How Good is the Fossil Record of the Dinosaurs

With something like 1,200 different genera of dinosaur now described, our knowledge of the Dinosauria has increased a great deal, especially over the last twenty years or so.  Many different types of dinosaur have been discovered and we at Everything Dinosaur try to keep a database using this blog.  For example, since the beginning of July, we have written articles about a newly discovered, very bird-like oviraptorid from southern China (Huanansaurus ganzhouensis), North America’s latest ceratopsian discovery (Wendiceratops), the new dromaeosaurid from Liaoning Province (Zhenyuanlong suni) and most recently, the basal sauropod Pulanesaura from South Africa.

How Good is the Dinosaur Fossil Record?

Just over the weekend, we reported on a giant horned dinosaur skull from South Dakota that might well turn out to be a new species of ceratopsian, albeit, one that would be very closely related to Triceratops.

However, will palaeontologists ever be able to create a definitive list of all the dinosaurs?  What percentage of the Dinosauria will ever be known?  Scientists at Bristol University have set about trying to find out by assessing just how good the fossil record for the dinosaurs actually is.

So Many Different Types of Dinosaurs Described

So many different types of dinosaur.

Picture credit: Everything Dinosaur

Trying to Calculate How Good the Dinosaur Fossil Record Is

Professor Mike Benton of the University of Bristol, set out to assess how good the fossil record is for the Dinosauria and for early tetrapods in a bid to answer the question as to whether the fossil record adequately represents the patterns of diversity of animals through time.  A number of other authors have attempted to assess the quality of the fossil record and in this new study, published in the journal “Palaeontology”, the journal of the Palaeontological Association, Professor Benton set out to plot how the knowledge of dinosaurs has been accumulated since the first scientific description (Megalosaurus) back in 1824.

The research does not provide a definitive answer with regards to how representative the vertebrate fossil record actually is, but this study does suggest caution needs to be taken when using some popular methods to try and remove bias from the known fossil record of the Dinosauria as well as the other Tetrapods included in the analysis.

Plotting the Number of New Species Named Against the Number of Newly Discovered Fossil Bearing Formations

Number of species against number of new fossil bearing formations.

Graph credit: Bristol University

Professor Benton Comments

Professor Benton explained:

“In the past ten years, many palaeontologists have tried to find the true pattern of evolution by using measures of sampling to estimate where the fossil record is well known or poorly known.  But it turns out that many of the popular methods are not doing what they are supposed to.”

The Bristol-based palaeontologist plotted the history of research into the Dinosauria from 1820 to the present day.  He logged the number of new species described and how the patterns of discovery match the patterns of discovery of new geological formations.  He noted that the patterns of discovery are closely linked, one or two new dinosaurs for each fossil-bearing geological formation that is newly explored.

More Fossil Bearing Geological Formations Discovered = More Dinosaurs Described

If there is a significant link between the number of dinosaurs described and the number of new geological formations discovered then how does this connection work?  This link can be explained in two ways:

1. Rock formation discoveries drives dinosaur fossil finds
2. Dinosaur fossil finds drives the discovery of new fossil-bearing formations

The usual view is that (1) is correct, that rocks drive fossil finds.  Palaeontologists are keen to find new dinosaur species, but the new species could only be found if they explored new rock formations around the world.  It could be argued that our ability to discover new types of dinosaurs (or any fossil group for that matter) is dependent on the availability of suitable rock formations to explore.

Plotting the Link between Early Tetrapod Discoveries and Rock Formations

Early tetrapod discoveries 1820-2015.

Graph credit: Bristol University

The graph above shows the same relationship in early tetrapod fossil discoveries from 1820 to the present day, but if there is a causal relationship between fossil finds and formations then how does this relationship work?

Fossil Record

The opposite view is that fossil discoveries drives the search for new rock formations.  Palaeontologists set out to look for new dinosaurs in a very focused and disciplined way.  When new dinosaurs are found they would often add a new dinosaur-bearing formation to the known list.  In this case, the limiting factor is not simply the availability of suitable rock formations to explore because scientists do not search systematically but they go straight to areas when they hear there are bones to be excavated.

