New Research Challenges Traditional View of Pterosaur Flight

Take a look at a picture of a pterosaur flying and you will see that most illustrations and life-reconstructions of these reptiles depict them travelling through the air with their hind limbs trailing behind them and their back legs wide apart.  However, a new study undertaken by scientists from Brown University (Rhode Island) and the University of California (Berkeley), suggests that we have got this all wrong, pterosaur joints did not permit them to fly with their hind limbs splayed far apart.

Pterosaurs in the Air – But Have we got Their Hind Limbs in the Wrong Position?

Picture credit: John Conway

We Look at the Bones, But What About the Ligaments?

Flying with the hind limbs splayed out, is a posture adopted by most bats when they take to the air.  Ever since the first flying reptiles were described and illustrated, these archosaurs have been depicted in the same way.  However, this new research, published in the Proceedings of the Royal Society B (biology), suggests that ligaments would restrict joint movement and pterosaurs and the volant dinosaurs such as Microraptor, could not have flown in the same way as bats.

Lead author of this study, Armita Manafzadeh, a PhD student at Brown University commented:

“Most of the work that’s being done right now to understand pterosaur flight relies on the assumption that their hips could get into a bat-like pose.  We think future studies should take into account that this pose was likely impossible, which might change our perspective when we consider the evolution of flight in pterosaurs and dinosaurs.”

The “Classical” Pterosaur Flying Posture

Picture credit: Armita Manafzadeh

The study undertaken in collaboration with Kevin Padian (University of California), attempted to infer the range of motion of joints in a way that takes into account the soft tissues such as ligaments surrounding the joint.  Usually, soft tissue such as ligament and cartilage does not fossilise, so palaeontologists have to work out joint motion from just the bones alone.  The pair of scientists set out to examine the joint movement of modern dinosaurs – birds, to test the extent to which ligaments influence joint motion.

Chickens at a Grocery Store

Student Manafzadeh explained that the idea started with grocery store chickens:

“If you pick up a raw chicken at the grocery store and move its joints, you’ll reach a point where you will hear a pop.  That’s the ligaments snapping, but if I handed you a chicken skeleton without the ligaments, you might think that its joints could do all kinds of crazy things,  So, the question is, if you were to dig up a fossil chicken, how would you think its joints could move and how wrong would you be?”

Quetzalcoatlus – A Giant Pterosaur Takes to the Air (Note the Splayed Out Back Legs)

Picture credit: Everything Dinosaur

Dead Quails and X-ray Images

Chickens may be easy to acquire, but for this scientific study, dead quails were used in order to assess joint mobility in a three-dimensional way, rather than just referring to the bones.  Birds are the closest living relatives to the extinct pterosaurs and the non-avian dinosaurs.  Birds (Aves), the Pterosauria and the Dinosauria are members of the Archosauria clade.  This clade is  usually divided into two distinct branches, on one branch (Crurotarsi), are the crocodilians and their ancestors plus several other extinct lineages such as the phytosaurs.  The second branch (Avemetatarsalia) groups all the reptiles more closely related to birds than crocodilians.

A sub-group of the Avemetatarsalia is the Ornithodira, which specifically nests the Pterosauria and their ancestors and the Dinosauria and their ancestors, plus the descendants of dinosaurs – birds, together.  Hence, the use of quail limbs to assess the range of movement and joint mobility.

The skin and muscle surrounding the joints was cut away and once the hip joints were exposed, the scientists manipulated them taking X-ray images to assess the likely range of motion.  By doing this, they could determine the exact positions of the bones in poses where the ligaments restricted and then prevented further joint movement.

Mapping Out the Joint Movements of Ornithodirans

This technique enabled Manafzadeh to map out the range of motion of the quail hip with ligaments attached.  She then compared this range of motion to what was inferred when the bones were considered in isolation.  For the bones-only poses, Manafzadeh used traditional criteria that palaeontologists often employ — stopping where the two bones hit each other and when the movement pulled the thigh bone out of its socket.

