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Fossil finds, new dinosaur discoveries, news and views from the world of palaeontology and other Earth sciences.

2 07, 2020

Tiny Dinosaur Eggs from Japan Reveal Small Theropods

By | July 2nd, 2020|Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Geology, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

Dinosaur Eggs Provide a View on a “Hidden Ecosystem”

Not all the dinosaurs that ever existed are likely to be named and described by scientists.  Identifying these long extinct creatures relies on there being a fossil record of some sort to study.  A team of researchers writing in the journal “Cretaceous Research”, report on a new Lower Cretaceous fossil egg locality in Hyogo Prefecture, Japan, that provides a tantalising glimpse into a hidden dinosaur dominated ecosystem.

The researchers, which include Kohei Tanaka (University of Tsukuba, Japan) and Darla Zelenitsky (University of Calgary, Canada), describe eggs and eggshell fragments associated with four ootaxa, two of which are new to science.  The site reveals a hidden diversity of small dinosaurs, particularly non-avian theropods, in the Hyogo region and indicates the area was utilised for nesting by various small dinosaur species in the Early Cretaceous.

The Newly Erected Ootaxa Himeoolithus murakamii the Most Abundant Ootaxa from the Quarry Site

Himeoolithus murakamii a new ootaxa from Japan.

Himeoolithus murakamii egg fossil, high resolution image, line drawing of egg showing elongated shape and life reconstruction.

Picture Credit: University of Tsukuba and Museum of Nature and Human Activities Hyogo Prefecture with life reconstruction by Ayaka Nagate

The Kamitaki Locality

The fossil site, known as the Kamitaki locality lies close to the  Sasayama River in Kamitaki, Sannan-cho, Tamba City,  Hyogo Prefecture.  One horizon has yielded a variety of small vertebrate fossils including frogs and lizards, plus a partial tail from a titanosaur that was formally named and described in 2014 (Tambatitanis amicitiae).  Eggshell fragments are also associated with this part of the site.  However, a horizon some 5.5 to 6.75 metres above the bonebed layer has yielded an astonishing quantity of egg fossils, including a nearly complete egg, several partial eggs and hundreds of eggshell fragments.  The researchers conclude that this horizon represents a nesting area in which a variety of small theropods raised their young.

As a result of this research, two new theropod egg taxa have been named – Himeoolithus murakamii and Subtiliolithus hyogoensis.  Although no skeletal remains of these little dinosaurs have been found, the presence of all the egg fossils suggests that there were numerous different types of small theropod co-existing in this ancient ecosystem.

The Location of the Fossil Site within Hyogo Prefecture

Fossil site location.

The location of the Kamitaki fossil site.

Picture Credit: University of Tsukuba and Museum of Nature and Human Activities Hyogo Prefecture/Cretaceous Research with additional annotation by Everything Dinosaur

The mudstone deposits are thought to have been laid down around 110 million years ago (Albian faunal stage of the Lower Cretaceous) and the palaeoenvironment has been described as floodplain which was subjected to a extremes of seasonality with long periods of very dry conditions punctuated by a very wet season that led to flood events.

The most abundant ootaxon at the quarry, Himeoolithus, is represented by four eggs and over 1300 scattered eggshell fragments. Himeoolithus accounts for over 96% of all the egg fossils associated with this site.  Himeoolithus is the smallest non-avian theropod egg known to date, the scientists estimate that the egg probably weighed about as much as a quail egg (around 9.9 grammes).  It is also a very unusual shape, being elongate with its length 2.25 times its width (length : width ratio 2.25).  The new egg fossil horizon was discovered in 2015 and was mapped and intensively excavated in the winter of 2019.  In total, the egg fossil horizon and the lower Kamitaki Bonebed (Ohyamashimo Formation), have yielded six small theropod ootaxa.

The Stratigraphy of the Kamitaki Locality and Examples of Associated Ootaxa

Stratigraphy of the Kamitaki locality with examples of theropod ootaxa from the site.

The stratigraphy of the Kamitaki locality with examples of theropod ootaxa from the site.  Subtiliolithus hyogoensis is the second of the new ootaxa to be reported in the scientific paper.

Picture Credit: University of Tsukuba and Museum of Nature and Human Activities Hyogo Prefecture/Cretaceous Research

Notable Biodiversity

The ootaxa demonstrate that this ancient habitat was home to a variety of small theropod dinosaurs.  It is likely that many other palaeoenvironments associated with the Lower Cretaceous were also home to a diverse variety of small theropods too, these animals being currently under-represented in the fossil record.

Lead author of the paper, Professor Kohei Tanaka, confirmed that the research team thought that the new egg fossil horizon was a nesting site and the deposit was not the result of a transportation and subsequent burial of egg material from another location:

“Our taphonomic analysis indicated that the nest we found was in situ, not transported and redeposited, because most of the eggshell fragments were positioned concave-up, not concave-down like we see when eggshells are transported.”

The professor added:

“The high diversity of these small theropod eggs makes this one of the most diverse Early Cretaceous egg localities known.  Small theropod skeletal fossils are quite scarce in this area.  Therefore, these fossil eggs provide a useful window into the hidden ecological diversity of dinosaurs in the Early Cretaceous of south-western Japan, as well as into the nesting behaviour of small non-avian theropods.”

Everything Dinosaur acknowledges the assistance of a media release from the University of Tsukuba (Japan), in the compilation of this article.

The scientific paper: “Exceptionally small theropod eggs from the Lower Cretaceous Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan” by
Kohei Tanaka, Darla K. Zelenitsky, François Therrien, Tadahiro Ikeda, Katsuhiro Kubota, Haruo Saegusa, Tomonori Tanaka and Kenji Ikuno published in the journal Cretaceous Research.

1 07, 2020

Guineafowl Contribute to a Better Understanding of Early Jurassic Dinosaur Tracks

By | July 1st, 2020|Adobe CS5, Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Photos/Pictures of Fossils|0 Comments

Guineafowl – Walking Like Dinosaurs

Researchers from Brown University (Rhode Island, USA) and Liverpool John Moores University, have plotted the tracks made by living birds in a bid to reveal new information about how some of the early theropod dinosaurs walked.  In a paper, published today in Biology Letters, the scientists describe how they analysed the locomotion of guineafowl (Order Galliformes) and discovered that dinosaurs may have moved in a similar way, despite the absence of a long, counter-balancing tail in modern Aves.

A X-ray Imagery was Used to Map the Movement of Bones in the Foot of Guineafowl

Modern birds help to interpret dinosaur tracks.

Plotting the foot movements of extant Guineafowl to help interpret Early Jurassic dinosaur footprints.

Picture Credit: Turner et al/Liverpool John Moores University

Retaining Features of Their Non-avian Dinosaur Ancestors

The researchers used X-rays to image and plot the bird tracks in three-dimensions, as the guineafowl walked through a variety of substrates with different properties.  The feet of ground-dwelling birds retain many features of their dinosaurian ancestors, after all, living birds are members of the Order Theropoda along with famous dinosaurs such as Velociraptor and Tyrannosaurus rex.  The locomotion of the guineafowl permits insights into the complex interplay between anatomy, foot motion (kinematics) and substrate.  The results can then be used to assess the tracks made by dinosaurs.

