Biology

Evolution and paleoecology of mosasaurs (Sarabosaurus dahli)

By ScientifiCult 12 December 2024

New insights into the evolution and paleoecology of mosasaurs (Sarabosaurus dahli): most comprehensive study to date

Iconic extinct marine lizards continue to surprise us

Mosasaurs are extinct marine lizards, spectacular examples of which were first discovered in 1766 near Maastricht in the Netherlands, fueling the rise of the field of vertebrate palaeontology (the study of fossil remains of animals with backbones). Palaeontologist Michael Polcyn presented the most comprehensive study to date on the early evolution and ecology of these extinct marine reptiles. On 16 December 2024, Polcyn will receive his PhD from Utrecht University for his research into the evolution of the mosasaurs.

“Mosasaurs are a textbook example of macroevolution, the emergence of new and distinct groups of animals, above the level of species. Although they have been studied for centuries, new discoveries, novel research approaches, and the application of technology, are still teaching us about their relationships and behaviors, some of which continues to surprise us. For example, through the use of detailed comparative anatomy aided by micro-CT scanning technology, we have gained a much better understanding of what group of lizards mosasaurs likely evolved from.”

Additionally, use of these advanced imaging technologies has allowed him to study the internal structures of the braincases of mosasaurs, and sort out the early evolutionary relationships of some previously problematic fossil taxa.

“This study not only addressed the early evolution of the group, but also explored small- and large-scale aspects of their feeding biology,” Polcyn continued. “One spectacular example was a specimen I discovered in Angola, that had the remains of three other mosasaurs in its stomach, one of which was the same taxon as the predator, and documented the first occurrence of cannibalism in mosasaurs.”

To the sea

Mosasaurs belong to a group of lizards that took to the sea about 100 million years ago (just like the ancestors of the whales later did). Throughout their 34-million-year history, they evolved into well-adapted marine animals that occupied a wide variety of niches and habitats. Together with a large number of other species, they became extinct 66 million years ago, in the aftermath of the meteorite impact that also wiped out the dinosaurs.

“A relatively large number of fossils are known from the second half of the evolutionary history of mosasaurs, allowing a good understanding of the relationships among those species, which have been classified into four major groups,” says Polcyn. “Much less is known about their early evolutionary history, and how those major groups are related to one another, their origins, and the origin of mosasaurs as a whole.”

To address these gaps, Polcyn has focused on bringing new discoveries to light and restudying historical specimens with advanced imaging technologies, providing significant new anatomical information that is used to infer phylogenetic relationships. Polcyn’s work helps resolve a long-running scientific debate, concluding mosasaurs are not very closely related to snakes, but supporting the idea that their closest relatives are near the monitor lizards.

You are what you eat

Not much was previously known about the feeding habits of mosasaurs either, but a small, yet no less remarkable gap in that knowledge was filled with the discovery, by Polcyn in Angola, of a fossilized mosasaur with three other mosasaurs in its stomach, one being the same species as the predator.

“Whether that mosasaur was a scavenger or actively hunted its prey cannot be said with certainty; however, we do have the first documented example of cannibalism in mosasaurs. Additionally, we gained insights into how mosasaurs processed their prey, and relative body size of prey and predator.”

Also included in his dissertation is a large-scale study of the feeding behaviour of mosasaurs, looking at how mosasaurs divided their foraging areas through the evolutionary history of the group. Polcyn integrated previously published data, along with a new, very large sample that covered a period from 92 to 66 million years ago and included finds from all over the world. The result of that study illuminate patterns of foraging area segregation, and feeding diversity in mosasaurs.

About

Polcyn’s entry into palaeontology followed a non-traditional academic path. After serving in the U.S. submarine service and a career in technology and engineering, he devoted himself to research on extinct vertebrates, with a focus on marine reptiles. He is currently a Senior Research Fellow at ISEM at Southern Methodist University in Dallas, Texas.

mosasaurs Sarabosaurus dahli life reconstruction. Credits: Andrey Atuchin — New insights into the evolution and paleoecology of mosasaurs (Sarabosaurus dahli): the most comprehensive study to date. Sarabosaurus dahli life reconstruction. Credits: Andrey Atuchin

Press release from Utrecht University

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Biology

Iani smithi from Utah lived at a time of major transition

By ScientifiCult 9 June 2023

New dinosaur species from Utah lived at a time of major transition: Iani smithi provides insights into how dinosaurs weather mid-Cretaceous ecological change.

