Asfaltovenator vialidadi – Linking Megalosaurs and Allosaurs

This week has seen the formal publication of a scientific paper announcing the discovery of a new type of meat-eating dinosaur from Chubut Province in the Patagonia of Argentina.  This dinosaur named Asfaltovenator vialidadi shows a range of anatomical characteristics which are similar to both Allosaurs and Megalosaurs and whilst it poses a bit of a phylogenetic puzzle when it comes to classifying tetanuran theropods (stiff tails), it does suggest that the Allosauroidea  and Megalosauroidea have a common ancestor.

A Life Reconstruction of the Newly Described Asfaltovenator vialidadi

Picture credit: Gabriel Lio/Conicet

Predator of Patagonia Around 175 to 170 Million Years Ago

Discovered back in 2002, from lacustrine deposits (sediments from an ancient lakebed), located about a mile north-east of the village of Cerro Cóndor (Patagonia), the fossil material consists of most of the front portion of the skeleton, including a well-preserved skull.  The genus name honours the geological formation from whence it came, the Cañadón Asfalto Formation and the word “venator” from the Latin for hunter.  The trivial epithet honours the Administración de Vialidad Provincial of Chubut and the Dirección Nacional de Vialidad, for their help with field expeditions of the Museo Paleontológico Egidio Feruglio.

Dating the deposits associated with the Cañadón Asfalto Formation has proved difficult.  Isotope analysis using material from volcanic ash layers has yielded varying results, but in the paper published in the academic journal “Scientific Reports”, the age of the strata associated with this fossil find is stated as late Toarcian to Bajocian, indicating that this predatory dinosaur roamed Gondwana around 175 to 170 million years ago.

Views of the Skull and Jaws of Asfaltovenator with Line Drawings

Picture credit: Scientific Reports

The skull is estimated to be around 80 cm in length and the overall body size of Asfaltovenator is estimated at between seven to eight metres in length.

A Tweak to the Tetanurae

Asfaltovenator demonstrates an unusual combination of anatomical characteristics.  Its discovery could have implications for the way in which palaeontologists arrange the family tree of meat-eating dinosaurs. 

The Suborder Theropoda, the lizard-hipped, primarily carnivorous dinosaurs, is further divided up into several sub-groups, for example the allosauroids, megalosauroids, ornithomimosaurs, tyrannosauroids, maniraptorans and their close relatives, the birds.  Arguably, the most successful part of the Theropoda were the Tetanurae (stiff tails), a clade that is defined as all theropods more closely related to modern birds than to Ceratosaurus.  It is thought that the Tetanurae diverged from its sister clade, the Ceratosauria, during the Late Triassic.

Asfaltovenator vialidadi

The discovery of Asfaltovenator is important, as most Middle Jurassic theropods are only known from quite fragmentary material and this dinosaur, described as a basal allosauroid, has traits linking it to both the allosauroids and the megalosauroids.

This suggests that the Allosauroidea and the Megalosauroidea evolved from a common ancestor and that these two parts of the Tetanurae are more closely related to each other than they are to the Coelurosauria, that part of the Tetanurae that gave rise to the tyrannosaurs, ornithomimids, Maniraptora and the birds.

Postcranial Material and a Skeletal Drawing Showing the Known Fossil Material (Asfaltovenator vialidadi)

Picture credit: Scientific Reports

Scientists hope that more large tetanurans can be found in Middle Jurassic strata, as further discoveries will help to hone Theropoda classification.

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Mimodactylus libanensis Newly Described Lebanese Pterosaur

The Pterosauria were very probably ubiquitous over much of our planet during the Mesozoic.  Once these flying reptiles had begun to diversify during the Late Triassic and into the Jurassic, these winged-wonders, the first vertebrates to master powered flight, would have spread far and wide.  Trouble is, although palaeontologists have described more than 120 genera, our knowledge of the Pterosauria is limited and scientists rely on a few key deposits to provide them with the majority of specimens to study.  Pterosaurs are now known from every continent, but surprisingly, very little material has been collected from Africa and the Arabian peninsula.