This experiment revealed that over 95 percent of the joint positions that seemed plausible with bones alone were actually impossible when the ligaments were attached.

Mapping Out the Range of Motion in Quail Hips

Picture credit: Armita Manafzadeh

The Implications for Pterosaurs and the Maniraptora

The team’s next move was to calculate how the range of motion in living birds might correlate to the range of motion expected for extinct pterosaurs and those members of the Maniraptora, such as Microraptor that are believed to have been able to fly.  The assumption has long been that these creatures flew in a similar way to bats.  That is partly because the wings of pterosaurs were made of skin and supported by an elongated fourth finger, which is superficially similar to the wings of bats.  Bat wings are also connected to their hind limbs, which they splay out widely during flight.

Many palaeontologists, Manafzadeh says, assume pterosaurs and four-winged dinosaurs did the same.  But this new study suggests that pose was impossible.

In quail, a bat-like hip pose seemed possible based on bones alone, but outward motion of the thigh bone was inhibited by one particular ligament, a ligament that’s present in a wide variety of birds and other reptiles related to the Pterosauria.  Consequently, in the absence of extraordinary evidence to the contrary, this analysis casts doubt on the “bat-like” hip pose traditionally inferred for pterosaurs and basal maniraptorans and underscores the point that reconstructions of joint mobility based on manipulations of bones alone can be misleading.

To achieve a “bat-like” flying posture, the ligament would have to stretch 63 percent more than the quail ligament can, the implication is that we have been illustrating flying reptiles and flying dinosaurs all wrong.

A Model of a Volant Dinosaur (Microraptor)

The image (above) shows a beautiful Microraptor model from PNSO.

To view this range of prehistoric animal models and figures: PNSO Age of Dinosaurs Models.

In addition to challenging traditional views about flight in pterosaurs and early birds, the research also provides new ways of assessing joint mobility for any joint of any extinct species by looking at its living relatives.

The scientific paper: “ROM Mapping of Ligamentous Constraints on Avian Hip Mobility: Implications for Extinct Ornithodirans” by Armita R. Manafzadeh, Kevin Padian published in the Proceedings of the Royal Society B

Everything Dinosaur acknowledges the assistance of a press release from Brown University in the compilation of this article.

View the award-winning Everything Dinosaur website: Everything Dinosaur.

Dinosaur and Early Bird Dandruff

A team of international scientists led by researchers from University College Cork (Ireland), have discovered the fossilised remains of skin flakes from feathered dinosaurs and primitive birds that lived during the Early Cretaceous.   The fossil flakes of skin, preserved amongst the plumage of the feathered creatures, has provided evidence on how dinosaurs shed their skin.  Unlike many reptiles alive today, animals such as lizards and snakes, which shed their skin as a single piece or as several large pieces, it seems that basal birds and non-avian dinosaurs shed small epidermal flakes just like modern birds and mammals and that includes us with our dandruff.

Preserved Soft Tissue Evidence – Flakes of Skin in Maniraptoran Dinosaurs and the Basal Bird Confuciusornis

Picture credit: Nature Communications

Fossil Flakes

The photographs above (labelled a to h), show scanning electron microscope generated images of tissue in the Early Cretaceous Aves C. sanctus (a,e and f), the dromaeosaurid Sinornithosaurus (S. millenii) in photographs c and h, along with the therizinosaur Beipiaosaurus (B. inexpectus), photos b and g.  The photograph labelled d, is a view of epidermal flakes preserved in association with the fossilised remains of Microraptor, which along with Sinornithosaurus is believed to have been capable of flight or at least gliding.

Studying the constituents of flakes of dinosaur skin, which come from animals that might have been volant, is very important.  Palaeontologists can compare these flakes to living birds which are capable of powered flight.  These flakes, in turn can be examined in relation to the flakes of terrestrial feathered dinosaurs such as Beipiaosaurus.  Any differences in the composition of these flakes might provide scientists with further information on the aerial abilities of dinosaurs such as Microraptor and Sinornithosaurus.