Iani smithi from Utah lived at a time of major transition — Location of holotype locality for Iani smithi. (A) Global map showing location of Mussentuchit Member outcrop in central Utah, western North America, and a stratigraphic section at the quarry with dated ash horizons; and (B) graphical representation of preserved skeletal elements of the holotype specimen. Preserved elements are colored on the left facing skeletal whether they derive from the right or left side of the body. Exact positions of chevrons and ribs unknown due to poor preservation. Credits: Zanno et al., 2023, PLoS ONE, CC-BY 4.0

A new species of dinosaur from Utah sheds light on major North American ecological changes around 100 million years ago, according to a study published June 7, 2023 in the open-access journal PLoS ONE by Lindsay Zanno of the North Carolina Museum of Natural Sciences and colleagues.

The boundary between the Early and Late Cretaceous Period saw major reassembly of global ecosystems associated with a peak in global temperatures. In the fossil record of western North America, this ecological shift has been well-documented for marine habitats, but less study has been done regarding terrestrial life. In this study, Zanno and colleagues identify a new dinosaur from the early Late Cretaceous Cedar Mountain Formation of Utah.

The new dinosaur, named Iani smithi, lived around 100 million years ago and is known from a single fossil specimen including a well-preserved skull and parts of the spine and limbs. The name derives from Ianus, a Roman deity who presided over transitions, referencing the changing world of the mid-Cretaceous.

Iani is a member of an early branch of the ornithopod dinosaurs, a group of mostly bipedal herbivores that also includes famous examples like Iguanodon and Tenontosaurus. Iani is the first early-diverging ornithopod known from the Late Cretaceous of North America.

This discovery, along with other recent reports from the same geologic formation, indicates that several major groups of dinosaurs survived into the early Late Cretaceous despite the ecological changes of the time, but exactly what these survivors were doing and how long they lasted is still unclear. Since Iani and its closest cousins are typically found in ancient coastal habitats along the shores of the now-vanished Western Interior Seaway, the authors suggest that more investigation into coastal deposits of similar age might yield further evidence to address these lingering questions.

The authors add: “Early ornithopods were once a common part of North American ecosystems, but we did not know they survived into the Late Cretaceous. The discovery of Iani helps us link their extinction on the continent with a major interval of global warming, one with striking similarities to our current climate crisis.”

Bibliographic information:

Zanno LE, Gates TA, Avrahami HM, Tucker RT, Makovicky PJ (2023) An early-diverging iguanodontian (Dinosauria: Rhabdodontomorpha) from the Late Cretaceous of North America, PLoS ONE 18(6): e0286042. https://doi.org/10.1371/journal.pone.0286042

Press release from the Public Library of Science.

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Predatory dinosaurs such as Tyrannosaurus rex sported lizard-like lips

By ScientifiCult 30 March 2023

The study challenges some of the best-known depictions of predatory dinosaurs and suggests that even the giant teeth of Tyrannosaurus rex would have been covered in scaly, lizard-like lips.

A juvenile Edmontosaurus disappears into the enormous, lipped mouth of Tyrannosaurus. Credits: Mark Witton

A new study suggests that predatory dinosaurs, such as Tyrannosaurus rex, did not have permanently exposed teeth as depicted in films such as Jurassic Park, but instead had scaly, lizard-like lips covering and sealing their mouths.

Researchers and artists have debated whether theropod dinosaurs, the group of two-legged dinosaurs that includes carnivores and top predators like T. rex and Velociraptor, as well as birds, had lipless mouths where perpetually visible upper teeth hung over their lower jaws, similar to the mouth of a crocodile.

However, an international team of researchers challenge some of the best-known depictions, and say these dinosaurs had lips similar to those of lizards and their relative, the tuatara – a rare reptile found only in New Zealand, which are the last survivors of an order of reptiles that thrived in the age of the dinosaurs.

A half-grown Tyrannosaurus, sporting a full set of lips, runs down Struthiomimus, a beaked ostrich dinosaur. Credits: Mark Witton

In the most detailed study of this issue yet, the researchers examined the tooth structure, wear patterns and jaw morphology of lipped and lipless reptile groups and found that theropod mouth anatomy and functionality resembles that of lizards more than crocodiles. This implies lizard-like oral tissues, including scaly lips covering their teeth.

