“Devilish” Riversleigh Marsupial Hyena from Queensland

Scientists including researchers from the University of New South Wales, have named a new species of carnivorous marsupial that would have terrorised Australia’s ancient forests some five million years ago.

The animal would have been roughly the size of a Labrador dog, but closely related to the extant Tasmanian Devil (Sarcophilus harrisii).  The Tasmanian Devil, with its powerful jaws, has a formidable reputation but this newly described meat-eating marsupial would have been two and half times the size of its modern relative.

An Illustration of the New “Devilish” Ancient Marsupial

An illustration of the new Riversleigh carnivore Whollydooleya.

Picture credit: University of New South Wales/Phil McKay

Whollydooleya tomnpatrichorum

Named  Whollydooleya tomnpatrichorum, it is the first creature to be formally identified from a remote fossil site located in north-western Queensland that has only recently been mapped.

W. tomnpatrichorum may have been an apex predator, or perhaps it filled the role of a hyena-like animal, hunting but also scavenging the kills of other predators.  Scientists who have studied the single molar tooth, from which the species has been erected, suggest that Whollydooleya could have weighed as much as twenty-five kilogrammes.

Lead author of the scientific paper, published in the Memoirs of Museum Victoria, Professor Mike Archer (University of New South Wales), commented:

“W. tomnpatrichorum had very powerful teeth capable of killing and slicing up the largest animals of its day.  The Late Miocene between twelve and five million years ago, when Australia began to dry out and megafauna began to evolve, is one of the least understood in the vast continent’s past.”

Whollydooleya tomnpatrichorum Size Comparison (Thylacine and Sarcophilus harrisii)

Comparing Whollydooleya with the extant Tasmanian Devil and the recently extinct Thylacine.

Picture credit: University of New South Wales

Rare Late Miocene Evidence

Fossils of terrestrial animals from Upper Miocene deposits of Australia are extremely rare, however, the remarkable outcrops located at Riversleigh in north-western Queensland hold the record for the density of fossil finds.  In 1983, a study of two cubic metres of rock from the Riversleigh site yielded an astonishing fifty-eight new species of prehistoric mammal.  The location from where the single tooth (a lower jaw molar), comes from is located outside the Riversleigh World Heritage site, but researchers are confident that this new site will yield a number of new prehistoric marsupial discoveries.

Two Views of the Prehistoric Tooth

Identified from a single tooth Whollydooleya tomnpatrichorum.  Stereo views of the single tooth (buccal view – viewed from the cheek side).

Picture credit: University of New South Wales

The new, highly fossiliferous site was found in 2012, thanks to aerial support from a local helicopter company that enabled field team members to cover large tracts of the remote outback.  The tooth, was found a year later, it represents the earliest fossil evidence yet of a “Tasmanian Devil-like” animal.

Professor Archer added:

“New Riversleigh is producing the remains of a bevy of strange new small to medium-sized creatures, with Whollydooleya tomnpatrichorum, the first one to be described.”

The Wholly Dooley Site

The genus name refers to the Wholly Dooley site, which was discovered and named by Phil Creaser following analysis of satellite data and Google Earth images.  The trivial name honours husband and wife Tom and Pat Rich, both vertebrate palaeontologists who have contributed significantly to the research into ancient marsupials of Australia.

Horned Dinosaurs Roamed Appalachia

For much of the Cretaceous, North America was split into two landmasses by a huge sea (the Western Interior Seaway), much is known about the variety of dinosaurs that roamed the land to the west of this seaway (Laramidia), we have the Cretaceous rock formations of New Mexico, Utah, Montana and southern Alberta to thank for that.  In comparison, palaeontologists know very little about the dinosaurs that roamed the eastern landmass, a much larger area of land called Appalachia.  Thanks to a lucky fossil find in northern Mississippi, scientists have found further evidence to indicate that horned dinosaurs made up part of the plant-eating dinosaur population on Appalachia.

A single fossil tooth, suggests that a car-sized ceratopsian lived in Mississippi some sixty-seven million years ago.  The tooth represents the first evidence of horned dinosaurs having roamed the “Magnolia State”.

During the Late Cretaceous Many Types of Horned Dinosaur Roamed Laramidia – What about Appalachia?

Plenty of Ceratopsidae on Laramidia, but what about Appalachia?