An International Team

The scientists include researchers from the Chinese Institute of Vertebrate Palaeontology and Palaeoanthropology, Bristol University, Linyi University (China), the Open University as well as Queen Mary University (London) and the University College Dublin (Ireland).   They studied the fossil cells and dandruff from a range of Early Cretaceous Theropods and compared the skin flakes to those of living, extant birds.

Lead author of the research, Dr Maria McNamara (University College Cork), stated:

“The fossil cells are preserved with incredible detail,  right down to the level of nanoscale keratin fibrils.  What’s remarkable is that the fossil dandruff is almost identical to that in modern birds – even the spiral twisting of individual fibres is still visible.”

Getting to Grips with Corneocytes

The scientists used a scanning electron microscope (SEM), to examine the beautifully preserved, but microscopic fossilised fragments of skin associated with three feathered dinosaur specimens (Microraptor, Beipiaosaurus and Sinornithosaurus) and one Early Cretaceous bird Confuciusornis (Confuciusornis sanctus).  All of these fossils are associated with the Jehol biota of north-eastern China.

A Pair of Fossilised Confuciusornis (Liaoning Province) Showing the Two Known Body Plans for these Ancient Birds

Just like our own flakes of skin, our dandruff, the fossil flakes consist of tough cells known as corneocytes.  These cells are full of protein fibres (keratin), such was the quality of preservation that the SEM analysis was able to identify bundles of these fibres and even to hone in on single strands.

Scanning Electron Micrographs of Skin Flakes Associated with C. sanctus

Picture credit: Nature Communications

The photographs (above) show highly magnified images of the skin flakes associated with Confuciusornis.  Closely packed polygons can be observed (a and b), whereas (c) shows a detailed view of the polygons and the first signs at this magnification of the bundles of fibrous keratin.  The drawing (d) interprets the bundles as more darkly shaded areas in the central part of each polygon.  Photograph (e) shows the area that was more closely observed (f and g) indicating the presence of fibres, whereas, (h) shows the fibrous bundle associated with a skin flake in an extreme close-up view.

Helical coiling of the tiny fibres is shown (picture i) and photographs j and k show polygons having been deformed by some form of stretching.

These structures were then compared to the flakes of skin associated with living birds, in this case, male specimens of Zebra Finches (Taeniopygia guttata) and the Java Sparrow (Lonchura oryzivora).  In addition, the fossil evidence was compared to the moulted, downy feathers of a male American Pekin Duck (Anas platyrhynchos domestica).

Fossil Flakes Provide Clues About Dinosaur Metabolism

This research suggests that this ability to constantly shed skin evolved sometime in the late Middle Jurassic, around the same time as a host of other skin features evolved.  The feathered epidermis of dinosaurs acquired many, but not all, anatomically modern attributes close to the base of the Maniraptora clade.

Dr McNamara explained:

“There was a burst of evolution of feathered dinosaurs and birds at this time, and it’s exciting to see evidence that the skin of early birds and dinosaurs was evolving rapidly in response to bearing feathers.”

Co-author, Professor Mike Benton (Bristol University), commented:

“It’s unusual to be able to study the skin of a dinosaur, and the fact this is dandruff proves the dinosaur was not shedding its whole skin like a modern lizard or snake but losing skin fragments from between its feathers.”

Corneocytes in Living Birds

Picture credit: Nature Communications

The four photographs above, show scanning electron micrographs of shed skin flakes in living birds.  Note the polygonal structure (a), which is reminiscent of the shapes seen when the corneocytes of extinct dinosaurs and birds were studied.  Photograph (b) shows a central depression in the cell associated with a pycnotic nucleus, whilst photographs (c and d) show skin flakes stuck to the bird’s feathers.