These lips were probably not muscular, like they are in mammals. Most reptile lips cover their teeth but cannot be moved independently – they cannot be curled back into a snarl, or make other sorts of movements we associate with lips in humans or other mammals.

Tyrannosaurus rex bellowing with its mouth shut, like a vocalising alligator. With its mouth closed, all of the enormous teeth of T. rex would be invisible behind its lips. Credits: Mark Witton

Study co-author Derek Larson, Collections Manager and Researcher in Palaeontology at the Royal BC Museum in Canada, said: “Palaeontologists often like to compare extinct animals to their closest living relatives, but in the case of dinosaurs, their closest relatives have been evolutionarily distinct for hundreds of millions of years and today are incredibly specialised.

“It’s quite remarkable how similar theropod teeth are to monitor lizards. From the smallest dwarf monitor to the Komodo dragon, the teeth function in much the same way. So, monitors can be compared quite favourably with extinct animals like theropod dinosaurs based on this similarity of function, even though they are not closely related.”

Co-author Dr Mark Witton from the University of Portsmouth said: “Dinosaur artists have gone back and forth on lips since we started restoring dinosaurs during the 19th century, but lipless dinosaurs became more prominent in the 1980s and 1990s. They were then deeply rooted in popular culture through films and documentaries — Jurassic Park and its sequels, Walking with Dinosaurs and so on.

“Curiously, there was never a dedicated study or discovery instigating this change and, to a large extent, it probably reflected preference for a new, ferocious-looking aesthetic rather than a shift in scientific thinking. We’re upending this popular depiction by covering their teeth with lizard-like lips. This means a lot of our favourite dinosaur depictions are incorrect, including the iconic Jurassic Park T. rex.”

The results, published in the journal Science, found that tooth wear in lipless animals was markedly different from that seen in carnivorous dinosaurs and that dinosaur teeth were no larger, relative to skull size, than those of modern lizards, implying they were not too big to cover with lips.

Also, the distribution of small holes around the jaws, which supply nerves and blood to the gums and tissues around the mouth, were more lizard-like in dinosaurs than crocodile-like. Furthermore, modelling mouth closure of lipless theropod jaws showed that the lower jaw either had to crush jaw-supporting bones or disarticulate the jaw joint to seal the mouth.

“As any dentist will tell you, saliva is important for maintaining the health of your teeth. Teeth that are not covered by lips risk drying out and can be subject to more damage during feeding or fighting, as we see in crocodiles, but not in dinosaurs,” said co-author Kirstin Brink, Assistant Professor of Palaeontology at the University of Manitoba.

She added: “Dinosaur teeth have very thin enamel and mammal teeth have thick enamel (with some exceptions). Crocodile enamel is a bit thicker than dinosaur enamel, but not as thick as mammalian enamel. There are some mammal groups that do have exposed enamel, but their enamel is modified to withstand exposure.”

Thomas Cullen, Assistant Professor of Paleobiology at Auburn University and study lead author, said: “Although it’s been argued in the past that the teeth of predatory dinosaurs might be too big to be covered by lips, our study shows that, in actuality, their teeth were not atypically large. Even the giant teeth of tyrannosaurs are proportionally similar in size to those of living predatory lizards when compared for skull size, rejecting the idea that their teeth were too big to cover with lips.”

dinosaurs lips T. rex — T. rex skull and head reconstructions. Credits: Mark Witton

The results provide new insights into how we reconstruct the soft-tissues and appearance of dinosaurs and other extinct species. This can give crucial information on how they fed, how they maintained their dental health, and the broader patterns of their evolution and ecology.

Dr Witton said: “Some take the view that we’re clueless about the appearance of dinosaurs beyond basic features like the number of fingers and toes. But our study, and others like it, show that we have an increasingly good handle on many aspects of dinosaur appearance. Far from being clueless, we’re now at a point where we can say ‘oh, that doesn’t have lips? Or a certain type of scale or feather?’ Then that’s as realistic a depiction of that species as a tiger without stripes.”

The researchers point out that their study doesn’t say that no extinct animals had exposed teeth — some, like sabre-toothed carnivorous mammals, or marine reptiles and flying reptiles with extremely long, interlocking teeth, almost certainly did.