Picture credit: University of Bath

The Discovery of a Ceratopsian Tooth

George Phillips, a curator at the Mississippi Museum of Natural Science was exploring a river bed near New Albany when he made the fossil find.  The strata exposed in this part of northern Mississippi make up a geological sequence called the Owl Creek Formation.  These deposits date from the Upper Cretaceous (Maastrichtian faunal stage) and represent marine deposits.  During the Late Cretaceous, the State of Mississippi was largely submerged beneath a shallow arm of the Western Interior Seaway that extended up the Mississippi River Valley to the southern tip of Illinois.  This body of water is referred to as the Mississippi Embayment.

Visit Everything Dinosaur’s website: Everything Dinosaur.

The layers of rock yield a variety of marine fossils, particularly bivalves, gastropods and ammonites, but vertebrate remains are rare.  Mosasaur fossils are associated with northern Mississippi and very occasionally evidence emerges of dinosaurs, animals that inhabited the coastal swamps and low lying inland areas that bordered the Western Interior Seaway.

A Photograph of the Fossil Tooth (Ceratopsidae)

Horned dinosaur tooth discovered in Mississippi.

Picture credit: Mississippi Museum of Natural Science (MDWFP)

Six Types of Late Cretaceous Dinosaur Known from the State of Mississippi

Very little is known about the dinosaur fauna of the State of Mississippi.  Everything Dinosaur wrote an article about dinosaur discoveries in the American States back in 2015, after we reported on the discovery of a partial dinosaur femur from Washington State, Everything Dinosaur team members attempted to plot which of the fifty U.S. States did not have dinosaur fossils.  In the resulting article we incorrectly discounted a number of dinosaur fossil discoveries from Mississippi, although the fossils are extremely fragmentary the ceratopsid tooth represents the sixth type of dinosaur known to have existed in northern Mississippi.

The five different types of dinosaur from Mississippi:

1. Tyrannosaurids
2. Hadrosaurs (duck-billed dinosaurs)
3. Ornithomimids (ostrich-like dinosaurs)
4. Dromaeosaurids (raptors)
5. Nodosaurid (armoured dinosaur)
6. Indeterminate Ceratopsidae (the fossil tooth found on July 14th 2016 indicates the presence of horned dinosaurs)

To read our article mapping the dinosaur fossil discoveries of America: The Dinosaur Fossil Discoveries of America.

The Importance of the Horned Dinosaur Tooth

George Phillips explained:

“This particular tooth is from a group of dinosaurs that is very poorly documented as to the Mississippi River and is the first of its kind ever found in the south-east.”

The Mississippi Museum of Natural Science curator explained how he felt when he first spotted the fossil:

“Oh, I was very excited.  I knew it was a dinosaur.  I miss-identified it initially but after a social media post my colleagues put me on the right track.  Dinosaurs in general from Mississippi are very rare.”

Handling the Extremely Rare Fossil Find

The fossil tooth of a horned dinosaur from Mississippi State.

Picture credit: Mississippi Museum of Natural Science (MDWFP)

The tooth has broken roots and looks like it has been subject to a lot erosion, however, it remains a significant find as it is one of only three ceratopsian fossils to have been found in eastern North America.

To read an Everything Dinosaur article about the chance discovery of a fragment of dinosaur jawbone in the Peabody Museum at Yale University that indicates basal ceratopsids inhabited eastern North America: Late Cretaceous Eastern North America and Leptoceratopsids.

At this stage it is not possible to determine whether the horned dinosaur was a member of the centrosaurine group or the chasmosaurine group of horned dinosaurs.  A copy of the specimen is on its way to California for further analysis and study.

A Picture of a Late Cretaceous Horned Dinosaur

Late Cretaceous Dinosaur Diversification in North America.

Picture credit: Everything Dinosaur

For articulated replicas of horned dinosaurs and other prehistoric animals: Beasts of the Mesozoic Models.

Scientists Use High Powered X-rays to Explore a Juvenile Heterodontosaurus

The European Synchrotron Radiation Facility (ESRF), located in Grenoble (France), had a very important visitor this week as an exceptionally well-preserved skeleton of a 200-million-year-old dinosaur was analysed using the high-energy, super strong X-rays of the synchrotron to peer inside the fossil’s rocky matrix.  The subsequent images revealed the fossil in almost perfect three-dimensions, providing palaeontologists with new information on Heterodontosaurus.