Modern birds have very fatty corneocytes with loosely packed keratin, which allows them to cool down quickly when they are flying for extended periods.  The corneocytes in the fossil dinosaurs and birds, however, were packed with tightly bundled keratin, suggesting that the extinct creatures didn’t get as warm as modern birds, presumably because they couldn’t fly at all or for as long.

This suggests that Confuciusornis did not fly that well, if probably flew in short bursts, but may not have been capable of making prolonged flights.  The lack of fatty corneocytes in those dinosaurs which are thought to have had some aerial ability (Microraptor and possibly Sinornithosaurus), sheds doubt on whether they were truly volant.

Could Some Dinosaurs Like Microraptor Fly?

Picture credit: Everything Dinosaur

The picture (above) shows a Microraptor model from Safari Ltd.

To view this range of models and figures: Wild Safari Prehistoric World.

Everything Dinosaur acknowledges the assistance of a press release from the University College Cork (Ireland) in the compilation of this article.

The scientific paper: “Fossilised Skin Reveals Coevolution with Feathers and Metabolism in Feathered Dinosaurs and Early Birds” by Maria E. McNamara, Fucheng Zhang, Stuart L. Kearns, Patrick J. Orr, André Toulouse, Tara Foley, David W. E. Hone, Chris S. Rogers, Michael J. Benton, Diane Johnson, Xing Xu and Zhonghe Zhou published in Nature Communications.

Visit the website of Everything Dinosaur: Everything Dinosaur.

Ground Dwelling Birds Survived Asteroid Strike

One of the fascinating conundrums about the end Cretaceous extinction event is how did the avian dinosaurs (birds) survive, but their very close cousins the non-avian dinosaurs, animals such as Tyrannosaurus rex, Triceratops and Edmontosaurus fail to make it through this calamitous time in Earth’s history?  A team of international researchers, writing in the journal “Current Biology” have put together a fascinating explanation as to why we have birds today, but no other theropods, or indeed any other representatives of the Dinosauria.

With the extra-terrestrial impact event some 66 million and 38 thousand years ago (plus or minus 11,000 years), the ecosystems on our planet were devastated.  Whether this single, huge impact was the sole cause of the mass extinction or whether this was the final “coup de grâce” is debatable, however, life would never be the same again.

Using a variety of data sources, the team, which included scientists from the University of Bath, the Denver Museum of Nature and Science, Yale University and the Field Museum amongst others, have pieced together what the impact event meant for the Aves.  Their scientific paper suggests that the only kinds of birds to survive the Cretaceous-Palaeogene (K-Pg) extinction were ground- dwellers.

How Our Feathered Friends Survived the Cretaceous-Palaeogene Extinction Event

Picture credit: Phillip Krzeminski

Why Did the Birds Survive?

A number of ideas and theories have been proposed to help explain why the birds are around today, but the non-avian dinosaurs are not.  Recently, Everything Dinosaur published an article on a piece of research that suggested that seed-eating may have contributed to the survival of birds during this devastating time in the history of our planet.

To read the article: Seed Eating May Have Helped the Birds Survive.

Commenting on the scientific paper, lead author Daniel Field of the Milner Centre for Evolution (University of Bath) stated:

“We drew on a variety of approaches to stitch this story together.  We concluded that the devastation of forests in the aftermath of the asteroid impact explains why tree-dwelling birds failed to survive across this extinction event.  The ancestors of modern tree-dwelling birds did not move into the trees until forests had recovered from the extinction-causing asteroid.”

The Collapse of Forests

The scientists analysed the plant fossil record and identified that the world’s woodlands and forests were virtually wiped out by the extra-terrestrial impact.  Huge forest fires would have raged in the immediate aftermath of the impact and it is likely that much of the world had to endure a period of extensive “acid rain” as a result of the catastrophic event.  In the months, or maybe even tens of years afterwards, our planet could have been blanketed in a cloud of dust and ash.  This would have blocked out the sun and led to the collapse of food chains which relied on photosynthesising plants.

