On The Origins Of Life's Phosphorus

During the early 19th century, one of the many products produced by British factories were matches.  One of the active, combustible ingredients was phosphorus. Its use, however, came at a price. The factory workers suffered from a condition known as 'phossy jaw.' The raw phosphorus caused the bone to decay in a painful and debilitating process.

The effects of 'phossy jaw. While incredibly dangerous in its pure form,
organic compounds of phosphorus are vital to living cells

Yet despite its toxic and combustible nature, life could not survive without it.

Phosphates, compounds of phosphorus and oxygen, make up the backbone of DNA molecules in conjunction with a form of sugar. Adenosine triphosphate (ATP), an organic, phosphorus-containing compound is the energy storing molecule used by every living cell on the planet. Therefore, a major challenge facing biochemists investigating the origins of life is to identify a source of phosphorus on the early Earth.

Due to its reactive nature, it is not found in nature in its pure form, and as most compounds of the element are toxic, only certain molecules are suitable. Yet certain meteorites contain a mineral called schreibersite, the chemical formula of which is (Fe, Ni)₃P. It is almost non-existent on Earth, with one tiny deposit on Disko Island off the coast of Greenland.

Dr Terry Kee from the University of Leeds realised that the schreibersite in meteorites could act as the source that bichemists were looking for. ATP is used by cells not only as an energy source, but as a way of building organic molecules vital to their existence such as proteins. Kee found a way to generate a chemical precursor to ATP using schreibersite. His method is beautifully simple. First, he took samples of naturally occurring acidic solutions from thermal springs in the Hveradalur geothermal area in Iceland. To each he added a small piece of material from a body known as the Sikhote Alin meteorite which contained schreibersite, then left the samples for incubation in the hot spring for four days, and then a further thirty at room temperature.

A reaction between phosphorus-containing minerals and compounds
within geothermal springs on the early Earth may have created a
primitive energy source for the first cells

When the contents were analysed it was found that a molecule known as pyrophosphite had formed. Pyrophosphite could react with a number of oxygen-containing compounds to create pyrophosphate, a precursor to ATP.

The question was could the same reaction occur in nature? Thermal springs with the same chemical composition as those at Hveradalur almost certainly existed on the early Earth. Schreibersite has been recorded in many other meteorites besides the Sikhote Alin specimens, all of which came from a body of rock 4.5 billion years old, showing that the source of phosphorus was present in the early days of the planet.

Matthew Pasek from the University of South Florida has confirmed that such a process may have occurred in nature. Pasek and his team extracted rock cores from localities in Australia, Zimbabwe, West Virginia, Wyoming and Florida and analysed their mineral composition. The oldest samples, collected from the 3.5 billion year old Archaean age Coonterunah carbonates in Australia, contained a mineral called phosphite. 

In Kee's experiment, this mineral was produced when the meteoric schreibersite dissolved in the acidic water from the thermal springs, which eventually formed pyrophosphite. While the latter molecule was not found within the Coonterunah carbonates one of its components, the phosphite salt, was present, meaning that the Archaean Earth had the capacity to manufacture the components of Kee's experiment and produce both an ATP precursor and a usable source of phosphorus.

An artist's impression of the first barren continents of the Archaean Earth
shrouded in a thick chemical laden smog. Yet life may have first evolved
the pools around the base of those rocky towers.

Phosphite is an unstable mineral and so the only way it could have been deposited within a carbonate formation was if conditions on the Archaean Earth were different enough to allow it to exist without decaying or reacting with other compounds in the surrounding environment. 'The present research shows that this is indeed the case,' said Patek. 'Phosphorus chemistry on the early Earth was substantially different billions of years ago than it is today.'

Other natural sources of phosphite include lightning strikes, geothermal fluids and occasionally microbial activity under extremely anaerobic condition, but no other terrestrial sources of phosphite have been identified. None could have produced the quantities of phosphite needed to be dissolved in early Earth oceans that gave rise to life. The only other available source would have been from the dissolution of schreibersite contained in meteorites.

'Meteorite phosphorus may have been a fuel that provided the energy and phosphorus necessary for the onset of life,' concludes Pasek.Yet while a more conclusive link will be needed before we can definitely say that life's source of phosphorus was extraterrestrial in origin, what this study does give us is a distinct method of manufacturing an ATP precursor, which may have made the difference between the first cells or a lifeless planet.

 

The Oldest Primate On The Planet

The beautiful, 47 million year old fossil of
Darwinius masillae, better known as Ida

When the fossil of Darwinius masillae, better known as Ida, was first discovered in 2008 in the Messel Pits, Germany, it caused a massive media stir. Jorn Hurum, the Swedish palaeontologist who described Ida in his 2009 paper, claimed that Darwinius was the common ancestor of both the two major groups of primates, the haplorhines (simians such as tarsiers, monkeys and humans) and the strepsirrhines (lemurs and lorises), making it what was considered to be the the discovery of the year.

If Hurum was correct, then Ida was not only the discovery of the year, but one of the the most important finds in palaeontological history. Yet skeptics gathered like vultures. It quickly became clear that Darwinius was more closely related to strepsirrhines than haplorhines and as a result could not be the common ancestor of both groups.

Ida is now believed to lie very close to the point of divergence. At 47 million years old, the common ancestor was probably around 50 million years old. Now a fossil discovery of a primate from China has shown that the split occurred further back than palaeontologists first thought. Around a decade ago, a farmer living in the Hubei Province of China uncovered a fossil from a rock formation close to the Yangtze River. The tiny, but well preserved remains embedded in a thin slab of dark grey slate were taken to the European Synchrotron Radiation Facility (ESRF) for analysis.

The fossil from near the Yangtze River in the Hubei Province of China

A synchrotron is a particle accelerator which fires electrons around a tunnel until they are close to the speed of light. At this point, they emit powerful x-rays which are focused onto a sample, to reveal its hidden features, allowing it to be reconstructed in detail. The parts of the skeleton still obscured by slate were brought into view. 'There's no way you can prepare the fossil any better to see its features,' explained Dr Paul Tafforeau from the ESRF. 'This gives you access to the general anatomy and we can achieve very high resolution.'

An artist's impression of Archicebus achilles in an ancient tropical forest.
Overall, it would have been about the size of a mouse

With its long legs and tail and grasping, prehensile feet, it was clearly arboreal and based on its small, pointed teeth, most likely fed on insects which would have been more than enough to satisfy the daily calorific need of a creature its size. Its importance, however, lies with its relationship to other primates. At just 7 centimetres in length and 30 grams in weight, it is the smallest known member of the group on Earth and the most primitive to date, coming in at an incredible 55 million years old, making it older than both Ida and the proposed point of divergence between the strepsirrhines and the haplorhines.

In response to this, the researchers gave it the name of Archicebus achilles which translates as 'ancient monkey.' While the general physiology with its small frame and long tail was similar to that of a lemur, its calcaneus (heel bone) showed without a shadow of a doubt that it was more closely related to the tarsiers and therefore monkeys and humans, a detail referenced by the species name of achilles.

