Trying to Unravel the Carcharodon Family Tree

The ancestry of the famous shark that starred in “Jaws” is better understood after the publication of a scientific paper by American researchers that provides details of a transitional fossil between prehistoric Mako sharks and extant Great Whites.

Great White Sharks

Carcharodon carcharias (Great White Shark), was believed by many scientists to be a direct descendant of the huge Megalodon shark (Carcharodon megalodon), one of the largest fish to have existed in the last twenty million years or so.    Fossil teeth of the Megalodon have been found in Europe, Asia, the Americas and in Australasia, this large predatory shark that could have reached lengths in excess of sixteen metres seems to have been very widely distributed.  However, scientists were uncertain as to the exact phylogenetic relationship between this giant shark that became extinct approximately 1.6 million years ago and extant species such as the Great White.

The problem with Lamniformes, the Order to which sharks belong is that they have skeletons made of cartilage.  This is rarely preserved in the fossil record, so there are few body fossils (other than the teeth) for palaeontologists to study.  However, the discovery of a remarkably well-preserved set of jaws, some articulated bones and numerous teeth, a number still “in situ” with the jaws, from a remote location in Peru has provided scientists with an important clue as to the origins of today’s Great Whites.  This fossil suggests that Great Whites, although having a similar body plan and lifestyle to the Megalodon, probably did not evolve from the same shark lineage.  It seems that Great White Sharks may share a common ancestor with the nektonic Mako shark.

The phylogenetic relationship between those shark species that make up the Carcharodon genus remains somewhat muddled.  Megalodon itself, may turn out to be more closely related to Tiger sharks (Galeocerdo cuvier) than to today’s Great Whites.

It is true that modern-day Great White Sharks have similar teeth to the extinct Megalodon.  The shape of the serrations along the teeth edge are very similar, but when examined under a microscope it can be seen that the denticles (the scientific term for these serrations) are very different.  Extinct Megalodon teeth show very fine serrations whilst the denticles on Great Whites are very coarse and much larger in comparison.

Transitional Fossil

Professor Dana Ehret, of Monmouth University (New Jersey, United States), the lead author of the research paper suggested that one of the reasons why Megalodon was believed to be the ancestor of Carcharodon carcharias was that Great Whites were used by anatomists and palaeontologists to make mounted exhibits of Megalodon for museums and other institutions.  If a modern shark had been used as the basis to put together Megalodon then it is not surprising that reconstructions of Megalodon resemble a Great White.

Professor Dana Ehret Examines the Shark Specimen

Fossil provides insight into the ancestry of Great White Sharks.

Picture credit: Florida Museum photograph by Jeff Gage.

Since both Carcharodon carcharias and Carcharodon megalodon have serrations (denticles) on the cutting edge of their teeth, this was thought to be an indication that these species were very closely related.  However, when examined under a microscope differences can be seen.  Today’s Great Whites have very coarse serrations whilst those on the extinct Megalodon are much finer.

Serrations on the cutting edge of shark teeth can be found in many species of extant and extinct shark.  Some indeed, do indicate phylogenetic relationships, whilst other examples are probably as a result of convergent evolution.  Convergent evolution occurs when two organisms, not necessarily closely related evolve in similar ways as they adapt to particular circumstances and environmental pressures.  For instance, both bats and most birds can fly, both have evolved wings but the structure of these wings is very different; birds and bats are not closely related.

Carcharodon hubbelli

The newly described species, known as Carcharodon hubbelli has been named from a beautifully preserved shark specimen that was found at a fossil dig site, part of the Pisco Formation of south-western Peru.  The very dry atmosphere has enabled fossils to be preserved in exceptional condition even when eroded out of the sedimentary rock.  Carcharodon hubbelli material consisted of the jaws, teeth, some of which were still in situ in the jaws and other elements of the fossil including part of the backbone of the animal.  The Pisco Formation has already provided scientists with some amazing fossils that give an insight into Pliocene marine fauna with the discovery of a gigantic predatory whale (Leviathan melvillei), that probably fed on Megalodons.

