Determining what killed the dinosaurs 66 million years ago at the end of the Cretaceous Period has long been the topic of debate, as scientists set out to determine what caused the five mass extinction events that reshaped life on planet Earth in a geological instant. Some scientists argue that comets or asteroids that crashed into Earth were the most likely agents of mass destruction, while others argue that large volcanic eruptions were the cause. A new Dartmouth-led study published in the Proceedings of the National Academy of Sciences (PNAS) reports that volcanic activity appears to have been the key driver of mass extinctions.

The findings provide the most compelling quantitative evidence so far that the link between major volcanic eruptions and wholesale species turnover is not simply a matter of chance.

Four of the five mass extinctions are contemporaneous with a type of volcanic outpouring called a flood basalt, the researchers say. These eruptions flood vast areas — even an entire continent — with lava in the blink of a geological eye, a mere million years. They leave behind giant fingerprints as evidence — extensive regions of step-like, igneous rock (solidified from the erupted lava) that geologists call “large igneous provinces.”

To count as “large,” a large igneous province must contain at least 100,000 cubic kilometers of magma. For context, the 1980 eruption of Mount St. Helens involved less than one cubic kilometer of magma. The researchers say that most of the volcanoes represented in the study erupted on the order of a million times more lava than that.

The team drew on three well-established datasets on geologic time scale, paleobiology, and large igneous provinces to examine the temporal connection between mass extinction and large igneous provinces.

“The large step-like areas of igneous rock from these big volcanic eruptions seem to line up in time with mass extinctions and other significant climatic and environmental events,”says lead author Theodore Green ’21, who conducted this research as part of the Senior Fellowship program at Dartmouth and is now a graduate student at Princeton.

In fact, a series of eruptions in present-day Siberia triggered the most destructive of the mass extinctions about 252 million years ago, releasing a gigantic pulse of carbon dioxide into the atmosphere and nearly choking off all life. Bearing witness are the Siberian Traps, a large region of volcanic rock roughly the size of Australia.

Volcanic eruptions also rocked the Indian subcontinent around the time of the great dinosaur die-off, creating what is known today as the Deccan plateau. This, much like the asteroid strike, would have had far-reaching global effects, blanketing the atmosphere in dust and toxic fumes, asphyxiating dinosaurs and other life in addition to altering the climate on long time scales.

On the other hand, the researchers say, the theories in favor of annihilation by asteroid impact hinge upon the Chicxulub impactor, a space rock that crash-landed into Mexico’s Yucatan Peninsula around the same time that the dinosaurs went extinct.

“All other theories that attempted to explain what killed the dinosaurs, including volcanism, got steamrolled when the Chicxulub impact crater was discovered,” says co-author Brenhin Keller, an assistant professor of earth sciences at Dartmouth. But there’s very little evidence of similar impact events that coincide with the other mass extinctions despite decades of exploration, he points out.

At Dartmouth, Green set out to find a way to quantify the apparent link between eruptions and extinctions and test whether the coincidence was just chance or whether there was evidence of a causal relationship between the two. Working with Keller and co-author Paul Renne, professor-in-residence of earth and planetary science at University of California, Berkeley and director of the Berkeley Geochronology Center, Green recruited the supercomputers at the Dartmouth Discovery Cluster to crunch the numbers.

The researchers compared the best available estimates of flood basalt eruptions with periods of drastic species kill-off in the geological timescale, including but not limited to the five mass extinctions. To prove that the timing was more than a random chance, they examined whether the eruptions would line up just as well with a randomly generated pattern and repeated the exercise with a 100 million such patterns. They found that the agreement with extinction periods was far greater than random chance.

“While it is difficult to determine if a particular volcanic outburst caused one particular mass extinction, our results make it hard to ignore the role of volcanism in extinction,” says Keller. If a causal link were to be found between volcanic flood basalts and mass extinctions, scientists expect that larger eruptions would entail more severe extinctions, but such a correlation has not been observed.

Rather than considering the absolute magnitude of eruptions, the research team ordered the volcanic events by the rate at which they spewed lava. They found that the volcanic events with the highest eruptive rates did indeed cause the most destruction, producing more severe extinctions up to the mass extinctions.

“Our results indicate that in all likelihood there would have been a mass extinction at the Cretaceous tertiary boundary of some significant magnitude, regardless of whether there was an impact or not, which can be shown more quantitatively now,” says Renne. “The fact that there was an impact undoubtedly made things worse.”

