The clade of very bird-like dinosaurs known as the Oviraptorosauria, were very successful and widely distributed in the Northern Hemisphere during the Late Cretaceous. For example, the Nemegt Formation (Mongolia), is famous for the numerous oviraptorosaur dinosaurs that have been named and described from fossils, dinosaurs such as Conchoraptor, Rinchenia, Gobiraptor and the recently described two-fingered Oksoko (O. avarsan) that we featured in an article in October 2020: A New Species of Two-fingered Oviraptorosaur is Described.

Analysis of fragmentary fossil remains attributed to the caenagnathid Elmisaurus suggests that these members of the oviraptorosaur clade (the Caenagnathidae) were actually rare in Mongolia compared to the much more numerous and diverse oviraptorids.

Researchers, which include the eminent Professor Phil Currie (University of Alberta), writing in PLOS One conclude that caenagnathids may have been outcompeted by other oviraptorosaurs and as such, caenagnathids like Elmisaurus only made up a tiny portion of the dinosaur population associated with the Nemegt Formation.

Examining the Oviraptorosauria

The Oviraptorosauria clade consists primarily of two large families of feathered dinosaur, the Caenagnathidae “recent jaws” and the closely related Oviraptoridae “egg thieves”.

Overall, the anatomy of caenagnathids is very similar to that of oviraptorids, but there are a number of differences. For example, caenagnathid jaws exhibited a distinct suite of specialisations not seen in other oviraptorosaurs. The jaws of caenagnathids tend to be relatively long and shallow, this suggests that their bite was not as powerful. The inside of the lower jaws also reveal a complex series of ridges and tooth-like processes, as well as a pair of horizontal, shelf-like ridges. Recent studies have demonstrated that as caenagnathids grew and got older they started to lose their teeth (ontogenetic edentulism).

The unusual jawbone morphology was produced by various tooth reduction patterns and this in turn, suggests that these dinosaurs changed their diet as they matured. Furthermore, the jaws of caenagnathids are unusual as the bones are hollow and air filled. In addition, in general terms caenagnathids tend to be more lightly built than the closely related oviraptorids.

Picture credit: Everything Dinosaur

Nomingia gobiensis Actually Elmisaurus rarus

Two members of the Caenagnathidae had been described from fossils associated with the Nemegt Formation, Elmisaurus rarus which was scientifically described back in 1981 and Nomingia gobiensis which was named in the year 2000. The research team which included Gregory Funston (University of Edinburgh), Chinzorig Tsogtbaatar (North Carolina State University), Tsogtbaatar Khishigjav (Mongolian Academy of Sciences) as well as Professor Currie, examined a partial skeleton which had been discovered in 2018, close to the site where the holotype fossils of Nomingia had been found.

The team were able to highlight similarities in the overlapping elements of Elmisaurus and Nomingia. They concluded that fossil material previously attributed to Nomingia gobiensis might represent Elmisaurus rarus and that just one species of caenagnathid is known from the Nemegt Formation.

Oviraptorids Outcompeted Caenagnathids

The researchers discount the idea that a bias in fieldwork has led to the lack of caenagnathid fossil specimens found. After all, numerous small dinosaurs such as dromaeosaurids and oviraptorids are known from Nemegt Formation. The team postulated that the caenagnathids were marginalised and out competed by the similarly sized oviraptorids.

Differences in Asian and North American Late Cretaceous Ecosystems

The lack of caenagnathids reported from the Nemegt Formation might reflect competition amongst different types of small, cursorial, feathered dinosaurs. In North America, caenagnathids were the only oviraptorosaurs present (no oviraptorids are currently known from North America). In contrast, both oviraptorids and another type of oviraptorosaur closely related to the Caenagnathidae – the avimimids Avimimus portentosus and Avimimus nemegtensis were present in Mongolia during the Late Cretaceous.

The researchers conclude that although the highly diverse Nemegt Formation oviraptorids probably had very specialised diets, they may have outcompeted the caenagnathids in the niche of small omnivores.

As Nomingia gobiensis was named and scientifically described some nineteen years after Elmisaurus rarus, the research team postulate that Nomingia gobiensis should be regarded as a junior synonym of Elmisaurus. In addition, low caenagnathid diversity in the Nemegt Formation might reflect their inability to compete with other oviraptorosaurs, particularly oviraptorids.

The scientific paper: “A partial oviraptorosaur skeleton suggests low caenagnathid diversity in the Late Cretaceous Nemegt Formation of Mongolia” by Gregory F. Funston, Philip J. Currie, Chinzorig Tsogtbaatar, Tsogtbaatar Khishigjav published in PLOS One.

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An Ichthyornis skull study sheds light on the evolution of brains within the Avialae.

Living birds are very diverse, globally distributed and occupy a huge number of ecological niches. Today, there are more species of birds than mammals, they are certainly extremely successful and they are the only members of the Dinosauria to have survived the end-Cretaceous extinction event. A new study published in Science Advances suggests the unique brain shape of the ancestors of modern birds may have helped them survive the mass extinction that wiped out all the other dinosaurs.

