Selenium Isotope Analysis Supports Idea of Progressive Oxidation

Most complex life on Earth, that is organisms that have evolved beyond the unicellular stage, depend on oxygen.  Fundamentally without O2, life on our planet would be very different, for one thing this highly reactive element is needed before amino acids and hence proteins can form.  Every breath you take reinforces the importance of oxygen to our planet’s great diversity and variation of life.  However, when did the oxygenation of our planet begin and how quickly did oxygen build up on Earth to allow complex life forms and more complicated ecosystems to evolve?

Earth Seven Hundred Million Years Ago – A Frozen Planet

“Snowball Earth” – progressive oxidation.

Picture credit: Everything Dinosaur

A new study published in the academic journal “Nature Communications” carried out by a team of international scientists, including researchers from University College London, Leeds University and the University of Washington, suggests that it took around 100 million years for oxygen levels in the atmosphere and oceans to rise to a level that allowed a rapid increase in the diversity and variety of life on Earth.

This research, that involved analysing selenium isotope concentrations from seven different locations, indicates that there was not a steady and sustained rise in O2 levels over this period, oxygen concentrations fluctuated, the amount of O2 increased in fits and starts leading to a substantial increase in life around 600 million years ago.

Which Came First More Animals or More Oxygen?

One of the fundamental questions that the scientists sought an answer to in this Natural Environment Research Council funded project was this – did rising oxygen levels permit the explosion of animal life recorded in the fossil record from about 600 million years onwards or was it a change in animal evolution that kick-started the rise of oxygen?

In simple terms:

• Did rising O2 levels lead to an expansion in complex animal life?

OR

• Did an expansion of more complex animal forms give rise to greater levels of oxygen?

This research suggests that the rise of O2 began significantly earlier than previously thought and the increase of oxygen was not a linear one, O2 levels rose, stalled and rose again over a vast period of geological time (at least 100 million years).  If the conclusions reached by the scientists are correct, then it is likely that early animal evolution was kick-started by an increase in the amount of oxygen available, rather than a change in animal behaviour leading to greater levels of O2 in the atmosphere and oceans.

Explaining the purpose of the isotope study, lead researcher Dr Philip Pogge von Strandmann (University College London) stated:

“We want to find out how the evolution of life links to the evolution of our climate.  The question on how strongly life has actively modified Earth’s climate, and why the Earth has been habitable for so long is extremely important for understanding both the climate system, and why life is on Earth in the first place.”

Starting at the Bottom – Marine Shales Actually…

To gain a better understanding of Earth’s climate during the Neoproterozoic (that vast era of geological time from about a billion years ago to 542 million years ago), the international team of scientists analysed selenium isotope data retrieved from samples of marine shales laid down at the bottom of the sea at different times from seven different locations to piece together a global picture of oxygen levels in the oceans and the atmosphere.

Strata studied included rocks across the United States, China and Canada and this work was conducted with the collaboration of Utah State University, Birkbeck (London) and Bristol University along with scientists from the University of Southern Denmark.

Selenium Isotopes

Selenium isotopes from marine shales can act as a indicator of global oxygenation conditions.  Lighter Se (selenium) isotopes recorded in shales generally indicate more oxygen rich conditions.  So by measuring the different selenium isotope ratios recorded in rocks of different ages, the scientists can start to build up a picture of the amount of O2 on the planet, specifically the level of oxygen in deep water, which in turn reflects on the amount of oxygen likely to exist elsewhere on the planet such as near to the coasts and in the atmosphere.

The selenium isotope analysis revealed that it took over 100 million years for the amount of oxygen in the atmosphere to climb from less than 1% to over 10% of today’s current level (20.8%).

Dr Pogge von Strandmann said:

“We took a new approach by using selenium isotope tracers to analyse marine shales which gave us more information about the gradual changes in oxygen levels than is possible using the more conventional techniques used previously.  We were surprised to see how long it took Earth to produce oxygen and our findings dispel theories that it was a quick process caused by a change in animal behaviour.”

Specifically the researchers focused on looking at strata laid down during the Cryogenian (720-635 million years ago) and Ediacaran (635-542 million years ago), towards the end of the Neoproterozoic.