Professor Benton added:

“I have been worried for a while that some of the popular correction methods actually make things worse.  By removing the numerical signal of the formations, localities or collections they were actually removing a huge amount of real information, and producing a resulting curve that is meaningless.  The fossil record is clearly incomplete, and it is clearly biased by many factors, but many of the supposedly “corrected” diversity curves we have seen recently may actually be further from the truth than the raw data.”

A New Analysis

This new analysis does not provide us with a definitive answer as to the diversity of the Dinosauria, or indeed, for any other fossil group of vertebrates.  However, we can infer from what we already have discovered that there are very probably a lot of weird and wonderful dinosaurs yet to be found.  It is not possible to state that we, after 195 years of research (1820 to 2015), have identified 10%, 50% or even 1% of all the types of dinosaurs that have ever existed, such statements by their very nature are likely to be invalid.

This new research does provide a clearer picture of why there is such a close correlation between dinosaur species numbers with formations, localities or collections.  The numbers of all four are connected because they are all telling much the same story, they are measuring the same history of life on Earth and our knowledge.  Professor Benton concludes that it is not possible to isolate one or other of these measures and then try to use it as an independent yardstick for sampling.

New Dinosaurs Will Be Discovered

There is one certainty, well, it’s almost a certainty.  New types of dinosaur will be discovered in the future and if the graph developed by Professor Benton is anything to go by, a lot of new dinosaurs (at least compared to the historical data), will be discovered in the next few years and Everything Dinosaur will do its best to blog about them.

For models and replicas of dinosaurs and prehistoric animals: Prehistoric Animals and Dinosaur Figures.

Everything Dinosaur acknowledges the help of a Bristol University press release in the compilation of this article.

Revising Lizard Evolution in Gondwana

The Squamata (lizards and snakes), might be the most diverse and specious of all the extant reptiles but their evolutionary history remains a mystery.  The preservation potential of these reptiles can vary dependent on the characteristics of the ancient ecosystems which they inhabited.  In addition, the small size of many of the early species of lizard and snake makes finding fossilised bones and other clues as to the history of this Order all the more difficult.

However, a team of scientists including Tiago R. Simões (Dept of Biological Science, University of Alberta), have published a paper in the journal “Nature Communications” that sheds light on the evolution of the iguanas and their near relatives.

Studying the Iguanians

The family of extant reptiles known as the iguanians (iguanas and agamids) are one of the most diverse and widespread type of lizard today.  However, like other types of lizard, their evolutionary origins are uncertain.  There are two main divisions within this family, firstly there is a sub-group called the acrodonts, these lizards have no root or socket to their teeth and the teeth are attached to the top of the jaw bones.  In the other sub-group, the pleurodonts they do not have roots on their teeth either, but instead the teeth attach to the inside portion of the jaw.

Acrodont iguanians are confined to the Old World, while pleurodont iguanians are found only in the Americas.  A newly described fossil however, breaks this pattern.  The international team of scientists have published a paper on a Late Cretaceous acrodont iguanian, the oldest known New World acrodont iguanian.

An Illustration of the First New World Acrodont Iguanian – G. sulamericana

The fossils date from around 80 million years ago.

Picture credit: Julius Csotonyi

Gueragama sulamericana

The fossils, including the holotype material, a partial lower jaw come from the Goio-Erê Formation, exposed near Cruzeiro do Oeste, in Paraná State, southern Brazil.  Fossils found in this locality represent an arid, very dry environment dominated by pterosaurs and large dinosaurs.  However, scurrying around the hot, desert-like environment was a short, rather stubby lizard.  It has been named Gueragama sulamericana, which translates from the local dialect and Portuguese as “ancient agama from South America”.

The discovery of these fossils of an ancient, New World acrodont means that in the distant past, lizards with the acrodont dentition had a worldwide distribution and were very probably widespread across the ancient landmass of Gondwana.