Studying Avian Dinosaur Tracks Provides a Fresh Perspective on Ancient Non-avian Dinosaur Fossil Tracks

Dinosaur footprint.

A dinosaur footprint from the Isle of Skye.  This new study can shed light on ancient dinosaur trackways.

Picture Credit: Scottish National Heritage

A Looping Pattern Below the Ground Identified

Despite substantial step-to-step variability, the foot consistently moves in a looping pattern below the ground, matching the “looping motion” of dinosaur feet captured in the fossil record from the Early Jurassic.

One of the scientific paper’s authors, Dr Peter Falkingham, a senior lecturer in vertebrate biology at Liverpool John Moores University stated:

“Dinosaurs were moving in very similar ways to modern birds even 200 million years- ago (many millions of years before birds evolved), even though they were quite different, having long, muscular tails, for instance.  The similarity of motion, and the similarity of foot shape (three-toed) between dinosaurs 200 million years ago and birds today tells us how successful and versatile that foot has been evolutionarily.”

A Lateral View Showing the Foot Movement and the Looping Pattern of the Toes

The consistant looping pattern.

Plotting the movement of digit III through a variety of substrates revealing the consistent looping pattern identified below the ground.

Picture Credit: Turner et al/Liverpool John Moores University

The scientists report that when a foot sinks into the sediment, a) the sub-surface motion gets recorded and b) the foot has to get out again.  Where it exits relative to where it went in can tell us how the foot was moving.  Despite substantial kinematic variation, the foot consistently moves in a looping pattern below ground.  As the foot sinks and then withdraws, the claws of the three main toes create entry and exit paths in different locations.  Sampling these paths at incremental horizons captures two-dimensional features just as fossil tracks do, allowing depth-based zones to be characterised by the presence and relative position of digit impressions.

Analysis of Early Jurassic Theropod Tracks

Analysis of Early Jurassic dinosaur tracks.

Exit features and depth zone attribution in Early Jurassic theropod fossil tracks.

Picture Credit: Turner et al/Liverpool John Moores University

When the fossilised tracks of a small, theropod dinosaur were examined, the scientists found an equivalent looping response to soft substrates.  This study, comparing extant and extinct track-makers provides important new data on substrate properties and will assist with the interpretation of dinosaur tracks providing a fresh perspective on these important trace fossils.

This paper provides a new theoretical framework and vocabulary for describing relative positions of entry and exit traces, offering a new way of studying fossil footprints.

For a related article where researchers from Brown University in collaboration with international colleagues conducted earlier research on dinosaur footprints using guineafowl: Walking with Dinosaurs – the Birth of a Dinosaur Footprint.

Everything Dinosaur acknowledges the assistance of Liverpool John Moores University in the compilation of this article.

The scientific paper: “It’s in the loop: shared sub-surface foot kinematics in birds and other dinosaurs shed light on a new dimension of fossil track diversity” by Morgan L. Turner, Peter L. Falkingham and Stephen M. Gatesy published in Biology Letters.

26 06, 2020

New Study Suggests “Marsupial Sabre-tooth” Was a Scavenger

By | June 26th, 2020|Dinosaur and Prehistoric Animal News Stories, Main Page, Photos/Pictures of Fossils|0 Comments

Thylacosmilus atrox – A Specialist Scavenger of Large Carcases

Huge canines in predatory mammals has developed on several occasions within the Class Mammalia.  Indeed, enormous sabre-like teeth can be found in the fossil record long before placentals and marsupials evolved, a case in point being the gorgonopsids of the Late Permian.  However, when the various types of mammal that developed such over-sized front teeth in their upper jaws are compared, it seems that not all sabre-toothed mammals were the ferocious predators that palaeontologists thought them to be.

Writing in the open access, on-line journal “PeerJ” researchers from the University of Birmingham, Bristol University and the Vanderbilt University (Nashville, Tennessee), conclude that the South American “marsupial sabre-tooth”, Thylacosmilus atrox may have been a scavenger, using its huge upper canines to eviscerate carcases before removing internal organs with a large tongue.

The South American Marsupial Thylacosmilus may not have been an Active Predator

Comparing the skulls of Thylacosmilus and Smilodon.

Skulls and life reconstructions of the marsupial sabre-tooth Thylacosmilus atrox (left) and the sabre-tooth cat Smilodon fatalis (right).  Examples of convergent evolution in unrelated animals, but a new study suggests that T. atrox may have behaved very differently, preferring to consume carcases rather than to actively hunt.

Picture Credit: Stephan Lautenschlager/University of Birmingham

Thylacosmilus atrox – A Very Peculiar Carnivore

Thylacosmilus (pronounced Thy-lak-o-smile-us), is a member of the extinct Order Sparassodonta and only distantly related to the marsupials of Australia.  Its fossils come mostly from northern Argentina, and it lived during the Late Miocene and Pliocene Epochs.  Described as a jaguar-sized marsupial with huge maxillary canines, bite force studies had indicated that, for its size, it had a relatively weak bite, much lower than modern, large felids.

Whilst most palaeontologists would agree that the placental genus Smilodon was an active predator, albeit with a different method of dispatching victims when compared to extant “big cats”.  This new research proposes that Thylacosmilus, in contrast, was not a fearsome hunter.  Skull comparisons and an analysis of fossil teeth indicate that, Thylacosmilus, with its generally longer and more slender upper canines, was not able to stab prey that effectively when compared to the likes of Smilodon fatalis.  What it lacked in penetration it made up for in pulling power, with a strong “pull-back” action using its jaws to rip apart the bodies of dead animals.

Dr Stephan Lautenschlager (University of Birmingham) explained:

“We found there was a difference in behaviour between the two species: Thylacosmilus’ skull and canines are weaker in a stabbing action than those of Smilodon but stronger in a ‘pull-back’ type of action.  This suggests Thylacosmilus was not using its canines to kill with, but to open carcasses.  We suspect it was some sort of specialised scavenger, using those canines to open carcasses and perhaps using a big tongue to help extract the innards.”

Convergent Evolution of a Sabre-toothed Skull

Convergent evolution of the sabre-toothed skull shape.

Convergent evolution.  A sabre-toothed skull has developed on several occasions in different types of tetrapod.  Note the presence of incisors in B, C and D but they are absent in the Thylacosmilus skull (A).

Picture Credit: Everything Dinosaur/C. R. Prothero/D. R. Prothero

The image (above), shows (A) the skull of Thylacosmilus, (B) the creodont Machaeroides, (C) Hoplophoneus, a member of the Nimravidae from North America and (D) the skull of the sabre-toothed cat Smilodon.  This is an example of convergent evolution – the similar body plan has evolved independently in several not closely related species.

The scientists discovered that the maxillary canines of Thylacosmilus were different from the teeth of other sabre-toothed mammals.  They were more triangular in shape, like a claw rather than flat like the blade of a knife.

Co-author, Dr Christine Janis (University of Bristol) added:

“The animal has impressive canines, but if you look at the whole picture of its anatomy, lots of things simply don’t add up.  It lacks incisors, which big cats today use to get meat off the bone and its lower jaws were not fused together.”

A Life Reconstruction of Thylacosmilus atrox

Thylacosmilus life reconstruction.

A life reconstruction of Thylacosmilus atrox from the Late Miocene/Pliocene of South America.  Note scale bar equals 10 cm.