'The heel, and the foot in general, was one of the most shocking parts of the anatomy of this fossil,' said Dr Chris Beard from the Carnegie Museum of Natural History, Pittsburgh, USA, 'because, frankly, the foot of this fossil primate looks like a small monkey, specifically like a marmoset.' What this tells us is that the split in the primate family must have occurred, and therefore the common ancestor itself lived, more than 55 million years ago.

A cladogram showing the position of Archicebus within the
primate group. Ida occupies the now extinct adapid branch. The
lower half of the phylogram comprises the haplorhines while the
upper half comprises the cladogram.

As Archicebus  is also more closely related to tarsiers rather than displaying the perfect mix of characteristics, which would make it the common ancestor of tarsiers and their sister group the anthropoids (the rest of the haplorhine group such as monkeys and humans), this shows that the first split in the primate family must be older still, perhaps occurring more than 60 million years ago. The dinosaurs died out 65 million years ago due to a meteorite impacting the Earth. The planet, while blighted, only remained a harsh place to live for a million years at the very most.

When plant life reclaimed its surface, the surviving animals followed in their wake. The dinosaurs were gone, leaving behind thousands of exploitable ecological niches. Tropical forests sprang up across the planet, hotbeds of evolutionary activity, in which the first, yet still undiscovered, primate evolved, giving rise to a diverse wave of descendants, including Archicebus and Darwinius.

Both creatures, based on their geological settings inhabited similar environments. Both were arboreal jungle-dwellers as seen in the plant fossil record at each locality. Ida was found in a piece of shale which originally formed on the bed of a lake. Archicebus, which has yet to receive a moniker of its own, was also found on a piece of slate, originally formed on the bed of a lake. Yet while the habitats were similar, they were separated by tens of thousands of miles.

The configuration of the continents barely changed between 55 and 47 million years ago, meaning that the ancient lakes in Hubei and Germany would have been tens of thousands of miles apart, as they are today. The fact that the older Archicebus was discovered in Asia rather than in Europe where the younger Darwinius made its home provides strong evidence that primates first evolved in the far east rather than in Africa or Europe.

Previously, the only fossil evidence backing this hypothesis were a few teeth from Myanmar. This discovery on the other hand is of a complete and distinct species with clear physiological links placing it close to the base of the primate family tree. In my opinion, the theory is most likely correct. Not only does the fossil evidence strongly point to this being the case, but the theory itself provides a solution to one of the major problems facing palaeontologists: how did monkeys reach the Americas?

The haplorhine family is divided into two groups: the Old World and New World monkeys, or catarrhines and platyrrhines to use the Latin names. The former inhabit Africa and Eurasia (the old world) while the latter live in the Americas (the new world). Previously, the fossil record suggested that the first primates evolved in Europe/Africa and gave rise to the catarrhines around 40 million years ago. The platyrrhines in turn evolved from Old World monkeys which somehow migrated across the Atlantic ocean.

Various theories were put forward to suggest this, including monkeys carried across on chunks of mangrove swamp broken off from the African coast by storms and pushed towards the Americas by the currents. Irrespective of the method, an ocean crossing would have been incredibly dangerous and unlikely to occur. Instead, if primates first evolved in Asia and split into the strepsirrhines and the haplorhines (composed of the catarrhines and the platyrrhines), the catarrhines could have simply migrated towards Europe and Africa.

A map showing how Asia and the Americas were originally connected by a
land bridge known as Beringia. The blue line indicates the path the
 platyrrhines may have taken to reach the new world

Meanwhile the platyrrhines could have crossed the land bridge connecting Asia and the Americas in order to reach the new world, thus cutting out the need for a lengthy and hazardous sea crossing. While the land bridge today is submerged beneath the Bering Sea, up until just 6000 years ago, it allowed for an easy crossing between the two continents. What is more, the oldest platyrrhine fossil, a monkey known as Branisella which was found in Bolivia, is just 26 million years old, giving primates over 10 million years to make the move from Asia to the Americas based on the oldest fossils of both haplorhine groups.

Of course, this is a lot to place on a single, mouse-sized fossil, which is why palaeontologists have been conducting detailed analyses of Archicebus for more than ten years. As a result, its placement on the primate family tree and the theories as to its impact on the group's evolutionary history can be considered accurate. 'We applied rigorous testing to all our ideas and hypotheses, convincing all our own collaborators first,' said John. J. Flynn, the curator of fossil mammals at the American Museum of Natural History.

This is in stark contrast to the discovery of Ida who was proclaimed the common ancestor and missing link in our evolutionary story barely a year after her remains were purchased. The past few years have been tantalising. While she was discarded as the common ancestor, Ida showed us that we were near to the base of the primate family tree. Archicebus has brought us closer still and while we continue to claw our way back through millions of years, I believe that the Discovery will be made sooner rather than later.

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For those of you who are interested, the article on
the first piece of fossil evidence backing up the theory of the Asian origins of primates can be found by following the link below:

http://prehistoricict.blogspot.co.uk/2012/06/revolution-in-primate-prehistory.html

Enjoy!

The Lizard King Of The Eocene Myanmar

The megafaunal lizard Megalania which existed in Oceania just
40, 000 years ago may be the source of the Maori legend of the
 giant Kumi lizard, a whisper of truth in a myth older than the
pyramids. There have been more recent yet unconfirmed sightings of
what some believe to be living specimens of Megalania. 

The Mesozoic Era is sometimes referred to as the Age of the Dinosaurs. In my opinion, this is a rather narrow view. While the dinosaurs dominated the land, the rivers were the haunt of the ancestors of the crocodiles and the seas were patrolled by marine lizards which would dwarf most creatures in the sea today. The Mesozoic should be known as the Age of Reptiles: these scaly-skinned, cold-blooded creatures were the lords of Earth. Yet this all changed 65 million years ago.

The asteroid which devastated Earth was responsible for the destruction of the dinosaurs and the marine reptiles alongside hundreds of other animal groups. Briefly birds and then the mammals became the dominant animals on the planet. Yet the crocodilians, turtles, tortoises and some lizards which remained as small dwellers in the undergrowth made it through to the Cenozoic to give rise to the reptiles which inhabit the planet today. Yet while their heyday was over, throughout the last 65 million years of geological history, they made brief encores.

Perhaps the greatest of these was between 3 million and 10,000 years ago with the Australian mega-fauna. These giants lived alongside the earliest settlers of Oceania and exist as the faintest myths and legends of the Aboriginal dream-time stories. Now a new episode has come to light. Discovered in Myanmar in the 1970s by Russell Ciochon from the University of Iowa, fossils of a mysterious creature sat, unstudied, in a storeroom of the University of California's Museum of Palaeontology.

The 40 million year old jawbone from Myanmar

They were examined earlier this year by a team led by Jackson Head of the University of Nebraska Lincoln. While the material consisted mainly of jawbones and other pieces of the skull, by looking at the size ratios between the body and the head of similar reptiles, the researchers were able to build up an image of what this creature was like. In short, it was big. Comparable in size to modern day Komodo dragons, it would have been around two metres in length and weighed in at over 30 kilograms.

