olelog

A team of a dozen scientists now report new in situ observations and laboratory studies of specimens of a small (diameter 2.4–7.5 cm) strikingly hexagonal form originally described from sedimented steps in a wall of the axial valley of the Mid-Atlantic Ridge (water depth 3430–3575 m) near 26°N, 45°W that appears to be identical to the iconic form Paleodictyon nodosum described as a trace fossil from Eocene flysch deposits at sites in Europe and Wales.


(This photo of Paleodictyon is from the Benkovac Stone Unit. The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. The Eocene was an epoch from ca. 56 - 34 million years ago.)

The team has gathered enough evidence to prove that the organism represents one of the world’s oldest living fossils, perhaps the oldest. The ancestors of the creature, Paleodictyon nodosum, go back to the dawn of complex life. And the creature itself, known from fossils, was once thought to have gone extinct some 50 million years ago.

So far it has not been possible to capture one of the creatures alive. It thrives in restricted areas of Atlantic seabed. Its only visible feature consists of tiny holes arranged in six-sided pattern. Until the real creature has been caught the scientists still vigorously debate what it is. The main question is whether the hexagonal patterns are burrows or body parts, vacant residences or animal remains.

The new paper seeks no consensus on the question of whether the holes and subsurface networks represent burrows or body parts. Dr. Seilacher, who backs the burrow idea, sees the tunnels as a kind of farm where an unknown type of worm or other organism raises micro-organisms to eat, while Dr. Rona sees the holes as body parts, perhaps from a type of compressed sponge. The lack of biological clues, he said in an interview, may arise because microbial predators eat the remains after the creatures die.

Reference:
Rona et al.
Paleodictyon nodosum: A living fossil on the deep-sea floor
doi:10.1016/j.dsr2.2009.05.015
(Article in Press)

• http://www.nytimes.com/2009/08/25/science/25fossil.html
  
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGC-4WD1BWS-4&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=989443494&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=900183d12bc1802d8470f85e1b961b5b
  
• http://my.opera.com/nielsol/blog/2008/11/03/tracefossils-paleodictyon
  
  

The Mesozoic Era from about 251 - 65 million years ago was the age of the dinosaurs. After their extinction the mammals took over. But the story is, as usual, not as simple as that. Although the dinosaurs dominated in the Mesozoic, the first mammals actually turned up only about 10 million years later than the first dinosaurs.

Repenomamus was an opossum-sized mammal about 1 m long and weighing around 14-15 kg living around 130 million years ago.


In China a fossil of Repenomamus robustus was discovered a few years ago with the remains of a juvenile psittacosaur in its stomach area. This fossil is a direct evidence that some primitive mammals fed on small vertebrates, including young dinosaurs.


Repenomamus giganticus was of similar size as Repenomamus robustus but a little bit larger, and thereby the largest mammal known from the Cretaceous (circa 145.5 ± 4 to 65.5 ± 0.3 million years ago).

The dinosaur-eating mammal fossil was found in the Liaoning Fossil Beds in China, sometimes called a Mesozoic Pompeii. Consisting of layers of volcanic and sedimentary rock, the Yixian Formation in China's Liaoning Province has yielded an enormous variety of fossil fish, birds, insects, reptiles, shrimp, flowers, mammals, and dinosaurs dating back to the late Jurassic (the Jurassic period extends from about 199.6± 0.6 to 145.5± 4 million years ago) and early Cretaceous periods-more than 128 million years ago. At that time, the region was dotted with freshwater lakes, streams, rivers, and volcanoes. Volcanic explosions rained fine ash into the lakes, and animals that died or fell into the water were quickly buried in the fine-grained sediment at the bottom where they were preserved with remarkable detail.

Both illustrations are from Wikipedia.

• http://www.nature.com/nature/journal/v433/n7022/full/nature03102.html
• http://www.amnh.org/science/papers/mesozoic_mammal.php
• http://news.bbc.co.uk/2/hi/science/nature/4165973.stm

I ought to write about sediments or sedimentology more often, but my pictures from outcrops are seldom spectacular. When I show a picture like this one:

who cares about the limestone. Everybody stares at the fossil, which is understandable. Nevertheless I stand there with questions like: Why did it die just there? No oxygen available? How did it get fossilised? Why wasn’t it torn apart by scavengers or waves? What was the environment? How come that you can see so many tiny details? and so on... In short questions that might be answered by studying the sediments in which the fossil is found.

My picture is of one of the most famous fossils ever found - the Archaeopteryx lithographica, a link between dinosaurs and birds. I am happy to see that Munnecke et al. have paid the attention to the rock itself that it deserves in a paper published in the December 2008 issue of Sedimentology.