A one-sheet summary of the main investigations and conclusions of the study. Credits: Mark Witton

Bibliographic information:

Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology, Science (31-Mar-2023), DOI: 10.1126/science.abo7877

Press release from the University of Portsmouth.

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Researchers uncover 92 fossil nests belonging to some of India’s largest dinosaurs

By ScientifiCult 18 January 2023

Researchers uncover 92 fossil nests belonging to some of India’s largest dinosaurs

Fossilized eggs reveal details of titanosaur reproduction, nesting, and early life

(A) Completely unhatched egg from the clutch P43. (B) Almost fully intact circular outline of egg possibly indicating it to be unhatched and no loose eggshells are found in the clutch P6. (C) Compressed egg from clutch DR10 showing hatching window (arrow showing gap) and few eggshells collected just around the hatching window (circled) which possibly represent the remnants of hatching window. (D) Egg from clutch P26 showing curved outline. (E) Deformed egg from clutch P30 showing egg surfaces slipping past each other. Credits: Dhiman et al., 2023, PLOS ONE, CC-BY 4.0

The discovery of more than 250 fossilized eggs reveals intimate details about the lives of titanosaurs in the Indian subcontinent, according to a study published January 18, 2022 in the open-access journal PLOS ONE by Harsha Dhiman of the University of Delhi, New Delhi and colleagues.

The Lameta Formation, located in the Narmada Valley of central India, is well-known for fossils of dinosaur skeletons and eggs of the Late Cretaceous Period. Recent work in the area uncovered 92 nesting sites containing a total of 256 fossil eggs belonging to titanosaurs, which were among the largest dinosaurs to have ever lived. Detailed examination of these nests has allowed Dhiman and colleagues to make inferences about the life habits of these dinosaurs.

Researchers uncover 92 fossil nests belonging to some of India’s largest dinosaurs. It is inferred that some of the clutches were laid close to the banks of the aquatic bodies (lakes/ponds) while others were deposited away from the lakes or ponds. The clutches laid close to the margins were prone to frequent submergence by water and thus got buried under sediment and remained unhatched, while the clutches laid away from the margins could hatch and hence showed more broken eggshells. Credits: Dhiman et al., 2023, PLOS ONE, CC-BY 4.0

The authors identified six different egg-species (oospecies), suggesting a higher diversity of titanosaurs than is represented by skeletal remains from this region. Based on the layout of the nests, the team inferred that these dinosaurs buried their eggs in shallow pits like modern-day crocodiles. Certain pathologies found in the eggs, such as a rare case of an “egg-in-egg”, indicate that titanosaur sauropods had a reproductive physiology that parallels that of birds and possibly laid their eggs in a sequential manner as seen in modern birds. The presence of many nests in the same area suggests these dinosaurs exhibited colonial nesting behavior like many modern birds. But the close spacing of the nests left little room for adult dinosaurs, supporting the idea that adults left the hatchlings (newborns) to fend for themselves.

Details of dinosaur reproductive habits can be difficult to determine. These fossil nests provide a wealth of data about some of the largest dinosaurs in history, and they come from a time shortly before the age of dinosaurs came to an end. The insights gleaned from this study contribute significantly to paleontologists’ understanding of how dinosaurs lived and evolved.

Harsha Dhiman, lead author of the research, adds: “Our research has revealed the presence of an extensive hatchery of titanosaur sauropod dinosaurs in the study area and offers new insights into the conditions of nest preservation and reproductive strategies of titanosaur sauropod dinosaurs just before they went extinct.”

Guntupalli V.R. Prasad, co-author and leader of the research team, adds: “Together with dinosaur nests from Jabalpur in the upper Narmada valley in the east and those from Balasinor in the west, the new nesting sites from Dhar District in Madhya Pradesh (Central India), covering an east-west stretch of about 1000 km, constitute one of the largest dinosaur hatcheries in the world.”

Bibliographic information:

Dhiman H, Verma V, Singh LR, Miglani V, Jha DK, Sanyal P, et al. (2023) New Late Cretaceous titanosaur sauropod dinosaur egg clutches from lower Narmada valley, India: Palaeobiology and taphonomy. PLoS ONE 18(1): e0278242. https://doi.org/10.1371/journal.pone.0278242

Press release from PLOS – Public Library of Science

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Fossils reveal dinosaurs of prehistoric Patagonia

By ScientifiCult 11 January 2023

Fossils reveal dinosaurs of prehistoric Patagonia

A study led by The University of Texas at Austin is providing a glimpse into dinosaur and bird diversity in Patagonia during the Late Cretaceous, just before the non-avian dinosaurs went extinct.