The Blocks of Fossil Material (Heterodontosaurus tucki)

The Heterodontosaurus blocks laid out in approximate anatomical order.

Picture credit: ESRF/P. Jayet

Heterodontosaurus tucki

Heterodontosaurus was a small, plant-eating dinosaur that roamed the very Early Jurassic of South Africa.  Named and described in 1962, the dinosaur’s name means “differently-toothed lizard”, a reference to the different types of teeth found in the jaws of this one metre long reptile.  Typical Heterodontosaurus tooth pattern consists of three pairs of short, but sharp teeth located in the front of the upper jaw.  The rearmost is much larger and proceeds a very large canine tooth located in the lower jaw.  The teeth at the back of the jaws are closely packed and blocky in shape indicating that these teeth evolved to help this animal chew tough vegetation.

Scientists have long debated what this animal ate.  Most palaeontologists believe that the fast-running Heterodontosaurus was vegetarian, however, omnivory cannot be ruled out.  Perhaps microscopic analysis of the tooth surfaces in conjunction with an exploration of the body cavity in this exceptionally well-preserved specimen might provide some clues.

An Illustration of Heterodontosaurus (Early Jurassic Ornithopod)

A family of the little, bird-hipped dinosaur (Heterodontosaurus).

Picture credit: Natural History Museum

A Week to Investigate

The fossil was discovered in South Africa’s Eastern Cape province by palaeontologist Billy de Klerk.  It was found eroding out of extremely hard bedrock that formed part of a river bed on Hannie van Heerden’s farm.  With the help of a crew from the Albany Museum in Grahamstown, Billy de Klerk and John Hepple, (Rhodes University Geology Department), were able to extract the blocks that comprised the skeleton.

Initial analysis identified the fossil as a Heterodontosaurus, the skeleton proved too difficult to study whilst still in its matrix and attempts to remove the bones entombed within the rock would have caused extensive damage.  Thankfully, the team of researchers from the Evolutionary Studies Institute (ESI), at the world famous University of Witwatersrand were able to turn to the ESRF for help.  Professor Jonah Choiniere (University of Witwatersrand), who supervised the study, explained that the high-energy, high brilliance, X-rays generated by the synchrotron could be used to peer inside the rock and to help produce a three-dimensional image of the fossils.

For models and replicas of Jurassic dinosaurs and other prehistoric creatures: CollectA Prehistoric Life Models.

This non-invasive technique would not harm the fossil in anyway and it would allow computer generated images to reconstruct the anatomy of Heterodontosaurus in great detail.  The week-long investigation commenced on the 21st July and the scans were complete by the 26th, generating copious amounts of data for the scientists to study.

The Skull of the Heterodontosaurus

The Heterodontosaurus skull (right lateral view).

Picture credit: Billy de Klerk

The European Synchrotron Radiation Facility (ESRF)

Over the last twenty years or so, the ESRF has been utilised by palaeontologists on a number of projects to help interpret the fossil record.

To read a 2014 article written by Everything Dinosaur on ESRF research into whether or not Archaeopteryx could fly: Could Archaeopteryx lithographica fly?

Professor Choiniere and Dr Vincent Fernandez Prepare the Skull for “Beamline” Analysis

Jonah Choiniere (left) and Vincent Fernandez set up the skull on one of the ESRF’s “beamlines” for scanning.

Picture credit: ESRF/P. Jayet

Professor Choiniere commented:

“There’s still a lot we don’t know about early plant-eating dinosaurs and we need new specimens like this one and new technology like the synchrotron to fill in those gaps”.

A Juvenile Heterodontosaurus

One of the first things the team were able to confirm was that the specimen represented a sub-adult.

Working with Dr Vincent Fernandez (ESRF), skull scans showed that the bones were not strongly sutured together.  This confirms the scientist’s suspicions that the animal was not fully grown when it died.  In addition, the first scans revealed the openings in the skull which house the balance organs.  An analysis of these structures will help the team to work out how this dinosaur held its head and how good at running it was.

Delighted with the Heterodontosaurus Results

Commented on the success of the collaborative research with ESRF, Billy de Klerk explained how he and the rest of the team were delighted with the results.  He emphasised that finding the specimen in the first place was very serendipitous, its location in the riverbed would have made it very vulnerable to erosion by the action of the river.

The Location of the Fossil Find

Billy de Klerk and the location of the Heterodontosaurus fossil material.