Picture Credit: Everything Dinosaur

A Puzzling Combination of Anatomical Traits

As well as lacking incisors, the researchers found that the molars of Thylacosmilus were proportionately small and not worn along their sides as expected in an animal that fed on meat.

Explaining the significance of this finding, Dr Larisa DeSantis (Vanderbilt University) commented:

“The molars tend to wear flat from the top, rather like you see in a bone crusher.  But if you examine the detailed microwear on tooth surfaces, it’s clear that it was eating soft food.  Its wear is most similar to that of cheetahs which eat from fresh carcasses and suggests an even softer diet than fed to captive lions.  Thylacosmilus was not a bone-crusher and may have instead specialised on internal organs.”

Far from being a sparassodont version of Smilodon, Thylacosmilus probably filled a very different niche in the ecosystem.  In addition, to the differences in the skull and the teeth, Thylacosmilus was relatively short-legged and lacked a very flexible spine.  These characteristics along with an absence of retractile claws suggests that Thylacosmilus would have struggled to pursue all but the slowest of prey and would have had difficulty pouncing and holding on to victims.

Everything Dinosaur acknowledges the assistance of a media release from the University of Birmingham in the compilation of this article.

The scientific paper: “Thylacosmilus was not a marsupial “saber-tooth predator’ ” by Christine Janis, Borja Figueirido, Larisa DeSantis and Stephan Lautenschlager published in PeerJ.

25 06, 2020

Is this the Demise of a Duck-billed Dinosaur?

By | June 25th, 2020|Adobe CS5, Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

Taxonomic status of Ugrunaaluk kuukpikensis is Challenged

Five years ago, Everything Dinosaur reported the naming of a new species of duck-billed dinosaur that lived well inside the Arctic circle during the Late Cretaceous.  The dinosaur was named Ugrunaaluk kuukpikensis (pronounced 00-grew-na-luck kook-pik-en-sis).  At the time of publication, Ugrunaaluk was thought to be closely related to Edmontosaurus.  Since then, there has been quite a debate regarding the taxonomic validity of Ugrunaaluk.  In the latest twist of a tale set in prehistoric polar latitudes, researchers writing in PLOS One conclude that this Arctic dinosaur is most probably a species of Edmontosaurus.

The Taxonomic Validity of the Arctic Hadrosaur Ugrunaaluk kuukpikensis is Challenged

Ugrunaaluk illustrated.

The taxonomic validity of Ugrunaaluk kuukpikensis is controversial as this species was erected based on the study of the bones of immature, not fully adult individuals.

Picture Credit: James Havens

The Prince Creek Formation Specimens

Duck-billed dinosaur fossils from the Liscomb Bonebed (Prince Creek Formation, North Slope, Alaska), were the first dinosaur bones discovered from the Arctic.  When originally assessed, it was proposed that these hadrosaurids were Edmontosaurus, members of the sub-clade Hadrosaurinae.  In 2015, a scientific paper was published that proposed the closely related species Ugrunaaluk kuukpikensis.  However, the taxonomic status of this material is problematical.  The fossils associated with the Liscomb Bonebed site represent immature, sub-adults and as such many of the anatomical traits used to characterise U. kuukpikensis, may reflect the developmental age of the individual and the shape of the bones may have altered as the dinosaur grew and matured.

A Model of an Adult Edmontosaurus

Wild Safari Prehistoric World Emontosaurus model.

The new for 2020 Wild Safari Prehistoric World Edmontosaurus dinosaur model.

Picture Credit: Everything Dinosaur

Looking at the Evidence

In this newly published paper, researchers from Okayama University of Science (Japan), the Perot Museum of Nature and Science (Texas) and Hokkaido University Museum (Japan), re-examined the skull bones from the Liscomb Bonebed and determined that the traits used to distinguish these Arctic fossils from those ascribed to Edmontosaurus were questionable.  In 2015, the scientific paper describing Ugrunaaluk kuukpikensis (Mori et al), proposed eight diagnostic characters for this new species.  Among the eight characters identified, three were proposed to distinguish Ugrunaaluk kuukpikensis from the Edmontosaurus genus.  Four of these eight characters distinguished Ugrunaaluk from Edmontosaurus annectens, which is known from Maastrichtian aged deposits from Montana and one character to distinguish Ugrunaaluk from the geologically older Edmontosaurus regalis, fossils of which are found in Canada.

It is likely that the shape of the skull of Edmontosaurus changed as it grew.  The bones forming the skull would also undergo change in shape and size, because of this, any taxon erected solely based on the shape of skull bones from young animals is questionable.  In this newly published paper, the researchers, which include Ryuji Takasaki, a researcher at the Okayama University of Science and Professor Yoshitsugu Kobayashi (Hokkaido University Museum), conclude that the Liscomb Bonebed hadrosaurid material should be ascribed to Edmontosaurus.

Comparing the Liscomb Bonebed Fossil Material with Known Edmontosaurus Skull Bones

Determining the identify of Alaskan duck-bills at the genus level.

A study of skull bones from the Prince Creek Formation (Alaska), suggests that the immature individual duck-billed dinosaurs found at this site are from the Edmontosaurus genus and that Ugrunaaluk kuukpikensis should be regarded as nomen dubium.

Picture Credit: PLOS One (Takasaki et al)

If the Arctic fossils are ascribed to Edmontosaurus, then this suggests that Edmontosaurus was geographically very widespread during the Late Cretaceous with fossils associated with this genus found in the northern states of the USA, Canada and Alaska.  The scientists consider that the Prince Creek Formation Edmontosaurus should be regarded as Edmontosaurus sp. until further discoveries of mature hadrosaurines from the Prince Creek Formation Bonebed and/or equivalently juvenile Edmontosaurus specimens from the lower latitudes allow direct comparisons.

Furthermore, if Edmontosaurus is associated with the very far north of Laramidia, this has implications for the ancestry of Late Cretaceous Asian hadrosaurids.  A number of duck-billed dinosaurs found in Asia may represent descendants of the Edmontosaurini lineage that migrated from Laramidia into Asia.

The Distribution of Edmontosaurus sp.

The distribution of Edmontosaurus.

The researchers suggest that Edmontosaurus was geographically very widespread occupying much of northern Laramidia and many of the Late Cretaceous Asian hadrosaurs may have been descended from the Edmontosaurus lineage.

Picture Credit: Scientific Reports with additional annotation by Everything Dinosaur

The map (above), illustrates the distribution of Edmontosaurus as proposed by the research paper.  There is some evidence to suggest that Edmontosaurus preferred coastal environments and that this genus was widely distributed across northern Laramidia during the Late Cretaceous.  If this assessment proves to be correct, Edmontosaurus had a geographical distribution spanning about 4,000 kilometres from north to south in North America.

The scientists speculate that the ancestor of Asian hadrosaurids such as Kamuysaurus migrated from North America.

Japanese Hadrosaurs Had North American Roots

Professor Kobayashi commented:

“It is possible that the ancestor of Kamuysaurus that adapted to the environment at the northern limit of the species’ habitat crossed from North America to Asia and eventually evolved to Kamuysaurus.”

To read Everything Dinosaur’s article on the naming of Kamuysaurus: Famous Fossils from Japan are Named.