The researchers ran the numbers for asteroids too. The coincidence of impacts with periods of species turnover was significantly weaker, and dramatically worsened when the Chicxulub impactor was not considered, suggesting that other smaller known impactors did not cause significant extinctions.

The eruption rate of the Deccan Traps in India suggests that the stage was set for widespread extinction even without the asteroid, says Green. The impact was the double whammy that loudly sounded the death knell for the dinosaurs, he adds.

Flood basalt eruptions aren’t common in the geologic record, says Green. The last one of comparable but significantly smaller scale happened about 16 million years ago in the Pacific Northwest.

“While the total amount of carbon dioxide being released into the atmosphere in modern climate change is still very much smaller than the amount emitted by a large igneous province, thankfully,” says Keller, “we’re emitting it very fast, which is reason to be concerned.” Green says that carbon dioxide emissions are uncomfortably similar to the rate of the environmentally impactful flood basalts they studied. This places climate change in the framework of historical periods of environmental catastrophe, he says.

Reference:
Theodore Green, Paul R. Renne and C. Brenhin Keller. Continental flood basalts drive Phanerozoic extinctions. PNAS, 2022 DOI: 10.1073/pnas.2120441119

Note: The above post is reprinted from materials provided by Dartmouth College. Original written by Harini Barath.

Smithsonian researchers have discovered a new extinct species of lizard-like reptile that belongs to the same ancient lineage as New Zealand’s living tuatara. A team of scientists, including the National Museum of Natural History’s curator of Dinosauria Matthew Carrano and research associate David DeMar Jr. as well as University College London and Natural History Museum, London scientific associate Marc Jones, describe the new species Opisthiamimus gregori, which once inhabited Jurassic North America about 150 million years ago alongside dinosaurs like Stegosaurus and Allosaurus, in a paper published today in the Journal of Systematic Palaeontology. In life, this prehistoric reptile would have been about 16 centimeters (about 6 inches) from nose to tail — and would fit curled up in the palm of an adult human hand — and likely survived on a diet of insects and other invertebrates.

“What’s important about the tuatara is that it represents this enormous evolutionary story that we are lucky enough to catch in what is likely its closing act,” Carrano said. “Even though it looks like a relatively simple lizard, it embodies an entire evolutionary epic going back more than 200 million years.”

The discovery comes from a handful of specimens including an extraordinarily complete and well-preserved fossil skeleton excavated from a site centered around an Allosaurus nest in northern Wyoming’s Morrison Formation. Further study of the find could help reveal why this animal’s ancient order of reptiles were winnowed down from being diverse and numerous in the Jurassic to just New Zealand’s tuatara surviving today.

The tuatara looks a bit like a particularly stout iguana, but the tuatara and its newly discovered relative are in fact not lizards at all. They are actually rhynchocephalians, an order that diverged from lizards at least 230 million years ago, Carrano said.

In their Jurassic heyday, rhynchocephalians were found nearly worldwide, came in sizes large and small, and filled ecological roles ranging from aquatic fish hunters to bulky plant munchers. But for reasons that still are not fully understood, rhynchocephalians all but disappeared as lizards and snakes grew to be the more common and more diverse reptiles across the globe.

This evolutionary chasm between lizards and rhynchocephalians helps explain the tuatara’s odd features such as teeth fused to the jaw bone, a unique chewing motion that slides the lower jaw back and forth like a saw blade, a 100-year-plus lifespan and a tolerance for colder climates.

Following O. gregori’s formal description, Carrano said the fossil has been added to the museum’s collections where it will remain available for future study, perhaps one day helping researchers figure out why the tuatara is all that remains of the rhynchocephalians, while lizards are now found across the globe.

“These animals may have disappeared partly because of competition from lizards but perhaps also due to global shifts in climate and changing habitats,” Carrano said. “It’s fascinating when you have the dominance of one group giving way to another group over evolutionary time, and we still need more evidence to explain exactly what happened, but fossils like this one are how we will put it together.”

The researchers named the new species after museum volunteer Joseph Gregor who spent hundreds of hours meticulously scraping and chiseling the bones from a block of stone that first caught museum fossil preparator Pete Kroehler’s eye back in 2010.