The scientists look at the record of fossil pollen and spores to assess the types of flora present and how quickly, ferns, flowering plants (angiosperms) and other types of flora recovered after the extinction event.

Plotting the Turnover of Different Types of Flora from Pollen and Spore Counts

Picture credit: Current Biology with additional annotation by Everything Dinosaur.

The diagram (above), plots the palynological record of the John’s Nose Section in North Dakota, a series of sequential strata laid down before, during and after the extinction event.  It helps to plot the demise of different types of plant and their recovery (floral turnover), as evidenced by changes in relative abundance of common pollen taxa across the K-Pg boundary.  Note, the “fern spike” recorded not long after the extinction event, ferns are usually the first type of plant to recover from natural disasters today, as evidenced by their ability to re-populate areas destroyed following volcanic activity.

Evolutionary Relationships of Living Birds

The research team examined the evolutionary relationships of extant birds and their ecological habits to map how bird ecology has changed over time.  The data revealed that the most common ancestor of all living birds, all the bird lineages that survived the K-Pg extinction event, most likely were ground-dwellers.  In contrast, many Aves that lived at the end of the age of dinosaurs (and there were lots of them), exhibited tree-dwelling, arboreal habits.  These species did not survive the mass extinction event and therefore they have no direct living descendants around today.

Daniel Field added:

“Today, birds are the most diverse and globally widespread group of terrestrial vertebrates, there are nearly 11,000 living species.  Only a handful of ancestral bird lineages succeeded in surviving the K-PG mass extinction event 66 million years ago and all of today’s amazing living bird diversity can be traced to these ancient survivors.”

The researchers conclude that their findings shed light on the fundamental influence major events in the history of our planet have on the evolution of living things.  The team hope to build on this initial research and to explore the timing of the recovery of the vegetation and to develop a better understanding of the early radiation of the birds.  After all, those lucky survivors inherited a brave new world, devoid of non-avian dinosaurs and many other terrestrial and marine organisms too.

The scientific paper: “Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction” by Daniel J. Field, Antoine Bercovici, Jacob S. Berv, Regan Dunn, David E. Fastovsky, Tyler R. Lyson, Vivi Vajda and Jacques A. Gauthier published in the journal Current Biology.

Visit the Everything Dinosaur website: Everything Dinosaur.

South American Giant Provides Further Information on Enigmatic Spinosaurs

A partial leg bone found in north-eastern Brazil has helped scientists to better understand the adaptations members of the Spinosauridae may have evolved to help them with their semi-aquatic lifestyles.  Furthermore, the fragmentary fossil, a large partial tibia from the Aptian-Albian Romualdo Formation, (Araripe Basin, north-eastern Brazil), when compared to other spinosaur remains, indicates an individual dinosaur much larger than other South American spinosaurids.  This single fossil suggests a sub-adult animal around ten metres in length, far larger than the other South American spinosaurids from the Araripe Basin such as Irritator and Angaturama.

Studying the Spinosauridae

A South American Lagoon Around 115-110 Million Years Ago – A Spinosaurid Attacks a Pterosaur

Picture credit: Julio Lacerda

For models and replicas of members of the Spinosauridae and other theropod dinosaurs: CollectA Deluxe Prehistoric Life Models.

Sail-back Dinosaur from the Heart of the Brazilian Outback

The Brazilian dinosaur fossil is providing another piece of the puzzle as palaeontologists strive to better understand the enigmatic spinosaurids.  The discovery of the fossil bone and its implications for Spinosaur research has been published in the academic journal “Cretaceous Research”.  The research was led by a team of Brazilian palaeontologists in collaboration with colleagues from Yale University, the University of Bonn and Trinity College (Dublin).

The partial tibia (lower leg bone) was found in Ceará, a state in the heart of the Brazilian outback.  Although only a fragment of bone, its size in relation to other spinosaurid fossils suggests a dinosaur measuring about ten metres in length, considerably bigger than other South American members of the Spinosauridae.