During the period studied, three big glaciations –the “Snowball Earth” Sturtian (about 716 million years ago), and the Marinoan (635 million years ago) glaciations and the smaller Gaskiers glaciation (about 580 million years ago) occurred in which much of the planet (if not all of it), was covered in ice with the seas frozen and glaciers dominating the land.

As temperatures dropped, so the conditions for life that did exist at the time became extremely harsh.  However, when the temperature of the Earth rose, the glaciers melted and released vast quantities of mineral nutrients into the oceans.  The research team hypothesise that the ice melt and increased nutrient mix in the sea helped cause oxygen levels to rise in the deep ocean.

Glaciation and Subsequent Melt Boosted Oxygen Levels

Increased oxygen due to glacier melt.

Picture credit: Everything Dinosaur

Increased nutrients in a marine environment leads to more ocean plankton, which will bury and trap organic carbon in sediments at the bottom of the sea when they die.  Burying carbon results in oxygen increasing, dramatically changing conditions on our planet.  Up until this paper was published, oxygenation was thought to have occurred after the relatively small Gaskiers glaciation melted in the middle of the Ediacaran.

The findings from this study suggests that oxygenation occurred much earlier, linking a rise in O2 levels to the Marinoan glaciation, after which animals began to flourish in the improved conditions.  As life flourished so more and more diversity came about.  This led to the Cambrian explosion, a burst of evolution that began around 542 million years ago.

Everything Dinosaur stocks a range of models of Palaeozoic creatures such as trilobites, horseshoe crabs and cephalopods: CollectA Prehistoric World Models.

Oxygen a Slow Fuse

Professor David Catling (University of Washington), a co-author of the scientific paper stated:

“Oxygen was like a slow fuse to the explosion of animal life.  Around 635 million years ago, enough oxygen probably existed to support tiny sponges.  Then, after 580 million years ago, strange creatures, as thin as crêpes, lived on a lightly oxygenated floor of the sea.  Fifty million years later, vertebrate ancestors were gliding through oxygen-rich seawater.  Tracking how oxygen increased is the first step towards understanding why it took so long.  Ultimately, a grasp of geologic controls on oxygen levels can help us understand whether animal-like life might exist or not on Earth-like planets elsewhere.”

Oxygen and the Slow Fuse to More Diverse Complex Life

Life in the Ediacaran.

Picture credit: John Sibbick

Related Articles

To read an article (2012), that looks at some of the world’s oldest fossils: Are these the oldest fossils known?

Research (2014), suggests that multicellular life began earlier than previously thought: New research suggests multicellular life started earlier.

From August 2015, an article covering details of a study into ancient animal reproduction: Earliest evidence of reproduction in a complex organism.

Nicolas Cage Agrees to Return Tarbosaurus bataar Dinosaur Skull to Mongolia

The film actor and producer Nicolas Cage, he of films such as “Lord of War” and “Con Air” has agreed to return a rare dinosaur skull back to the Mongolian Government.  The Oscar-winning actor purchased the skull back in 2007, unaware that the specimen he had bought was stolen.  The Upper Cretaceous cranial material is from an Asian tyrannosaur, Tarbosaurus bataar, a close relative of the famous North American dinosaur Tyrannosaurus rex.

Nicholas Cage Dinosaur Fan

At the time of the purchase, it was reported that Mr Cage had out-bid fellow Hollywood “A-lister” Leonardo DiCaprio for the mounted skull fossil.

A Mounted Tarbosaurus bataar Fossil Skeleton

Mounted Tarbosaurus Specimen.

Picture credit: Heritage Auctions

Mr Cage purchased the skull for $276,000 USD (£185,000 GBP) from a Beverley Hills gallery (I. M. Chait), he was subsequently issued with a certificate of authenticity by the gallery.  U.S. Customs officials have not accused the actor or the gallery of any wrong doing.

Contacted by the Department of Homeland Security

A publicist for Mr Cage, Alex Schack commented that the actor had been contacted last year by officials from the Department of Homeland Security and informed that the skull was most likely illegally smuggled out of Mongolia.  The removal of artefacts and other items of “cultural significance” has been outlawed in Mongolia for decades, in fact, we at Everything Dinosaur believe that this law was in place before T. bataar was officially named and described (1955).