Picture credit: ESRF/P. Jayet

Billy de Klerk explained:

“A few more years on the stream bed and the specimen might have been washed away.  We just happened to be at the right place at the right time.”

Images Generated Shed New Light on Dinosaur Anatomy

The first scans from the ESRF revealed lots of information about Heterodontosaurus.

Picture credit: ESRF/P. Jayet

Master’s student at Witwatersrand University and member of the scientific team, Kathleen Dollman, hopes to apply synchrotron technology in her bid to understand the evolution of crocodilians.

She stated:

“X-ray computed tomography (CT) methods have revolutionised palaeontology and we can use these methods to understand so much more about the biology of these extinct animals.”

Learning More About Early Jurassic Dinosaurs

When it comes to understanding more about Early Jurassic plant-eating dinosaurs such as Heterodontosaurus, the collaboration with the ESRF is producing a tremendous amount of data.  For example, according to Kathleen Dollman, the data from the Heterodontosaurus study amounts to 1 terabyte (sixty piles of stacked paper as tall as the Eiffel tower).  That’s an awful lot of “dino data” to process, as the diagram below illustrates.

An Illustration of the Size of the Data from the Heterodontosaurus Study

Huge amount of data from the ESRF Heterodontosaurus research.

Picture credit: Everything Dinosaur

Everything Dinosaur acknowledges the European Synchrotron Radiation Facility for their help in the compiling of this article.

Visit Everything Dinosaur’s website: Everything Dinosaur.

Huge Dinosaur Footprint Discovered in Bolivia

Everything Dinosaur has received reports of a super-sized, meat-eating dinosaur’s footprint being found in Bolivia.  The footprint, measuring some 1.15 metres wide is the largest tridactyl (three-toed) print ever discovered in Bolivia.  The huge footprint represents a track probably made by an abelisaurid, a type of Cretaceous theropod dinosaur, however, it suggests a carnivorous dinosaur much larger than most of the Abelisauridae.

Probably an Abelisaurid Track

The fossilised footprint was found in the municipality of Sucre in southern Bolivia.  Dinosaur tracks have been recorded from Bolivia before, but the three-toed print indicates that something extremely large and fierce roamed this part of South America sometime between 80 and 78 million years ago.

An Illustration of a Typical Abelisaurid Theropod Dinosaur

Abelisaurid artwork. An illustration of an abelisaurid theropod dinosaur.  Picture credit: Zhao Chuang.

Picture credit: Zhao Chuang

Omar Medina, a palaeontologist with the Bolivian Palaeontology Network explained that the single footprint could represent one of the largest footprints associated with an abelisaurid dinosaur ever found.

For models and replicas of abelisaurids and other dinosaurs: PNSO Age of Dinosaurs Replicas and Models.

The Geology of Southern Bolivia

The fossil discovery emphasises the significance of the geology in this part of southern Bolivia which has provided ichnologists (scientists who specialise in studying trace fossils such as footprints and tracks), with thousands of dinosaur footprints to study.

To read an article about a Bolivian farmer finding the tracks of an ancient ankylosaurid: Farmer Finds Dinosaur Tracks.

An article highlighting the threats to one of the most remarkable dinosaur fossil tracks found anywhere in the world (The “Huellas de Dinosaurio de Cal Orck”, close to the Bolivian town of Sucre): Dinosaur Tracks in Danger of Becoming Extinct.

Perhaps Twelve Metres in Length

Argentine palaeontologist Sebastian Apestiguia, who verified the find and is in the photograph circulated by media outlets, commented that the carnivorous dinosaur that made this print in soft sediments could have measured more that twelve metres in length, making it much larger than most abelisaurids.  For example, Rugops (R. primus) known from Niger in Africa, measured around nine metres in length, whilst the South American Abelisaurus (A. comahuensis), from which the family derives its name, probably reached a maximum size of about six and half metres.  To put this into context, that is around half the length of an adult Tyrannosaurus rex.

An Illustration of a Typical Abelisaurid Dinosaur

A typical member of the Abelisauridae.

Picture credit: Everything Dinosaur/Mike Fredericks

A Lucky Fossil Find

Tour guide Grover Marquina, literally stumbled over the footprint whilst exploring the area in a bid to identify suitable tourist sites.  The fossil track might represent the largest known member of the Abelisauridae dinosaur family, although a spokesperson from Everything Dinosaur commented that they were aware of an, as yet, not scientifically described Abelisauridae specimen from Turkana in Kenya that might have reached a length of around eleven to twelve metres.