The Partial Tibia Bone (Various Views)

Picture credit: Cretaceous Research

Large Predators with an Aquatic Lifestyle

Over the last five years or so, there have been a number of papers published looking at how these large predators lived.  Many palaeontologists believe that these theropods adopted a specialist lifestyle, becoming semi-aquatic and essentially piscivores.  Interest in these enigmatic dinosaurs has certainly been piqued in recent years, especially with the publication of a fascinating paper in 2014 that proposed that Spinosaurus aegyptiacus was a semi-aquatic, obligate quadruped.

The partial tibia has anatomical traits previously only observed in the north African S. aegyptiacus, traits such as a reduced fibular crest and dense bones (osteosclerotic bones).  These types of bones are characteristic of the limb bones of vertebrates that spend a lot of their time in water.  The leg bones of hippos, for example, exhibit this condition.  The partial tibia from north-eastern Brazil, supports the idea that spinosaurids were adapted to an aquatic environment, in addition, the Brazilian fossil is many millions of years older than those fossils associated with S. aegyptiacus, so, this suggests that high bone compactness was already present in Brazilian spinosaurids long before S. aegyptiacus evolved.

Cross-sectional Views of LPP-PV-0042 Indicating Bone Density and Growth Rate

Picture credit: Cretaceous Research

Fossilised bone cells in detail, observed under the microscope.  Different growth pulses of the animal are represented by the red arrows.  Absence of certain characteristics in the bone tissue lead palaeontologists to conclude the spinosaurid was a sub-adult and still growing when it died.

To read Everything Dinosaur’s article on the 2014 Spinosaurus paper: Spinosaurus – Four Legs are Better Than Two.

“Heavy Bones” of the Spinosauridae

The study was led by postgraduate student Tito Aureliano (Campinas State University, Unicamp, Brazil), along with researchers from the Federal University of Sao Carlos (Brazil).  The dense bones of the Brazilian Spinosaur would have helped the animal to dive and to move in water in a similar way to a hippopotamus.

The dense bones are analogous to the lead weights used by divers to counteract their own buoyancy.  This research suggests that osteosclerotic bones were present in the South American Spinosaurinae at least ten million years earlier than those associated with their north African cousins.  It is not known when osteosclerotic bones evolved in spinosaurs, but this characteristic may have evolved relatively early in these types of dinosaurs.

Bone Density Comparisons

Picture credit: Cretaceous Research

Commenting on the significance of this study, Tito Aureliano stated:

“It may be possible that Brazilian spinosaurs were the first to adopt this way of life.  Now we need to investigate an even older species.”

An Example of Convergent Evolution

Several types of not-closely related vertebrates have dense bones, reflecting an adaptation to an aquatic lifestyle.  Penguins, crocodiles and sealions along with hippos and spinosaurids have these types of bones, this is an example of convergent evolution.

Aline Ghilardi (Federal University of Sao Carlos) explained:

“It is interesting how this adaptation evolved multiple times in different groups of animals that adopted the same lifestyle.”

The spinosaurids evolved in a different direction when compared to most of the Theropoda.  Whilst most dinosaurs evolved ways to make the skeleton lighter, epitomised in the extreme pneumaticity observed in birds, the spinosaurs developed a way to make their skeleton heavier.  This aided them when it came to occupying a very distinct and specialised niche amongst the Dinosauria.

South American Giants

South America might be famous for its huge Cretaceous plant-eating dinosaurs such as the titanosaurids Argentinosaurus, Patagotitan and Dreadnoughtus but the partial tibia bone hints at super-sized predators too.  An analysis of the fossilised cells showed that the studied dinosaur had not reached its maximum size by the time of its death and was still growing.  This indicates that these dinosaurs could reach larger sizes than previously thought, the Araripe Basin Spinosaurinae could have been giants, which would make them the top predators of the Cretaceous coastal lagoons of Ceará.