Writing in the academic journal “Scientific Reports”, a team of international scientists have announced the discovery of a Late Cretaceous pterosaur from Lebanon.  Mimodactylus libanensis is the most complete pterosaur specimen to have been discovered from the Afro-Arabian continent.  Intriguingly, the fossil material shows a strong taxonomic affinity with a genus known from China (Haopterus gracilis), together the pair form a new clade of toothy pterosaurs – the Mimodactylidae.

A Life Reconstruction of the Newly Described Pterosaur Mimodactylus libanensis

Picture credit: Julius Csotonyi

Pterosaurs with Long, Narrow Wings

The fossil specimen comes from the famous Hjoûla Lagerstätte of Lebanon, a deposit famous for its beautifully preserved fossil fish, but tetrapod fossils are exceptionally rare.  The nearly complete and articulated skeleton indicates that Mimodactylus had long, narrow wings and that it would have been well-adapted to soaring over the sea, in a similar way to extant frigate birds.  As to what this pterosaur ate, that is open to speculation, but the robust, conical teeth located at the front of the jaws suggest a durophagus diet.  Perhaps this pterosaur fed on molluscs and other shelled creatures.

A View of the Fossilised Remains of Mimodactylus libanensis

Picture credit: Kellner et al/Scientific Reports

The Mimodactylidae

The single specimen represents a sub-adult, the wingspan is estimated to be around 1.3 metres, but in the absence of any fossil material representing an adult animal, the actual size of a fully grown Mimodactylus is not known.  A phylogenetic analysis of the 95 million-year-old specimen suggests that Mimodactylus libanensis is closely related to pterosaurs from Asia and that with the taxon Haopterus gracilis, which is known from the Yixian Formation of Liaoning Province (north-eastern China), it forms a new clade of derived toothy pterosaurs, the Mimodactylidae.

One of the co-authors of the scientific paper, Michael Caldwell (University of Alberta), commented:

“This means that this Lebanese pterodactyloid was part of a radiation of flying reptiles living in and around and across the ancient Tethys Seaway, from China to a great reef system in what is today Lebanon.”

What’s in a Name?

The genus name is from the acronym (MIM), the Mineral Museum of Beirut in Lebanon, where the specimen is housed and the Greek “dactylos” meaning digit.  The trivial epithet honours Lebanon where this rare specimen was found.  An honourable mention to the anonymous philanthropist who acquired the fossil and ensured this important pterosaur was kept in Lebanon.

A Closer View of the Skull and Jaws of Mimodactylus libanensis

Picture credit: Kellner et al/Scientific Reports

The scientific paper: “First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity” by Alexander W. A. Kellner, Michael W. Caldwell, Borja Holgado, Fabio M. Dalla Vecchia, Roy Nohra, Juliana M. Sayão and Philip J. Currie published in Scientific Reports.

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Majungasaurus – Elevated Tooth Replacement Rate

Scientists writing in the academic journal “PLOS One”, have really got their teeth into an aspect of dinosaur anatomy, that surprisingly has not attracted that much research to date.  Dinosaurs replaced their teeth, as teeth were shed, perhaps when feeding or fighting, then replacements would erupt from the gumline permitting these reptiles to retain their toothy grins.

The speed of tooth replacement can provide palaeontologists with important information about feeding ecology.  The fastest tooth replacement rates had been associated with herbivorous dinosaurs, the likes of the Ceratopsia and the hadrosaurids.  After all, these plant-eaters fed on very coarse plant material so their teeth were subjected to plenty of wear and tear.  In this new study, undertaken by researchers at Ohio University and Adelphi University (New York), tooth replacement rates for three carnivorous dinosaurs were calculated.

Surprisingly, Majungasaurus (M. crenatissimus), from the Late Cretaceous of Madagascar, had a much faster tooth replacement than the other theropods studied.  Its tooth replacement rate puts it on a par with the rates associated with the horned dinosaurs and the duck-bills.