To read more about L. melvillei: Nightmare Whale from Prehistory.

A Replica of the “Nightmare Whale from Prehistory”

PNSO Requena the Livyatan prehistoric whale model anterior view.

The new shark species provides evidence that Great Whites are descended from ancient Mako (mackerel) sharks.  Described as a “transitional species”, C. hubbelli, named after Gordon Hubbell, the scientist who first found the fossil, suggests that Great Whites are not the descendants of Carcharodon megalodon.

The blend of Mako and Great White anatomical characteristics include the curving outwards of the third anterior tooth in the jaws of the Peruvian specimen.  This is very similar to the dentition seen in modern Mako sharks today.  Initially, the fossil had been dated to around five million years ago, but this presented a problem to the palaeontologists who suspected that this specimen represented an ancestor of today’s Great Whites.  Five million years ago, the Great White lineage was already around so how could C. hubbelli be ancestral to this part of the Carcharodon family?

A biostratigraphical study of invertebrate fossils found in the strata established that this fossil was actually much older, around 6.5 million years old, making it more likely that this specimen does represent an ancestral or intermediate from of Great White.

The American based research team have concluded that “Jaws” is essentially a highly modified Mako shark (Isurus genus).  Mako sharks are predators of open water and very streamlined.  They are primarily fish-eaters (piscivores), but they have been known to become aggressive and attack people.  The Great White lineage adapted to eating larger prey such as dolphins, turtles and seals.  Mako sharks are occasionally caught by fishermen off the coast of Cornwall.  These sharks having followed the Gulf Stream eastwards, but Makos are more normally associated with warmer water.

Everything Dinosaur acknowledges the assistance of a media release from Florida Museum in the compilation of this article.

Please note

The taxonomic classification of Megalodon has been revised, it is now known as Otodus megalodon.

To purchase a replica of the giant, prehistoric whale L. melvillei and models of prehistoric fish: PNSO Age of Dinosaurs Models and Figures.

Fossilised Mammoth shows Evidence of Neanderthal/Mammoth Interaction

A team of French scientists from the public institute responsible for protecting the archaeological heritage of France have been busy excavating an almost complete fossil of a Woolly Mammoth (Mammuthus primigenius) that has been found near to the river Marne.  A spokesperson for the National Institute for Preventative Archaeological Research (INRAP) stated that such a discovery was extremely rare in France as only three such near complete specimens had been discovered in the country since 1859.

Woolly Mammoth

The adult Mammoth has been nick-named “Helmut” by the research team.

Isolated Mammoth bones and teeth have been found in France, the remains of prehistoric elephants that once roamed this part of Europe, a small fragment of their extensive range across the northern hemisphere, but the discovery at Changis-sur-Marne in the  Île-de-France region in north-central France represents a single, almost entire individual skeleton.  Initial examination of the fossil material revealed shards and chips of flint amongst the bones.  The French team have speculated that these flakes were most probably from the stone tools of Neanderthals.  Although at this stage it is uncertain whether the Mammoth was killed by a hunting party or whether a group of Neanderthals took meat from the carcase.

“Prehistoric Battle” Circa 200,000 Years Ago?

Picture credit: Everything Dinosaur

Analysis of Shards of Flint

Analysis of the shards of flint may provide clues as to how the stone chips got there and the bones themselves may reveal evidence of injury caused by flint spears or perhaps distinct cut marks where the meat would have been taken off the bone.  Researchers hope to be able to date the specimen accurately.  At the moment it is suggested that the bones may be up to 200,000 years old, or perhaps from an animal that lived just 50,000 years ago.

The circumstances of the animal’s death will also be investigated.  It remains unclear as to whether this animal drowned, whether it was trapped in mud, or the victim of a successful hunt by Neanderthals.