The fossils represent the first record of theropods — a dinosaur group that includes both modern birds and their closest non-avian dinosaur relatives — from the Chilean portion of Patagonia. The researchers’ finds include giant megaraptors with large sickle-like claws and birds from the group that also includes today’s modern species.

“The fauna of Patagonia leading up to the mass extinction was really diverse,” said lead author Sarah Davis, who completed this work as part of her doctoral studies with Professor Julia Clarke at the UT Jackson School of Geosciences Department of Geological Sciences. “You’ve got your large theropod carnivores and smaller carnivores as well as these bird groups coexisting alongside other reptiles and small mammals.”

The study was published in the Journal of South American Earth Sciences.

Since 2017, members of the Clarke lab, including graduate and undergraduate students, have joined scientific collaborators from Chile in Patagonia to collect fossils and build a record of ancient life from the region. Over the years, researchers have found abundant plant and animal fossils from before the asteroid strike that killed off the dinosaurs.

The study focuses specifically on theropods, with the fossils dating from 66 to 75 million years ago.

Non-avian theropod dinosaurs were mostly carnivorous, and include the top predators in the food chain. This study shows that in prehistoric Patagonia, these predators included dinosaurs from two groups — megaraptors and unenlagiines.

Reaching over 25 feet long, megaraptors were among the larger theropod dinosaurs in South America during the Late Cretaceous. The unenlagiines — a group with members that ranged from chicken-sized to over 10 feet tall — were probably covered with feathers, just like their close relative the velociraptor. The unenlagiinae fossils described in the study are the southernmost known instance of this dinosaur group.

The bird fossils were also from two groups — enantiornithines and ornithurines. Although now extinct, enantiornithines were the most diverse and abundant birds millions of years ago. These resembled sparrows — but with beaks lined with teeth. The group ornithurae includes all modern birds living today. The ones living in ancient Patagonia may have resembled a goose or duck, though the fossils are too fragmentary to tell for sure.

The researchers identified the theropods from small fossil fragments; the dinosaurs mostly from teeth and toes, the birds from small bone pieces. Davis said that the enamel glinting on the dinosaur teeth helped with spotting them among the rocky terrain.

Some researchers have suggested that the Southern Hemisphere faced less extreme or more gradual climatic changes than the Northern Hemisphere after the asteroid strike. This may have made Patagonia, and other places in the Southern Hemisphere, a refuge for birds and mammals and other life that survived the extinction. Davis said that this study can aid in investigating this theory by building up a record of ancient life before and after the extinction event.

Study co-author Marcelo Leppe, the director of the Antarctic Institute of Chile, said that these past records are key to understanding life as it exists today.

“We still need to know how life made its way in that apocalyptic scenario and gave rise to our southern environments in South America, New Zealand and Australia,” he said. “Here theropods are still present — no longer as dinosaurs as imposing as megaraptorids — but as the diverse array of birds found in the forests, swamps and marshes of Patagonia, and in Antarctica and Australia.”

The research was funded by the National Science Foundation, the National Agency for Research and Development of Chile, and the Jackson School of Geosciences.

The study’s co-authors include Clarke and researchers at the University of Chile, Major University, the University of Concepción and the Chilean National Museum of Natural History.

The researchers in Patagonia in 2017. Lead author Sarah Davis is in the center of the front row in a blue jacket. The researchers include members from the Jackson School of Geosciences, INACH, the University of Chile, and the University of Concepción. Credits: Sarah Davis

Bibliographic information:

New records of Theropoda from a Late Cretaceous (Campanian-Maastrichtian) locality in the Magallanes-Austral Basin, Patagonia, and insights into end Cretaceous theropod diversity, Journal of South American Earth Sciences (30-Dec-2022), DOI:
10.1016/j.jsames.2022.104163

Press release from The University of Texas at Austin

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New research questions hypotheses about climate-controlled ecosystem change during the origin of dinosaurs in Argentina