Visit Everything Dinosaur’s website: Everything Dinosaur.

Temperature Spikes Point to Two Events Causing End Cretaceous Mass Extinction

A study of the fossilised shells of several species of bivalves that existed towards the end of the Cretaceous suggests two distinct phases of global warming occurred that instigated mass extinctions.

Scientists have debated how much of an impact the eruption of the Deccan Traps in India had on the mass extinction event that caused the extinction of the dinosaurs along with about seventy percent of all terrestrial animals.  Much of the difficulties surrounding this debate concern the separating of the consequences of the extensive volcanism from the devastation caused by the Chicxulub impact event.

Deccan Traps and the Chicxulub Impact Event

Approximately sixty-six million years ago, a massive extra-terrestrial body slammed into our planet in the Gulf of Mexico.  This new research suggests that these two cataclysmic events combined to bring about the mass extinction.

The Location of the Deccan Traps (Flood Basalts)

The location of the Deccan Traps (flood basalts).

Picture credit: Everything Dinosaur

Researchers from the University of Florida, in collaboration with colleagues at the University of Michigan examined the fossil record of a series of Upper Cretaceous bivalve shells, representing part of a mollusc biota that lived at depths of around 200 metres in a shallow marine environment that is represented by sequences of Maastrichtian faunal stage strata preserved on the Antarctic Seymour Island.

The Strata of Seymour Island

The Upper Cretaceous/Lower Palaeogene strata is particularly well suited for studying the end Cretaceous extinction event as the rocks here form a continuous sequence covering a time interval dating from around sixty-nine million years ago into the Palaeogene.

The abundant and well-preserved fossils of sea creatures are ideal study material and some understanding of the extinction process and its selectivity can be gained as several genera represented in the fossil record survive across the Cretaceous-Palaeogene boundary (K-Pg).

Cretaceous Extinction Event – Extra-terrestrial Impact

A contributory factor in the mass extinction?

Using a New Technique to Plot Temperature Spikes

Geochemist Andrea Dutton (University of Florida), working with Sierra Petersen and Kyger Lohmann (University of Michigan), used a new analytical technique to establish sea temperatures in the Antarctic towards the end of the Cretaceous and into the Palaeogene.  Their analysis, published in the journal “Nature Communications”, supports the idea of the combined effects of excessive volcanism on the Indian sub-continent and the  Chicxulub impact brought about the mass extinction event.

A spokesperson from Everything Dinosaur commented:

“It’s a double whammy for the end Cretaceous.  Two distinct ocean temperature spikes as a result of these two events.  Such temperature variations at high latitudes indicate a huge change in global climates, these would have most definitely resulted in extinctions and the stratigraphic record of Seymour Island provides the most conclusive evidence yet.”

Clumping Isotopes of Carbonates

The team used a new analytical technique called carbonate clumped isotope palaeothermometer to study the chemical composition of twenty-nine fossil bivalve shells, from a sampling set of one hundred and sixteen.  A total of five species of bivalve were studied (Lahillia larseni, Cucullaea antarctica, Cucullaea ellioti, Eselaevitrigonia regina and Nordenskjoldia nordenskjoldi).

The analysis shows that ocean temperatures rose approximately 14 degrees Fahrenheit, and links these measurements to two previously documented warming events that occurred near the end of the Cretaceous Period, one related to volcanic eruptions in India (Deccan Traps), the other, related to the Chicxulub impact on the Yucatan Peninsula of Mexico.

Studying Fossilised Shells

The isotopic composition of the fossilised shells provided a map of the ancient temperatures at high latitudes spanning some 3.5 million years, covering the crucial end Cretaceous (Maastrichtian faunal stage and into the Palaeocene (Danian faunal stage).  Whilst a graduate student at the University of Michigan, Andrea Dutton studied the palaeoclimate of Seymour Island

At the time, existing analytical techniques determined combined signals of salinity and temperature fluctuations over geological time but the salt-water effect could not be isolated providing temperature increases/decreases as a single determinant factor.  Clumped isotope palaeothermometery allows the effect of temperature changes to be isolated.

