Saturday, February 28, 2009

The toes have it

The recent paper by Bennet et al on early hominin footprints has been covered by several people now (PZ does his usual good job here - except "lumpy rocks"?! Typical biologist!), and I don't have much to add.

It's a great find, documenting probable Homo ergaster footprints which show clear bipedal locomotion. No a great surprise there.

But the find resonates because it is a link to our past, and leaving footprints is something everyone has done at some time or other, and that makes it more personal.

However, there is one thing no-one appears to have picked up. Check out the image of one of the footprints. Although there's a gap between the big toe and the second toe, and in this specimen, the second and third toe overlap (probably a result on the walking action leaving the print looking like that. But it is clear that the second toe is smaller than the big toe.

This "Egyptian" toe configuration is clearly the one true configuration, and the "Greek" configuration (with the second toe larger than the big toe) is clearly a degenerate, deleterious mutation. :-)

Bennet MR, Harris JWK, Richmond BG, Braun DR, Mbua E, Kiura P, Olago D, Kibunjia M, Omuombo C, Behrensmeyer AK, Huddart D, Gonzalez S (2009) Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya. Science 323(5918):1197-1201.

Sunday, February 22, 2009

Darwin and (Lake) Wallace

For Darwin Day, I wrote about Darwin's visit to Australia, and in particular his stay at Wallerawang homestead on his way from the Blue Mountains to Bathurst in January 1836.

It was at his stay at Wallerawang that he saw his first live - or at least recently dead (the homestead owner shot one for him) platypus. Which, he remarked, was very different from the dried specimens available in Britain.

It was here, on a river bank, that he noted the local Lion-Ant, and made some comments in his diary that some have equated with the first evidence of his thinking on the theory of evolution.

At the end of that post, I mentioned that the spot where he probably encountered the Lion-Ant, and the homestead, has subsequently been drowned to make Lake Wallace.

View Larger Map

I know, I know. There has to be some connection, right?

Sadly, no.

It took me some time to find out the details, but the lake was formed to provide cooling water for the local power station, and was named after the manager of a local colliery, not Alfred Wallace.

However, the application to dam the Cox River there, and flood the homestead, was the second such application. The first application, made in 1948 was for the lake to be called Lake Darwin. This was superseded by a second application, with the name change, which was granted, and the dam was built in the late 1970s.

Given the 200th anniversary of Darwin's birth and 150th of the publication of 'Origin' maybe there's a case to be made to consider renaming the lake.

Tuesday, February 17, 2009

Palaeoporn 10

This is Isoxys communis a phyllocarid crustacean from the Lower Cambrian Emu Bay Shale, in South Australia. (click on the image to enlarge)

Isoxys is an arthropod with a curved bi-valved carapace, inside which the organism lives. In this case, all the organism lived within the cavity created by the carapace, except for the tips of the appendages, and, visible in the specimen above, eyes. This is the first occurrence of eyes in I communis, and allowed the correct orientation of the organism to be established. I communis has two spines along the top of the organism, pointing forwards and backwards. The backwards facing spine is longer that the forward facing spine, but the original reconstruction of I communis had the long spine facing forwards.

The specimen above shows two stalked eyes, and most of the organism, with the posterior missing. If you check the enlarged image, and follow the margin of the bi-valved carapace from behind the eyes downwards and around the bottom of the animal, the carapace ends at a fracture line. However a thin pink line in the matrix continues on backwards. This is the other valve of the carapace, showing the sediment filling most of the cavity between the bi-valves.

The forward spine on the specimen with eyes above is almost the correct size, just the tip is missing. The larger specimen lying directly beneath it is showing the posterior spine, it's much longer

Isoxys is quite common in the Emu Bay Shale fauna (there are parts of 4 specimens in the sample above), making up 13% of the fossils. The genus is also found in the Burgess Shale, and in the Chengjiang fauna in China, but they are whimps compared with I communis, which is up to 4 times bigger. Go Aussie!

Saturday, February 14, 2009

Australian Bushfires - Update on Sam the Koala

Sam is safe.