The Holotype Jaw Fossil (Various Views)

An ancient toothy lizard.

Picture credit: Universidade do Contestado, Santa Catarina, Brazil.

Scale bar in the picture = 2 mm.

Fossil Discovery Raises Questions

A number of questions have been raised with this discovery, for example, if only the pleurodont iguanians are found in the New World today, then what happened to the acrodonts that once lived in this part of the world too?

Lead author of the scientific paper, Tiago R. Simões stated:

“It becomes clear acrodontan iguanians migrated throughout the southern continents much earlier than previously thought (actually reaching regions where they do not inhabit today) by the order of tens of millions of years.”

This new research extends the fossil diversity of Late Cretaceous Brazil and suggests that the arid deserts of this part of the world may have supported a greater range of lizards than previously thought.  The scientists hope to find more lizard fossils, including material representing Gueragama so that they will be better able to understand the evolution and radiation of the stem acrodontans.

As for the date given to the G. sulamericana fossil material, we at Everything Dinosaur estimate these fossils to be more than 80 million years of age.  The strata which makes up this part of the Goio-Erê Formation is believed to date from the Turonian to the early Campanian faunal stages of the Late Cretaceous (90-80 million years ago, approximately).

Late Cretaceous South America

South America in the Late Cretaceous

Picture credit: Nature Communications

Fossil Finds in South America

Between the Aptian/Albian faunal stages and the Campanian faunal stage of the Cretaceous, sphenodontians were thought to be the dominate animals filling the iguanian niche.  Sphenodontian fossils have been found in northern Patagonia, in the provinces of Chubut (Tres Cerros), Río Negro (Los Alamitos, Cerro Tortuga, Cerro Bonaparte and La Buitrera) and Neuquén (El Chocón), these discoveries are represented by black circles on the map above.

Lizards were present in the state of Ceará in north-eastern Brazil (Araripe Basin), as well as in the south-eastern/southern states of Minas Gerais (Peirópolis), São Paulo (Marília and Presidente Prudente) and Paraná (Cruzeiro do Oeste), and in the province of Río Negro (Cinco Saltos and La Buitrera), Argentina, represented by yellow stars on the map. The red star indicates the type locality of G. sulamericana in southern Brazil.

Recently, Everything Dinosaur reported on another Brazilian Squamata fossil discovery.  Spotted by chance on a tour of a German museum, scientists have identified the first example of a four-footed snake, an animal believed to be a transitional creature between limbed lizards and true snakes.

To read this article: Fossil Snake with Four Limbs Described.

Horned Dinosaur Skull Found in South Dakota Might Be New Species

The small town in Buffalo in the north-west of South Dakota was so named as back in the 19th century vast herds of buffalo (American bison), roamed across this part of the world.  However, another type of horned animal has got local townsfolk excited, one that would have dwarfed even the largest of today’s hoofed giants, a very-well preserved partial skull and jaws of a huge horned dinosaur which might turn out to be a new species.

Acquired from a Fossil Collector

Fossil collector and dealer Alan Detrich purchased the dinosaur skull found in Harding County from another fossil collector John Carter back in 2012, but it has taken more than two and a half years to prepare the specimen ready for sale.  When the fossil skull and lower jaw were first excavated it was thought that the bones represented a very large specimen of Triceratops (T. horridus).  However, with the fossil completely exposed, Alan along with Neal Larson (Larson Paleontology Ltd) who was tasked with preparing the fossil, believe that this could be a brand new species of horned dinosaur.

Over the last fifteen years or so, a number of new North American horned dinosaurs have been named and described, however, if proved to represent a new species, this dinosaur skull could be heralded as one of the most spectacular dinosaur discoveries of all, the nasal horn alone measures nearly forty-five centimetres long and the skull itself is over 1.82 metres in length.

Ceratopsian Skull

Commenting on the unusually large nasal horn, Alan Detrich stated:

“They are [Triceratops nose horns] usually half that size and the skull is eight feet long, which would be a monster skull for a Triceratops.”