“Pete is one of those people who has a kind of X-ray vision for this sort of thing,” Carrano said. “He noticed two tiny specks of bone on the side of this block and marked it to be brought back with no real idea what was in it. As it turns out, he hit the jackpot.”

The fossil is almost entirely complete, with the exception of the tail and parts of the hind legs. Carrano said that such a complete skeleton is rare for small prehistoric creatures like this because their frail bones were often destroyed either before they fossilized or as they emerge from an eroding rock formation in the present day. As a result, rhynchocephalians are mostly known to paleontologists from small fragments of their jaws and teeth.

After Kroehler, Gregor and others had freed as much of the tiny fossil from the rock as was practical given its fragility, the team, led by DeMar, set about scanning the fossil with high-resolution computerized tomography (CT), a method that uses multiple X-ray images from different angles to create a 3D representation of the specimen. The team used three separate CT scanning facilities, including one housed at the National Museum of Natural History, to capture everything they possibly could about the fossil.

Once the fossil’s bones had been digitally rendered with accuracy smaller than a millimeter, DeMar set about reassembling the digitized bones of the skull, some of which were crushed, out of place or missing on one side, using software to eventually create a nearly complete 3D reconstruction. The reconstructed 3D skull now provides researchers an unprecedented look at this Jurassic-age reptile’s head.

Given Opisthiamimus’s diminutive size, tooth shape and rigid skull, it likely ate insects, said DeMar, adding that prey with harder shells such as beetles or water bugs might have also been on the menu. Broadly speaking, the new species looks quite a bit like a miniaturized version of its only surviving relative (tuataras are about five times longer).

“Such a complete specimen has huge potential for making comparisons with fossils collected in the future and for identifying or reclassifying specimens already sitting in a museum drawer somewhere,” DeMar said. “With the 3D models we have, at some point we could also do studies that use software to look at this critter’s jaw mechanics.”

Funding and support for this research were provided by the Smithsonian and the Australian Research Council.

Reference:
David G. DeMar, Marc E. H. Jones, Matthew T. Carrano. A nearly complete skeleton of a new eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchocephalia (Reptilia: Lepidosauria). Journal of Systematic Palaeontology, 2022; 20 (1) DOI: 10.1080/14772019.2022.2093139

Note: The above post is reprinted from materials provided by Smithsonian.

Researchers have discovered a huge new mosasaur from Morocco, named Thalassotitan atrox, which filled the apex predator niche. With massive jaws and teeth like those of killer whales, Thalassotitan hunted other marine reptiles — plesiosaurs, sea turtles, and other mosasaurs.

At the end of the Cretaceous period, 66 million years ago, sea monsters really existed. While dinosaurs flourished on land, the seas were ruled by the mosasaurs, giant marine reptiles.

Mosasaurs weren’t dinosaurs, but enormous marine lizards growing up to 12 metres (40 feet) in length. They were distant relatives of modern iguanas and monitor lizards.

Mosasaurs looked like a Komodo dragon with flippers instead of legs, and a shark-like tail fin. Mosasaurs became larger and more specialised in the last 25 million years of the Cretaceous, taking niches once filled by marine reptiles like plesiosaurs and ichthyosaurs. Some evolved to eat small prey like fish and squid. Others crushed ammonites and clams. The new mosasaur, named Thalassotitan atrox, evolved to prey on all the other marine reptiles.

The remains of the new species were dug up in Morocco, about an hour outside Casablanca. Here, near the end of the Cretaceous, the Atlantic flooded northern Africa. Nutrient rich waters upwelling from the depths fed blooms of plankton. Those fed small fish, feeding larger fish, which fed mosasaurs and plesiosaurs — and so on, with these marine reptiles becoming food for the giant, carnivorous Thalassotitan.

Thalassotitan, had an enormous skull measuring 1.4 metres (5 feet long), and grew to nearly 30 feet (9 metres) long, the size of a killer whale. While most mosasaurs had long jaws and slender teeth for catching fish, Thalassotitan had a short, wide muzzle and massive, conical teeth like those of an orca. These let it seize and rip apart huge prey. These adaptations suggest Thalassotitan was an apex predator, sitting at the top of the food chain. The giant mosasaur occupied the same ecological niche as today’s killer whales and great white sharks.

Thalassotitan’s teeth are often broken and worn, however eating fish wouldn’t have produced this sort of tooth wear. Instead, this suggests that the giant mosasaur attacked other marine reptiles, chipping, breaking, and grinding its teeth as it bit into their bones and tore them apart. Some teeth are so heavily damaged they have been almost ground down to the root.