Sam (or rather Samantha as she is a female) has become famous thanks to the footage of her being helped by Country Fire Service officer David Tree in the aftermath of the deadly bushfires.

The CFS team had to leave shortly after the footage was taken to protect a house, but a few minutes later, Sam was picked up by wildlife carers and taken to the Mountain Ash Wildlife Shelter in Rawson, Victoria. There Sam has been treated with antibiotics and pain and burn relief medication.

Sam has even found a new friend, a male Koala also saved from the bushfires.

Sam is expected to make a full recovery and will be fit enough to be released into the wild in around 4 months

Meanwhile, pictures of Sam are being sold, with proceeds going to the CFS.

Photo: Sam after treatment. Credit: Rebecca Michael.

Friday, February 13, 2009

Thursday, February 12, 2009

Darwin 200 - Australia, 19 January 1836

Darwin visited Australia in January 1836 and stopped for several days in Sydney. During this time he made a trip inland as far as Bathurst. On his way through the inland from the Blue Mountains to Bathurst, Darwin spent a day and a night at a property called Wallerawang. There he wrote what is probably the most discussed of his diary entries recorded in Australia.

Earlier in the evening, I had been lying on a sunny bank and was reflecting on the strange character of the animals of this country as compared to the rest of the World. A Disbeliever in everything beyond his own reason, might exclaim, “surely two distinct Creators must have been [at] work; their object however, has been the same & certainly in each case the end is compete”.-
Whilst thus thinking, I observed the conical pitfall of a Lion-Ant:- a fly fell in & immediately disappeared; then came a large but unwary Ant; His struggles to escape being very violent, the little jets of sand described by Kirby (Vol I P 425) were promptly directed against him.- his fate however was better than that of the poor fly’s:- without a doubt this predacious Larva belongs to the same genus, but to a different species from the European one – Now what would the Disbeliever say to this? Would any two workmen ever hit on so beautiful, so simple & yet so artificial a contrivance? I cannot think so. – The one hand has worked over the whole world. –A Geologist perhaps would suggest, that the periods of Creation have been distinct & remote, the one from the other; That the creator rested in his labor.

Some have claimed that this is the first evidence of Darwin’s doubts about a creation, and the first inklings of his thoughts on evolution – his doubts (the Disbeliever/the Geologist), deep time (the Geologist), and convergence (Lion-Ants).

Much as I would like to claim that Australia was where it all started to come together for Darwin, I’m not convinced. It’s all a bit vague. While Darwin certainly took copious geological notes, I don’t think that “the Geologist” was code for himself, and, sorry Australia, I don’t think that this was the ‘eureka‘ moment.

But then I don’t think there was a ‘eureka moment’. I think the theory was painstakingly crafted from years of observation, collecting, study, hypothesising, testing and writing. It was more a series of mini ‘eurekas’ as the ideas flowed, the evidence came and the testing proceeded.

The theory of evolution is truly a global theory. The evidence is all around us, and Darwin gathered information from around the globe to build the theory. From North Wales, from Patagonia, from Tierra del Fuego, from Chile, from the Galapagos Islands, from Australia, from Keeling Island. From the minds of philosophers, economists, geologists, botanists, zoologists.

As global theory, there is no one point, no one place, that can lay claim to it.

It belongs to everyone.

Having said that though, just where was he when he had these thoughts?

Well, we know he was as the Wallerawang homestead and on a sunny bank. In other notes Darwin mentions the Cox River (Coxes River to be exact). The Wallerawang homestead was on the Cox River, and since he was alone, it's fair to assume that he wouldn't have gone far, so it was probably the Cox River. He mentions that "earlier in the evening I had been lying on a sunny bank". In the evening, the sun would be in the west, which means that he was probably on the east bank.

So putting all this together, Darwin was probably on the east bank of the Cox river, close to the Warrerawang homestead.

Exactly where? well, further south of the homestead, the Cox river enters a region of shallow, but steep sided gorges.

Unfortunately, the Warrerawang homestead was flooded in 1957 to produce Lake Wallace, so in all probability, Darwin's sunny bank is now below Lake Wallace just to the east of present day Warrerawang.