Neal Larson, the founder of Larson Paleontology Unlimited and a co-founder of the Black Hills Institute of Geological Research with his brother Pete Larson, who coincidently is also working on a centrosaurine specimen at the moment, was given the task of trying to prepare the specimen.  It took over 1,000 pain-staking hours to carefully excavate the fossil from its iron siderite matrix.  The preparation work was extremely difficult, as despite the robust nature of the fossil bones, the matrix with its iron component (iron carbonate) was extremely hard.

A Ceratopsian Exhibit at a Museum (Triceratops)

A cast of a Triceratops skeleton on display at the Naturmuseum Senckenberg (Natural History Museum – Frankfurt). On the left a wall mounted example of a Plateosaurus can be seen.  Is the Buffalo skull a new species?

Picture credit: Everything Dinosaur

For articulated models of ceratopsians and other dinosaurs: Beasts of the Mesozoic Articulated Dinosaur Models.

A Large Centrosaurine Skull

A spokesperson from Everything Dinosaur exclaimed:

“It’s only when you see a person stood next to the beautifully preserved skull that you can really appreciate just how big the animal actually was.  This is certainly one of the largest centrosaurine skulls that we have seen.”

For Neal, who holds a degree in geology and has been excavating fossils for some forty years now, the ceratopsian skull represented a tough challenge given the hardness of the surrounding matrix.

He stated:

“I immediately had my suspicions this was something new because of the size and placement of the nasal horn.  They’re usually in the middle of the nose, not the front and it’s twice as large as most of them.  On top of that, the frill at the top of the skull curves upward. They usually lay back.”

Ceratopsian Skull Could Represent a New Species

The skull has a strange ridge under the jaw, something that is not seen in Triceratops skull material.  Mr Detrich is now trying to find a museum to house this specimen, preferably in the United States, potential buyers for this huge dinosaur skull are currently being contacted.

The Ceratopsians of North American seem to have evolved into a very diverse range of forms during the Late Cretaceous.  Some of the skulls of these herbivorous dinosaurs were truly immense.  As a clade, the ceratopsians are considered to have the largest skulls in proportion to the rest of their bodies of any known vertebrate.  A few years ago, Everything Dinosaur reported on the discovery of another enormous horned dinosaur skull, this time from Alberta, Canada, a dinosaur that was believed to be an ancestor of Triceratops.

To read about this fossil discovery: Enormous Skull of Eotriceratops Discovered.

Fossilised Dinosaur Feathers Do Contain Evidence of Original Colours

Over the last five years or so, a number of scientists from around the world have been trying to crack a dinosaur-sized puzzle.  Could fossils preserve some evidence of the colouration of long dead animals?  Could palaeontologists and that talented body of palaeoartists that work with them, finally be able to depict a prehistoric animal as it would have looked like in real life?

A New Scientific Study

A new paper published in the academic journal “Scientific Reports” moves the debate forwards to some extent.  Researchers, led by Johan Lindgren (Lund University, southern Sweden), including graduate students from the aptly named Brown University (Rhode Island, U.S.A) have analysed the fossilised remains of a Middle Jurassic dinosaur and found that the melanosomes preserved within the fossil not only resemble animal pigment structures found today but they also have a very similar, almost identical chemical signature.

This study supports the hypothesis and indeed, strengthens it, that scientists can work out the colouration of long extinct animals including feathered dinosaurs.

The Specimen Used in the Study – Anchiornis Fossil

Feathers reveal chemical signatures that supports colour hypothesis.

Picture credit: Thierry Hubin

Anchiornis huxleyi

Named and described back in 2009, from fossil material found in Liaoning Province (north-eastern China), this little dinosaur was covered in feathers.  It stood about twenty centimetres tall and it had long flight feathers on its forelimbs and hind legs.  Three specimens have been described in detail, but there are believed to be many more examples held in private collections.  The exact geological age of this very bird-like dinosaur remains controversial.