An Important Discovery

This French discovery is making vertebrate palaeontologists who specialise in the study of Pleistocene Epoch mammals very excited.  The flint flakes indicate interaction between the Mammoth and a human species, such finds in palaeontology are extremely rare.  In the Calvados region of Lower Normandy (Basse Normandie), scientists excavated the partial remains of an ancient, straight-tusked elephant (Elephas antiquus), the fossilised bones of this extremely large elephant, distantly related to the modern, extant Asian elephant (Elephas maximus), showed signs of having been cut by stone tools.  Evidently, a party of human hunters scavenged this carcase.  Scientists suspect that here to, as with the Woolly Mammoth of Changis-sur-Marne, the butchery was carried out by Neanderthals.

A Replica of a Woolly Mammoth and Calf

Two other sites are known from the Middle Palaeolithic of western Europe (the second sub-division of the Old Stone Age), both in Germany, where evidence of a human species have interacted with prehistoric elephants.  In both the German cases the elephant species concerned was a Woolly Mammoth.  The French team in collaboration with German researchers are hopeful that their River Marne discovery will help to build up a picture regarding the hunting and survival skills of Neanderthals.

Studying the Flint Flakes

Our species being responsible for the flint flakes found in association with the Changis-sur-Marne Mammoth has not been completely ruled out.  Homo sapiens may have reached western Europe around 50,000 years ago so it remains possible that modern humans could have interacted with this particular Woolly Mammoth if it had lived around 50,000 years ago.  The French research team hope to use radiometric dating in combination with a stratigraphic analysis of the surrounding matrix to accurately date the fossil material.

Changis-sur-Marne

The quarry site at Changis-sur-Marne may look like the surface of a strange alien planet with the mounds of excavated material and bare rock exposed at the site but the research team are determined to extract as much information about the Mammoth and the environment in which it lived as possible.  The fossilised bones of the Mammoth were originally found by chance as archaeologists excavated the remains of a settlement dating back to the Roman occupation of Gaul.  Once it had been determined that the bones found did not represent those of livestock the Regional Directorate of Cultural Affairs (DRAC) was alerted and a specialist team from INRAP was dispatched to investigate the site.

Once the excavation at the quarry has been completed, the fossilised bones will be sent to a museum laboratory for further preparation and it is hoped this specimen will form part of a museum exhibit, perhaps in the Natural History Museum of Paris.

To view the range of prehistoric animal models including Woolly Mammoth replicas in the Mojo Fun series: Mojo Fun Prehistoric and Extinct.

Sauroniops pachytholus – Palaeontologists turn to Tolkien to Name a New Dinosaur

A new species of theropod dinosaur has been named by a team of scientists after the evil Eye of Sauron from the Lord of the Rings books written by J.R. R. Tolkien.  The inspiration for naming a new genus of organism can come from many things, but since this new predatory dinosaur is only known from a fragment of skull bone that was positioned directly above the eye socket (orbit) the name Sauroniops pachytholus seems entirely appropriate.

The name means “thick domed eye of Sauron”, in reference to the bump and thickened portion of the skull fragment studied.

New Species of Theropod

The Fossilised Element from the Skull

Views of the portion of the skull accompanied by scientific illustrations.

Picture credit: Andrea Cau

The Kem Kem Formation

The Kem Kem Formation of Morocco and Algeria represents a series of strata laid down in the Cretaceous (Albian to Cenomanian faunal stages), approximately 95 to 100 million years ago.  The majority of the deposits represent an inter-tidal, estuarine environment, with wide lagoons, and broad, flat flood plains crossed by many rivers further inland.  The environment supported and extensive and diverse flora and fauna.  This area probably supported the largest number of giant predators in any known Mesozoic habitat.

A number of meat-eating dinosaurs have been associated with the Kem Kem Formation, most named from fragmentary fossil material just like Sauroniops.  The list of predators reads like a “who’s who” of theropod dinosaurs – Carcharodontosaurus, Deltadromeus, Spinosaurus, Rugops and now the 13-metre-long Sauroniops joins their ranks.