If the Prince Creek Formation hadrosaurs are established as members of the Edmontosaurus genus, then they could represent a new species of Edmontosaurus.  The large latitudinal distribution of this taxon could be re-established, the latitudinal range for Edmontosaurus would extend from about 40 degrees north to at least 70 degrees north.  The researchers conclude that despite the extensive geographical and temporal range of this taxon, the morphological disparity within different species associated with this genus is relatively small when compared to other members of the Hadrosaurinae.  The lack of any substantial anatomical differences between widely distributed species could reflect the relatively low latitudinal temperature gradient during the Late Cretaceous compared to today.  A relatively benign and unchanging environment would not have imposed significant pressure on species to evolve in order to adapt to new conditions.

To read our original article on the naming of Ugrunaaluk kuukpikensis: The Latest Dinosaur from Polar Latitudes.

Our article published in 2017, following a study of Edmontosaurus cranial material that also cast doubt on the taxonomic validity of U. kuukpikensisStudying the Skulls – Getting our Heads Around Edmontosaurus.

The scientific paper: “Re-examination of the cranial osteology of the Arctic Alaskan hadrosaurine with implications for its taxonomic status” by Ryuji Takasaki, Anthony R. Fiorillo, Ronald S. Tykoski and Yoshitsugu Kobayashi published in PLOS One.

22 06, 2020

Getting To Grips with the Jaws of Clevosaurus

By | June 22nd, 2020|Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Palaeontological articles, Photos|0 Comments

Did the Ancient Rhynchocephalians Out Compete Early Mammaliaforms?

Had you been around south Wales or south-western England some 200 million years ago, you would most probably have required a boat to get about.  The area around the Bristol channel today (where you still need a boat), during the Early Jurassic, consisted of a series of small islands surrounded by a warm, shallow tropical sea.  This archipelago (referred to as the Mendip Archipelago), was home to small dinosaurs and also to a variety of other reptiles including five species of Clevosaurus.  Clevosaurs are members of an ancient Order of reptiles called the Rhynchocephalia.  A new study published in the journal of the Palaeontological Association, suggests that these hardy reptiles may have filled the roles performed by early mammaliaforms on some of these small islands.

In addition, where Clevosaurus fossils are found, mammaliaform fossils tend to be lacking, so did these two types of tetrapod compete with each other for the same food resources?  This new research carried out by members of the School of Earth Sciences (University of Bristol), indicates that this could have been the case.  The scientists examined the biomechanics of the skulls of these lizard-like reptiles in a bid to gain an understanding of the likely diets of the species studied.  Different species of Clevosaur had different bite forces, which hints at a degree of niche partitioning within this genus.  This may explain why five different species were able to exist within a relatively small area.

Different Species of Clevosaurus may have had Slightly Different Diets

Niche partitioning within the Cleovosaurus genus.

Clevosaurus feeding habits – niche partitioning in Early Jurassic Clevosaurs.  The illustration shows two species of Clevosaurus associated with the Mendip Archipelago feeding on different types of insect prey.  Clevosaurus hudsoni feeding on a hard-shelled beetle, whilst (bottom), Clevosaurus cambrica consumes a softer insect without a carapace.

Picture Credit: Sofia Chambi-Trowell (University of Bristol)

Computerised Tomography Used to Analyse Skull Biomechanics

PhD student, Sofia Chambi-Trowell, from Bristol’s School of Earth Sciences, worked on CT scanned skulls of ancient rhynchocephalians and found differences in their jaws and teeth.

The student commented:

“I looked at skulls of two closely related species of Clevosaurus, Clevosaurus hudsoni and the slightly smaller Clevosaurus cambrica – the first one came from a limestone quarry near Bristol and the other one from South Wales.  Clevosaurus was a lizard-like reptile, but its teeth occluded precisely, meaning they fit together perfectly when it was feeding.  But what was it eating?”

Rhynochocephalians (beak heads), were a very successful, globally distributed group of diapsid reptiles that flourished during the Mesozoic.  The Tuatara (Sphenodon punctatus), is the only living member of this order, the Tuatara is confined to small islands off the coast of New Zealand and some specially designated and protected release sites on North Island.

Whilst studying the extant Tuatara is of great assistance to palaeontologists, expanding any findings to extinct members of this group is challenging.  Likewise, identifying the feeding habits of long extinct species is equally difficult.  However, finite element analysis conducted on two, near complete, three-dimensionally preserved skulls (Clevosaurus hudsoni and Clevosaurus cambrica respectively), provided bite force data and an assessment of jaw biometrics.  From this information, the potential feeding preferences of these two closely related reptiles could be inferred.

The Last of the Rhynochocephalians – A Tuatara

Tuatara.

A Tuatara.  It may resemble a lizard but the Tuatara is the last living example of the Order Rhynchocephalia.

Picture Credit: Everything Dinosaur

The researchers found that Clevosaurus had bite forces and pressures sufficient to break down beetles, and even small vertebrates easily, suggesting they could have taken the same prey items as the early mammals on the islands.  Calculations of muscle forces show that Clevosaurus hudsoni could take larger and tougher prey than the more slender jaws of Clevosaurus cambrica.

Co-author of the scientific paper and the project supervisor, Professor Emily Rayfield (University of Bristol) stated:

“We wanted to know how Clevosaurus interacted with the world’s first mammals, which lived on the Bristol islands at the same time.  I had studied their jaw mechanics a few years ago and found they had similar diets and that some fed on tough insects, others on softer insects.”

This study, having identified difference in jaw mechanics between different species of Clevosaurus provides a hypothesis as to why several species of Clevosaurus could co-exist in the same habitat.  Niche partitioning could have been taking place with each species avoiding competition by specialising in hunting and eating different types of prey.  As the data generated in this study is roughly comparable to what is known about the jaws of early mammaliaforms, it raises the intriguing prospect that the jaws may have been functionally similar and thus rhynochocephalians and early mammaliaforms were in direct competition with each other for food resources.

Everything Dinosaur acknowledges the assistance of a media release from the University of Bristol in the compilation of this article.

The scientific paper: “Biomechanical properties of the jaws of two species of Clevosaurus and a reanalysis of rhynchocephalian dentary morphospace” by Sofia A. V. Chambi‐Trowell, David I. Whiteside, Michael J. Benton and Emily J. Rayfield published in Palaeontology.

20 06, 2020

Fossil “Stick” Proves to be New Species of Ancient Plant

By | June 20th, 2020|Dinosaur and Prehistoric Animal News Stories, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

Keraphyton mawsoniae – Late Devonian Fern-like Plant

A fossil found more than fifty years ago and described as a “fossilised stick” has proved to be a new species of Late Devonian plant and it is helping scientists to better understand the flora of the landmass of Gondwana.  The specimen measures a little over 9 cm in length, with a width across its ribbed surface of around 2 cm.  It was found by amateur geologist John Irving whilst exploring the banks of the Manilla River in Barraba (New South Wales, Australia), after a period of extensive flooding.  It remained unstudied in the fossil collection of the geological survey of New South Wales for five decades until it was despatched to France as part of a wider study to map plant evolution.

The Fossil and Cross-sectional Slices (K. mawsoniae)

Keraphyton mawsoniae fossil.

The newly described Keraphyton mawsoniae a fern-like land plant from the Late Devonian of Australia.  Scale bar in (B) equals 2 mm and scale bars in C-H equal 500 μm.