A Model of Anchiornis huxleyi (PNSO Age of Dinosaurs)

The PNSO Luffy the Anchiornis dinosaur model from the “Age of Dinosaurs” model range.  A replica of Anchiornis.

To view the PNSO Age of Dinosaurs model range: PNSO Age of Dinosaurs Model Range.

It has proved very difficult to date the lake environment deposits where these fossils have been found.  Some palaeontologists have suggested that Anchiornis could be as young as 150 million years old, other scientists have proposed that the fossils date from around ten million years earlier.

To read about the scientific description of Anchiornis (A. huxleyi): Older than Archaeopteryx?

Fossilised Dinosaur Feathers

Colour analysis on the very well preserved second specimen (see picture above), has been carried out before, but this time, as well as finding melanosome structures, the researchers conducted two different kinds of chemical analysis to see if animal eumelanin pigment could be detected.  Melanin is a natural pigment found in most animals, there are three main sub-components of melanin, the most common form is the pigment eumelanin.

The researchers conducted an ion mass spectrometry test and also an infrared reflectance spectroscopy analysis to discern the chemical signatures of the rod-like structures that have been observed in the fossilised feathers of the dinosaur once the fossil had been subjected to electron microscopy.  The team then compared the molecular signatures of the fossil sample to the signature of melanin in living animals.  The observed signatures were almost identical.  The only small difference in the chemical make-up was attributed to the presence of sulphur in the fossil material.

Electron Microscopy Shows Tiny Structures in the Fossil Feathers

Structures identified under extreme magnification.

Picture credit: Lund University (Johan Lindgren)

A Palaeontological “Hot Potato”

The hypothesis that the structures which produce the melanin pigmentation, the melanosomes could be preserved in fossils is controversial.  Electron microscope studies of a number of feathered dinosaur fossils has revealed strange structures which have been interpreted as melanosomes by some scientists.

The shape of these structures providing clues to the colouration of the animal.  For example, in the case of Anchiornis, the rod-like, sausage-shaped structures, if they are melanosomes, indicate that this little Chinese dinosaur was mostly covered in dark, probably black feathers.

Controversial Conclusions Regarding Fossilised Dinosaur Feathers

Such conclusions have been hotly debated.  Some opponents have argued that the structures observed could be other types of organic residue such as the fossilised remains of microbes.  Other scientists have argued that there is a “fossilisation bias” when it comes to the colour spectrum and that melanosomes that give dark pigments may be more likely to survive the fossilisation process than other types, so there is a strong, black bias when it comes to interpreting the colour palette of a long, extinct animal.

Rod-Like Structures the Melanosomes

Sausage-shapes – potential melanosomes.

Picture credit: Lund University (Johan Lindgren)

Commenting on this latest research, Ryan Carney (Brown University) stated:

“We have integrated structural and molecular evidence that demonstrates that melanosomes do persist in the fossil record.  The evidence of animal-specific melanin in fossil feathers is the final nail in the coffin that shows that these microbodies are indeed melanosomes and not microbes.”

In essence, what this team has done is to move on the debate.  Morphological evidence (structures that look like melanosomes), are no longer the only evidence being put forward to suggest the colour of feathered dinosaurs.  There is now chemical evidence to support the theory that melanosomes can be preserved in fossils.

Dinosaur Colours

In order to help rule out a misinterpretation of the data, the team also analysed the observed spectral signatures of the melanins produced by microbes.  The closest match the team achieved was between the fossil material and the signature from extant animal melanin.

Student Carney, went onto add:

“This is animal melanin, not microbial melanin and it is associated with these melanosome-like structures in the fossil feathers.”

To read other articles published by Everything Dinosaur which relate to the colour of extinct animals:

Melanosomes in feathered dinosaurs: Melanosomes Provide Further Evidence for Feathered Dinosaurs.

Working out the colour, a problem: Working Out the Colour of Prehistoric Animals just got Harder.

Marine Reptiles and colour: Marine Reptiles Dressed in “Little Black Numbers”.