View Larger Map

Happy Birthday Charlie.

Australian Bushfires

This is Marysville, Victoria.
Approximately 500 people lived there.
Approximately 100 people died there.

Story here

Tuesday, February 10, 2009

More Devonian Anomalocaris

Thanks to John and Callan I now have a copy of the paper. It’s brief but interesting.

So lets have a look at Schinderhannes bartelsi from the Lower Devonian Hunsrück Slate.

S. bartelsi is a great appendage arthropod with radial jaws. Great appendage arthropods, as the name suggests, are a group of arthropods with big frontal appendages, which are not known after the Middle Cambrian. Some, like Anomalocaris had radial jaws, but most did not. It may be that the great appendage is homologous (or directly comparable) to the frontal appendages in chelicerates. So finding a great appendage arthropod in the Lower Devonian could be something of a missing link, if indeed the great appendage and chelicerate appendage is homologous.

In this instance, it is S. bartelsi's shared characters with Anomalocaris that are really interesting.
Fig. 1. Holotype of Schinderhannes bartelsi. (A) Ventral. (B) Interpretative drawing of ventral side. l, left; r, right; A1, great appendage; A2, flaplike appendage; sp, spine; fm, flap margin; te, tergite; ta, trunk appendage. (C) Partly exposed dorsal side, horizontally mirrored. (D) Interpretative drawing of dorsal side. (E) Interpretative drawing of great appendages, combining information from the dorsal and ventral sides. (F) Radiograph. (G) Reconstruction. Scale bar, 10 mm [for (A) to (G)]. (H) Mouth-part. Scale bar, 5 mm.

2, spiny, check.
But the reconstruction has weird cross-linkages between the two appendages. What’s with that? It looks like the appendages have been tied together. This means that the appendages have no independent movement and must work as a locked pair. I’m not convinced of this interpretation. It might be that what is overlapping is the series of up to five or six regularly spaced orthogonal spines along the length of the main spines which are attached to most of the segments of the appendage. In other words the segments of the appendage have a large spine attached to it, which would point downwards if the appendage were stretched out in front of the head. These spines in turn have a smaller set of spines coming off the leading edge, kind of like a comb, with the backbone of the comb representing the large spine coming off the appendage segment, and the set of five or six smaller spines, the teeth of the comb.

They could be used as a net to trap small prey, or, more likely given that they are short, as a means of added grip to ensure the prey doesn’t get away once in the grasp of the appendages. But the bondage reconstruction doesn’t work for me (maybe I need to more adventurous?)

2, massive, check
They are enormous! This means S. bartelsi was most probably a predator, possibly adapted for low light conditions, close to the bottom.

1, radial, check.
This is the most interesting feature that really links S. bartelsi to Anomalocaris. Radial jaws are so rare, and while the one in S. bartelsi has a lot less plates that the traditional Anomalocaris, it’s hard to argue against S. bartelsi as being distantly related in some way to Anomalocaris. A great appendage on it’s own? Meh. But a great appendage AND a radial jaw? That's fairly convincing.

Highly specialised swimming appendage
2, weird, check
No, wait! Hang on! What? This is just too weird. Highly specialised swimming appendages on the trunk I could accept, but not attached to the head. That just will not work. We rarely have large, functioning, head appendages posterior of the mouth. Maybe if it was some weird rigid structure coming off the posterior margin of the head shield, then yeah, but you just can’t have your highly specialised swimming head appendages AND flap them.

They are most probably highly specialised appendages on the first trunk segment. This would explain the spines along the leading edge of the appendage (exopod flaps maybe?), and would allow them to move as the trunk appendaged are set up for movement. They may be highly modified flukes, such as those on the last but one trunk segment.

There's something wierd going on with the trunk appendages, but they are not well preseved, and the paper doesn't make much of them as it isn't critical to the classification.

100 Million year gap
The authors place S. bartelsi between Anomalocaris and the other arthropods, with some justification. So where did all the round mouthed great appendage arthropods go for 100 million years?