Picture Credit: Champreux et al (PeerJ)

The picture (above), shows (A) the fossil specimen before preparation, (B) a general view of the stem system shown in cross-section, with (C-H) highly magnified areas showing the internal structure of the plant.  The fossil is from the Mandowa Mudstone Formation (Upper Devonian) and it is believed to represent a plant stem.

A Very Rare Fossil Discovery

During the Middle to Late Devonian land plants were becoming larger, more complex and diverse.  Major groups of plants that were to dominate the flora of the Mesozoic evolved and the first widespread forests and land-based ecosystems became established.  Well-preserved plant fossils from this time in Earth’s history are exceptionally rare.  Plants related to ferns and other types that produce seeds (Euphyllophytina), became more specious during this time in Earth’s history, fossils of fern-like plants are known from the northern hemisphere but the Gondwanan record is extremely sparse.

The French laboratory of Botany and Modelling of Plant Architecture and Vegetation (AMAP) in Montpellier has been collating data on early plant species from the Devonian/Carboniferous of Australia and Antoine Champreux, studied the fossil specimen as part of his Master’s Degree before completing his research whilst a PhD student at Flinders University in South Australia.

Gondwana During the Late Devonian (Position of Australia)

Map showing the location of the Barraba fossil find in relation to Gondwana.

A map showing the location of Australia in relation to the rest of Gondwana during the Middle to Late Devonian.  The position of the fossil discovery is highlighted.

Picture Credit: University of Witwatersrand with additional annotation from Everything Dinosaur

Antoine commented:

“It’s nothing much to look at – just a fossilised stick – but it’s far more interesting once we cut it and had a look inside.  The anatomy is preserved, meaning that we can still observe the walls of million-year-old cells.  We compared the plant with other plants from the same period based on its anatomy only, which provide a lot of information.”

The research team found that this early land plant represents a new genus of plant, sharing some similarities with modern ferns and horsetails.

Antoine added:

“It is an extraordinary discovery, since such exquisitely-preserved fossils from this period are extremely rare.  We named the genus Keraphyton (like the horn plant in Greek), and the species Keraphyton mawsoniae, in honour of our partner Professor Ruth Mawson, a distinguished Australian palaeontologist who died in 2019.”

To read about a bizarre, giant predatory marine worm from the Devonian: Monster Worm of the Devonian.

The scientific paper: “Keraphyton gen. nov., a new Late Devonian fern-like plant from Australia” by Antoine Champreux​, Brigitte Meyer-Berthaud, and Anne-Laure Decombeix published in the open access journal PeerJ.

19 06, 2020

The First Dinosaur Eggs were Soft

By | June 19th, 2020|Adobe CS5, Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

The First Dinosaur Eggs were Soft like a Turtle’s

The scientific paper has a succinct title, but the repercussions for vertebrate palaeontologists are seismic.  This week has seen the publication in the journal Nature of a paper entitled “The first dinosaur egg was soft”.  Palaeontologists have inferred and implied a great deal about dinosaur reproduction, but the assumption had been that, just like living archosaurs today, the crocodiles and birds, dinosaurs laid hard-shelled eggs.  Dr Mark Norell (American Museum of Natural History) and his co-authors propose that calcified, hard eggshells were not the “default setting” for the Dinosauria, the first dinosaur eggs were soft-shelled like those of a turtle or a snake.  In addition, the researchers conclude that hard-shelled, calcified eggs evolved at least three times independently within the Dinosauria.

Protoceratops Protects a Nest from a Marauding Oviraptorosaur

Protoceratops defends its nest from Oviraptor.

Protoceratops confronts Oviraptor- the egg thief.  An inaccurate portrayal of both the Oviraptorosaur and Protoceratops, but until now, not many had questioned the accuracy of those hard-shelled eggs.

Picture Credit: Everything Dinosaur (from Zalinger)

Unscrambling Dinosaur Eggs

The research led by the American Museum of Natural History in collaboration with colleagues from Yale University, Universidad de Buenos Aires (Argentina), Montana State University, University of Calgary (Canada) and the Museo Paleontológico Egidio Feruglio, Trelew, (Argentina), applied a series of sophisticated geochemical techniques to analyse the eggs of two different non-avian dinosaurs.  They discovered that the eggs resembled those of extant turtles in their composition, microstructure and mechanical properties.

Commenting on the significance of this research, corresponding author Mark Norrell stated:

“The assumption has always been that the ancestral dinosaur egg was hard-shelled.  Over the last 20 years, we’ve found dinosaur eggs around the world.  But for the most part, they only represent three groups – theropod dinosaurs, which includes modern birds, advanced hadrosaurs like the duck-billed dinosaurs and advanced sauropods, the long-necked dinosaurs.  At the same time, we’ve found thousands of skeletal remains of ceratopsian dinosaurs, but almost none of their eggs.  So why weren’t their eggs preserved?  My guess – and what we ended up proving through this study, is that they were soft-shelled.”

Ceratopsian Eggs Were Probably Soft-shelled and This Explains their Rarity in the Fossil Record

The leathery, soft shells of turtle eggs.

The leathery, soft shell of the common snapping turtle (Chelydra serpentina). The eggs of the first dinosaurs were probably very similar.

Picture Credit: Jasmina Wiemann (Yale University)

Calcified Eggshells – An Evolutionary Hedge Against Environmental Stress

The amniotes, a group of tetrapods that includes the mammals, birds and the reptiles all produce eggs with an inner membrane, known as the amnion.  This inner membrane helps to prevent the embryo from drying out.  Some amniotes such as many turtles and squamates (lizards and snakes), lay soft-shelled, leathery eggs, whilst others such as birds and crocodilians produce eggs with a heavily calcified shell.  It is thought that these calcified eggs help to protect the developing embryos inside the eggs from environmental stresses, thus giving the calcified egg layers an evolutionary advantage.  The evolution of the hard-shelled egg is seen as a major step in the global dominance of the amniotes, it leading to greater reproductive success for those members of this group that developed this trait.

The Eggs from a Member of the Theropoda (Domestic Chicken)

Chicken eggs (theropod dinosaur eggs).

Calcified, hard-shelled eggs such as these from a theropod (domestic chicken) were thought to be representative of all Dinosauria eggs.

Picture Credit: Everything Dinosaur

The Fossil Record Shows Bias in Favour of Calcified Eggs

Soft-shelled eggs rarely preserve in the fossil record.  It is very likely that ancient turtles laid soft-shelled eggs, just like their modern counterparts, but such evidence is hard to find in the fossil record.  The same could be inferred for other amniotes, they too might have laid soft-shelled eggs but such evidence would be very difficult to find.  Therefore, studying the transition from soft-shelled eggs to biomineralised, calcified eggs is a substantial challenge for palaeontologists.  As birds and extant crocodilians lay hard-shelled eggs, this type of eggshell has been inferred for all the non-avian dinosaurs.

Protoceratops and Mussaurus

The research team undertook an intensive study of two fossil egg specimens appertaining to two very different dinosaurs – the neoceratopsian Protoceratops (P. andrewsi), known from the Upper Cretaceous Djadokhta Formation exposed in the Gobi Desert of Mongolia and Mussaurus (M. patagonicus) from the Upper Triassic-aged El Tranquilo Formation located in southern Argentina.   The beautifully preserved Protoceratops fossils include a clutch of at least a dozen eggs with embryos, half of which preserve nearly complete skeletons.  Most of the Protoceratops embryos are preserved in a posture in which their vertebrae and limbs are flexed, synonymous with a posture adopted by animals still inside their eggs.

