New Study Looks at the Growth Rates of Polar Hypsilophodonts

Researchers from Museums Victoria (Melbourne, Australia) and the Oklahoma State University Centre for Health Studies, have published a new paper in the academic journal “Scientific Reports” that examines the growth rates of polar dinosaurs, specifically the growth rates of those fleet-footed ornithischians the hypsilophodontids.  Palaeontologists have long-debated whether these small dinosaurs, which were geographically widespread during the Early Cretaceous, showed different growth rates between high latitude forms and those that lived closer to the Equator.

An Illustration of a Typical Hypsilophodont Dinosaur

Picture credit: Everything Dinosaur

The Perils of Being a “Polar” Dinosaur

Dinosaurs that lived in high latitude habitats such as those that lived on the southernmost portions of Gondwana, had to endure low temperatures, plus periods of prolonged darkness as the sun dropped below the horizon.  Although, nowhere near is as cold as the Antarctic today, close to the South Pole in the Early Cretaceous was quite a foreboding, formidable environment.  However, several types of non-avian dinosaurs, including several hypsilophodonts seem to have flourished.  Four taxa have been described to date, from two principle locations namely:

• Fulgurotherium australe from the Flat Rocks and Dinosaur Cove locations (Victoria)
• Qantassaurus intrepidus (Flat Rocks location)
• Leaellynasaura amicagraphica from Dinosaur Cove
• Atlascopcosaurus loadsi (Dinosaur Cove)

As all these genera are named from fragmentary remains (elements from the jaw and individual teeth), with the exception of L. amicagraphica, which is known from more substantial material, in the absence of more fossil remains some of these taxa are regarded as nomen dubia.

The microstructure of limb bones (femora and tibias) were analysed to identify growth trends, the study revealed that there were probably two genera present in those fossils studied which had come from Dinosaur Cove.  Bone microstructure alone, could not distinguish taxa within the sample of bones from the Flat Rocks area.  The researchers, which included Dr Thomas Rich and his partner Dr Patricia Vickers-Rich conclude that further histological study of hypsilophodont material from these sites may help to confirm the number of genera present as well as to help improve the data on polar dinosaur growth rates.  Leaellynasaura was named in honour of the couple’s daughter Leaellyn Rich.

Several Hypsilophont Species Likely

Flat Rocks and the Dinosaur Cove locations are separated by Port Phillip Bay, they are approximately 120 miles (200 kilometres) apart.  These areas are also distant from a geological perspective, with the Flat Rocks locality being made up of sedimentary rocks that date from around 133 – 128 million years ago (Late Valanginian or Barremian faunal stages of the Early Cretaceous).

Whereas, the rocks that formed Dinosaur Cove on the other side of Cape Otway, are much younger, being laid down approximately 106 million years ago (Albian faunal stage of the Early Cretaceous).  Based on the temporal range that these fossils represent, then it is quite likely that these dinosaur fossils from the coast of Victoria do, indeed, represent several genera.

Growth Rates Amongst Polar Hypsilophodonts

The research into the bone microstructure of the limb bones of these types of polar dinosaur reveals that both the Flat Rocks and Dinosaur Cove specimens were growing in a similar way, at a similar rate to many typical small-bodied vertebrates.  These animals tended to have lower annual growth rates when compared to larger vertebrates.

The palaeontologists note that the large (eight metres long), ornithischian Maiasaura from the Late Cretaceous of the United States took around eight years to reach adult size, whereas one of the specimens in the study seems to have reached maturity a year earlier, but it was a much smaller-bodied dinosaur, only growing at a fraction of the rate of the larger Maiasaura.

Transverse Sections from the Femur of a Hypsilophodont Used in the Study

Picture credit: Scientific Reports

A Slow Growth Rate

The researchers did note that although the polar hypsilophodontids grew quite slowly compared to their larger relatives, the bone histology studies revealed that they had a relatively elevated growth rate for the first few years of their life.  Growing up relatively quickly, or at least reaching a certain threshold body size could have been an evolutionary response to avoid predation.

The paper published in “Scientific Reports”, is the first study of its kind into the growth rates of Australian polar hypsilophodonts.  The team conclude that these dinosaurs might have reached maturity in about five to seven years.  As adults, these genera only rarely exceeded lengths of 2.8 metres, most of which was tail and individual body mass for most of these dinosaurs was under fifty kilograms.

The research could be extended to include an analysis of hypsilophodontid limb bones excavated from lower latitudes.  A more complete comparison between the ontogeny of hypsilophodonts from different parts of the world could then be made.

Visit the website of Everything Dinosaur: Everything Dinosaur.

Dinosaurs Reveal the Geographical Signature of an Evolutionary Radiation

Yesterday, Everything Dinosaur posted an article on the newly published scientific paper that examined how the Dinosauria radiated out from their suspected South American origins and came to dominate terrestrial ecosystems around the world.  The research was conducted by scientists based at Reading University and their paper was published this week in the academic journal “Nature Ecology & Evolution”.