While large reptiles are well known for going for long periods of time without eating, when they do refuel, they need substantial prey. Komodo dragons live alongside water buffalo which are their primary source of food. Based on what fossil record exists from Myanmar 40 million years ago, the environment which this creature inhabited was a tropical jungle.

Barbaturex may have been very similar in form to a Komodo dragon

Yet such places are not known for their large mammals. Therefore this creature must have been feeding on something else in order to sustain its significant size. Based on its teeth, Jackson Head thought that plants made up its diet. When he first examined the fossils, he noticed the creature's bones were characteristic of a group of modern lizards that includes bearded dragons and chameleons.

'When I started studying its modern relatives, I realized just how big this lizard was. It struck me that we had something here that was quite large and unique,' said Head. What we are left with is rather strange. Today the only plant-eating reptiles are small. This creature from Myanmar is a throwback from the time of the giant herbivorous reptiles of the Mesozoic.

The brightly coloured chin flaps of a species
of south east Asian lizard

Ridges on the underside of the jaw suggested that there were once flaps of soft tissue attached to them which may have been multicolored as they are in modern day species. The researchers called it Barbaturex morrisoni. The genus name translates as 'bearded king' while the species name honors Jim Morrison, the lead singer of the 1960s' rock-band The Doors, whose lyrics earned him the moniker of 'Lizard King.'

'I was listening to The Doors quite a bit during the research,' said Head. 'Some of their musical imagery includes reptiles and ancient Barbaturex would have been a true king.'

It is easy to imagine this reptile as it was 40 million years ago, its bulk spread out over a large boulder, displaying its resplendent chin flaps to other members of its species as a sign of dominance. In the future there is a distinct possibility that giant reptiles may once again dominate the face of the Earth, but for now the time of reptiles is certainly not over.

Pushing The Evolutionary History Of Turtles Back Slowly But Surely

On Australian beaches, for part of the year at night, a very special event can be witnessed. A patch of sand moves. The grains bounce and slide away as the sediment beneath is pushed upwards. In the stark light of the moon the glint on the edge of a beak or scaled fin maybe visible. Slowly but surely, a creature digs its way to the surface to reveal a tiny sea turtle nestling within a depression of sand.

Spawning team for turtles on the beach

Six months ago its mother buried a clutch of eggs. All around this pioneer the sand shifts as more baby turtles claw their way out of their shells towards the surface. As soon as they are free, they scurry as quickly as they can towards the sea, tumbling down the sand dunes into the froth of the waves. In 30 years they will return and lay eggs of their own, to start the cycle again.

The ritual of turtles hatching from sand-swamped eggs is most likely as old as the group themselves, extending back in time to the first chelonians (turtles) on Earth. The fact that the same kind of behavior (burying eggs close to a body of water) is found in all members of the group means we can be pretty certain about this. What is less certain is what the first chelonian on Earth was like or when it lived. A discovery made in 2008 of a creature known as Odontochelys semitestacea set the benchmark at 220 million years ago.
 

A fossil of the 260 million year old Eunotosaurus
africanus, the oldest known turtle on Earth

This creature's morphology, however, was by no means primitive. It had a fully developed plastron (the shell on the underside of the body) and broadened ribs which were well on the way to becoming the supports for a scaly carapace on its back. There was no way that this odd creature was the first turtle on the planet. Indeed, the first turtles with fully formed shells appear in the fossil record just 10 million years later. 

For years Odontochelys remained paleontology's best attempt to get close to the earliest chelonians. Yet now, a discovery from South Africa has pushed the group's evolutionary history back by an incredible 40 million years, a massive jump in terms of the history of animal life.

The first specimens of Eunotosaurus africanus were actually found in 1892 in South Africa in 260 million year old rocks. It was only in 1914 that British Zoologist D.M.S Watson classified it as a chelonian.

For years specimens of Eunotosaurus remained simply as proof of the existence of yet another denizen of the fossil record until its bones were re-examined in detail earlier this year by Dr Tyler Lyson from the Smithsonian National Museum of Natural History. The study revealed the presence of multiple primitive versions of features found in more advanced turtles both in the fossil record and alive today. The most prominent examples are no intercostal muscles running in between the ribs, paired belly ribs and a specialized mode of rib development, all of which indicate that Eunotosaurus represents one of the first species to form the evolutionary branch of turtles. 

'Eunotosaurus neatly fills an approximately 30-55-million year gap in the turtle fossil record,' said Dr Tyler Lyson. 'There are several anatomical and developmental features that indicate Eunotosaurus is an early representative of the turtle lineage; however, its morphology is intermediate between the specialized shell found in modern turtles and primitive features found in other vertebrates. As such, Eunotosaurus helps bridge the morphological gap between turtles and other reptiles.'

An artist's impression of Eunotosaurus africanus

What is interesting is what this tells us about why turtles took on their distinctive form. The fossil of Eunotosaurus shows that it was a land-based creature, confirming the theory that chelonians were terrestrial in origin. As a result, we can say that turtles would have made a gradual move into water. The early forms, which may have included Eunotosaurus, would have lived in the shallows. The flatter, wider bodies supported by the wide ribs would have made movement in shallow water easier as well as giving them some hydrodynamic properties.

In later forms, such as Odontochelys, the plastron was the first part of the shell to develop. The trigger for developing any type of armour is biological defence. The Permian seas were filled with predatory fish. During the Great Dying, an extinction event which wiped out 90% of marine life, oceanic predators all but vanished as food webs collapsed. This gave turtles the chance to make their move into the oceans. When predators returned, the newly marine chelonians required a form of defence. As surface dwellers, they were most vulnerable to attacks from below and so evolved the plastron.

Marine reptiles were quite common by 220 million years ago, providing the selective pressure which resulted in the perfection of the turtle's shell 10 million years later. Indeed it is wonderful to think that the drama played out on the beaches of Australia is a microcosm of the evolutionary struggle which resulted in the first turtles to walk on the face of the Earth and of their descendants who later swam through its oceans.

My Family And Other Animals

The 150 million year old fossil of Archaeopteryx
lithographica, the first bird on the planet, from the
Solnhofen Limestones the Bavaria Region of Germany.

150 million years ago above the limey, predator infested waters of a lagoon which would become Bavaria, lived Archaeopteryx lithographica, the first ever bird on our planet.

Archaeopteryx, for many palaeontologists has always occupied a spot of certainty. What has always been less clear is its evolutionary run up  and how this connects to its descendants.

Diagrams of relationships have been drawn up over the years, but each new fossil discovery throws up problems with the existing schemes of classification. Now, a new fossil discovery from China provides a new link. 

Archaeopteryx and its descendants are all part of the family aves. In turn, these are part of a larger group known as the avialans, a tight knit group consisting of all birds and three immediate dinosaur ancestors/relatives, including Anchiornis which in 2010 became the first prehistoric creature to have its complete colours reconstructed.

The very name 'avialan' means 'bird wing.' Indeed, even the non-avian members of this very select group are often referred to as proto-birds, as the boundaries separating the true avians from the rest are blurry. As a result, while the origins of birds with Archaeopteryx was clear, the origins of avialans was less defined, until now.