South American Spinosaur Size Comparison

Picture credit: Cretaceous Research

The image (above), shows all the known spinosaurid fossils from the Araripe Basin.  The fossil used in this study is marked in pink (F).   Note, figure 1 shows the fossil bones not to scale but figure 2 provides a scale comparison between the spinosaur specimens from the Araripe Basin.  The largest spinosaurid found to date (LPP-PV-0042), was the subject of the research paper.

Pterosaur Vertebrae from Ceará

The Ceará state has been synonymous with amazing spinosaur fossil finds.  In 2004, researchers led by the famous French palaeontologist Eric Buffetaut, described a remarkable fossil find from this region, three articulated pterosaur vertebrae (Ornithocheiridae) were found with the tooth of a spinosaurid embedded in one of the bones.  This fossil represents direct evidence that spinosaurs included other prey items in their diets as well as fish.  The broken tooth also provides evidence that the light bones of pterosaurs were much stronger than previously assumed.

A Food Chain of the Lagoonal Environment (Araripe Basin in the Early Cretaceous)

Picture credit: Cretaceous Research

Lots of questions about the Spinosauridae remain.  For example, whether these aquatic adaptations are related to the establishment of a large system of lagoons between South America and Africa caused by the opening of the Atlantic Ocean during this period in Earth’s history.  As with many whales today, was the adaptation of an aquatic lifestyle the trigger that enabled these theropods to evolve into giants?

Our thanks to Tito Aureliano ((Campinas State University, Unicamp, Brazil) for their help in the compilation of this article.

The scientific paper: “Semi-aquatic Adaptations in a Spinosaur from the Lower Cretaceous of Brazil” by Tito Aureliano, Aline M. Ghilardi, Pedro V. Buck, Matteo Fabbri, Adun Samathi, Rafael Delcourt, Marcelo A. Fernandes and Martin Sander published in the journal Cretaceous Research.

Visit the Everything Dinosaur website: Everything Dinosaur.

Dinosaur Teeth Provide Information on the Diet of Theropods

Palaeontologists have speculated on the preferred prey of theropod dinosaurs for decades.  These mainly meat-eating dinosaurs did not chew their food but bit into their victims and tore off chunks of flesh, a feeding technique named “puncture and pull”.  In newly published research, scientists have looked at the serrations on the sides of theropod teeth and assessed their role in feeding.

An analysis of microscopic scratches and wear patterns on the teeth of several different types of Canadian and Spanish carnivorous dinosaur has revealed that the troodontid dinosaurs with their large, broad and hooked, serrations (denticles) may have specialised in hunting smaller, softer prey as their teeth might have been damaged if they had bitten into a struggling, large animal.

Study of Dinosaur Tooth Serrations Suggest Differences in Preferred Prey

Picture credit: Current Biology

The Ziphodont Teeth of Theropods

The teeth of meat-eating dinosaurs tend to be curved, with sharp, serrated edges (ziphodont), the shape and size of the tooth serrations (the denticles) varies considerably between different species.  Tyrannosaurids such as the North American Gorgosaurus and dromaeosaurids such as Dromaeosaurus both have rounded, almost rectangular denticles, despite these animals being very different sizes, with the Gorgosaurus having much larger teeth.

In contrast, the dromaeosaurid Saurornitholestes has more pointed denticles that, over time can become worn and then they resemble the serrations found on the tooth of Dromaeosaurus.  Troodontids, such as Troodon have unique hooked denticles, that are proportionally much bigger than the denticles found on similarly sized theropods.  Troodon means “wounding tooth”, a reference to the large, distinctive serrations on its teeth.

This new study under taken by University of Alberta scientists, along with colleagues from the Universidad de Zaragoza and the Universidad de La Rioja (Spain) and the Royal Ontario Museum, examined the strength of the teeth and their serrations to see whether they provided any clues about potential prey as these dinosaurs fed using the “puncture and pull” technique.