Studying a Fossil Skull

A beautifully preserved skull and jaws of the toothed stem bird (Avialae) Ichthyornis (I. dispar) was subjected to x-ray computed tomography at the University of Texas at Austin so that researchers could gain an better understanding of the shape of the brain of this Late Cretaceous bird.

Brain morphology in Mesozoic birds is very poorly understood. Only two other Mesozoic birds have had their brains mapped – Archaeopteryx lithographica from the Late Jurassic of Germany and the probable enantiornithine Cerebavis cenomanica from the Volgograd Region of Russia which is known from the Middle Cenomanian of the Cretaceous.

With the CT-imaging data, the researchers used the skull of Ichthyornis like a mould to create a three-dimensional replica of the brain called an endocast. They then compared that endocast with ones created for living birds and more distantly related, non-avian members of the Dinosauria.

To read a blog post from 2018 about an earlier study of an Ichthyornis skull that provided new information on the evolution of the beak in birds: The First Beak Under the Noses of Scientists.

Ichthyornis Skull Study

The scientists found that the brain of Ichthyornis had more in common with non-avian dinosaurs than it did with living birds. Specifically, the cerebral hemispheres – where higher cognitive functions such as speech, thought and emotion occur in humans – are much bigger in living birds than in Ichthyornis. That pattern suggests that these functions could be connected to surviving the mass extinction.

Lead author of the study, PhD student Christopher Torres (The University of Texas at Austin), commented:

“Living birds have brains more complex than any known animals except mammals. This new fossil finally lets us test the idea that those brains played a major role in their survival.”

Co-author of the study Julia Clarke, a professor at the University of Texas Jackson School of Geosciences added:

“Ichthyornis is key to unravelling that mystery. This fossil helps bring us much closer to answering some persistent questions concerning living birds and their survivorship among dinosaurs.”

To read a related article published in 2013, that suggested that dinosaur brains were pre-programmed to permit complicated co-ordinated moves, helpful when evolving powered flight : Study Shows Dinosaur Brains Pre-programmed for Flight.

The scientific paper: “Bird neurocranial and body mass evolution across the end-Cretaceous mass extinction: The avian brain shape left other dinosaurs behind” by Christopher R. Torres, Mark A. Norell and Julia A. Clarke published in Science Advances.

Visit the Everything Dinosaur website: Dinosaur Toys and Models.

Researchers have described a new species of crocodilian from the Late Jurassic of Chile. Named Burkesuchus (B. mallingrandensis), it heralds from the Toqui Formation of southern Chile. As such, this 70-centimetre-long reptile shared its home with sauropods and the bizarre Chilesaurus (C. diegosuarezi). Analysis of the fragmentary fossil bones, including all important skull material suggests that Burkesuchus was a basal member of the Mesoeucrocodylia, the crocodilian lineage that led to modern crocodiles.

Shedding Light on the Fauna Associated with the Toqui Formation

Fossils of Burkesuchus were collected from outcrops of the Toqui Formation (Tithonian stage of the Late Jurassic). Analysis of zircon samples subjected to radiometric dating suggest that this small crocodilian lived around 147 million years ago. The fossils found consist of skull material, dorsal vertebrae, elements from the limbs including a right scapula and coracoid (shoulder bones) a nearly complete right femur (thigh bone) and several osteoderms (body armour).

A “Missing Link” in Crocodile Evolution

The genus name honours the American Coleman Burke for his financial support of the field work and “suchus” from Latin, meaning crocodile. The species name is a reference to Mallín Grande, the name given to this scenic, very beautiful but remote part of Chile, south of General Carrera Lake.

Semi-aquatic crocodilian fossils dating from the Jurassic of South America are rare. To date, the only other non-marine crocodilian known from this continent is Batrachomimus from the Upper Jurassic of Brazil, which is thought to be a paralligatorid. However, analysis of the limb bones associated with Burkesuchus reveals that it possibly represents an intermediate form between crocodilians with a more semi-erect gait and sprawling forms reflecting the gait and locomotion of modern crocodilians. Burkesuchus could represent a transitional form, helping palaeontologists to understand the evolutionary history of this important group of archosaurs.

Picture credit: Everything Dinosaur

The Significance of a Prehistoric Crocodile

The discovery of Burkesuchus expands the meagre record of non-marine crocodile representatives from the Late Jurassic of South America and the researchers conclude that Batrachomimus and Burkesuchus indicate that the evolution of more derived crocodyliforms could have occurred in South America.

The scientific paper: “New transitional fossil from late Jurassic of Chile sheds light on the origin of modern crocodiles” by Fernando E. Novas, Federico L. Agnolin, Gabriel L. Lio, Sebastián Rozadilla, Manuel Suárez, Rita de la Cruz, Ismar de Souza Carvalho, David Rubilar-Rogers and Marcelo P. Isasi published in Scientific Reports.