Unearthed from 160 million year old rocks of the Tiaojishan Formation in the world famous Liaoning Province, this new specimen was purchased from a local fossil dealer and examined by a team led by Pascal Godefroit from the Royal Belgian Institute of Natural Sciences. Without knowledge of the the locality from which the fossil came, it would have been impossible to date the fossil accurately. A study of the sediment which made up the fossil's matrix showed it to be linked with the Tiaojishan fossil beds. The fossil itself was well preserved, with all the bones present and delicate feather impressions marking out the creature's original dimensions. In life, it would have been around 50 centimetres in length with a toothy beak, long tail, clawed hands and feathers covering the entire body.

 

The 160 million year old fossil of Aurornis xui, the first avialan on the
planet, from the Tiaojishan Formation in the Liaoning Province of China.

From the outset, it was clear that it was not a true avian on the basis of its short forelimbs, which could not have been used for gliding let alone flying. Yet it was very similar to other, ancestral avialans. This placed it within that group. What was interesting was its forelimbs which were shorter than the most primitive members of the group to date.

Other features common to avialans were poorly defined in this creature yet similar to other relatives, such as troodontid dinosaurs. It was clear that the dinosaur, now named Aurornis xui (dawn bird) was very close to the base of its group's evolutionary family tree. "Previous phylogenetic investigations were based on maybe only 200 morphological characteristics. Here, we recognise almost 1,500 characteristics,' explained Dr Godefroit. 'The new creature we describe is also a basal bird; and in fact it is even more primitive than Archaeopteryx.'

 

A reconstruction of Aurornis xui which clearly
shows its bird-like characteristics

The researchers placed Aurornis at the very beginning of avialan evolutionary history. So while Archaeopteryx represents the first bird on the planet. Aurornis represents the beginning of the lineage. The ten million years separating the two was the time in which the more advanced avialans developed the muscles, bone structure and the physiology required for flight. 

It is rare for a discovery to be marked out as the first of its group. Most of the time, a fossilized creature will be another group member or lie close to its group's evolutionary origin. Yet just occasionally a specimen hits the mark.

On The Demise Of The Stromatolites

Beautifully coloured modern day stromatolites, relics of the Precambrian.

People often talk about Earth history in relation to a particular group of organisms: the Mesozoic is known as the Age of the Dinosaurs and the Cenozoic the Age of Mammals. If we extend this, then the Precambrian ought to be known as the Age of Stromatolites.

On a semi-barren planet shrouded in toxic oceans and volatile continents, the stromatolites were the only form of life. They built the first biological empire on the planet: giant, layered colonies of bacteria and sediment.

Collections of stromatolites could exist on a scale rivaling that of Ancient Rome with swaying pillars and mounds of slime anchored to the sea bed. They dominated the oceans for over 3 billion years, but towards the end of the Precambrian they went into decline. Yet from the Cambrian onwards, they still existed and are found in the fossil record, living in the shadows. Today, stromatolites can be found in the most inhospitable places on Earth only, from alkaline lakes and hyper-saline bays to the sub zero beds of Antarctic pools and the oxygen starved, oxide-laden streams.

'Stromatolites were one of the earliest examples of the intimate connection between biology -- living things -- and geology -- the structure of the Earth itself,' said Woods Hole Oceanograpic Institute (WHOI) geobiologist Joan Bernhard. Their decline was an event comparable to the extinction of the dinosaurs, a global event which affected the entirety of the Earth's biosphere. For years the causes of this semi-extinction were completely unknown.

Some put it down to the two ice ages which wracked the Precambrian Earth, others to massive geochemical changes, such as the appearance of oxygen in the atmosphere. Yet while these things had a impact on stromatolite populations, the bacterial colonies simply returned in force afterwards. Even together, this would not have been enough to spell the end for the first biological empire on Earth. Now, a study conducted by the Woods Hole Oceanographic Institute throws up a strong potential candidate for the driving force behind the stomatolites' decline.

The laminations within stromatolites. Thrombolites bare no such
structures and have a more clotted and clumpy texture.

The trigger for the study is rather interesting. The stomatolites' decline marked the appearance in the fossil record of another type of bacterial formation known as a thrombolite. Stromatolites are characterized by their very finely laminated layers of bacteria and sediment. Thrombolites on the other hand do not possess any form of layering. While both types of colony are dome-shaped, thrombolites have a clumpy structure rather than lamination.

Various hypotheses were put forward to explain this. Bernhard and fellow WHOI microbial ecologist Virginia Edgcomb suggested the appearance of predatory foraminifera in the oceans. New predators had already been put forward as the reason for the change from stromatolite to thrombolite. Bernhard and Edgcomb's theory, however, is the only one to have strong supporting evidence. Foraminifera, forams for short, are a group of marine single-celled protoctists which use pseudopodia to engulf their prey.

Despite their known ability to disturb modern sediments, their possible role in the loss of stromatolites and appearance of thrombolites had never been considered until now. The researchers sampled material from both types of modern day bacterial formations from Highbourne Cay in the Bahamas. Using microscopy and rRNA sequencing techniques, they examined the foram content of each type of formation.

The organic sheaths of thecate foraminifera. While they are highly
complex, each one is only home to a single cell.

The thrombolites were home to a greater concentration of forams than stromatolites. What is more, the majority of these microscopic inhabitants were what are known as thecate foraminifera, so-called because they secrete a protective sheath of organic matter around themselves. These thecate foraminifera were probably the first kinds of forams to evolve, not long in geologic terms before stromatolites began to decline.

'The timing of their appearance corresponds with the decline of layered stromatolites and the appearance of thrombolites in the fossil record,' said Edgcomb. 'That lends support to the idea that it could have been forams that drove their evolution.' The connection, of course, may have been arbitrary. To disprove this possibility, the researchers decided to recreate a Precambrian ocean environment. They seeded chunks of stromatolites with forams found in thrombolites.

After six months, the laminated structures had been almost entirely destroyed and had taken on a clotted texture. 'The forams obliterated the microfabric,' said Bernhard. As a control to make sure that the forams were the trigger for the clotting, they added micro-organisms to a stromatolite sample but then treated the sample with colchicine a drug that prevented them from sending out pseudopodia. "They're held hostage," said Bernhard. "They're in there, but they can't eat, they can't move."

After about six months, the foraminifera were still present and alive, but the structure of the colony had not become more clotted like a thrombolite. It was still layered. There was no doubt that forams were the clotting trigger. From this, the researchers concluded that these micro-organisms may have been the cause of the decline of the stromatolites during the late Precambrian. The theory fits nicely with the problem in hand.

A foram embedded within a stromatolite. The small thread-like lines
 coming off of the body and its pseudopodia. The green colour is not
natural and comes from a dye used to enhance the microscope image.

Complex cells, or eukaryotes as they are properly known, evolved around two billion years ago; long before the decline of stromatolites. What is more, forams have been found in the late Precambrian fossil record, meaning that they were around and could have acted as the event trigger. The theory fits the bill. Now all it requires is evidence from the fossil record of an increase in oceanic forams and forams living within thrombolites.