To read our article on this research: The Evolutionary Radiation of the Dinosauria Mapped.

Building on an Earlier Study

Building upon earlier research, the Reading University scientists believe that the dinosaurs were already in decline before the final coup de grâce that marked the end of the Cretaceous and the demise of the non-avian dinosaurs.  The dinosaurs spread across the planet, but they began to run out of space to migrate into, becoming victims of their own success.

Everything Dinosaur has received special permission from the University to publish some of the images created by the researchers that plot the routes taken by various dinosaur species as they spread across the world.

The pictures (below), show six reconstructed paths from the dinosaurian root node (black circle) to the fossilised species (black square).  The coloured circles represent the centroids of the reconstructed ancestral locations (these are used for visualisation purposes only and posterior distributions of estimated ancestral locations are used in all analyses).  These maps help to demonstrate the conclusions drawn by the researchers.  Take for example, the first image, that of the path of Rhoetosaurus (R. brownei).  R. brownei was a sauropod, its fossils are found in eastern Australia and it lived some 170 million years ago.

The Evolutionary Path of Rhoetosaurus brownei

Picture credit: University of Reading (silhouette credit: Remes K, Ortega F, Fierro I, Joger U, Kosma R et al, silhouette represents Spinophorosaurus nigerensis)

The Evolutionary Path of Archaeopteryx lithographica is Plotted

Picture credit: University of Reading (silhouette credit: Scott Hartman)

Studying the Dinosauria

Archaeopteryx lithographica lived around 150 million years ago, its fossils have been found in the limestone quarries of southern Germany.  All the evolutionary paths that have been created by the researchers have been plotted onto geological age level palaeomaps from the time at which the fossil species is dated to (grey).  All preceding age level palaeomaps are plotted in white.

Plotting the Path of the Ornithischian Dinosaur Stegosaurus stenops

Picture credit: University of Reading (silhouette credit: Scott Hartman)

Like Archaeopteryx, Stegosaurus stenops fossils are associated with Upper Jurassic strata.  However, this research suggests that unlike the Archaeopteryx lineage, which migrated into eastern Laurasia, the evolutionary path of S. stenops was oriented towards western Laurasia, fossils of this iconic armoured ornithischian being associated with the Morrison Formation of the western United States.

The Evolutionary Path of Andesaurus delgadoi is Plotted

Picture credit: University of Reading (silhouette credit: T. Tischler, the silhouette represents the related titanosaurid Wintonotitan wattsi)

Late Cretaceous Migrations

The titanosaurid A. delgadoi lived some 97 million years ago (Cenomanian faunal stage of the Late Cretaceous).  Note how the world map has changed in the illustrations, reflecting the change in the position of the continents.  The known fossil evidence suggests that the majority of the titanosaurids were restricted to Gondwana for most of the Cretaceous species.  Only in the very Late Cretaceous did a land bridge form, permitting these dinosaurs to migrate into North America.

Path of Dromaeosaurus albertensis 

Picture credit: University of Reading (silhouette represents Dromaeosauroides bornholmensis known from Upper Cretaceous rocks from Denmark)

The researchers conclude that the dromaeosaurids associated with North America crossed over from northern Asia.

Last but not least, no evolutionary study mapping the spread of the dinosaurs would be complete without reference being made to the Tyrannosauroidea.  The map below, shows the path plotted for Tyrannosaurus rex.

Plotting the Path for T. rex

Picture credit: University of Reading

From their South America origins, this most famous of the Theropoda seems to have traversed Laurasia before heading westwards to become the dominant, apex predators in the Late Cretaceous (Laramidia and (most likely) Appalachia).

The authors of the scientific paper state that all silhouettes were downloaded from www.phylopicdotorg.

The scientific paper: “Dinosaurs Reveal the Geographical Signature of an Evolutionary Radiation” by Ciara O’Donovan, Andrew Meade and Chris Venditti published in Nature Ecology & Evolution.

Everything Dinosaur acknowledges the help of Reading University in the compilation of this article.

Visit the Everything Dinosaur website: Everything Dinosaur.

Dinosaurs Reveal the Geographical Signature of an Evolutionary Radiation

The fact that the dinosaurs came to dominate terrestrial ecosystems during the Mesozoic is not controversial.  There is plenty of fossil evidence to suggest that dinosaurs evolved into a myriad of different species (some 1,300 genera have been described to date), these fossils are geographically widespread.  Thanks, in part, to their origins on the supercontinent Pangaea and to the vagaries of continental drift, dinosaurs lived all over the world, from the Antarctic to the Arctic circle.