Clumped Isotope Palaeothermometery

Assistant Professor Dutton explained:

“Now, years later, everyone is using this new tool called clumped isotope palaeothermometery, which is a bit different than the traditional method.  This technique is only a function of temperature.  Salinity has nothing to do with it.  We’re looking at the clumping of oxygen isotopes rather than the relative amount of oxygen isotopes in the shell, and this is helping us re-interpret the data.”

Two Significant Temperature Spikes Coinciding with Catastrophic Events

Sea shells provide clues to Cretaceous extinction event.

Picture credit: Nature Communications

Two Distinct Temperature Spikes

The data show two significant temperature spikes. The first corresponds to the eruption of the Deccan traps flood basalts. The other lines up exactly with the proposed date for the extra-terrestrial impact.  Just to make matters worse for life on Earth at the time, the Chicxulub event may have led to a renewed phase of volcanism on the Indian sub-continent.  Both events are directly linked with extinction events recorded in the fossil record of Seymour Island (decrease in faunal biota).

To read a recently published article on a study of the marine fossils of Seymour Island and the consequences with regards to the mass extinction event: Global Catastrophe Caused End Cretaceous Extinction.

The Cretaceous/Palaeogene (K-Pg) Boundary

There is a physical boundary preserved in the geological record of our planet known as the Cretaceous/Palaeogene boundary (K-Pg), the “K” represents the Cretaceous, it comes from the German word for chalk “kreide”, “Pg” is the traditional abbreviation for the Palaeogene Period.  It is represented by a thin band of iridium rich rock.  Iridium is a rare Earth element associated with asteroids, meteorites and comets, this suggests an extra-terrestrial impact event contributed to the Cretaceous extinction event.

The Cretaceous/Palaeogene Boundary (K-Pg)

Marking the end of the Cretaceous.

Picture credit: Open University/Everything Dinosaur

K-T boundary = Cretaceous/Tertiary boundary also referred to as the K-Pg boundary.

Andrea Dutton added:

“We have evidence on this site on Seymour Island in Antarctica that climate change is linked to both of these extinction events, right before the boundary and right at the boundary.  If you look at what types of species that went extinct during the first extinction pulse, they’re different than the types that went extinct during the second pulse.”

Assistant Professor Dutton continued:

“That indicates that it may have been a different kill mechanism for those two different extinction pulses.  It’s quite likely both the volcanism and the asteroid were to blame for the ultimate mass extinction.  The Deccan Traps weakened the ecosystems before the asteroid slammed into the Earth.  It’s consistent with an idea called the press-pulse hypothesis: a ‘one-two punch’ that proved devastating for life on Earth.”

The published paper also refers to variability in shell composition that indicate a potential reduction in seasonality after the Deccan eruptions commenced, continuing through to the Chicxulub event.  Species extinction recorded at Seymour Island occurred in two pulses, these coincide with two observed global warming events, directly linking the end Cretaceous extinction at high latitudes to both the Deccan Traps and the extra-terrestrial impact.

To read an article the suggests the dinosaurs were in decline some fifty million years before they finally became extinct: The Fifty-Million-Year Decline of the Dinosaurs.

An Explanation of Polarity Reversals with the Earth’s Magnetic Field

Assisting the dating of the geological timescale is the science of magnetostratigraphy.  Periodically, the polarity of Earth’s magnetic field is reversed.  Iron rich minerals within strata align themselves with the prevailing magnetic field during formation.  By combining the polarity of these minerals with radiometric dating methods, geologists have produced a timescale of these magnetic reversals – the polarity chron.

The Polarity Chron Helps Chart Geological Deep Time

Magnetostratigraphy helps to chart deep time.

Picture credit: Nature Communications with additional notation by Everything Dinosaur

The Polarity Chron

The polarity chron (sometimes simply referred to as the chron), is the time interval between polarity shifts in the Earth’s magnetic field.  The switching of polarity is highly variable, on average they seem to occur every 200,000 years or so, but the last one took place more than three-quarters of a million years ago.

Why they occur has not been fully explained, but it is believed that the molten nickel and iron core at the centre of the Earth occasionally produces vortexes that persist long enough for a polarity reversal to take place as a result of the electromagnetic fields that they generate.  Polarity chrons are numbered in order starting from today and increasing retrospectively as we go further back in time.  Each number has two phases “N” for normal field and “R” to represent the reversal of that field, hence in the diagram above the ringed area labelled 31R through to 29N.

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