Computer Generated Images of the Skull of Majungasaurus

Picture credit: Memoirs of the Society of Vertebrate Paleontology/Ohio University/from Sampson, S. D. and L. M. Witmer (2007)

Rapid Replacement of Majungasaurus Teeth

CT scans and detailed cross-sectional analysis were carried out on individual teeth and jaw elements associated with three theropod dinosaurs.  These dinosaurs were the blunt-snouted, deep-skulled Majungasaurus along with Allosaurus and Ceratosaurus.  High tooth replacement rates were identified in three genera, but the researchers concluded that Majungasaurus replaced its teeth much faster than either Allosaurus or Ceratosaurus.  Majungasaurus would form a new tooth in each socket every fifty-six days or so, whilst Allosaurus and Ceratosaurus took in excess of a hundred days.

Lead author of the research, Michael D. D’Emic, (Adelphi University), explained the significance of this finding by commenting:

“This meant they [Majungasaurus] were wearing down their teeth quickly, possibly because they were gnawing on bones.  There is independent evidence for this in the form of scratches and gouges that match the spacing and size of their teeth on a variety of bones — bones from animals that would have been their prey.”

An Accelerated Replacement Strategy

Assistant professor D’Emic went onto add that extant animals too, gnaw on bones, this is a way for them to get certain nutrients, but to feed like this requires exceptionally tough and strong teeth, Majungasaurus did not have teeth like that, so they evolved an accelerated replacement strategy to compensate.

Examining Tooth Replacement in Theropod Dinosaurs

Picture credit: M. D. D’Emic et al/PLOS One with additional annotation by Everything Dinosaur

The picture (above), shows computer generated images of jaw elements of each dinosaur associated with the study (a) Allosaurus, (b) Ceratosaurus and (c) Majungasaurus.  The images (d-f) show histological tooth sections which reveal incremental growth lines that can help to determine the individual age of teeth (d) Majungasaurus, (e) Ceratosaurus and (f) Allosaurus.

Using a statistical model to predict tooth age from tooth length measured in CT slices, replacement rates for these three genera are estimated at:

• Majungasaurus 56 days
• Allosaurus 104 days
• Ceratosaurus 107 days

The rapid replacement rate recorded in Majungasaurus puts it on a par with living sharks and herbivorous dinosaurs.

Building on Research from Twenty Years Ago

This research builds on an earlier paper published twenty years ago, the authors of this new study suggest that with so many new dinosaurs being named and described over the last two decades or so, there is a lot of scope to build on the data collected so far and to provide further insights into dinosaur feeding ecology.

Michael D’Emic stated:

“I’m hoping this latest project spurs more people to study other species.  I bet that it will reveal further surprises and hopefully that will lead to a better understanding of how dinosaurs evolved to be successful for so long.”

Now that less destructive forms of study are available to scientists, the analysis of tooth wear and the internal structures of dinosaur teeth will help to provide a clearer picture regarding dinosaur feeding behaviour and dietary preferences – now that’s something to smile about.

An Illustration of the Late Cretaceous Abelisaurid Majungasaurus (M. crenatissimus)

Picture credit: Everything Dinosaur

The scientific paper: “Evolution of high tooth replacement rates in theropod dinosaurs” by Michael D. D’Emic , Patrick M. O’Connor, Thomas R. Pascucci, Joanna N. Gavras, Elizabeth Mardakhayav and Eric K. Lund published in PLOS One.

The Everything Dinosaur website: Everything Dinosaur.

Asymmetrical Styracosaurus Skull Could Change the Way in Which Dinosaur Species are Erected

A team of researchers based at the University of Alberta have published a scientific paper that might just turn some assumptions when it comes to naming a new dinosaur species on their head.  Cranial fossil material can provide palaeontologists with important indicators that can help them establish that a newly found fossil represents a new species.