The office of Preet Bharara, U.S. attorney in Manhattan, filed a civil forfeiture complaint last week to take formal possession of the tyrannosaur skull material.  Preet Bharara had acted in 2012 as the prosecutor in the case involving Florida resident Eric Prokopi, who was found guilty over the falsifying of import documents related to a Tarbosaurus fossil skeleton that he had arranged to ship into the United States.  Mr Prokopi was imprisoned for his actions but as part of his guilty plea he helped U.S. Customs recover a further seventeen dinosaur fossils that had been smuggled out of Mongolia.

The Tarbosaurus Fossil Auction

To read the original article on the auction of a Tarbosaurus dinosaur fossil: Tyrannosaurid Fossil Goes Up for Auction.

At the time this first article was posted (May 2012), Everything Dinosaur along with other vertebrate palaeontologists and dinosaur fans supported a petition to stop the auction taking place.

To read an article about the seizure of the Tarbosaurus specimen (June 2012): Seizing a Tyrannosaur!

The outcome of the case against Mr Eric Prokopi (December 2012): Florida Man Pleads Guilty in Dinosaur Smuggling Case.

The return of the Tarbosaurus fossil skeleton to Mongolia (May 2013): Dinosaur Fossils to be Handed Back to Mongolia.

Tarbosaurus bataar Apex Predator of Late Cretaceous Asia

Alarming Reptile – Mounted Skeleton sold at Auction led to a legal dispute.

Picture credit: Everything Dinosaur

PNSO include a replica of a Tarbosaurus in their dinosaur model range: PNSO Dinosaur Models.

Dinosaur Skeletons in Auctions

It is unclear whether Mr Cage or his associates had any dealings with Mr Prokopi.  The I. M. Chait gallery has previously purchased and sold an illegally smuggled hadrosaurid dinosaur skeleton which had been procured from Mr Prokopi.

U.S. attorney, Preet Bharara had described Eric Prokopi as a “one-man black market in prehistoric fossils”, but we at Everything Dinosaur suspect things are very different.  Sadly, the practice of smuggling fossils and other rare and precious objects out of Asian, South American and African countries is relatively common place.   A spokesperson from Everything Dinosaur stated:

“Whilst we are delighted to hear that dinosaur fossils are being returned to their country of origin, so long as there are people prepared to pay vast sums for fossils, so the smuggling racket will continue.  There will always be a black market in fossils and it’s not just the “headliners” like dinosaur skulls that concern us, we shudder to think how many Christmas fossil gifts purchased on line in all innocence have their origins in the murky world of falsifying documents, fossil smuggling and the black market.”

Tarbosaurus bataar Compared to Tyrannosaurus rex

The table published below provides a comparison between these Late Cretaceous tyrannosaurids:

Tarbosaurus bataar Compared to Tyrannosaurus rex

A tale of the tape for two tyrannosaurids.

Table credit: Everything Dinosaur

Well Mr Cage, here’s one “National Treasure” heading home to its rightful owners.

Computer Simulations, Penguins, Plesiosaurs and Underwater Flight

Recently, Everything Dinosaur published an article on a fascinating piece of research published in the academic journal “PLOS Computational Biology” which focused on how plesiosaurs propelled themselves through the water.  The paper had been written by researchers at the School of Interactive Computing, (Georgia Institute of Technology, Atlanta, Georgia, USA) with the collaboration of Dr Adam Smith (Nottingham Natural History Museum, Wollaton Hall, Nottinghamshire).

Plesiosaur Swimming Speed

A three-dimensional model of a plesiosaur based on the Early Jurassic Meyerasaurus was used to examine how this marine reptile might have swam.  The computer simulations implied a forelimb dominated approach with the hind-limbs having a likely role not in active locomotion but in manoeuvring and stability.

Recently Published Paper Tackles How Plesiosaurs Moved in Water

The most effective swimming motion for the plesiosaur is flapping the two front flippers in an underwater flight motion

Picture credit: Royal Tyrrell Museum/Sabrowski/CP

In essence, these extinct reptiles may have “flown” through the water in the same way that extant penguins and turtles do today.

Swimming Plesiosaurs

One point team members at Everything Dinosaur picked up on was the velocities recorded during computer simulations of different limb configurations and different ranges of movement within the joints.  The speeds seemed remarkably low to us, especially when one considers how robust some of the limb bones of plesiosaurs seem to be.  A few weeks ago, team members were allowed to view some fossil bones from a plesiosaur that had been excavated over a series of dives off the coast of Dorset.  The humerus (upper arm bone) in particular was most impressive and it obviously came from a large and powerful swimmer.