Sauroniops Illustrated (Feeding on a Young Spinosaurus)

Sauroniops feeds on a Spinosaurus (background), whilst a pair of Spinosaurs flee the scene.

Picture credit: Emiliano Troco

New Dinosaurs Awaiting Discovery

Palaeontologists had long suspected that there were other theropod dinosaurs awaiting discovery from the rocks of this region.  The strata from south-west Morocco for example, had yielded a large number of fossilised theropod teeth.  These had yet to be assigned to any particular genus.  One of the problems with the strata in this part of the world is that the fossils found within them are extremely fragmentary in nature.

The action of river water and the tides has jumbled up and dis-articulated any fossil bones and teeth that have survived.  The fossiliferous deposits have been described by palaeontologists as if all the fossils had been put into a blender, the blender turned on and the resulting mix re-deposited.

Fragments of Fossil Material Typical of the Kem Kem Formation

Typical fossils from the Kem Kem Formation.

Picture credit: Everything Dinosaur

The Skull Fragment Superimposed on a Carcharodontid Skull with Human Skull for Comparison

Sauroniops compared to a human skull.

Picture credit: Andrea Cau

The Age of the Formation

The age of the fossil bearing rocks of south-eastern Morocco is disputed.  In the case of this new dinosaur genus, the exact age of the fossils appertaining to Sauroniops is further complicated as it is difficult to pinpoint exactly where this fossil material was found.

A private collector purchased the fossil bone from a local fossil trader in Morocco.  The trader stated that the fossil was purchased himself from local fossil hunters near to the small village of Taouz.  This village is located in a mountainous region close to the border with Algeria.  The private collector later donated this specimen to a Museum located at Montevarchi in central Italy (Tuscany).

With just an isolated fragment of skull material measuring 18.5 centimetres in length to work with, a team of Italian scientists compared the shape and structure of this part of the skull (left frontal bone) with those of other meat-eating dinosaurs known from the Kem Kem Formation.  They concluded that this fragment (assigned the identification code of MPM 2594) was indeed attributable to a new type of carnivorous dinosaur.

An Academic Paper

An academic paper has just been published in the scientific journal Acta Palaeontologica Polonica.  It has been published some five years after the fossil was acquired by the private collector.

For models of African theropod dinosaurs and other prehistoric creatures: Scale Models of Theropod Dinosaurs (CollectA Deluxe).

Based on comparisons with the skulls of other theropods, the palaeontologists have estimated that Sauroniops may have been up to thirteen metres in length.  Sauroniops – “the eye of Sauron” would have been an apex predators.  One of the lead authors of the scientific paper, Andrea Cau commented that with the frontal bone to study, the only part of this dinosaur known, it seemed appropriate to name the fearsome creature after the evil eye of Sauron from the J. R. R. Tolkien novels.

Given the paucity of the fossil material, it is extremely difficult to assign any further characteristics to this new dinosaur species.  However, S. pachytholus has been tentatively assigned to the Carcharodontosauridae and placed close to Eocarcharia, which itself has been described from a maxilla and a parietal bone (skull bones found in the Sahara).

Phylogenetic Assessment of S. pachytholus

Assigning a place for S. pachytholus in the theropod family tree.

Diagram credit: Andrea Cau

The orange arrow in the cladogram indicates the potential position of S. pachytholus amongst the carcharodontosaurids.

A New Theropod Species – S. pachytholus

The bump and raised portion of the skull has been seen in other carcharodontosaurids as well as abelisaurids.  The scientists have speculated that these animals had crests over their eyes which indicated that they were mature, breeding adults.  These bumps and crests may have been brightly coloured and acted as signalling devices in non-verbal communication between members of the same species.  It has even been suggested that these thickened portions of the skull evolved as a result of intra-specific competition.

Animals of the same species competing with each other to win mates, social status, fight over the carcases of other dinosaurs and so on.  Perhaps the Carcharodontosaurids and their relatives were “head bumpers”.