Microscopic Scratches on Dinosaur Teeth Identified by Scanning Electron Microscopy

Picture credit: Current Biology

The picture (above), shows microwear patterns on three different theropod teeth (scale bar = 100 um).  Each pair of pictures shows the same section of tooth with the microwear and scratches highlighted in yellow on the picture (right).  Two scratch orientations were present on all studied teeth, one oriented parallel to the border of the tooth, and one oriented 30°–40° to the tooth border, this supports the idea of “puncture and pull” feeding behaviour.

The photographs at the top show the denticles of Pyroraptor, a dromaeosaurid from Laño, Spain.  The middle photographs represent the tyrannosaurid Gorgosaurus from the Dinosaur Provincial Park (Alberta, Canada).  The photographs (bottom) show the denticles of Troodon (T. inequalis), also from the Dinosaur Provincial Park (Alberta, Canada).

Microwear and Finite Element Analysis of Dinosaur Teeth

The researchers used scanning electron microscopy to map the wear and scratches on individual serrations in conjunction with a statistical method (finite element analysis), to identify stress patterns in teeth as they were involved in feeding.

Commenting on the research, one of the authors of the scientific paper, Ryan Wilkinson (University of Alberta), explained that their study supported the idea of “puncture and pull” feeding:

“We found the microwear patterns were similar in all of the teeth we examined, regardless of the size of the dinosaur, the size of the tooth or the shape of the denticles.”

It was concluded that the shape and strength of the dinosaurs’ teeth made them more or less vulnerable to breakage, forcing them to select different types of prey.  For troodontids, their tooth serrations were particularly prone to stress and therefore not suited to coping with struggling prey.  This suggests that although troodontids were of a similar size to many dromaeosaurs, they may have selected much smaller, less mobile prey, hinting at niche partitioning in those environments were dromaeosaurs and troodontids may have been coeval.

Stress Tests on Different Theropod Teeth

Picture credit: Current Biology

The picture above shows plotted stress tests on three types of theropod dinosaur teeth – Dromaeosaurus (top), the dromaeosaurid Saurornitholestes (middle) and a troodontid (bottom).  The “hotter” the colour ie. red, orange, yellow, the greater the stress on that part of the tooth during a bite.

The teeth of troodontids were identified as being particularly susceptible to breakage when biting into struggling prey.

Ryan Wilkinson added:

“The large hooked denticles of troodontids acted like a lever and caused high stress within the denticles and the tooth, which may cause the tooth to break.”

Implications for Feeding Troodontids (Studying Dinosaur Teeth)

The researchers, which included renowned ankylosaur expert Victoria Arbour of the Royal Ontario Museum and a former student at the University of Alberta working with Professor Phil Currie, who also contributed to the study, conclude that the microwear evidence supports the idea of “puncture and pull” feeding in theropod dinosaurs and that troodontids may have favoured smaller prey than dromaeosaurids, as their teeth did not stand up so well to the stresses and strains of coping with struggling prey.

The “Puncture and Pull” Feeding Technique as Demonstrated by the Dromaeosaurid Saurornitholestes

Picture credit: Sydney Mohr with additional annotation by Everything Dinosaur

Dromaeosaurus and Saurornitholestes were well-adapted for handling struggling prey, whilst troodontid teeth indicate that these dinosaurs may have had a different diet.

Troodon May Have Tackled Small Prey

For articulated models of dromaeosaurids and other theropods: Beasts of the Mesozoic Models and Figures.

The scientific paper: “Puncture-and-Pull Biomechanics in the Teeth of Predatory Coelurosaurian Dinosaurs” by Angelica Torices, Ryan Wilkinson, Victoria M. Arbour, Jose Ignacio Ruiz-Omeñaca and Philip J. Currie published in “Current Biology”.

Visit the Everything Dinosaur website: Everything Dinosaur.