The limestone in which so far ten Archaeopteryx fossils were found are limestone successions of Upper Jurassic (Tithonian) age in the Solnhofen/Eichstätt area. They consist of alternate layers of thin-bedded, laminated, fine-grained, very pure (hard) limestone and softer (inter)layers with slightly lower carbonate contents that are also laminated and show a foliaceous weathering appearance. The extremely fine grained structure explains why so many fine details are visible in fossils from the area. It has also made some of these rocks perfect for lithography, that is one of the early methods of printing images using a flat stone with a completely smooth surface. In one of the geological museums at Solnhofen you can learn more about this printing process. This use of the rock lead to the naming of Archaeopteryx lithographica.

The author was concerned with the proper name for these rocks. Lithographic limestones may sound appropriate, but only a small portion of plattenkalk limestones, namely less than 1% from the classic Solnhofen occurrences, is usable for lithographic techniques. The German word plattenkalk means something like platy limestone, but this term (platy limestone) appears too wide. In 2005 Röper defined plattenkalk as all carbonate marine sediments, in which bioturbation – for whatever reason – partially or completely stopped, so that the primary lamination and fine stratification of the sediments is preserved. (Bioturbation means stirring or mixing of sediment or soil by organisms, especially by burrowing, boring, or ingestion). Now this lack of bioturbation is another reason that the fossils are so well preserved.

The monotonous appearance of these fine-grained mudstones, in particular the softer layers, made it difficult to study them in detail, even with the use of normal microscopes. Todays techniques with electron microscopical examination has made better studies possible.

There is a general agreement that the plattenkalk was deposited in individual basins at the northern margin of the Tethys Sea, where 30 to 90 m thick successions accumulated. The fine lamination of the plattenkalk indicates that life was absent in the bottom of the basins. Possible causes for hostile conditions at the bottom include oxygen depletion, possibly in conjunction with a toxic hydrogen sulphide regime, or hypersaline conditions. Hydrogen sulphide is a smelly nuisance known from stink bombs or rotten eggs. It is a highly toxic gas which hinders respiration just like carbon monoxide. The posture of the dead Archeopteryx indicates damage to the brain, maybe due to suffocation or poisoning. The poor creature died a long, slow death, unable to breath properly.

Plattenkalk successions like these are rare, but often famous, and include examples from the Ordovician of Scandinavia, the Devonian of Germany, the Carboniferous of Montana, the Permian of eastern Greenland, the Triassic of Spain and the Cretaceous of Italy. The most famous example of plattenkalk is probably, however, this Upper Jurassic occurrence of the Solnhofen (or Eichstätt) plattenkalk series. The Altmühl valley is often visited by fossil hunters, but my experience tells me that you have to hunt for several hours to find anything worth collecting (if any at all). Instead enjoy the landscape and the limestone and (coral) reef geology, and not least the splendid geological museums with beautiful (local fossil) collections spread over the area.

Reference:
Diagenesis of plattenkalk: examples from the Solnhofen area (Upper Jurassic, southern Germany) by Munnecke et al. in the December 2008 issue of Sedimentology (doi: 10.1111/j.1365-3091.2008.00975.x).

• http://my.opera.com/nielsol/blog/2007/06/14/interdisciplinarity
• http://my.opera.com/nielsol/blog/2008/03/18/most-famous-fossil-i-was-in-berlin-all-last-week-the-timing-was-not-optimal

For the past 50 years oxygen isotopes in fossil marine carbonate shells like foraminfera or brachiopods have regularly been used to estimate ancient sea-surface temperature. This seems to work quite well for temperatures over the last 100 million years or so, but for various reasons doubt has recently arisen whether this type of thermometry is sufficiently reliable for periods as old as say 250 million years.

In a study published in the journal Science of 25. july 2008 Trotter et al. used a different global climate record determined by oxygen isotope analyses of conodonts from a period of around 488 to 416 million years ago (Ordovician-Silurian) .


Conodonts are extinct eel-like creatures. For many years, conodonts were known only from tooth-like microfossils, which occur commonly but always in isolation, and were not associated with any other fossil. Most of the conodont animal was soft-bodied, thus everything but the “teeth” were not suited for preservation under normal circumstances. Conodonts are small, ~0.1 to 3 mm long, These micro-fossils are composed of phosphate (apatite or calcium phosphate). They lived from Late Cambrian to Late Triassic and in this time they evolved rapidly, providing a fine stratigraphic resolution for the studied period. The phosphate minerals of conodont micro-fossils are more stable than carbonates of marine fossils. Conodont is by the way derived from Greek “cone-shaped” (konos + odont).