Particularly Favourable for Herbivorous Dinosaurs

The palaeontologists have concluded that the environment in this part of northern Africa during the Cretaceous must have been particularly favourable to herbivorous dinosaurs.  It would have needed to be to support the number of large, predatory dinosaurs now known from this part of the world.

The Kem Kem Formation may yet yield more theropod dinosaurs as these sediments are explored, the number of different carnivores found to date suggests that there must have been an abundance of food.

The scientific paper: “Evidence of a new carcharodontosaurid from the Upper Cretaceous of Morocco” by Andrea Cau, Fabio Marco Dalla Vecchia, and Matteo Fabbri published in Acta Palaeontologica Polonica.

The First Jaws with Teeth – Scientists Identify The Toothy Grin of the Placoderms

An international team of researchers have used high powered X-rays to look inside the mouths of an ancient group of fishes and discovered that some of these marine creatures had teeth, whose structure was very similar to our own teeth.  With the development of teeth, these fish had an evolutionary advantage over other marine animals and teeth capable of biting would have upped the evolutionary arms race between hunter and the hunted accelerating other evolutionary adaptations and developments.

Fish Fossils

Fish fossils from a rock formation, known as the Go Go Formation (Kimberley region, Western Australia) had been collected by scientists ever since this fossil rich area was discovered more than seventy years ago.  The strata represents a reef environment in a warm, shallow tropical sea that existed in the Late Devonian geological period (approximately 380 million years ago – Frasnian faunal stage).

A wide variety of Devonian fish specimens have been collected from this location, including many placoderms.  Placoderms were a highly successful and diverse clade of fish that had primitive jaws.  The name “placoderm” means plated skins as these nektonic animals had broad, flat bony plates over the head and the front of their bodies, protection against attack from other predatory fish and eurypterids (sea scorpions).

Palaeontologists have classified the Placodermi into seven main groups, it is fish fossils from one such group that show signs of modern teeth in this new study.

An Illustration of a Typical Placoderm

Evidence that arthrodires had the first teeth.

Picture credit: Everything Dinosaur

The Jaws of Placoderms

It has long been believed that teeth are highly modified fish scales, although it has been hotly debated how teeth with a pulp canal, dentine and an outer surface made of enamel like our teeth first evolved.  Placoderms had jaws but until now it was not thought that they had teeth-like structures.  This particular group of fish probably had a skeleton made of cartilage, indicating that they may share a common ancestor with sharks and rays.

The jaws of most placoderms had self-sharpening bony plates that served as teeth.  Placoderms evolved a pair of sharp bony plates that hung from the top jaw, whilst the edges of the lower jaw were also bony and razor sharp.  These jaws could be closed together like a pair of self-sharpening shears.

A team of scientists led by researchers from Bristol University, in collaboration with Australian colleagues studied the fossilised remains of a particular type of placoderm, a member of one of the largest families that make up the placoderm clade, (Arthrodira), a species known as Compagopiscis croucheri using powerful X-ray tomographic microscopy.  The X-rays are produced by a huge circular device known as a synchrotron.  This machine, located in Switzerland, fires electrons round a circuit which is encased  in powerful magnets.

Powerful X-rays are emitted and this permits scientists to see internal structures of fossil material without damaging the fossil material itself.  The images generated showed teeth inside the jaws that consisted of dentine and bone with a distinct pulp cavity.

The scientists have concluded that teeth and jaws may have evolved simultaneously in the Arthrodira.  The researchers suggest that more complicated teeth evolved within the gnathostomes (vertebrates with jaws) very soon after jaws themselves evolved.

Dr Kate Trinajstic, from Western Australia’s Curtin University, one of the scientists involved in the study explained that to determine whether teeth were present in the jaws of placoderms would have meant the destruction of the fossil material so that the internal structure could be studied, if conventional methods had been used.

She stated:

The problem has been that to look at teeth you have to look at internally and museum directors aren’t too fussed on the idea of cutting up their specimens.”

