Monday, November 22, 2010

Palaeoporn 20

Pambikalbae hasenohrae

Frondose (frond-bearing) forms are the most complex and interesting of the Ediacaran fossils, but rare. This is because most of the organism lives above the sea floor, to which they are anchored by a round holdfast, and so are not preserved. A number of frondose forms have been found, but Pambikalbae is different.

Pambikalbae hasenohrae (a) complete block showing several specimens (upper right and lower left). Slab 45 cms. (b) same slab but tilted to show fossil is interlayers with the sandstone matrix (cracks on left side of slab). (c) part of the right hand frond in (a) showing a complex arrangement of chambers.

Pambikalbae was made up of numerous chambered vanes, making up a frond, supported by a tapering central stem and an anchoring stalk. Several series of chambers occured on the vanes, joined together at zigzag sutures, and were commonly filled with sediment on burial. However, the complexity is probably an artifact of complex composite moulding of various nearby chambers, one on the other. It appears that the chambers curve away from the central stem out to the free, or outer, margin. The chambers also appear to be set on the vane in a regular patter so as to limit overlap.

These chambers are big. Bigger than anything else so far found. Here's a reconstruction.

Pambikalbae is clearly not a pennatulacean or cnidarian 'sea pen' like Charnodiscus. However, it does contain characters that suggest an evolutionary grade of organisation comparable to known cnidarians. The configuration and size of the chambers seems ideal to house symbiotic algae or bacteria . . . however, here's some wild speculation.

There is a group of cnidarians which do share similarities with Pambikalbae, and that's the physophorid Siphonophorida. Here's one below (photo credit)

Interesting isn't it. The chambers are especially similar. However, there is one thing wrong. The physophorid is upside down. The chambers actually point downwards. Why? Because physophorids float, they are not anchored to the sea floor like Pambikalbae.

But it's not as problematic getting from Pambikalbae to a physophorid, as it would appear.

(a) inverted Pambikalbae. (b) a hypothtical ancestral 'calycophore' siphonophore. (c) generalised modern physonect.

Just change a water-filled bulb as an holdfast, for an air filled bulb for a float. Simple folding inwards of the holdfast could produce the physonect and ancestral calycophore pneumatophore. A futher point of comparison is that the vane of Pambikalbae has three serial rows of chambers, as in calycophore and physonect siphonophores.

So a frondose form with wanderlust as ancestral to the modern siphonophore cnidarians? Maybe. But is could also be a derived hyrozoan, or a sister group to the early Chondrophorina. Whatever it is, it ain't no pennatulacean!

Jenkins, R.J.F. and Nedin, C. (2007) The provenance and palaeobiology of a new multi-vane, chambered frodose organism from the ediacaran (later Neoproterozoic) of South Australia. In P. Vickers-Rich, P. and Komarower, P. (eds) The Rise and Fall of the Ediacaran Biota. Geological Society Special Publication 286, 195-222. doi: 10.1144/SP286.15

Saturday, November 6, 2010

The Royal Society Archive and Optick Glaffes

The Royal Society is 350 years old in 2010. To mark the event, the Royal Society archives have been made freely available online.

ALL of them.

From 1665.

350 years worth.

The archives contain more than 66,000 articles, including the first ever article published in the world's first science journal Philosophical Transactions.

Here's a nerdy quiz question for you to ask, "What was the subject of the first paper in the first scientific journal?" Answer - Optick Glaffes.

The archive will remain free to access until 30 November 2010. So go in now and download some original articles from people such as Mr Issac Newton (a promising young mathematiks Profeffor)

and a Mr Charles Darwin (recently back from an around-the-world cruise).

Friday, November 5, 2010

Lower Cambrian Sea Anemones from China

Holotype and paratypes of Eolympia pediculata from Han et al. 2010

Yet more exquisitely preserved fossils from the phosphorite deposits in the lowest Cambrian sediments of the Kuanchuanpu Formation, Shaanxi, China. And by "lowest" they really mean lowest! The deposits are only a couple of million years younger that the Cambrian-PreCambrian boundary, which is currently taken as 542 million years ago.

The new fossils have been identified as a possible stem member of the Cnidarian Hexacorallia, suggesting that the diversification of the Cnidaria either occurred very rapidly after the start of the Cambrian, or, more likely (as far as I am concerned), in the Ediacaran.

I don't have much comment to make. The interpretation appears reasonable. The paper is freely available at PLoS (thank you PLoS). I would have liked some larger specimens, but the size is an artifact of the preservation.

There's a nice comparison with some extant polyps from an extant species.

Young polyps from a modern species, from Han et al. 2010

The similarity in form and size is striking. Morphological similarity isn't everything, but it's something!

The authors end with:
The cnidarian diversification might have occurred rather quickly during the early half of the Cambrian or it may be deeply rooted into the Neoproterozoic.
I prefer the latter option, which is a nice intro to Palaeoporn 20!

Han J, Kubota S, Uchida H-o, Stanley GD Jr, Yao X, et al. (2010) Tiny Sea Anemone from the Lower Cambrian of China. PLoS ONE 5(10): e13276. doi:10.1371/journal.pone.0013276