Many Precambrian bacterial colonies are preserved down to the cellular level, meaning that forams living within the structures should be detectable. If their presence in the fossil record is concordant with the results of Bernard and Edgcomb's experiments, the theory will certainly become the foremost explanation for the decline in Precambrian stromatolites.

On The Origin Of Hummingbirds

A silhouette of an emerald hummingbird I saw while in Ecuador 

Hummingbirds are extraordinarily beautiful creatures. Even the largest species is no bigger than a satuma. Yet they compact a complete set of organs and a pair of wings capable of beating hundreds of times a second; true miracles of evolutionary engineering.

They perform some of the most complex aerobatics of any animal in existence. They are able to hover, keeping their heads perfectly still while feeding from nectar-rich flowers with long, needle-thin beaks with a degree of precision comparable to keyhole surgery .

Their swift-beating wings, generate lift and move in a figure of eight pattern unique to the group. The wing thrust acts in both directions, so the overall motion forwards or backwards is virtually zero. This aerial ballet is so specialist that the origins of the creatures' powers of flight baffled palaeontologists for decades. Yet a fossil discovery from Wyoming by researchers working at the Field Museum of Natural History in Chicago offers a few clues. The specimen is beautiful and so well preserved that it looks like a painting against a background of speckled shale. While it is only 12 centimetres in length, every bone is present, with feathers consisting of reddish halos which fringe the skeleton.

The species, named Eocypselus rowei, after examination, showed that it was not in fact a hummingbird, but a precursor to the group. It has been a long-held fact that hummingbirds split from the swift family. 'This fossil bird represents the closest we've gotten to the point where swifts and hummingbirds went their separate ways,' said Daniel Ksepka from the National Evolutionary Synthesis Center in Durham, North Carolina.

The 50 million year old, beautifully preserved fossil of the hummingbird ancestor Eocypselus rowei from the Green River Formation in Wyoming,

A comparison of Eocypselus' wings with those found in members of the two descendant groups showed that it combined elements from both. Swifts have long wings designed for high speed flight and gliding. Hummingbirds have shorter wings designed for hovering and quick darting motions. As a result, we can see that Eocypselus would have been proficient in the air, yet was showing signs of the specialized structures needed for more complex methods of flight.

Of course, a small size is requisite to both groups, so it seems, based on the fossil's size, that the ancestors became small before their complicated means of flight began to develop. Due to its well preserved nature, the researchers were able also to extract information beyond flight. By studying preserved melanosomes within the feathers, they determined that Eocypselus would have been glossy black, similar to modern swifts, while an examination of its beak revealed that it was probably an insect eater.

Birds underwent an evolutionary radiation after the demise of the dinosaurs. The skies were no longer ruled by pterosaurs, dinosaurs no longer threatened their nests and mammals had yet to become either large or fearsome. The birds were able to flourish.  Some became predators in their environment, growing to over three metres tall with beaks built like cleavers. While others took an alternative route. These became diminutive, yet more complex, evolving ultimately into the hummingbird.

A Precambrian Postprandial

Lunch is an integral part of our everyday lives. For some (myself included) it is semi sacred. Yet fossil evidence shows that the history of eating extends further back in time than previously imagined. Strange beasts from the Cambrian period 520 million years ago were predatory in nature.

Specimens of Gunflintia being consumed by the predatory bacteria
(the brown  rods and spheres) from the 1.9 billion year old Gunflint
Chert near Lake Superior.

Yet fossils of bacteria from Lake Superior now push the origins of 'lunch time' definitively back into the Proterozoic eon. Specimens of micro-organisms from the 1.9 billion year old Gunflint Chert have been found preserved in the process of consuming a bacterium called Gunflintia.

A team of palaeontologists, led by Dr David Wacey from the University of Western Australia and Professor Martin Brasier from Oxford University found the bacterial community preserved within the super fine-grained chert minerals earlier this year.

The fossils only gave up their secrets, however, when the scientists magnified them at scales of 3 to 15 micrometres. They found that certain species of bacteria formed clusters around the Gunflintia and were engaged in heterotrophic activity. Autotrophs have the ability to manufacture organic material from inorganic constituents. Plants are a prominent example, using photosynthesis to turn carbon dioxide and water into glucose. Heterotrophs have to consume autotrophs in order to obtain organic molecules for their food.

All animals are heterotrophs, as are the predators of Gunflintia from the Gunflint Chert. Of course the clustering may have been random, or to allow the different species to feed off of the others' metabolic waste products, but certain features of the fossils dispel this theory. Some of the Gunflintia fossils were riddled with holes and displayed damage to their insides, surrounded by the heterotrophic bacteria, linking the damage to the predatory behaviour.

Fossils of Huroniospora from the Gunflint Chert

What is more, other species of bacteria were found within the chert, including a particularly abundant creature called Huroniospora. Yet they were untouched by the predatory heterotrophs. This suggests a degree of choice in prey and a far more complex ecosystem than previously thought.

'Whilst there is chemical evidence suggesting that this mode of feeding dates back 3,500 million years, in this study for the first time we identify how it was happening and 'who was eating who,' said Dr Brasier. The study also gave scientists an indication of what the early Earth smelled like. While the idea of vents choking the Earth to produce the smell of rotten eggs is a classic image, these fossils provide direct evidence as to the gases released, mainly hydrogen sulphide.

Iron sulphide, a byproduct of brimstone.

Many of the fossils were actually casts in-filled with iron sulphide minerals, better known as pyrite. This is a highly visible marker of sulphate-reducing heterotrophic bacteria. Sulphate reduction produces hydrogen sulphide as a waste product, the gas responsible for the hellish smell of rotten eggs.

'Recent geochemical analyses have shown that the sulfur-based activities of bacteria can likely be traced back to 3,500 million years or so, a finding reported by our group in Nature Geoscience in 2011. Whilst the Gunflint fossils are only about half as old, they confirm that such bacteria were indeed flourishing by 1,900 million years ago. And that they were also highly particular about what they chose to eat,' said Dr Wacey.

The Precambrian is a mysterious time in Earth history. Evidence is sparse and more often than not warped by heat and tectonic forces. Yet occasionally we get a clear glimpse into the world of 600 million years ago. There is still much to learn about the Precambrian, but with each new study, each new fossil, each new serendipitous find, we gain a better understanding of our planet's origins.

More On Yeast And Multicellularity

N.B: I would advise reading the post in the link at the end of the article before reading this one, just for clarity. Enjoy!

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Yeast cells (Saccharomyces cerevisiae)

A year ago, I reported on two fantastic experiments regarding the origins of multicellular animals. One was conducted at Harvard University, the other at the University of Minnesota's College of Biological Sciences. What they have in common is yeast.

The Minnesota study found that in conditions when food was scarce, yeast cells would form closely packed colonies in order to maximize the capture of nutrients. They hypothesised that this survival behaviour may have been an integral part of the origin of multicellularity.