By ScientifiCult 13 June 2022

New research questions hypotheses about climate-controlled ecosystem change during the origin of dinosaurs in Argentina

A group of researchers from CONICET and the University of Utah demonstrated that during the time of the first dinosaurs, variations in the diversity and abundance of the plant and vertebrate animal species cannot be related to the climatic changes recorded throughout its deposition, in contrast with previous hypotheses.

origin dinosaurs Argentina Triassic Ischigualasto Formation — Artist’s reconstruction of the Triassic ecosystem preserved in the Ischigualasto Formation. Animals include amphibians (bottom center-left underwater), rhynchosaurian reptiles (left mid-ground on riverbank), early crocodilian relatives (far left mid-ground and center far background), early mammal relatives (center mid-ground in river and along riverbank, and far right foreground), and early dinosaurs (far left foreground, center right foreground, and far right mid-ground). Credits: Jorge Gonzalez/Natural History Museum of Utah

In the new study, published in the open access journal Frontiers in Earth Science, the team of scientists investigated multiple independent lines of evidence (sedimentology, clay mineralogy, and geochemistry) to elucidate changes paleoclimatic conditions (such as mean annual precipitation and mean annual temperature) within the Ischigualasto Formation. These fossil-rich sedimentary rocks were deposited by rivers and streams between ~231 and 226 million years ago during the Late Triassic Period in what is now northwestern Argentina (La Rioja and San Juan provinces). In the middle of the formation, the researchers observed a clear change in conditions approximately from warmer, drier conditions to more temperate humid conditions, but no concurrent major changes could be identified in the fossil record.

An overview of extensive Ischigulasto Formation outcrops in the study area, located in La Rioja Province, northwestern Argentina. Credits: Randall Irmis/Natural History Museum of Utah

“We conclude that variations in the abundance and diversity of species, as recorded by their first and last appearances in the fossil record, are better explained by preservation and sampling biases biases than by changes in climate,” said Adriana Mancuso, lead author and CONICET independent researcher at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales in Mendoza, Argentina.

“What we see is that how many specimens collected from each interval of the sequence, and the chemical & physical characteristics that allow greater or lesser preservation of the remains of animals and plants, were significant factors. These two factors, collection and preservation, have more influence on the increase or decrease of abundance and diversity than the climate changes recorded,” explained Mancuso.

However, although the evolution of the ecosystem does not generally show a biotic response associated with climate change, the research group did observe a relationship between climatic variations and two groups of reptiles, rhynchosaurs (herbivorous early archosauromorphs) and pseudosuchians (crocodilian-line archosaurs).

“We did find that the abundance of rhynchosaurs and extinction of a few pseudosuchian species appear to coincide with a climate shift,” said Randall Irmis, co-author from the U and the Natural History Museum of Utah.

New research questions hypotheses about climate-controlled ecosystem change during the origin of dinosaurs in Argentina: a team member exposes fresh rock to obtain a geologic sample for geochemical lab analysis to reconstruct the paleoclimate record of the Ischigualasto Formation. Credits: Adriana Mancuso

Beyond conclusions about this specific fossil and paleoclimate record from Argentina, the new research emphasizes the importance of an explicit framework for testing hypotheses about the link between climatic changes and the fossil record.

“In addition to the contribution on the relationship of biotic and climatic events in the Ischigualasto Formation, the work provides a methodological framework to test climate-biota associations, highlighting the data gaps that must be filled, and makes new testable predictions that can be tested in future studies,” concludes Mancuso.

Other authors include Tomás Pedernera and Cecilia Benavente of the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (CONICET), Leandro Gaetano from the Instituto de Estudios Andinos (CONICET) and Departamento de Ciencias Geológicas of the Universidad de Buenos Aires, and Benjamin Breeden of the University of Utah.

Bibliographical information:

Paleoenvironmental and biotic changes in the Late Triassic of Argentina: testing hypotheses of abiotic forcing at the basin scale, Frontiers in Earth Science (13-Jun-2022), DOI: 10.3389/feart.2022.883788

Press release from the University of Utah

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Bashanosaurus primitivus: the oldest stegosaurs in Asia

By ScientifiCult 6 March 2022

New species of stegosaur is oldest discovered in Asia, and possibly the world

Bashanosaurus primitivus roamed the earth around 168 million years ago during the Middle Jurassic period, suggesting that stegosaurs may have originated in Asia

Bashanosaurus primitivus species Stegosaurs Asia — Bashanosaurus primitivus – the newest and oldest species of stegosaur in Asia. *Bashanosaurus primitivus* roamed the earth around 168 million years ago during the Middle Jurassic period, suggesting that stegosaurs may have originated in Asia. Credits: Credit Banana Art Studio

Relatively small, but fearsome-looking stegosaur measured about 2.8 metres (9 feet) from nose to tail—but scientists can’t tell whether the remains are those of an adult or juvenile.