Evolutionary Radiation of the Dinosaurs

However, not that much is known about how the dinosaurs spread and became globally distributed.  Indeed, just how quickly the Dinosauria radiated and how soon they rose to prominence in terrestrial ecosystems remains very much open to debate.  Researchers from the University of Reading have attempted to map the geographical spread of the “terrible lizards” and they conclude that the migration of dinosaurs around the world was so rapid, that eventually they ran out of land to colonise and this might have contributed to their extinction.

Dinosaurs Spread from South America to the Rest of the World

Picture credit: Everything Dinosaur

The Evolution of the Dinosaurs – It’s a Bit of a Puzzle

Just when and where the dinosaurs rose to dominate the land is hotly debated.  The fossil record for early dinosaurs is very poor and extremely fragmentary.  This problem is compounded by the blurring of the definition of the Dinosauria, as living alongside the true dinosaurs for tens of millions of years were their closely related counterparts which together with the dinosaurs comprise the clade Dinosauromorpha.  Palaeontologists can find it extremely difficult to distinguish between a true Triassic dinosaur and a contemporary dinosauromorph.  It seems that in the Triassic, the ancestral forms of the Dinosauria, lived alongside the true dinosaurs for millions of years.

This problem is compounded by the fact that the dinosaur/pterosaur/bird branch of the Archosauria (Avemetatarsalia), were in the evolutionary shadow of the crocodile branch of the “ruling reptiles” the Crurotarsi, for much of the Middle and Late Triassic.  If you were able to interview a Coelophysis or a Tawa (both dinosaurs from the famous Ghost Ranch location of New Mexico), they would have described an ecosystem dominated by other types of archosaur, not dinosaurs.  With the exception of the abundance of Coelophysis specimens, there are relatively few dinosaur fossils from the Ghost Ranch location, dinosaurs may have only made up around 20% of the terrestrial fauna.

Coelophysis – A Typical Example of a Triassic Theropod

Picture credit: Matt Celeskey

Jumping into the Jurassic

After the End Triassic mass extinction event, it seems to have been a different story.  The dinosaurs seem to have rapidly risen to dominance and soon the landscape was being dominated by giant herbivores such as the long-necked cetiosaurs and the first super-sized carnivores such as Dilophosaurus, Cryolophosaurus and the first of the megalosaurs.  The Reading University team modelled the spread of the dinosaurs by reconstructing the dinosaurs’ ancestral locations (using South America as the starting point for the dinosaur radiation), they then examined the spatial mechanisms that underpinned the spread of the Dinosauria.  The research shows that the speed of this expansion meant that the dinosaurs quickly became cosmopolitan and subsequently ran out of land.  This lack of space then seriously impeded their ability to produce new species.

Typical Early Jurassic Dinosaurs Show an Increase in Size Compared to Late Triassic Counterparts

Picture credit: Everything Dinosaur

Building Upon Previous Research

This new study, published in “Nature Ecology and Evolution”, builds upon previous research from Reading University, published in 2016, that concluded that the dinosaurs were in decline around 50 million years before the mass extinction event that saw the demise of the non-avian forms.

To read Everything Dinosaur’s article about the 2016 study: The Fifty Million Year Decline of the Dinosaurs.

Lead author of this new research, evolutionary biologist at the University of Reading, Ciara O’Donovan explained:

“Fossil evidence has shown us where the dinosaurs started out and where they died, but there is an important middle period that little was known about.  Our research fills this gap in prehistory by revealing how the dinosaurs spread, how fast they moved and what directions they moved in through time.  The dinosaurs exploded out of South America in a frenzy of movement to cover the planet.  It was during this time that diverse forms evolved and eventually led to species such as the fearsome Tyrannosaurus rex, Archaeopteryx (the earliest bird) and the gigantic, long necked Diplodocus.  This honeymoon period could not last forever though, and the dinosaurs eventually filled every available habitat on Earth.  There was nowhere new for species to move to, which may have prevented new species from arising, contributing to the dinosaurs’ pre-asteroid decline.  In essence, they were perhaps too successful for their own good.”

Using a Novel Statistical Analysis

The Reading University team developed a novel, statistical analytical method to help reveal where the ancestor of every dinosaur species lived.  This data was plotted onto a three-dimensional world map.  The analysis revealed that the dinosaurs spread virtually unchecked across the landmass of Pangaea at a rate of 1,000 kilometres (600 hundred miles), per million years.  They dominated every terrestrial habitat, across the globe as the supercontinent of Pangaea broke apart.

Sympatric Speciation

As the space left available for the Dinosauria to expand into was used up, the evolutionary driver for the development of new species might have changed.  The scientists conclude that dinosaurs initially diversified into new kinds driven by the expansion into new environments and habitats, but this driver for change was gradually replaced by sympatric speciation (new species evolving to exploit new niches within their existing environment).  This fundamental change in the way that dinosaurs evolved could have left them vulnerable to global catastrophes such as the extra-terrestrial impact event and the subsequent climate devastation that occurred some sixty-six million years ago.