The Protoceratops (P. andrewsi) Nest Fossil

Protoceratops Fossil Nest

The beautifully preserved nest with embryos of Protoceratops andrewsi.

Picture Credit: M. Ellison (American Museum of Natural History)

Some of the skeletal material is obscured by a black and white egg-shaped halo.  In contrast, two potentially recently hatched Protoceratops in the fossil specimen are largely free of this mineral halo.  The research team analysed tiny slices of this halo material using a petrographic microscope.  Further analysis was undertaken using Raman microspectroscopy, where light scattered by a high powered laser provides information on the molecular composition of a sample.  The scientists discovered chemically altered trace residues of the proteinaceous eggshell membrane that makes up the innermost layer of the eggshell of extant archosaurs.  Almost identical results were observed when the Mussaurus specimen was examined.

The Fossilised Remains of the Mussaurus Egg

Mussaurus fossil egg.

The fossilised remains of a Mussaurus.

Picture Credit: Diego Pol (Museo Paleontológico Egidio Feruglio, CONICET)

Comparing Biomineralisation Residue Signatures

The research team which included Diego Pol (Museo Paleontológico Egidio Feruglio CONICET), Darla Zelenitsky (University of Calgary) and Jasmina Wiemann (Yale University) then compared the data from the fossil material to eggshell data from other living amniotes such as turtles, birds, lizards and crocodiles.  They determined that the Mussaurus and the Protoceratops eggs were non-biomineralised and therefore they would have resembled the leathery, soft-shelled eggs of living turtles.

Graduate student Jasmina Wiemann explained:

“It’s an exceptional claim, so we need exceptional data.  We had to come up with a brand-new proxy to be sure that what we were seeing was how the eggs were in life and not just the result of some strange fossilisation effect.  We now have a new method that can be applied to all other sorts of questions, as well as unambiguous evidence that compliments the morphological and histological case for soft-shelled eggs in these animals.”

Creating a “Supertree” to Track Eggshell Evolution

In total, data from 112 extinct and living amniotes was analysed by the research team.  This enabled them to build a “supertree” to track the phylogeny of egg-shell evolution over geological time.  They concluded that the ancestors of the Dinosauria probably produced an egg that lacked a calcified layer, that these animals laid soft-shelled eggs and that the first, true dinosaurs had the same type of egg.  This element of the research suggests that calcified, hard-shelled eggs evolved independently at least three times throughout the Mesozoic era in the Dinosauria, explaining the bias towards eggshells of derived dinosaurs in the fossil record.  The calcified layer of eggshell evolved independently in ornithischian, sauropodomorph and theropod dinosaurs.

Co-author Matteo Fabbri (Yale University) added:

“From an evolutionary perspective this makes much more sense than previous hypotheses, since we’ve known for a while that the ancestral egg of all amniotes was soft.  From our study, we can also now say that the earliest archosaurs, the group that includes dinosaurs, crocodiles and pterosaurs had soft eggs.  Up to this point, people just got stuck using the extant archosaurs – crocodiles and birds to understand dinosaurs.”

Implications for the Pterosauria

This research has implications for the Pterosauria clade.  Pterosaur eggs are exceptionally rare, a fossil of the wukongopterid (Darwinopterus modularis), reveals the outline of a single egg inside the body cavity. The egg confirms that the pterosaur fossil represents a female that was gravid when she died.  More significantly, scientific papers detailing extensive fossil remains associated with the debris from a nesting colony of the pterosaur Hamipterus tianshanensis have been published and the three-dimensionally preserved eggs do resemble the leathery soft-shelled eggs now associated with members of the Dinosauria.

Fossilised Eggs of Hamipterus tianshanensis – Could They have the Same Biomineralisation Profile of Soft-shelled Dinosaur Eggs?

Egg fossils (Pterosaur).

Pterosaur egg fossils (Hamipterus tianshanensis).

Picture Credit: Xinhua/Wang Xiaolin

To read our 2017 blog post about the Hamipterus colony: Hamipterus Nesting Ground Discovery.

To read our recent article about the discovery of a giant soft-shelled egg associated with a marine reptile: It’s Not a Deflated Football, it’s Probably an Egg from a Mosasaur.

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

The scientific paper: “The first dinosaur egg was soft” by Mark A. Norell, Jasmina Wiemann, Matteo Fabbri, Congyu Yu, Claudia A. Marsicano, Anita Moore-Nall, David J. Varricchio, Diego Pol and Darla K. Zelenitsky published in the journal Nature.

18 06, 2020

Tracking Down Australia’s Big Carnivorous Dinosaurs

By | June 18th, 2020|Adobe CS5, Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Photos/Pictures of Fossils|0 Comments

Tracking Down Australia’s Largest Ever Terrestrial Predator

Scientists from the University of Queensland have conducted a review of the data associated with a series of Jurassic-aged theropod dinosaur prints preserved on the ceilings of coal mine galleries deep underground.  They conclude that some of these prints represent predatory dinosaurs around ten metres in length, making these trace fossils evidence of the largest terrestrial carnivores ever to have lived in Australia.

A Life Reconstruction of a Large Carnosaur Compared to a Person and a Silhouette of Tyrannosaurus rex

Calculating the size of a theropod dinosaur from its tracks.

By measuring the length of a print the approximate hip height of the track-maker can be calculated.  In this case, the largest theropod tracks indicate a hip height of 3 metres.  This suggests an overall length of around 10 metres.

Picture Credit: Dr Anthony Romilio et al (University of Queensland)

Australia’s Big Carnivorous Dinosaurs

Dinosaur tracks from the coal-mines from Rosewood near Ipswich, and Oakey just north of Toowoomba in southern Queensland have been known about for decades.  The prints and trackways are located in sediments directly above coal seams and give the impression of dinosaurs defying gravity by walking on the ceiling.  The explanation for the trace fossils is rather more mundane but still quite remarkable when the age of these tracks (estimated at around 151 to 161 million years old) is considered.

Large Theropods (Carnosauria) Left the Prints When Walking Across Swampy Ground

T. gurneyi.

Trace fossils from theropod dinosaurs indicate that giant carnosaurs roamed southern Queensland during the Middle to Late Jurassic (Callovian to Tithonian).

Picture Credit:  Sergey Krasovskiy

How Were These Trace Fossils Formed?

Tridactyl prints made by theropod dinosaurs onto mats of compressed swamp-vegetation became covered with silt, mud and sand from flood-water.  Over millions of years the remains of the swamp vegetation became compressed and turned into coal, which was then excavated by Australian miners deep underground during the 19th and 20th centuries.  As the coal seams were removed, these left exposed on the ceiling of the mine galleries, the inlaid 160 million-year-old dinosaur tracks.  Many of the mines exploiting the Walloon Coal Measures from the Clarence-Morton Basin have been closed, with their access shafts filled in.  Access to many of these prints in the mines is no longer possible, so the researchers relied on previous research and unpublished archival photographs from which they were able to create three-dimensional images of some of the individual prints.