Visit the Everything Dinosaur website: Dinosaur Figures and Prehistoric Animal Toys.

When asked to name an armoured dinosaur, we suspect that most readers would quickly reply with “Stegosaurus” or possibly “Ankylosaurus”. True, some armoured dinosaurs are very famous, having seeped into the public consciousness thanks to countless appearances in the media, dinosaur documentaries and films. However, very little is known about the origins of this diverse and highly successful ornithischian clade. Newly, published research on the labrador-sized early thyreophoran Scutellosaurus (S. lawleri) is helping scientists to better understand the evolutionary origin of these dinosaurs.

A Palaeontological Project Lasting Sixteen Years

The scientific paper, the first detailed anatomical assessment of Scutellosaurus covering its entire skeleton, has been published in the on-line, open access journal Royal Society Publishing. The dedicated research team consisted of PhD student Benjamin Breeden (University of Utah), Professor Richard Butler (University of Birmingham), Professor Timothy Rowe (University of Texas at Austin) along with PhD student Tom Raven and Dr Susannah Maidment (Natural History Museum, London).

This research project was first proposed back in 2005. Sixteen years after the project’s inception, the paper has been published providing a new perspective on the evolution of the armoured dinosaurs.

Scutellosaurus lawleri

Named and described in 1981, from material discovered ten years earlier. Scutellosaurus lawleri fossils come from the Kayenta Formation of Arizona, more specifically mudstones associated with the “middle third” of this Formation (Lower Jurassic). It has been estimated that the Scutellosaurus fossils are around 181 to 186 million years old (Pliensbachian and Toarcian stages).

More than seventy Scutellosaurus specimens are known, representing all parts of the skeleton. As such, Scutellosaurus fossil material is much more abundant than that of other early armoured dinosaurs such as Scelidosaurus (S. harrisoni), which was named and described by the famous Victorian anatomist Richard Owen. This relative abundance of fossil material in comparison with other early armoured dinosaurs makes Scutellosaurus an ideal candidate to help palaeontologists to better understand the evolution of this important group of plant-eating dinosaurs.

Scutellosaurus was a Biped

One of the key findings of this research is that based on limb proportions and postcranial skeletal assessments, Scutellosaurus was bipedal. As such, it is the only bipedal thyreophoran known to science. It had been suggested that as thyreophorans evolved into larger and more heavily armoured forms they lost this ability to adopt a bipedal posture.

Although the exact layout of the dermal armour of Scutellosaurus is not known, the researchers tested the hypothesis that heavier armour led these dinosaurs to adopt a quadrupedal stance.

The research team calculated the centre of mass of Scutellosaurus with its armour, without armour, with the armour of Stegosaurus and with the armour of the Late Cretaceous ankylosaurid Euoplocephalus. They found that the addition of armour did cause the centre of mass to move slightly further back in the body in all the tests. However, the team concluded that the evolution of armour probably was not the reason to cause early armoured dinosaurs to adopt quadrupedal locomotion.

More derived taxa of armoured dinosaurs required forelimb support for their body weight for other, as yet not understood reasons.

Armoured Dinosaurs Grew Slowly

Detailed analysis of Scutellosaurus bones indicate that this dinosaur grew very slowly throughout its life. This supports other studies that suggest that thyreophorans had lower metabolic rates when compared to other dinosaurs, even closely related ornithischians.

Lots of Variety in Early Jurassic Dinosaur Faunas

The supercontinent Pangaea did begin to break-up during the Jurassic, but at the time Scutellosaurus roamed what was to become the western United States, this landmass was largely intact, which in theory would have helped homologous populations of dinosaurs to evolve. That is to say, that given the absence of any geographical barriers preventing movement, similar dinosaur faunas would have existed across Pangaea. When this study of Scutellosaurus is looked at from the wider perspective of dinosaur evolution and radiation, a different picture emerges.

The ornithischian dinosaurs from the Kayenta Formation are represented by Scutellosaurus lawleri, a larger unnamed thyreophoran known from isolated bones and an undescribed hetrodontosaurid. Scutellosaurus fossils are the most abundant dinosaur fossils associated with the Kayenta Formation, they are much more common than theropod or sauropodomorph fossils. In contrast, the roughly contemporaneous upper Elliot Formation of South Africa has many more sauropodomorphs than ornithischians and the dinosaur biota of the Lufeng Formation of China is dominated by sauropodomorphs with ornithischian material exceptionally rare.

This suggests that there was considerable variation in the composition of dinosaur biotas during the Early Jurassic.

The scientific paper: “The anatomy and palaeobiology of the early armoured dinosaur Scutellosaurus lawleri (Ornithischia: Thyreophora) from the Kayenta Formation (Lower Jurassic) of Arizona” by Benjamin T. Breeden, Thomas J. Raven, Richard J. Butler, Timothy B. Rowe and Susannah C. R. Maidment published by Royal Society Publishing.

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