Swimming Speeds Recorded in the 3-D Study

Rear flippers don’t seem to contribute much to velocity.

Picture credit: Liu at el/PLOS Computational Biology

The bar graph above shows the speed of the best motions that were found by the optimisation for each of the joint ranges (narrow, medium, wide).  They do not correspond to the maximum swimming speed likely to be achieved by a plesiosaur, although previous studies involving the plesiosaur genus used as the basis for the three-dimensional model (Meyerasaurus), suggested a swimming speed of around 0.4 metres/second.

Dr Smith Provides Clarification

We expressed our surprise with regards to the velocity cited in this research and emailed Adam Smith asking him to clarify the readings obtained.  Dr Smith email swiftly back explaining:

“The speeds we reported are not estimates of maximum swimming speeds.  We used speed only as a way to compare efficiency of simulations using all limbs versus simulations using just one pair of limbs (using identical joint ranges).  Comparison between simulations under *different* joint ranges are meaningless because all the simulations have the same beat frequency.  This is why the simulations with wider ranges are faster – the limbs move further in the same amount of time.”

The focus of this particular piece of research, the utilisation of state-of-the-art computer modelling to examine the locomotion of a Plesiosaur whose fossilised remains come from Lower Jurassic strata located in Germany, was on the range of motion of the limbs, calculating the maximum speed of the animal did not come within the parameters of the research brief.

Dr Smith added:

“If we put more energy into the simulations [by increasing the frequency of the limb beats] then they would certainly move more rapidly.  However, we wanted to ensure that our swimming motions were biologically possible, so we made sure the beat frequency was quite conservative.”

The Plesiosaur Clade (Plesiosauria)

The plesiosaur clade (Plesiosauria) consists of a very wide variety of prehistoric creatures ranging in size from around 1.5 metres in length to more than 15 metres long.  Swimming speeds are likely to have varied amongst species with different swimming abilities being consistent with different forms of feeding and hunting strategies.

To determine the maximum velocity of these creatures would involve calculating the muscle mass of a number of different sized individuals and looking at the influence on forward speed of different speeds of limb movement within a framework of what was biologically possible.  In addition, the metabolism of the animal would have to be considered.

Papo have a number of marine reptiles in their model range including a Plesiosaurus figure: Papo Marine Reptile and Dinosaur Models.

Estimating Maximum Velocity

Dr Smith explained that estimating the maximum velocity of a plesiosaur was beyond the scope of this project but he teased:

“Maybe a future research project!”

Perhaps, we will have the answer one day to the theoretical question, how close to the beach would you have to be to allow you to escape before a large predatory marine reptile caught up with you?

How Much of a Head Start Would You Have Needed?

A scale drawing of a Pliosaurus. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

To read the recent article which highlighted the research into the locomotion of plesiosaurs: Computer Simulations, Penguins, Plesiosaurs and Underwater Flight.

Plesiosaurs “Flew” Through the Water Like Penguins

Plesiosaurs roamed the seas for much of the Mesozoic.  The fossil record demonstrates that this group of long-necked, round-bodied marine reptiles were highly successful, with a global distribution and a geological record of some 135 million years or so.  However, ever since Mary Anning discovered the “sea dragon”, plesiosaur fossil at Lyme Regis in 1823, scientists have puzzled over how these animals actually moved through the water.

Studying Plesiosaurs

A team of scientists including Dr Adam Smith (Nottingham Natural History Museum, Wollaton Hall), have used computer modelling to recreate plesiosaur locomotion.  It turns out that these extinct creatures most likely used their two front flippers to effectively “fly” through the water, much in the same way as penguins and turtles do today.

Scientists Use a Computer Simulation to Unravel the “Flight” of a Plesiosaur

The most effective swimming motion for the plesiosaur is flapping the two front flippers in an underwater flight motion.

Picture credit: Liu et al. 

The Plesiosaurians

Plesiosaurs are part of the Sauropterygia, taxonomically a Superorder which was defined by Richard Owen in 1860 and encompasses a diverse range of marine reptiles such as the nothosaurs, the Pistosauroidea and the Plesiosauria.  Although the Sauropterygia consist of a myriad of marine reptiles with many different bauplans (body plans), they are united by having a modified pectoral girdle designed to provide support for the powerful strokes of the front flippers.