The Harvard study took this further. They placed yeast cells in a mix of sugar rich and low sugar environments in test tubes, put the test tubes in a centrifuge for a few days and then examined the contents. In the low sugar environments, the yeast cells had formed small, spherical colonies of conjoined cells all descended from a single ancestor. Apart from maximizing nutrient capture, as the cells shared identical genetic material they were able to act with a certain degree of cooperation, with some damaged or defective cells committing a form of biological suicide known as apoptosis, in order to conserve nutrients for healthy, useful cells.

The cooperative colonies from Harvard were even closer to multicellular animals than the Minnesota colonies. This was as far as my article went, a link to which is at the bottom of this post. Now, the University of Minnesota have published results from their original study which takes the story of these cooperative colonies further towards multicellular organisms. The experiment, conducted by William Ratcliff and Michael Traversano, followed a similar line to Harvard's work. They placed yeast cells in a low sugar environment and then agitated the mixture for a few days during which some cells died and others survived in a process mimicking natural selection. The researchers then took the surviving cells and repeated the process. After a few weeks, they had created cooperative colonies.

Unlike the spherical Harvard forms, the Minnesota specimens were similar in form to snowflakes, far more complex. The results did not end there. Some cells within the colony committed apoptosis, lying on vital connecting points within the snowflakes. Their death caused the tips of the structures to break away and form new colonies. Not only could the Minnesota colonies act semi cooperatively, feed more effectively and 'evolve' in a sense, they even had a way of reproducing.

One of the cooperative multicellular yeast colonies

This was over five months ago. Their most recent results are even more remarkable. In order to transfer the more successful inhabitants to fresh test tubes, they allowed the contents of the test tubes to sink to the bottom. The larger, heavier particles sank to the bottom while the lighter particles lay on top. Right at the beginning, all the layers were composed of single cells. When colonies arose, they formed a layer right at the bottom as they were larger, heavier and more successful than the single cells which sat on top in their own layer.

As the months progressed, Ratcliff and Traversano found that the speed at which the colonies sank increased by 45%. Some had simply increased their cell count, with the average changing from 42 to 115 individuals, resulting in a greater overall weight and so sank faster. Others achieved a greater mass by increasing the weight of each cell with the average mass doubling over the five month period. What is interesting is the impact this had in the selective processes which fuelled the 'evolution' of the colonies.

They formed originally in order to maximize the amount of nutrients. However, the larger colonies eventually became so massive that the cells in the centre were unable to feed and so began to die, weakening the overall structure, decreasing their chances of survival into the next test tube generation. The ones with larger cells faced a problem as each member required a far greater amount of nutrients in order to survive, meaning that they had a harder time surviving in the low sugar environment despite their combined efforts to capture food.

A snowflake colony. The green stained cells are about to commit
apoptosis and allow small parts of the structure to break away
to form new colonies in a process mimicking reproduction.

As a result, some colonies found a third option which addressed this cost of living. The cells became larger but less dense, meaning that they required less energy to live, whilst maintaining their weight. The overall colony also changed its shape, moving away from the multi-branched snowflake forms of its ancestors and towards a more spherical shape similar to those from the Harvard experiment. This made them more hydrodynamic and so were able to sink faster than the snowflakes whose branches created drag, hindering  process through the water.

In the context of the natural world, the snowflakes would be easy targets for predators or slower when moving towards food sources. Eventually, they would fall foul of natural selection as the spherical colonies would have become increasingly dominant in their environment. The results of the Minnesota experiment show something incredible: simple cells finding solutions to the problems of living as a multicellular body, creating levels of complexity and diversity in the process.

What is more, as the colonies had arisen through successive 'naturally selected' generations, Ratcliff and Travisano were able to show, through simple genetic sequencing, that the reason for the creation of colonies composed of conjoined cells was not due to the yeast utilizing a set of pre-existing genes (or 'latent multicellular genes' as the author described them) which existed for the purpose colonial survival in nature. Instead they had actually evolved the ability to reproduce via cell division, yet remain attached afterwards, in the lab.

Indeed, once the snowflake forms had evolved, almost none reverted to a single celled state. Many things could have resulted in this, but the researchers hypothesised that reason was a genetic mutation which interrupted the process of mitosis (the form of cell division which creates a new, identical cell), resulting in the conjoined colonies. What is important about this fact is that this could easily have occurred in nature as mutations are more likely to break a biological process rather than fix, enhance or create a completely new one.

While scientists have yet to artificially create multicellular organisms from unicellular ones, the Minnesota study has shown how the leap from one to many cells could have occurred in nature. Various other studies have revealed the environmental conditions around the time when multicellularity is thought to have evolved, conditions which would have created selective pressures similar to those in both Minnesota and Harvard's experiments. While fossil evidence has yet to be found, we can say that there is a clear pathway linking the microscopic world of the single cell with the giants which inhabit our planet today.

http://prehistoricict.blogspot.co.uk/2012/01/another-step-taken-down-evolutionary.html

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I would just like to apologize for the recent lack of posts. Hopefully the length of this one should make up for the gap somewhat. I have been rather busy with work which is only going to increase. I shall try to continue posting, but things are going to be hectic up until the end of July. Nevertheless, keep checking for  new posts. Thank you.

New Research Into The End Of Snowball Earth

A artist's impression of Snowball Earth.

800 million years ago, ice sheets advanced from the poles, encircling the planet. The oceans froze. Glaciers scraped and scarred volcanic mountains and the red deserts of Rodinia. For over 200 million years, our planet languished under its grip as the continents continued their slow trek across the surface of the Earth.

Drop stones, fragments of rock embedded in foreign formations by the weight and pressure exerted by the glaciers, showed that the coverage extended to within less than 20 degrees of the equator. These feature in the geological record for 200 million years and is where, amongst other things, we derive our number for the duration of Snowball Earth. Yet 580 million years ago drop stones take a break from the geological record, showing the end of the glaciation period.

Volcanoes are most likely the demise of Snowball Earth.

So what caused the glaciers to retreat? Volcanoes were always thought to be the reason. Carbon dioxide amongst other greenhouse gases, produced by volcanic activity during the breakup of Rodinia, would have trapped heat, melting the ice and ending Snowball Earth. The problem with this theory is evidence. Studying the composition of the ancient atmosphere is not an easy task, particularly as the events are remote in time and the ice covering the Earth would have restricted the geological processes which preserve the composition of the air in past times.

Isotopes provide the answer. Isotopes of an element have identical chemical properties, but different physical properties, relating specifically to their weight. Using these subtle differences, geologists from Louisiana State University found evidence of a massive increase in the carbon dioxide composition of the end Snowball Earth atmosphere.

'The story is to put a time limit on how fast our Earth system can recover from a total frozen state,' said Huiming Bao. 'It is about a unique and rapidly changing post-glacial world, but is also about the incredible resilience of life and life's remarkable ability to restore a new balance between atmosphere, hydrosphere and biosphere after a global glaciation.' To find out this time limit, Bao and his team examined the chemical composition of crystalline 'fans' composed of barite (barium sulphate).

