturally fits with their need to lay eggs. For more info on pterosaur sex, see here. For the press release, see here.

Palaeobiology is important for conservation

For a while now I have been making the claim that palaeobiology is important for our understanding of how organisms respond to environmental change and that this data is important for conservation efforts. (I most often make this claim to creationists when they claim evolutionary biology is not fruitful.) It is good to see that this is occurring, see here.

Two oxygen related stories for the price of one

It turns out that the early oceans were oxygen-free, which puts considerable constraints on what sort of life can exist. This helps explain why the Earth has been barren with regards to complex life for the majority of its history. See here. Oxygen has also impacted the early evolution of animals more than we realised as it has fluctuated a fair bit. See here.

Pterygotus dethroned

Last summer, while volunteering at Doncaster museum, I had the pleasure of carefully examining and photographing around twenty eurypterid fossils. Eurypterids are extinct sea scorpions, one group of which - the pterygotids - grew incredibly large, reaching lengths of eight or nine feet. All of the pterygotids I looked at were tiny in comparison, but they are still a fascinating group. It has long been thought that Pterygotus was a terror of the Silurian seas, the top predator, causing chaos as it consumed other hard-bodied prey with ease. Attenborough's recent documentary, First Life, depicted them this way, surprising other eurypterids by snapping them up voraciously. This view is already out of date. A study has shown that they would not have had the strength to do this and had limited movement. Instead they could only have preyed on small, soft-bodied animals, and may even have been scavengers or herbivores.

Their sheer size has led to at least one imaginative rendering:

Saturday, 8 January 2011

Ah, geologising...

Also, happy new year. Should I get back to blogging again? I've neglected it so much that I don't know where to start.