Professor Philip Donoghue (University of Bristol’s School of Earth Sciences) went onto add:

“This is solid evidence for the presence of teeth in these first jawed vertebrates and solves the debate on the origin of teeth.”

The Placodermi

The placoderms themselves were a very successful and diverse group of fishes during the Late Devonian, perhaps their success can be put down in part to their sophisticated jaws and nascent teeth.  Some of the Arthrodires were apex predators, such as the giant Dunkleosteus that grew up to six metres in length.

Many placoderms adapted to freshwater environments and this group of fish were some of the first animals with backbones to adapt to living in freshwater.  However, despite their adaptations, it seems that the toothy placoderms were doomed to extinction.

Very few fossils of these creatures are found in rocks dating from the very end of the Devonian geological period and it seems that by around 360 million years ago (beginning of the Carboniferous), these fish had become extinct.

In June 2008, scientists published remarkable evidence indicating that some types of placoderm my have given birth to live young (viviparous behaviour), to read more about this: Placoderm Parents.

A Model of Dunkleosteus

A stunning model of a placoderm – the PNSO Dunkleosteus model.

The model (above) is from the Age of Dinosaurs replica range from PNSO, to view this excellent range of prehistoric animal models: PNSO Age of Dinosaurs Models and Figures.

Study of Pachycephalosaur Skulls Sheds Light on Dinosaur Behaviour

The “Bone-headed” dinosaurs, otherwise known as pachycephalosaurids were a group of Cretaceous ornithischian dinosaurs related to the horned dinosaurs (members of the Marginocephalia).  Most of what palaeontologists know about these dinosaurs has come from fossils of these animal’s thickened, and in some cases domed skulls.  In a paper presented at the Society of Vertebrate Palaeontology (United States), in a conference held in North Carolina,  a research team have suggested that the pathology found on the skulls of these dinosaurs indicate that these animals did indeed butt each other.  In addition, the scientists propose that lesions and scars on different parts of the skull indicate that different types of Pachycephalosaur may have used butting contests in different ways.

Pachycephalosaurs – Skull Study Sheds Light on Potential Intraspecific Combat

Charging pachycephalosaurs – Did they butt heads?

Picture credit: Everything Dinosaur

Although examples of pachycephalosaurs such as Dracorex and the largest known – Pachycephalosaurus are often featured in children’s dinosaur books, the remains of these dinosaurs are extremely rare in the fossil record.  Apart from elements of the skull, only a few other body fossils ascribed to this type of dinosaur have been found.  One of the most complete fossil specimens was that of a pachycephalosaur named as Stegoceras (Stegoceras validum).  Fossils of this bone-headed dinosaur have been found in the Dinosaur Provincial Park Formation (Alberta, Canada), indeed most of the illustrations of all pachycephalosaurs are based on interpretations of Stegoceras fossil material.

Pachycephalosaurid Skull Study

These bipeds are characterised by a thickening of the dermal skull roof, particularly the frontal and parietal bones.  These bones are to be found at the top and towards the back of the head.  In a number of genera this thickening is accompanied by distinctive bumps and ridges that are found on the postorbital, squamosal and other facial bones.  Palaeontologists have speculated for many years as to what these bizarre skull structures were used for.

Dr Joseph Peterson (University of Wisconsin) and his colleague Collin Dischler, who has researched pathology on dinosaur skulls, presented the paper at the Society of Vertebrate Palaeontology’s annual meeting held in Raleigh.  After examining one pachycephalosaur skull, the team went onto compare the pathology found on this specimen with those of other pachycephalosaurs.  They also studied the skulls of extant animals such as birds, crocodiles and mammals looking for similar types of injury and signs of damage.

The research team looked at the over one hundred pachycephalosaur specimens from North America and Asia.  Of these twenty-three had signs of injury.  A three-dimensional computer generated model of the skulls were made and the lesions and injuries mapped onto them.  From this model, the team noticed that the placement of the injuries depended on the morphology, the shape of the skull.  Fossilised skulls with low domes tended to have injuries towards their front, whilst skulls with higher domed structures tended to show an even spread of injuries from the front to around the back.