A new species of one of the most recognisable types of dinosaur is the oldest stegosaur ever found in Asia, and one of the earliest unearthed anywhere in the world, according to research published today in the peer-reviewed Journal of Vertebrate Paleontology.

Remains of the stegosaur, which included bones from the back, shoulder, thigh, feet, and ribs, as well as several armour plates, date to the Bajocian stage of the Middle Jurassic period – much earlier than most known stegosaurs.

A team from the Chongqing Bureau of Geological and Mineral Resource Exploration and Development in China and London’s Natural History Museum named it Bashanosaurus primitivus – “Bashan” in reference to the ancient name for the area of Chongqing in China where the dinosaur was found, and the Latin for ‘first’ – primitivus.

The new dinosaur, which roamed the planet 168 million years ago, plays a part in uncovering how the stegosaurs evolved – of which, to this day, little is known.

It has a smaller and less developed should blade, narrower and thicker bases to its armour plates and other features that are different from all other Middle Jurassic stegosaurs discovered so far. However, it does have similarities with some of the first armoured dinosaurs, which are over 20 million years older.

“All these features are clues to the stegosaurs’ place on the dinosaur family tree”, says Dr Dai Hui from Chongqing Bureau of Geological and Mineral Resource Exploration and Development who led the research. “Bashanosaurus can be distinguished from other Middle Jurassic stegosaurs, and clearly represents a new species.

“What’s more, our analysis of the family tree indicates that it is one of the earliest-diverging stegosaurs along with the Chongqing Lizard (Chungkingosaurus) and Huayangosaurus. These were all unearthed from the Middle to Late Jurassic Shaximiao Formation in China, suggesting that stegosaurs might have originated in Asia”, adds Hui.

Instantly recognisable by the huge back plates, long tail spikes and tiny head, stegosaurs were four-legged, plant-eating dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaur fossils have been found on all continents except for Antarctica and Australia, and 14 species of stegosaur have been identified so far.

Well-known members of Stegosauria include Huayangosaurus (one of the most primitive stegosaurs), Gigantspinosaurus, notable for its enormous shoulder spines, and Miragaia for its extremely long neck. However, the fragmentary fossil material has hindered attempts to understand how the stegosaurs evolved and how they relate to one another.

With the discovery of this new species the mystery has started to clear up. Bashanosaurus primitivus has several primitive features that are similar to the earliest stegosaurs like Huayangosaurus and Gigantspinosaurus and early-branching thyreophorans (armoured dinosaurs). These include longer tail vertebrae, a shoulder blade that is narrower and flares out, and features of the back vertebrae that are similar to the early armoured dinosaur Scelidosaurus, which lived during the Early Jurassic.

The fossilised remains of Bashanosaurus also reveal a host of features that make it unique from other known stegosaurs. For example, the bony point at the end of the shoulder blade is small and less well developed than in other stegosaurs; a bony projection of the thighbone (fourth trochanter) is positioned below the middle of the shaft; and the bases of the armour plates curve outwards and are thicker than the plates on the backs of its later relatives.

“The discovery of this stegosaur from the Middle Jurassic of China adds to an increasing body of evidence that the group evolved in the early Middle Jurassic, or perhaps even in the Early Jurassic, and as such represent some of the earliest known bird-hipped dinosaurs,” says Dr Susannah Maidment, co-author and palaeontologist at London’s Natural History Museum.

“China seems to have been a hotspot for stegosaur diversity, with numerous species now known from the Middle Jurassic right the way through until the end of the Early Cretaceous period.”

New stegosaurs from the Middle Jurassic Lower Member of the Shaximiao Formation of Chongqing, China, Journal of Vertebrate Paleontology (4/03/2022), DOI: 10.1080/02724634.2021.1995737

Press release from Taylor & Francis Group.

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