A high quality barite mineral fan (this is an
example rather than the ones used in the study)

The fans dated from just before and just after the end of the glaciation, allowing for a comparison between the atmosphere during and after the event. 16-O is the most common isotope of oxygen on Earth. In normal air, the more uncommon isotopes of 17-O and 18-O make up the remaining portion of oxygen and exist in a fixed ratio to each other. In the barite minerals Bao's team found, the ratio was different.

Not only was the ratio higher, but the rarer isotopes were in greater abundance in the barite. This showed an increased uptake of oxygen from the atmosphere. However, the rate of mineral formation is slow, too slow to have altered the composition of the atmosphere.

A sample of barium sediments

The only way the isotopic composition of the barite could have resulted was if the common 16-O was in short supply. The researchers' hypothesis is that this was due to volcanic activity. The combustion of material in Precambrian volcanoes would have stripped oxygen from the air, but to affect the isotopic composition of the atmosphere, volcanic activity must have been unusually high.

As a result, there would have been a massively increased concentration of carbon dioxide in the atmosphere as the volcanic carbon reacted to oxygen to produce its gaseous oxide.

It was this carbon dioxide which would have trapped heat, ending the Snowball Earth. 'Something significant happened in the atmosphere,' said Killingsworth. 'This kind of an atmospheric shift in carbon dioxide is not observed during any other period of Earth's history.' By studying the isotopic composition of the layers of barite deposits, Bao's team came up with what they have dubbed the MOSD event, Marinoan Oxygen-17 Depletion, which lasted for about 1 million years.

What is more, the team were able to date the layered barite beds by examining their stratigraphic position relative to igneous formations. They found that each mineral deposit was almost exactly the same age as a volcanic deposit, strengthening the links between the MOSD event, volcanic activity and the barite layers. Indeed, Bao himself stated that he was originally a casual disbeliever of the Snowball Earth event. Then he received barite samples from a colleague at Louisiana State University, samples which led to this study and what might be the answer to the end of the biggest glaciation in the planet's long history.

The Long Fuse To The Cambrian Explosion

Trilobites: one of the many heralds
of the Cambrian Explosion

The Cambrian Explosion is the reason for the diversity of life around us today. Had it not been for this single event, the oceans would be almost empty and the invasion of land may never have happened. The only visible life would have been immobile sacks of cells, the first primitive animals, and towering pillars of slime built by trillions of bacteria. Yet as the planet spun into the Phanerozoic eon, life diversified, giving rise to almost all of the existing animal phyla today.

One question baffled palaeontologists: why did the Cambrian Explosion not occur sooner? About 20 million years prior to the base of the Cambrian, there was an event which is known as the Avalon Explosion which produced those strange creatures known as the Ediacara biota. The transition between the two events was punctuated by a period of little evolutionary change, resulting in a delay between the origins of the fist animals and the Cambrian Explosion.

A discovery made in 2011 showed that the oceans which the Ediacarans inhabited were lacking in oxygen, yet that did not explain the exact conditions that early animals endured. Now a model has been created which gives an explanation for the long fuse to the Cambrian Explosion. The model, created in collaboration between the University of Leeds, Exeter and South Denmark, University College London and Plymouth Marine Laboratory has shown that the reason for the delay was due to the oceanic nitrogen cycle between 700 and 550 million years ago.

A simple version of the nitrogen cycle. 

Nitrogen is vital to life as it is needed to make proteins and DNA. However, it can only enter the global food chain through the action of bacteria. Upset either the nitrogen cycle or a food chain and it spells disaster for global biodiversity. This is what the research team hypothesized as to the cause of the long fuse. The exact details suggest that interruption was due to fluctuations between a hydrogen sulphide-rich and toxic ocean and an iron-rich, anoxic one.

The iron rich and anoxic oceans favoured anaerobically respiring bacteria. As they thrived, their metabolic processes produced hydrogen sulphide which built up in the water and sediment, creating an inhospitable environment for animals, stalling their evolutionary advance. Animals use nitrate from their food to build their bodies. Many bacteria on the other hand can extract nitrogen directly from the molecule itself or from more volatile compounds such as ammonia.

As a result, nitrate would have built up in the oceans during the hydrogen sulphide phases to the point that it was in abundance, leading to a sudden increase in the number of bacteria which used it. Nitrate-consuming bacteria can produce more energy than anaerobically respiring forms, and so would have out-competed other species of microorganisms. The upshot of this is that hydrogen sulphide-producing species would have been a minority in oceanic ecosystems, preventing the build-up of hydrogen sulphide.

Bacterial blooms in the oceans. Sites like this
would have dominated the Precambrian Earth

'Data from the modern ocean suggests that even in an oxygen-poor ocean, this apparent global-scale interchange between sulphidic and non-sulphidic conditions is difficult to achieve,' said Dr Richard Boyle from the University of Exeter. 'We've shown here how feedbacks arising from the fact that life uses nitrate as both a nutrient, and in respiration, controlled the interchange between two ocean states. For as long as sulphidic conditions remained frequent, Earth's oceans were inhospitable towards complex life.'

It was only due to the build-up of nitrate that complex life was able to advance further, leading to the Cambrian Explosion 520 million years ago. This was perhaps the most important event in the history of the planet. In hospitable worlds, life is a near inevitability. The Cambrian Explosion, however, is unique to the Earth. It is responsible for the world we see today. Yet understanding its mechanics is vital to our understanding of the plant and its history.

A Predator To Match The Dinosaurs

It is often said that dinosaurs dominated the Earth during the Mesozoic era. Tyrannosaurus rex, the tyrant king of the lizards, was the deadliest carnivore on the face of Pangaea. Raptors terrorized entire herds of herbivorous dinosaurs. Even though Baryonyx was a fish feeder, with its giant sickle claws, it was more than a match for any creature it encountered. Yet an even older lineage of reptiles whose members still lurk in the rivers and swamp lands of Africa and Florida were equally fierce if a little cumbersome on land: the crocodilians. Creatures such as Deinosuchus were longer than the tyrannosaurids and had a far stronger bite force.

An artist's impression of Deinosuchus, the largest
crocodile to have ever walked the Earth.

Such creatures began to evolve towards the end of the Cretaceous period when the empire of the marine reptiles was slowly crumbling. They were the top predators in their environments, feeding on fish, turtles and dinosaurs, including large carnivores.

New fossil evidence has shown that it was not only the large dinosaurs who suffered at the jaws of their aquatic cousins. A number of bone fragments were uncovered at the Grand Staircase Escalante - National Monument in southern Utah. They were taken to the South Dakota School of Mines and Technology for analysis. The research team, led by Dr Clint Boyd, found that many of the bones, including a relatively complete femur and partial skull, belonged to a new species of dinosaur.

While the name and identity of this newcomer has not yet been released (a paper is due soon) what made these specimens particularly interesting was that many of them displayed bite marks from what were potentially fatal skirmishes with a predator. The marks were associated with the joints in particular which is the modus operandi of the crocodilians.

The femur and associated crocodilian tooth from the
Grand Staircase Escalante National Monument.