Fossilised remains of prey

Remarkably, possible remains of Thalassotitan’s victims have been discovered. Fossils from the same beds show damage from acids, with teeth and bone eaten away. Fossils with this peculiar damage include large predatory fish, a sea turtle, a half-meter long plesiosaur head, and jaws and skulls of at least three different mosasaur species. They would have been digested in Thalassotitan’s stomach before it spat out their bones.

“It’s circumstantial evidence,” said Dr Nick Longrich, Senior Lecturer from the Milner Centre for Evolution at the University of Bath and lead author on the study, published in Cretaceous Research.

“We can’t say for certain which species of animal ate all these other mosasaurs. But we have the bones of marine reptiles killed and eaten by a large predator.

“And in the same location, we find Thalassotitan, a species that fits the profile of the killer — it’s a mosasaur specialised to prey on other marine reptiles. That’s probably not a coincidence.”

Thalassotitan was a threat to everything in the oceans — including other Thalassotitan. The huge mosasaurs bear injuries sustained in violent combat with other mosasaurs, with injuries to their face and jaws sustained in fights. Other mosasaurs show similar injuries, but in Thalassotitan these wounds were exceptionally common, suggesting frequent, intense fights over feeding grounds or mates.

“Thalassotitan was an amazing, terrifying animal,” said Dr Nick Longrich, who led the study. “Imagine a Komodo Dragon crossed with a great white shark crossed with a T. rex crossed with a killer whale.”

The new mosasaur lived in the final million years of the Age of Dinosaurs, a contemporary of animals like T. rex and Triceratops. Along with recent discoveries of mosasaurs from Morocco, it suggests that mosasaurs weren’t in decline before the asteroid impact that drove the Cretaceous mass extinction. Instead, they flourished.

Professor Nour-Eddine Jalil, a co-author on the paper from the Museum of Natural History in Paris, said: “The phosphate fossils of Morocco offer an unparalleled window on the paleobiodiversity at the end of Cretaceous.

“They tell us how life was rich and diversified just before the end of the ‘dinosaur era’, where animals had to specialise to have a place in their ecosystems. Thalassotitan completes the picture by taking on the role of the megapredator at the top of the food chain.”

“There’s so much more to be done,” said Longrich. “Morocco has one of the richest and most diverse marine faunas known from the Cretaceous. We’re just getting started understanding the diversity and the biology of the mosasaurs.”

Reference:
Nicholas R. Longrich, Nour-Eddine Jalil, Fatima Khaldoune, Oussama Khadiri Yazami, Xabier Pereda-Suberbiola, Nathalie Bardet. Thalassotitan atrox, a giant predatory mosasaurid (Squamata) from the Upper Maastrichtian Phosphates of Morocco. Cretaceous Research, 2022; 105315 DOI: 10.1016/j.cretres.2022.105315

Note: The above post is reprinted from materials provided by University of Bath.

Large dinosaur predators, such as Tyrannosaurus rex, evolved different shapes of eye sockets to better deal with high bite forces, new research has shown.

While in many animals — and most dinosaurs — the eye socket is just a circular hole in the skull housing the eyeball, this is very different in large carnivores.

In a new study, published today in Communications Biology, researchers at the University of Birmingham reveal how the unusual elliptical, or oval eye sockets found in the skulls of these predators, could have evolved to help the skull absorb impact as they pounced on prey.

Dr Stephan Lautenschlager, Senior Lecturer for Palaeobiology at the University of Birmingham and author of the new study, analysed the shape of the eye sockets of ca. 500 different dinosaurs and related species.

“The results show that only some dinosaurs had eye sockets that were elliptical or keyhole-shaped,” said Dr Stephan Lautenschlager. “However, all of those were large, carnivorous dinosaurs with skull lengths of 1 m or more.”

Using computer simulations and stress analysis, Dr Lautenschlager tested what purpose these unusual eye socket shapes could have.

The results demonstrated that a skull with a circular eye socket was more prone to high stresses during biting. However, if these were replaced with other eye socket shapes stresses were considerably reduced allowing top predators, including Tyrannosaurus rex, to evolve high bite forces without compromising skull stability.

The study also showed that most plant-eating species and juvenile individuals retained a circular eye socket. Only large carnivores adopted other morphologies, such as elliptical, keyhole-shaped or figure-of-eight-shaped eye sockets.