Using the Skulls in Different Ways

The team’s findings indicate that pachycephalosaurs with different shaped skulls may have used their heads in butting contests in different ways.  Commenting on the scientific paper, Dr Peterson stated:

“The lesions we were seeing were strikingly similar to those that we often see on the skulls of modern mammals that ram heads.”

Earlier studies had concluded that some skulls of pachycephalosaurs were not suited to direct head-butting combat.  It had been speculated that some types of pachycephalosaurs may have indulged in flank-butting contests to settle disputes amongst herd members.  Most scientists believe that it was only the males that indulged in such behaviours, after all, such contests seen today amongst bovines and ovines (cattle and sheep) tend to be limited to only the males of the species.

To read an article on an earlier study into the skulls of pachycephalosaurs: Striking a Blow for Head-Butting Pachycephalosaurs.

When the behaviour of modern animals in intraspecific combat (competition between animals of the same species) was studied, in seems that certain animals such as the North American Bison (B. bison) wrestle with their horns in direct head-to-head battles, whereas other animals such as the North American Mountain Goat (Oreamos americanus) resolve disputes by bumping one another along the flanks.  Dr Peterson and his co-researchers have concluded that the high-domed  pachycephalosaurs with signs of injury in the parietal area of their skulls were bumping the flanks of their rivals.  The team suggests that a dinosaur such as Pachycephalosaurus wyomingenis with its twenty-five centimetre thick skull may have been a “flank bumper”.  Other types of pachycephalosaur whose skulls show injury to the bones slightly forward of the parietal bone were probably animals that conducted front-on wrestling matches with each other, in a similar fashion to modern North American Bison.

Did Different Types of Pachycephalosaurid Butt in Different Ways?

Boneheads settled disputes in different ways according to new study.

Picture credit: Everything Dinosaur

Lack of Fossils to Study

The lack of extensive pachycephalosaur fossil material to study weakens the arguments put forward to some degree.  Andrew Farke, a vertebrate palaeontologist at the Raymond Alf Museum (Claremont, California), commented that the different species resolving intraspecific disputes in different ways could actual be a single species with adult and juvenile skulls showing different pathologies.

He stated:

“It could be that we are seeing two different species bashing in different ways, but it could also be a single dinosaur species where juveniles and adults exhibit different bashing behaviours.”

One of the problems scientists face when studying the fossils of this particular group of dinosaurs is that the skulls may have been transported and deposited a long way from where the animal actually lived.  A number of specimens show signs of having been eroded as a result of the action of being bumped along a river bed.  It has been speculated that these herbivorous dinosaurs lived in dry, mountainous regions.

The lack of fossils could be explained by such areas having a poor preservation potential for fossil material.  Occasionally the remains of a pachycephalosaur would be washed downstream as a result of a flood or similar event.  The tough, thick skull bones being more robust than the other parts of the skeleton were the only bones to survive this physical process.  As the skulls were subjected to erosion the skull bones would have been bashed and chipped.  Other palaeontologists who have read the paper associated with this study have concluded that some of the injuries attributed to butting contests could have been made after the animal’s death (post mortem).  The skulls may have been chipped and damaged whilst being transported to their final resting place downstream.

Dr Farke has concluded that evidence as to whether these lesions were caused post mortem can be gathered when the skull bone microstructure is examined using high magnification CT scans.  Such analysis would provide evidence of some of the injuries beginning to heal, indicating that the lesions occurred when the dinosaur was very much alive.

It is likely that the debate over the pachycephalosaurs and their bizarre skulls is likely to go on, with palaeontologists “locking horns” as they argue over the evidence.

For models and figures of pachycephalosaurid dinosaurs and other prehistoric animals: Wild Dinos Figures (Safari Ltd).