In the water, these giant reptiles grasp onto their prey and perform what is known as a death roll designed to tear flesh from the victim. On land, while they do not roll over they still shake their heads in a vice-like grip. From their relatively low vantage point, just a few inches off the ground, legs are an easy and obvious target, as well as the dual effect of preventing the prey from escaping. Even if the animal did manage to break free, the leg would have been left behind, making the creature easy to recapture.

The clinching piece of evidence, however, was a crocodilian tooth embedded in the femur. Until now, there was only evidence of interaction between large dinosaurs and the crocodilians. This adds a new dimension to the Cretaceous Earth, showing that these predators targeted smaller and easier meals. Indeed, a study of the bones showed that they came from dinosaurs which would have been no more than two metres in length.

'A lot of times you find material in close association or you can find some feeding marks or traces on the outside of the bone and you can hypothesize that maybe it was a certain animal doing this, but this was only the second time we have really good definitive evidence of a crocodyliform feeding on a prey animal and in this case an ornithischian dinosaur,' said Boyd. It's an interesting note that as the dinosaurs slowly declined, the crocodiles began to rise.

The number of species which existed towards the end of the Cretaceous was staggering and while they suffered a decline during the K-T boundary extinction event, they survived while the dinosaurs did not. Indeed, had the asteroid never struck the Earth, it is still possible that dinosaurs might have gone extinct, out-competed by the hardy crocodilians, while the smaller ecological niches were overrun by the mammals and the birds. The world may well have been very different.

The Oldest Nervous System On The Planet

The 520 million years old, early Cambrian fossil of
the fuxianhuiid Chenjiangocaris kunmingensis

Fossils are a rarity. Of all the creatures which have ever lived on the Earth, only a minute portion have been preserved in the fossil record.

Ammonites and sea urchins in a collection are one surviving piece of a far larger picture. Even so, only a small portion of preserved specimens are of good, useful quality.

Moroccan trilobites or arthropods from the Burgess Shale are truly incredible, having escaped plate boundaries or damage by scavengers.

Yet treasures have recently been discovered in 520 million year old rocks in the Kunming Region of south-west China. Earlier this year, a team of palaeontologists led by Javier Ortega-Hernandez from Cambridge's Department of Earth Sciences uncovered the perfectly preserved remains of a creature known as Chenjiangocaris kunmingensis, part of a group of creatures called the fuxianhuiids.

The fossil itself is reddish pink and contrasts beautifully with its grainy, ochre matrix. What makes it special is at the point of death, instead of settling with its underside on the seabed, it sunk to the bottom of its ocean home and was buried face up. In the case of most arthropod fossils, their face down preservation means that the delicate innards of the head are obscured by the hard carapace of the cephalon.

A reconstruction of Chenjiangocaris, showing its sensory organs, gills and carapace

This creature on the other hand with its face up orientation displayed the contents of its head for all to see.

Underneath the cephalon lay two claw-like structures, antennae and more than 10 pairs of small feeding tentacles with each section perfectly preserved. By examining similar body parts in living creatures, the researchers have concluded that the apparatus was used to help the creature feed. The small tentacles were used to stir up the detritus on the sea bed and pass its organic content to the mouth.

'Since biologists rely heavily on organisation of head appendages to classify arthropod groups, such as insects and spiders, our study provides a crucial reference point for reconstructing the evolutionary history and relationships of the most diverse and abundant animals on Earth,' said Ortega-Hernandez. 'This is as early as we can currently see into arthropod limb development.' Controlling limbs requires a complex nervous system. A nervous system was also present in the fossil and represents the earliest known neural net in the fossil record.

The super-junction of nerves which constituted its brain was post-cephalic, meaning it existed beyond the head. In terms of its construction, it was very simple, consisting of a linear bundle of neurons connecting the eyes, antennae and feeding tentacles. 'These fossils are our best window to see the most primitive state of animals as we know them, including us,' said Ortega-Hernandez. Before that there is no clear indication in the fossil record of whether something was an animal or a plant.'

Fossils from the Burgess Shale were the first found
which documented the Cambrian Explosion

The development of the central nervous system and sensory organs was a vital part of the Cambrian Explosion. Chenjiangocaris may represent the earliest stages of this explosion. The Burgess Shale was the place where the first fossils of the Cambrian Explosion were uncovered. In recent years, the Chenjiang Shale in China has yielded so many fossils of early animals that it has come to be known as the Burgess Shale of the East.

While, as its name suggests, Chenjiangocaris was first discovered at the Chenjiang Shale, this particular specimen actually came from the Xiaoshioba Formation. 'The Xiaoshioba biota is amazingly rich in such extraordinary fossils of early organisms,' said Ortega-Hernandez. 'Over 50 specimens of fuxianhuiids have been found in just over a year.  There's massive potential for Xiaoshioba to become a huge deal for new discoveries in early animal evolution.'

A New Species Of Tiny Dinosaur

The newly discovered, late Cretaceous fossil of Yulong mini. 

Most people think of dinosaurs as big, brash creatures which roamed across the supercontinent of Pangaea, trampling forests whilst shaking the ground beneath them. The name Seismosaurus is nothing short of a testament to size. Sauroposeidon is named after the Greek god Poseidon, the god of earthquakes as well as the oceans. Yet not all dinosaurs were giants.

Instead of of the sound of trampled tropical forests, branches echoed with the cries and rustles of miniature, bird-sized creatures no more threatening than a crow. The newest of these diminutive dinosaurs is Yulong mini, discovered earlier this year at the late Cretaceous Qiupa Formation in the Henan Province in central China. It is one of the smallest recorded members of its group.

'Yulong looks like chicken with a tail,' said lead author of the paper published on the specimen Junchang Lü. 'Its behaviour was similar to living birds. Based on the primitive oviraptors such as Caudipteryx, Yulong should be feathered, although we could not find feathers due to the poor preservation condition.' Despite this, the researchers were still able to extract a large amount of information from the fossil.

An artist's impression of Yulong mini.

Specimens of hatchlings were found in the same formation as adults of the species. Yet a lack of proximity between the juveniles and the adults suggests that there was very little parental care in the species and the young had to fend for themselves from birth. Indeed, the jaws, even in hatchlings, were tough and capable of coping with an array of foodstuffs from meat, nuts to molluscs and eggs.

The oviraptorids were notorious egg feeders and the beak-shaped jaw of Yulong suggests that it too was adapted to cope with the hard shells of dinosaur eggs.

What is interesting is that it lacked the long legs of other members of its group, restricting its speed capacity. That combined with its diminutive stature means that it was most likely a herbivore. Though probably a scavenger on the side. Yulong was also the prey of other dinosaurs. Larger carnivores were found in the formation and would have occupied the space at the top of the ecosystem's food web.

The discovery of Yulong suggests something more incredible: that multiple groups of dinosaurs were following an evolutionary pathway which led to increasingly more bird-like forms. In essence, the different strands of the dinosaur family were converging on the birds, lending credence to the theory of convergent evolution. While it may be just that, a theory, if it is proved correct, it has major implications for the history of life on Earth and for life itself. Maybe there is some grand, overarching evolutionary design. The presence of Yulong scratches tantalisingly at the prospect.