Photograph and False-Colour 3-D Map of a Tridactyl Print from the Oakey Coal Mine

Photograph and false-colour image of a theropod print.

One of the dinosaur footprints from the Oakey mine (photograph on the right and corresponding false-colour deep map on the left).

Picture Credit: Dr Anthony Romilio et al (University of Queensland)

The three-toed (tridactyl), prints with claw marks, typical of theropod dinosaurs, dominate the tracksites.  The size of the prints varies, most of the prints measure between 30 to 50 cm long.  However, a number of trace fossils from the eleven track-bearing sites analysed in this study, are much bigger.  The largest measures 79 cm in length, the biggest carnivorous dinosaur footprint discovered to date in Australia.

Footprint size can be used to calculate an approximate hip-height of the theropod dinosaur that made the track.  Once a hip-height has been estimated, then palaeontologists can quickly work out just how big that dinosaur actually was.

Lead author of the research, published in Historical Biology, Dr Dr Anthony Romilio explained:

“Most of these footprints are around 50 to 60 centimetres in length, with some of the really huge tracks measuring nearly 80 centimetres.  We estimate these tracks were made by large-bodied carnivorous dinosaurs, some of which were up to three metres high at the hips and probably around 10 metres long.  To put that into perspective, T. rex got to about 3.25 metres at the hips and attained lengths of 12 to 13 metres long, but it didn’t appear until 90 million years after our Queensland giants.”

Examining the Theropod Prints from the Walloon Coal Measures

False colour images and an assessment of theropod size

A variety of different sized theropod tracks were identified with the largest 79 cm long.

Picture Credit: Dr Anthony Romilio et al (University of Queensland)

Intriguingly, all the tracksites studied are dominated by the three-toed prints of theropods.  These theropod dominated trace fossil assemblages are unique among Australian dinosaur tracksites.  In the absence of any contemporaneous dinosaur body-fossils, these prints and tracks preserved on the ceilings of the coal mines provide palaeontologists with important data helping them to fill in gaps about the composition of Middle and Late Jurassic Australian dinosaur fauna.

What Type of Meat-eating Dinosaur Made the Tracks?

The strata in which the tracks are preserved span around ten million years or so (Callovian to Tithonian faunal stages of the Jurassic).  Palaeontologists are aware that during this time there was a change in the types of large, carnivorous dinosaurs that dominated terrestrial ecosystems.  The fossil record, although far from complete, suggests a decline in the Megalosauroidea during the Middle Jurassic and the rise to prominence of the Avetheropoda clade consisting of the Allosauroidea and the Coelurosauria.

A Faunal Turnover in Theropod Dinosaurs During the Jurassic

Theropod faunal turnover in the Jurassic.

Theropod faunal turnover (taxa estimated to be <250 kgs) the rise of the Allosauroidea.  It is likely that the type of dinosaur(s) that made the Queensland ceiling prints will never be known.

Picture Credit: Palaeontologica Electronica

However, the taxonomy of the Theropoda, even at the superfamily level is controversial and open to debate.  For example, the Carnosauria clade had been redefined, constraining it to the allosaurs and their closest relatives.  In 2019, a new basal allosauroid from the Middle Jurassic of Argentina was described Asfaltovenator (A. vialidadi).  Asfaltovenator had a combination of primitive and more derived anatomical features.  As a result, a new phylogenetic analysis extended the Carnosauria clade to once again include the Megalosauroidea.

A Life Reconstruction of Asfaltovenator from the Middle Jurassic of Argentina

Asfaltovenator illustration.

Asfaltovenator life reconstruction.  The scientific description of this carnivorous dinosaur led to a reassessment of the components of the Carnosauria clade.

Picture Credit: Gabriel Lio/Conicet

In short, the researchers are uncertain as to what types of meat-eating dinosaur left the prints.  In the absence of any other fossil evidence, we shall probably never know.

To read a related article examining three-toed tracks from the ceiling of the Australian Mount Morgan caves complex preserved in Lower Jurassic deposits: Mystery of Dinosaur Prints on Cave Ceiling Solved.

The scientific paper: “Footprints of large theropod dinosaurs in the Middle–Upper Jurassic (lower Callovian–lower Tithonian) Walloon Coal Measures of southern Queensland, Australia” by Anthony Romilio, Steven W. Salisbury and Andréas Jannel published in Historical Biology.

17 06, 2020

It’s Not a Deflated Football – It’s Probably an Egg from a Mosasaur

By | June 17th, 2020|Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

Antarcticoolithus bradyi – An Egg from a Giant Mosasaur

A football-sized palaeontological mystery might have been solved.   A strange object found by a research team from Chile whilst exploring the López de Bertodano Formation on Seymour Island, in Antarctica back in 2011, is probably the fossilised remains of a mosasaur egg.  That is the conclusion of a scientific paper published this week in the journal Nature.  The strange object, described as looking like a deflated football was found in Upper Cretaceous (Maastrichtian) deposits and these strata yield the fossils of dinosaurs and early birds, but they are essentially near-shore marine deposits and mosasaur fossils are found in the vicinity.  The massive egg is the largest soft-shelled egg known to science and the second largest egg ever recorded.  Only the enormous, hard-shelled eggs of elephant birds (family Aepyornithidae), that once lived on the island of Madagascar, are larger.

A Scientist Holding the Strange “Deflated Football” – Probably the Egg of a Giant Mosasaur

The largest soft-shelled egg known to science.

The strange object identified as the giant egg from a mosasaur.  It was nicknamed “the Thing” in recognition of the 1982 American science fiction horror film directed by John Carpenter that told the story of an alien life form attacking a base in Antarctica.

Picture Credit: Legendre et al (Universidad de Chile)

One of the scientific paper’s co-authors, David Rubilar-Rogers from Chile’s National Museum of Natural History had been part of the field team that found the fossil.  It remained in the Museum’s fossil collection for years, unstudied and not classified.  Visiting scientists and academics were not able to identify what it was until Julia Clarke from the University of Texas at Austin visited in 2018 and proposed that the specimen represented a giant, soft-shelled egg.

A Thin Eggshell

Microscopy confirmed that the object was indeed an egg, one with a shell five times thinner than that associated with the hard-shelled eggs of elephant birds.  The structure of the fossil was similar to vestigial eggs laid by some snakes and lizards today (lepidosaurs).  These types of eggs are laid but hatch almost immediately, the babies are fully developed and entirely altricial.  Further analysis of the fossil discovered no evidence of an embryo to help confirm identification of the egg-layer, this was an eggshell, the baby having hatched.  However, mosasaurs are lepidosaurs, (Order Squamata) and the scientists propose that the egg was laid by a giant mosasaur.

Photographs, Illustrations and Microscopic Analysis of the Fossil Egg

Photographs, drawings and a microscopic analysis of the fossil egg.

Photographs and illustrations of the fossil egg with (bottom) a microscopic structure analysis of the eggshell layers.  In the illustrations (b, d and f) actual eggshell is shown in dark grey whilst the surrounding matrix is light grey.  Note the scale comparison with a person on the far right.