Well, as the paper suggests, preservation plays a role here. These great appendage arthropods tend to be only lightly mineralized, and so do not preserve in normal situations. They are generally found only in areas of exceptional preservation, which would limit the numbers of fossils as there are just too few decent sites with exceptional preservation.

Also competition with the new predators on the block (cephalopods, the new-fangled vertebrates, etc), may well have pushed these arthropods to marginal areas, reducing and restricting their distribution.

It is a great pity that there is only one specimen, and an even greater pity that the quarry where S. bartelsi was found has now closed.

One way to check to see if great appendage arthropods with radial jaws are around, is to find evidence of their attacks – they leave distinctive bite marks. Has anyone surveyed the Hunsrück Slate fossils for bite marks?

Gabriele Kühl, Derek E. G. Briggs, and Jus Rust. A Great-Appendage Arthropod with a Radial Mouth from the Lower Devonian Hunsrück Slate, Germany.
Science 323, 771 (2009). DOI: 10.1126/science.1166586

P.S. I note that Derek resisted the urge to reference Anomalocaris briggsi in the paper, which is a pity 'cos then I would have got a citation in Science!

P.P.S. I've just received word that there will be paper on a new "funky" Anomalocaris coming soon. Details when it's published.

Monday, February 9, 2009

Devonian Anomalocaris!?

Well, actually, no. But it got your attention!

What we have here is Schinderhannes bartelsi from the Devonian aged Hunsrück Slate, near Bundenbach in Germany.

The find is described in the latest issue of Science, but I haven't got a copy so I can't say too much yet, but I'll be writing more once I get hold of the paper.

The appendages (the ones up front, not the ones sticking out the sides making S. bartelsi look like Thunderbird 2) sure look like Anomalocaris appendages, but there is only so many ways you can do large frontal appendages before you start repeating them.

The real interesting thing is the mouth. There are lots of ways you can do jaws, but radial jaws are very rare.

I wonder if there are any examples of fossils with bite marks from the Hunsrück Slate?

There is a Science Daily story here.

The critter is approximately 4 inches long.

Honestly! I'd hardly finished banging on about how Anomalocaris was crucified on the spandrals of San Marco, when up pops S. bartelsi! Still, in my defence, S. bartelsi does look like it comes pre-crucified!

More soon.

Dawkins talks Darwin

Larry Moran at Sandwalk has a link to several short videos by Richard Dawkins on Darwin and evolution.

I don't agree with Dawkin's stance on natural selection, but as a science communicator there are few better.

Thursday, February 5, 2009

Indian Ocean affects Australian drought

The Climate Change Research Centre at the University of New South Wales has been doing some interesting research. They have found a correlation between three of Australia's largest droughts (1895-1902, 1937-1945, and the present one, since 1995) and oceanic conditions - in the Indian ocean!

Say what? Shouldn't that be the Pacific and El Nino?

Apparently not.

In a paper to be published in Geophysical Research Letters, the team have linked the last three major droughts in Australia with the Indian Ocean Dipole (IOD).

Basically, the dipole consists of a cooler body of water in the central Indian Ocean, and a warmer body of water to the north east. This is a negative IOD (-IOD).

Under these conditions, warm, moist air forms along Indonesia, and is channeled from there, across western Australia and then across southern Australia. This happens because the warm moist air formed over Indonesia is influenced by the weather patterns that run west to east across southern Australia, and the moist air is dragged diagonally across the continent.

This is good, because it brings rain to western and southern Australia

However, when things are reversed, with a warm body of water in the central Indian Ocean, and a cool body of water to the north east (a positive IOD), warm, moist air does not form.

This is bad because it results in drought to western and southern Australia.

So -IOD good, +IOD bad.

The team has found that throughout the period 1995 to present, no -IODs have formed, and similarly -IODs were rare in previous times of extended drought.

What about El Nino? Well, we are actually in an El Nina at the moment, and there have been several in the last 12 years.

So it looks like there is a better fit with IOD than with El Nino/El Nina.