Dr Lautenschlager added: “In these species, just the upper part of the eye socket was actually occupied by the eyeball. This also led to a relative reduction of eye size compared with skull size.”

The researchers also investigated what would have happened if eye size had increased at the same rate as skull length. In such a case, the eyes of Tyrannosaurus rex would have been up to 30 cm in diameter and weighing nearly 20 kg (instead of estimated 13 cm and 2 kg).

Reference:
Stephan Lautenschlager. Functional and ecomorphological evolution of orbit shape in mesozoic archosaurs is driven by body size and diet. Communications Biology, 2022; 5 (1) DOI: 10.1038/s42003-022-03706-0

Note: The above post is reprinted from materials provided by University of Birmingham.

This has been confirmed in the article ‘New contributions to the skull anatomy of spinosaurid theropods: Baryonychinae maxilla from the Early Cretaceous of Igea (La Rioja, Spain)’ published in the journal Historical Biology by Iker Isasmendi (lead author) and Xavier Pereda of the UPV/EHU-University of the Basque Country, Pablo Navarro of the UR-University of La Rioja, Angélica Torices, director of the Chair of Palaeontology at the UR, plus other experts of the Complutense University of Madrid and the Palaeontological Visitors’ Centre of La Rioja.

Scientists have reassessed fossil jaw remains published by Viera and Torres in 1995 and found in 1983 in a Lower Cretaceous site at Igea (La Rioja, Spain). The remains constitute a fragment of a left maxilla belonging to a carnivorous dinosaur and in which 8 alveoli have been preserved. Using microCT techniques, they discovered the remains of several teeth developing simultaneously in one of these dental sockets.

“We recognised up to three generations of teeth in the same alveolus: the functional tooth of the animal, another tooth being formed and which would replace the first, and the germ of the one that would end up replacing the second,” explained Pablo Navarro of the UR.

“This suggests very rapid tooth replacement and is probably one of the reasons why so many spinosaurid teeth can be found on the Iberian Peninsula during the Lower Cretaceous,” added the co-author of the paper.

To date, some species of spinosaurids -medium/large carnivorous dinosaurs with elongated skulls and crocodile-like conical teeth- were known to replace their teeth faster than other theropods, in just two months (replacement rate estimated to be 60-68 days); the research confirms that this is a trait shared by the whole group and provides evidence of how this change occurred, i.e. it was made possible by the development of several replacement teeth at the same time.

“Throughout their lives these animals grew new teeth that gradually replaced the original ones and caused them to fall out. This means that the same animal could generate multiple teeth,” said Pablo Navarro.

“These teeth, more or less conical in shape and a centimetre in size, were transported by rivers, accumulated in lake areas and, over time, became fossilised,” said the researcher. They are one of the most common vertebrate remains in Iberian sites of the Lower Cretaceous (between 145 and 113 million years ago).”

Although it is not known precisely why their teeth were replaced so often, it is believed that this allowed them to possess a greater number of functional teeth at all times. This was a decisive advantage when withstanding the considerable effort required to hold their prey by trapping them between their jaws.

In addition to these findings, the research has enabled the classification of the jaw studied to be clarified: the experts do not attribute it, as previously thought, to the genus Baryonix, but to another type of spinosaurid very close to it, an indeterminate baryonychid.

The palaeontological studies carried out to date at Igea are significant because of the presence of numerous spinosaur skeletal remains, including partial skeletons belonging to several individuals. “The current research will allow our knowledge about the diversity of this unique group of carnivorous dinosaurs to be improved. It is likely that at least two different species are represented at the Igea sites,” said Erik Isasmendi and Xabier Pereda-Suberbiola, palaeontologists in the UPV/EHU’s Department of Geology; consequently, this Riojan locality is one of the world’s leading locations in the study of spinosaurs.

Reference:
Erik Isasmendi, Pablo Navarro-Lorbés, Patxi Sáez-Benito, Luis I. Viera, Angelica Torices, Xabier Pereda-Suberbiola. New contributions to the skull anatomy of spinosaurid theropods: Baryonychinae maxilla from the Early Cretaceous of Igea (La Rioja, Spain). Historical Biology, 2022; 1 DOI: 10.1080/08912963.2022.2069019

Note: The above post is reprinted from materials provided by University of the Basque Country.