Often it is the skull and jaws that provide the important morphological evidence to help palaeontologist establish taxonomic relationships between genera.  However, the mainly University of Alberta-based team challenge some of these assumptions, all thanks to “Hannah” a Styracosaurus skull named after one of the researcher’s dogs.

Palaeontologist Scott Persons with “Hannah” the Styracosaurus and his Dog Hannah

Picture credit: Scott Persons/University of Alberta

Studying Styracosaurus

In 2015, a field team working in the Dinosaur Provincial Park of southern Alberta uncovered the skull of a five-metre-long horned dinosaur (Styracosaurus).  Nothing too unusual so far, after all this spiky-frilled horned dinosaur was scientifically described based on an almost complete skull (the type specimen), found in the Dinosaur Provincial Park, but Hannah’s skull was different – very different!  It is not symmetrical, the left half of the skull looks different from the right half – cue concerns being raised over how dinosaur genera and species are erected.

Co-author of the scientific paper published this week in the journal “Cretaceous Research” Scott Persons commented:

“When parts of one side of the skull were missing, palaeontologists have assumed that the missing side was symmetrical to the one that was preserved.  Turns out, it isn’t necessarily.  Today, deer often have left and right antlers that are different in terms of their branching patterns.  This fossil shows dramatically that dinosaurs could be the same way.”

An Asymmetrical Dinosaur Skull

The well-preserved Styracosaurus skull (UALVP55900), has cranial imperfections that could change how palaeontologists identify new species of dinosaurs.  Differences in the shape of horned dinosaur’s skulls and their bony frills have been noted before, after all, there is variability recorded in fossils assigned to a species due to differences in age, in growth stages and from the effects of pathology.  In this case, the Styracosaurus called “Hannah” demonstrates previously unrecorded differences between the left side and the right side of the skull.

As with the type specimen collected by the famous scientist C H. Sternberg, the right lateral parietal bar (the right side of the skull frill) has seven bony projections (epiossifications), but the left parietal bar is not symmetrical it has eight epiossifications!

A Computer Rendered Image Showing the Skull of the Styracosaurus

Picture credit: Scott Persons/University of Alberta

The skull (UALVP55900) is shown in right lateral view (top) and left lateral view (middle).  The dorsal view (bottom) shows the clear differences in the shape of the left and right sides of the skull (asymmetry).

Marked Differences in the Styracosaurus Skull

The differences are so marked, that if the scientists had found only isolated halves, they could have concluded that each half represented a different horned dinosaur species.

Lead author of the study, Robert Holmes (University of Alberta), explained that “Hannah” shows that the pattern of a dinosaur’s horns could vary so much from one side of the skull to the other.  This raises doubts over the validity of some species such as Rubeosaurus ovatus.  Rubeosaurus was originally described as a species of Styracosaurus (1930), based on a single parietal bone (part of the skull frill), collected in the Two Medicine Formation of Montana.  This fossil and a second more complete skull fossil found in 1986, were subsequently reviewed and the genus Rubeosaurus (R. ovatus) erected in 2010.

Thanks to Hannah, it looks like the research undertaken in 1930 was right, the authors of the newly published paper suggest that Rubeosaurus ovatus is a junior synonym of Styracosaurus.

What are the Implications for the Naming of Dinosaur Species?

Picture credit: Everything Dinosaur

Since working on the paper, Scott Persons has moved on, becoming a professor and museum curator at the College of Charleston.  He may have had to leave “Hannah” the Styracosaurus behind but we presume Hannah the dog is still with him.

Persons commented:

“Hannah the dinosaur is named after my dog.  She’s a good dog, and I knew she was home missing me while I was away on the expedition.”

Despite the nickname, palaeontologists are not able to determine whether specimen number UALVP55900 represents a male or a female Styracosaurus.

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

The scientific paper: “Morphological variation and asymmetrical development in the skull of Styracosaurus albertensis” by Robert B. Holmes, Walter Scott Persons, Baltej Singh Rupal, Ahmed Jawad Qureshi and Philip J. Currie published in Cretaceous Research.

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