Tuesday, February 3, 2009

Allopatric and synpatric speciation are the pits

Suvrat Kher in a comment to the ongoing discussion of pits here, asked:

"Are you applying this equally to both sympatric and allopatric modes of speciation? My thinking is that the difference between your speciation model and random drift model will be more apparent for the sympatric situation where natural selection may cause a divergence within a population while drift may not.

In case of allopatry both natural selection and/ or drift may cause divergence."

Yes, you are right. The first example shown would be allopatric sympatric speciation, as the new population forms from within the parent population.

Sympatric Allopatric speciation would be different, as it includes the physically separating of a sub-population from the parent population. In my model, this separation would also occur in morphospace instantly, as the allele frequency of the parent population has changed.

While the allele frequency of a population is an average over the whole population, this frequency would not occur at every point within the population. At any given point some allele would be more frequent, others less frequent.

If a sub-population becomes isolated, it's allele frequency will not change much, but the allele frequency of the parent population will. This is because some allele have now been relatively concentrated in the parent population (those alleles occurring less in the sub population), compared with others that have been relatively diluted in the parent population (those occurring more in the sub-population).

Thus, in this model, isolation would be represented as a shift in the position of the parent population in morphospace, with the sub-population orbiting close by.

I'll try and get some diagrams up shortly.

Sunday, February 1, 2009

Palaeoporn 9

This is the Ediacaran form Kimberella quadrata, or rather traces of K. quadrata, from the Flinders Ranges of South Australia (click on the image to enlarge).

Kimberella is considered to be closely related to molluscs, primarily because of the specific trace fossil it is associated with, which are seen in this slab.

Kimberella has been reconstructed as a mollusc-like form with an oval shaped body including a non-mineralised outer shell, and a probosis-like feeding organ which contains a radula-like organ. Radulas are a distinctive trait of molluscs, and is a toothed organ for cutting and chewing food.

A radula leaves a distinctive trace fossil - Radulichnus, which is what the traces (marked "R") are interpreted to be on this slab.

This slab tells us quite a lot about the palaeoenvironment at the time of deposition. Remember that you are looking at the underside of a sand bed, which has mantled and moulded a preexisting surface, on which the animals were moving.

This surface would have been muddy and covered by a microbal mat. This is what the Kimberella (K) and the Dickinsonia (D) would have been feeding on.

The Radulichnus covers almost the whole of the upper left quadrant of the slab, with the lower left quadrant also showing some signs of Radulichnus and a blotchy appearance which is caused by microbal mats.

Kimberella itself is represented by another trace fossil. The mantling sand moved in from the 7.00 o'clock position and moved the Kimberella from it's original position K' (marked by a flat area representing where the flat 'foot' of Kimberella rested on the muddy surface) and pushed it into the mud and microbal mat at position "K". Note that the right hand side margin in slightly more distinct, meaning that it was pushed into the underlying mud more than the left hand side. The distinct line probably represents the edge of the non-mineralised shell covering the body.

Because Kimberella was quite a tall organism, the body appears to have then been lifted up by the current carrying the sand, and been removed.

The Dickinsonia (D) also shows signs of being moved from it's original resting postion (D') to it's final resting place, in the same direction as Kimberella. However, since Dickinsonia was flat and thin, the sand covered it, pushed it into the mud, and trapped it there. The fossil actually created a hollow in the base of the sand body indicating that the sand is not infilling a hollow in the underlying mud, but has been displaced by something sitting on and above the plane of the underlying mud.

If Kimberella is a protomollusc, this has implications for the possible presence of spiral determinate cleavage (oh goody I get to use "cleavage" in a Palaeoporn post), which has something to do with early development. PZ thinks this stuff is important so there must be something to it!

More information can be found here, and here - although the Berkeley site continues to call Ediacaran fossils "Vendian" fossils).

Kimberella reconstruction credit

Fedonkin, M.A. and Waggoner, B.M (1997) The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism. Nature, vol. 388, p. 868-871.

Fedonkin, M.A.; Simonetta, A. and Ivantsov, A. Y.(2007) New data on Kimberella, the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications. Geological Society, London, Special Publications; 2007; vol. 286, p. 157-179; DOI: 10.1144/SP286.12.