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

Today's Critter: Bomakellia

Today I spent most of my time looking at Cretaceous rocks, so it would not be surprising if I said this critter was Cretaceous. It wasn't. Not even close. Bomakellia kelleri is another fascinating fossil of the Ediacaran fauna, dated to 555 million years old. It is known only from this 9cm long specimen:

It was originally classified as a potential arthropod, possibly even a primitive trilobite or anomalocarid. If it had arthropod affinities then it was certainly primitive. The possible semicircular cephalon and tri-lobed appearance may link it to trilobites, though it does not have segmented limbs or antennae (which may be due to its primitive nature or due to preservation as these parts often do not fossilise in trilobites). Trilobites also have gills on the body, which Bomakellia may be sporting, though this has been a possible connection with the anomalocarids. Below is a reconstruction which fits with the arthropod interpretation:

More recently, as with many of the Ediacaran fauna, it has been interpreted as a possible rangeomorph. The most famous rangeomorph is perhaps Charnia. Rangeomorphs have a frond like structure and were possibly colonial animals, attaching themselves to the sea floor by a hold-fast (interpreted as the head when classed as a proto-arthropod). Spriggina is another Ediacaran organism which has been seen as both a possible arthropod with trilobite affinities and a rangeomorph. Below is Bomakellia reconstructed as a rangeomorph:

Thaumaptilon - Today's Critter

Today I decided to look at an organism called Thaumaptilon (wonderful soft-feather)  as it is believed to be a survivor from the Ediacaran fauna which was found in the Burgess Shale of the mid-Cambrian. This superficially leaf-like animal is considered to be a cnidarian and lived its life attached to the sea floor by a holdfast. It grew to around 8 inches and was covered in spots on one side which may have been zooids, suggesting it was a colonial animal.

These animals were once thought to be sea pens, like the one in the image on the right, however, this has been strongly questioned on numerous lines of evidence. So why have I chosen something which is similar to a sea pen and didn't really do much? Well, Thaumaptilon was linked to Ediacaran forms such as Charnia which had long been tricky to classify (it still is). If Thaumaptilon was indeed both related to Charnia and to modern pennatulacean cnidarians (sea-pens) then it would be strong case against the concept of the Vendobionta of Adolf Seilacher. Seilacher proposed that the Ediacaran organisms were an evolutionary experiment in multicellularity which left no descendants. He also proposed that these quilted forms, of which Charnia  was one, had a hard outer layer which explained why they fossilised so well. Modern sea-pens do not have this outer layer and so the link would have dealt a heavy blow against it.

This image shows Thaumaptilon  along with the Ediacaran forms Charnia  and Spriggina. Charnia is named after Charnwood Forest in Leicestershire where it was initially discovered (so I have managed to keep most of the critters British so far). Spriggina is quite fascinating as it has been classified as an annelid worm, a rangeomorph frond, an arthropod (possible trilobite ancestor), and a proarticulate. In this image is another Cambrian form, Stromatoveris, which has been classified as a ctenophore. The image below shows a potential phylogeny on which both Thaumaptilon  and Stromatoveris can be seen.

I wouldn't like to comment on the potential relationship with Charnia  at the moment. Current popular opinion seems to be that we just don't know. The Ediacaran and early Cambrian fauna are some of the most difficult to study enigmatic organisms known to palaeontology. Thaumaptilon may not have been doing much when it was alive, but from a palaeontological perspective it is fascinating.