Picture Credit: Legendre et al

A Massive Egg Laid by a Massive Mosasaur

The scientists, which include lead author Lucas Legendre, of the Department of Geological Sciences (University of Texas at Austin), estimate that the egg would have weighed around 6.5 kilogrammes and it would have measured about 29 cm long when it was laid.  The actual fossil measures 28 cm by 18 cm.  The team compiled a data set comparing the body sizes of living and extinct amniotes to calculate the potential size of the animal that produced the massive egg.  They calculate that the egg was probably laid by a mosasaur that had a length of around 7 metres (excluding the tail).

A Mosasaur Hatching

A hatching mosasaur.

An artist’s impression of the hatching mosasaur emerging from the soft-shelled egg moments after the egg was laid.

Picture Credit: Legendre et al (Universidad de Chile)

A Scale Drawing Showing the Proposed Size of the Female Mosasaur that Laid the Egg

Scale drawing showing the size of the female mosasaur.

Scale drawing showing the female mosasaur, the egg and the size of the hatchling with the fossil specimen.  Scale bar = 1 metre

Picture Credit: Francisco Hueichaleo

The First Fossil Egg from Antarctica

The visibly collapsed and folded fossil specimen represents the first vertebrate egg of any kind to be discovered in Antarctica.  The researchers speculate that the near-shore, marine sediments of the López de Bertodano Formation represent an estuarine environment that linked onto a large, shallow bay.  Vertebrate fossils found on Seymour Island include dinosaur bones and poorly preserved footprints, shorebird and waterfowl fossils as well as the remains of marine reptiles such as elasmosaurs and mosasaurs.

Legendre, a Postdoctoral Fellow at the Department of Geological Sciences, commented:

“Many authors have hypothesised that this was sort of a nursery site with shallow protected water, a cove environment where the young ones would have had a quiet setting to grow up.”

Was the Egg Laid on Land or Was it Laid in the Sea?

Did mosasaur females struggle ashore to lay their eggs in nests like turtles or did they lay vestigial eggs that hatched almost immediately having been laid in the open sea.  The scientific paper does not specifically discuss how mosasaurs reproduced, but there are three competing hypotheses:

1).  Mosasaur females left the water and excavated nests on the beach in which their eggs were deposited.  When the eggs hatched, the young mosasaurs would scuttle down the beach and enter the water.

2). Mosasaurs were ovoviviparous – mosasaur embryos developed inside eggs that were retained inside the mother’s body until they were ready to hatch. This method of reproduction is similar to viviparity, but the embryos have no placental connection with the mother and they receive their nourishment from the yolk sac although some gaseous exchange between the egg and the mother takes place.

Ovoviviparity Reproduction in a Mosasaur

A hypothesis that mosasaurs were ovoviviparous

Ovoviviparity reproduction in mosasaurs.

Picture Credit: Legendre et al (Universidad de Chile)

3).  The female mosasaur remained mostly in the water, which helped to support its body weight, but manoeuvred its body so that it could reverse out of the water and deposits its eggs on the shore.

Although not convinced that mosasaurs laid their eggs on land, co-author of the scientific paper Julia Clarke explained:

“We can’t exclude the idea that they shoved their tail end up on shore because nothing like this has ever been discovered.”

An Artist’s Impression of an Ovoviviparous Marine Reptile

The Seymour Island fossil site could represent a mosasaur nursery.

An ovoviviparous mosasaur lays its egg in the bay and the young mosasaur quickly emerges.

Picture Credit: Legendre et al (Universidad de Chile)

This remarkable egg fossil has been given the oogenus Antarcticoolithus which translates as “late Antarctic stone egg”.

Everything Dinosaur acknowledges the assistance of a media release from the Universidad de Chile in the compilation of this article.

The scientific paper: “A giant soft-shelled egg from the Late Cretaceous of Antarctica” by Lucas J. Legendre, David Rubilar-Rogers, Grace M. Musser, Sarah N. Davis, Rodrigo A. Otero, Alexander O. Vargas and Julia A. Clarke published in the journal Nature.

15 06, 2020

Overoraptor chimentoi On the Road to the Birds

By | June 15th, 2020|Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

Overoraptor chimentoi – Closer to Birds than Most other “Raptors”

Time for Everything Dinosaur team members to catch up on their reading.  Whilst browsing through the various press releases, emails and news bulletins from around the world, our attention was drawn to the scientific description of a new, gracile “raptor” from the Upper Cretaceous of Argentina.  Named Overoraptor chimentoi, fossils of this 1.3 metre-long, theropod dinosaur were first discovered in 2013 during field work on 90 million-year-old strata associated with the Huincul Formation in the Patagonian province of Rio Negro.  Further fossils were found during excavations in the same area in 2018.  Although fragmentary, the bones of this small dinosaur suggest that it was more closely related to that lineage of dinosaurs that led to the birds than it is to the likes of Velociraptor and other dromaeosaurids.

A Life Reconstruction of a Pair of Overoraptor chimentoi

Overoraptor life reconstruction.

A life reconstruction of a pair Overoraptors.  Although no feather impressions were found in association with the fragmentary fossils, it is very likely that Overoraptor chimentoi had feathers.

Picture Credit: Gabriel Lio

A Very Bird-like Theropod

The fossil record of members of the Eumaniraptora group of dinosaurs known from the southern hemisphere is sparse.  Evidence of those “raptors” that were closely related to that branch of this group that led to the modern birds is even rarer.  At present, (2020), the fossil evidence is limited to the Unenlagiinae (mostly from the Late Cretaceous of Argentina such as Buitreraptor [B. gonzalezorum]) and the bizarre, bird-like Rahonavis (R. ostromi) from the Upper Cretaceous Maevarano Formation of north-western Madagascar.

Overoraptor exhibits a range of anatomical traits.  The feet and legs are very typical of a dromaeosaurid.  There is the second toe “killing claw” associated with the “raptors” and the lower limb bones indicate that this was a fast-running, cursorial predator.  However, the upper limb bones are very different.  The ulna for example, is very robust and long, reminiscent of the upper limb bones of modern birds.

The Fragmentary Fossils of Overoraptor chimentoi

Overoraptor fossil remains.

Tiny but very significant Overoraptor fossil material including unguals.

Picture Credit: Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”

The picture above shows the fragmentary fossils associated with the new species – Overoraptor chimentoi.  The genus name is from the Spanish “overo” which means piebald, a reference to the mixed colour of the fossil bones.  The trivial name honours Roberto Nicolás Chimento who found the first remains.

Close to the Bird Part of the Dinosaur Family Tree

A phylogenetic analysis conducted by the researchers revealed that Overoraptor was closely related to Rahonavis, that roamed Madagascar some twenty million years later.   The analysis suggests that these two dinosaurs are descended from a common ancestor (they form a monophyletic clade).  Together they are stem avialans within the Eumaniraptora, a line of theropods in which some flight-related adaptations of the forelimbs are present in non-flying taxa.

Commenting on the importance of Overoraptor, one of the co-authors of the paper, Fernando Novas (Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”) stated:

“Contrary to what we originally assumed, the Overoraptor is not part of the Unenlagia family, but from another group including a Madagascan species called Rahonavis.”

The discovery of Overoraptor sheds light on the acquisition of flight-related traits in non-avian dinosaurs and on the still poorly known paravian radiation in Gondwana.

The scientific paper: “New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana” by Matías J. Motta, Federico L. Agnolín, Federico Brissón Egli and Fernando E. Novas published in The Science of Nature.

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