It seems that in some of the Plesiosauria at least, this modified pectoral girdle and other anatomical adaptations permitted these animals to swim primarily with the forelimbs, using an unmodified flight stroke to “fly” through the water.

A Long Evolutionary History

Throughout that long evolutionary history of the plesiosaurs,  a unique body plan with two pairs of large, wing-like flippers was maintained, but just how these animals propelled themselves through the water has remained a controversial subject.   In this new study, published in the open access publication “PLOS Computational Biology” the researchers adopted a novel approach using a digital, three-dimensional, articulated computer model to simulate the actions of this type of marine reptile swimming.

A large number of simulations were conducted to test the efficiency of various swimming methods and the team concluded that within the biologically possible range of limb motion, the simulated plesiosaur moved primarily with its forelimbs using an unmodified underwater flight stroke, in essence, the same locomotion method found in extant penguins and turtles.

Plesiosaurs “Flew” in the Water Like Penguins

A replica of a long-necked plesiosaur swims into view.

Picture credit: Everything Dinosaur

Using a Computer Model

Surprisingly, the computer model demonstrated that the rear flippers flapping added little to the forward speed of the plesiosaur studied.  Instead, the back flippers of plesiosaurs were probably used for steering and stability, a sort of underwater version of rear wheel steer and front wheel drive.

The researchers involved in the study were Shiqiu Liu, Yuting Gu, Jie Tan, C. Karen Liu and Greg Turk from the School of Interactive Computing, (Georgia Institute of Technology, Atlanta, Georgia) along with palaeontologist Dr. Adam Smith (Nottingham Natural History Museum, Wollaton Hall).

Commenting on the study, Dr Smith stated:

“Plesiosaur swimming has remained a mystery for almost 200 years, so it was exciting to see the plesiosaur come alive on the computer screen.  Our results show that the front limbs provide the powerhouse for plesiosaur propulsion while the hind limbs are more passive”.

A Bar Chart Comparing the Forward Speeds Achieved in the Simulation

Rear flippers don’t seem to contribute much to velocity.

Chart credit: Liu at el/PLOS Computational Biology

Plesiosaur Velocity

In the table above the velocity of a typical plesiosaur was calculated over a series of joint ranges (wide, medium and narrow).  Measurements were taken when forelimb-only flapping, hind-limb-only flapping and both pairs of limbs together were flapped.  Note that the forward speed in the forelimb-only tests are superior or broadly equivalent to the velocity achieved when both pairs of limbs moved together.  When hind-limb-only optimisations were tested the speed was greatly reduced.

Interestingly, these swimming speeds are relatively slow given the length of time these creatures had to evolve.  Elite human athletes can swim at around two metres per second for short periods.  Although plesiosaurs are likely to be much more agile in water than a person, the velocity recorded in the computer simulation is much lower than we, at Everything Dinosaur would have expected.  Most fish would have easily been able to swim faster, perhaps, as most palaeontologists predict, that long neck holds the key to the hunting strategy of the plesiosaurs.

Plesiosaurs and Marine Reptile Models

The CollectA Prehistoric Life model range contains several plesiosaur models: CollectA Prehistoric Life Models.

The species used as the template for the computer model was Meyerasaurus victor, known from the Lower Jurassic of Germany.  This small (3.5 metre long), plesiosaur is known from an almost complete articulated skeleton which is on display at the Natural History Museum of Stuttgart (Germany).  Meyerasaurus had a typical body plan amongst the Plesiosauria, with a moderately long neck, so it was considered to be an ideal candidate to represent the clade.

The research team  hopes to modify their computer programme to assess how the rear flippers helped in the manoeuvrability of these marine reptiles.  Just how agile were plesiosaurs in water?  The computer model can also be used to better understand the swimming motion of other prehistoric animals such as the short-necked plesiosaurs – the pliosaurs.

A Surrey Pliosaur

To read a recently published article about a Surrey pliosaur specimen that links Dorking to Kansas: Pliosaur Skull Links Dorking to Kansas.

Everything Dinosaur acknowledges the help of the press release from the Georgia Institute of Technology and Dr Adam Smith in the production of this article.