Dinosaurs in Decline Many Millions of Years Before the End Cretaceous Mass Extinction

Picture credit: Don Davis (commissioned by NASA)

Dr Chris Venditti, evolutionary biologist at the University of Reading and co-author of the paper, commented:

“Early dinosaurs had a blank canvas and spread quickly across the devastated Earth, taking up every opportunity in their path.  Virtually every door was open to them as there was no competition from other species.  The inability of the dinosaurs to adapt rapidly enough as the Earth became full may explain why they were in decline prior to the asteroid strike, and why they were so they were so susceptible to almost total extinction when it hit.”

The scientific paper: “Dinosaurs Reveal the Geographical Signature of an Evolutionary Radiation” by Ciara O’Donovan, Andrew Meade and Chris Venditti published in Nature Ecology & Evolution.

Everything Dinosaur acknowledges the help of the University of Reading in the compilation of this article.

View the Everything Dinosaur website: Everything Dinosaur.

Fossil from South Wales Identified as New Triassic Species

In the 1950s the Pant-y-ffynnon Quarry in South Glamorgan (Wales), provided a wide variety of vertebrate fossils giving palaeontologists an insight into the fauna of an ancient Triassic archipelago.  However, a comprehensive analysis of the fossil material was not carried out.  Scientists from the University of Bristol including an undergraduate student have undertaken a systematic review of the specimens and this has resulted in the naming of a new species of Rhynchocephalian.  The little reptile has been named Clevosaurus cambrica and this newly described animal hints at adaptive radiation for the clevosaurs on the island chain.  In addition, since the researchers found no evidence of any reptiles in excess of two metres, they propose that the palaeofauna represents a possible example of insular dwarfism.

The concept of insular dwarfism (sometimes referred to as the “island rule” involves residents of islands with limited resources tending to become smaller overtime when compared to their mainland counterparts.

A Three-Dimensional Computer-generated Image of the Jawbone of C. cambrica

Picture credit: Bristol University

Clevosaurus cambrica – “Gloucester Lizard from Wales”

Emily Keeble’s final-year project for a degree in palaeontology at the School of Earth Sciences, (Bristol University) involved a reappraisal of the  Pant-y-ffynnon Quarry specimens.  Working alongside her course supervisors, the undergraduate was able to identify a new species of Clevosaurus, a type of reptile that was widespread across the supercontinent Pangaea in the Late Triassic.  Clevosaurus was named after “Clevum”, the Latin name for the city of Gloucester, as a number of species have been identified from this locality.  The trivial name “cambrica” honours Wales, where the fossil quarry is located.

In the Late Triassic, the hills of South Wales and the south-western part of England formed an archipelago that was inhabited by early dinosaurs, crocodylomorphs distantly related to modern crocodiles and alligators along with representatives of the Sphenodontidae such as the clevosaurs.  The once diverse and geographically reptile family – the Sphenodontidae is today, represented by the rare Tuatara (Sphenodon punctatus) which is limited to a few small islands off New Zealand.

Clevosaurus cambrica Would Have Looked Like a Tuatara

Picture credit: Everything Dinosaur

Commenting on the significance of her discovery, Emily said:

“The new species, Clevosaurus cambrica lived side-by-side with a small dinosaur, Pantydraco, and an early crocodile-like animal, Terrestrisuchus.  We compared it with other examples of Clevosaurus from locations around Bristol and South Gloucestershire, but our new beast is quite different in the arrangement of its teeth.”

Clevosaurus cambrica has been identified based on some articulated bones and some isolated fragments.  An analysis of the teeth in the jaws provided evidence that this small reptile probably was an insectivore.  The shape of the teeth and their arrangement identified the fossil as a new species.

Professor Mike Benton, a co-author of the paper and one of Emily’s supervisors added:

“We were lucky to find quite a lot of the skeleton and Emily was able to scan the blocks and make 3-D reconstructions of the skull, neck, shoulder and arm region.”

Evidence of Insular Dwarfism

The researchers conclude that the archipelago held a relatively impoverished fauna, dominated by rhynchocephalians such as the clevosaurs.  The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago.  Adaptive radiation is the term used to describe the evolutionary process whereby organisms diverge from a common ancestor to fill a multitude of different ecological niches, think of Darwin’s finches on the Galapagos Islands, for example.

Co-author of the paper and co-supervisor of Emily Dr Whiteside (Bristol University) explained:

“The dinosaurs, crocodiles, and lizards were isolated to some extent on their islands, and perhaps smaller ones were better at surviving in the changed ecologies of the islands.”

The scientific paper: “The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures, South Wales, UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)” by Keeble et al published in the Proceedings of the Geologists’ Association.

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

Visit the Everything Dinosaur website: Everything Dinosaur.