The researchers found that marine water at the beginning of the Ordovician (480 million years ago) was very warm (around 45°C), too warm for complex living organisms to develop. From then on a progressive ocean cooling of about 15°C took place over a period of 40 million until the ocean about 465 million years ago reached (sea-surface) temperatures comparable with those of today, around 30°C in the equatorial range. The temperature stayed around this for the next 15 million years, and the interesting thing is that the global change in climate might explain the explosion in marine biodiversity that took place 460 million years ago. The cooling of the oceans was coupled with atmospheric cooling, indicating that a global change in climate took place. The progressive ocean cooling coincided with an explosion in marine biomass and biodiversity (the number of genera and families jumped by a factor of three to four). This event took place during the Upper Ordovician, around 460 million years ago, when ocean temperatures became comparable to those of present day equatorial waters. Not only did marine animals diversify, but their range also spread to the seafloor, and the first coral reefs appeared.

At the end of Ordovician sea-surface temperatures dropped drastically and the so-called Great Ordovician Biodiversification Event (GOBE) was terminated with sudden and catastrophic extinctions during the latest Ordovician (Hirnantian), probably associated with rapid ice sheet growth at the South Palaeo-pole.

Reference:
Trotter et al, Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry, Science, 25 July 2008 (DOI: 10.1126/science.1155814)

• http://www.sciencemag.org/cgi/content/abstract/321/5888/550
• http://www.alphagalileo.org/index.cfm?_rss=1&fuseaction=readrelease&releaseid=531188
• http://www.scientificblogging.com/news_releases/marine_biodiversity_got_a_climate_change_boost

Maybe we have a tendency to stress negative events like mass extinctions, and forget telling about positive events like biodiversifation events - the GOBE is only one of several. The “Cambrian explosion” is the better known. Read for instance about evil or good volcanoes at Highly Allochtonous. Without life there would be no extinctions!

Julia (The Ethical Palaeontologist) has already commented on the Science article Molecular Phylogenetics of Mastodon and Tyrannosaurus rex here and here.

There is not much meat on the article itself, it is just one single page, so it may be no surprise, that the media add lots of feathers. Never the less I found the article quite interesting because of the method used to confirm the relationship between dinosaurs and birds.

Evidence of close evolutionary relationships among birds and non-avian dinosaurs have been accumulating for a long time. See a.o. my post on the Archaeopteryx - probably the most famous fossil, and considered an important link between dinosaurs and birds.

In 2005 it became known that a group of dinosaur researchers had discovered soft tissues in fossil Tyrannosaurus rex bone unearthed in 2003 by Jack Horner in the Hell Creek Formation in Montana, USA. As the bone was 68 million years old it is surprising to have found still elastic soft tissues looking like blood vessels and cells. We are not talking Jurassic park and no DNA could be analysed. By using mass spectrometry protein sequenced from collagen were however detected. Collagen is a protein that is the basic building block of connective tissues.

Phylogenetics is the classification of organisms based on how closely they are related in terms of evolutionary differences - or in other words the construction of a (phylogenetic) tree structure, a diagram that represent the evolutionary tree of life. A tree of life for the 22 organisms compared in the study is shown in figure 1 of the article. For those of you who do not have access to Science I can refer to this account - NB in Norwegian - of the article, where the figure is shown. Please do note that this tree does not indicate that chicken “descended from the fearsome Tyrannosaurus rex” as mentioned in the heading of Sun here, but merely that Tyrannosaurus, Ostrich (Struthio) and Chicken (Gallus gallus) are related (within the taxon Archosauria). I have redrawn the Archosauria bit from the figure.

A serious problem with using molecular methods, be it on DNA or collagen, is that the samples are extremely easily contaminated (from other organisms, including living species). Furthermore fossil material is destroyed by the analysis, and the analysis is expensive. Of course nondestructive examination of unique fossils are preferred if possible.

Molecular palaeontology in the modern sense probably began with a report by Abelson in 1956 of the recovery of proteinaceous components of fossils. As technology expanded and increased in accuracy, sensitivity, and reliability, new analytical methods began to be applied to fossil material. A piece on the future of molecular paleontology by Mary Highby Schweitzer is found here.

• http://www.livescience.com//animals/080424-dino-birds.html
• http://www.msnbc.msn.com/id/24297066/
• http://www.eurekalert.org/pub_releases/2008-04/hu-mac041808.php
• http://www.thesun.co.uk/sol/homepage/news/article1087903.ece
• http://palaeo-electronica.org/2002_2/editor/r_and_p.htm