��Ī - Dinosaurs

Bird beak evolved before dinosaur extinction

sc604 — Wed, 30 Nov 2022 15:18:58 +0000

Fossilised fragments of a skeleton, hidden within a rock the size of a grapefruit, have helped upend one of the longest-standing assumptions about the origins of modern birds.

Shaking the dinosaur family tree: how did ‘bird-hipped’ dinosaurs evolve?

sc604 — Wed, 21 Sep 2022 14:57:37 +0000

Researchers have conducted a new analysis of the origins of ‘bird-hipped’ dinosaurs – the group which includes iconic species such as Triceratops – and found that they likely evolved from a group of animals known as silesaurs, which were first identified two decades ago.

Dense bones allowed Spinosaurus to hunt underwater

sc604 — Wed, 23 Mar 2022 15:39:48 +0000

Spinosaurus is the biggest carnivorous dinosaur ever discovered—even bigger than T. rex—but the way it hunted has been a subject of debate for decades. Based on its skeleton, some scientists have proposed that Spinosaurus could swim, but others believe that it waded in the water like a heron.

To help solve this mystery, palaeontologists from the Universities of ��Ī and Oxford, and the Field Museum in Chicago, USA, have taken a different approach by examining the density of their bones and comparing them to animals like penguins, hippos and alligators.

The team’s analysis, published in the journal Nature, found that Spinosaurus and its close relative Baryonyx had dense bones that likely would have allowed them to submerge themselves underwater to hunt. Meanwhile, another related dinosaur called Suchomimus had lighter bones that would have made swimming more difficult, so it likely waded instead or spent more time on land like other dinosaurs.

“The fossil record is tricky — there are only a handful of partial spinosaurid skeletons, and we don’t have any complete skeletons for these dinosaurs,” said co-lead author Dr Matteo Fabbri from the Field Museum. “Other studies have focused on interpretation of anatomy, but if there are such opposite interpretations regarding the same bones, this is already a clear signal that maybe those are not the best proxies for us to infer the ecology of extinct animals.”

“There’s nothing like Spinosaurus in our modern world, but they had a number of traits that we see today in semi-aquatic animals who specialise in aquatic prey,” said co-lead author Dr Guillermo Navalón from ��Ī’s Department of Earth Sciences.

All life initially came from water, and most groups of terrestrial vertebrates contain members that have returned to it—for instance, while most mammals are land-dwellers, we’ve got whales and seals that live in the ocean, and other mammals like otters, tapirs, and hippos that are semi-aquatic. For a long time, non-avian dinosaurs (those that didn’t branch off into birds) were the only group without any water-dwellers. That changed in 2014, when a new Spinosaurus skeleton was described.

Scientists already knew that spinosaurids spent some time by water—their long, crocodile-like jaws and cone-shaped teeth are like those of other aquatic predators, and some fossils had been found with bellies full of fish. But the Spinosaurus specimen described in 2014 had retracted nostrils, short hind legs, paddle-like feet, and a fin-like tail: all signs that pointed to an aquatic lifestyle. But researchers have continued to debate whether spinosaurids swam for their food or if they just stood in the shallows and dipped their heads in to snap up prey.

This continued back-and-forth led the researchers to try to find another way to solve the problem.

“Instead of trying to know as much as possible about the whole skeleton of Spinosaurus, we asked a much simpler question — what are the most important small-scale observations that would tell you whether animals routinely swim or not?” said co-lead author Professor Roger Benson from the University of Oxford.

Across the animal kingdom, bone density is a tell in terms of whether that animal can sink beneath the surface and swim. Dense bone works as buoyancy control and allows the animal to submerge itself.

“We thought maybe this is the proxy we can use to determine if spinosaurids were actually aquatic,” says Fabbri.

The researchers put together a dataset of femur and rib bone cross-sections from 250 species of extinct and living animals, from seals, whales, elephants, mice and hummingbirds, to dinosaurs of different sizes, to extinct marine reptiles like mosasaurs and plesiosaurs.

They compared these cross-sections to bone from Spinosaurus and its relatives Baryonyx and Suchomimus. “We had to divide this study into successive steps,” said Navalón. “The first was to understand if there is actually a universal correlation between bone density and ecology. And the second was to infer ecological adaptations in extinct taxa.”

Essentially, the team had to show a proof of concept among present-day animals that we know for sure are aquatic or not, and then apply it to extinct animals that we can’t observe.

The study revealed a clear link between bone density and aquatic foraging behaviour: animals that submerge themselves underwater to find food have bones that are almost completely solid throughout, whereas cross-sections of land-dwellers’ bones look more like doughnuts, with hollow centres.

“Aquatic animals need to be able to control their buoyancy, but terrestrial animals don't have this problem,” said Navalón. “Because bones are mineralised tissue, controlling the rate of deposition of mineralised tissue within them is the easiest route to become denser or lighter for a land-dwelling vertebrate. This happened in many groups that underwent the ‘back to water’ evolutionary journey: from whales and hippopotamuses to penguins and marine reptiles that lived in the distant past.”

When the researchers applied spinosaurid dinosaur bones to this paradigm, they found that Spinosaurus and Baryonyx both had the sort of dense bone associated with full submersion.

“If we combine all these pieces of evidence, Spinosaurus might have moved through shallow water using a combination of ‘bottom-walking’ – like modern hippos – and side-to-side strokes of its giant tail,” said Navalón. “It probably used this means of locomotion not to pursue prey for long distances in open water, but to ambush and catch very large fish like lungfishes or coelacanths that lived in the same environment.”

Meanwhile, the closely-related Suchomimus had hollower bones. It still lived by water and ate fish, as evidenced by its crocodile-mimic snout and conical teeth, but based on its bone density, it wasn’t actually swimming.

Other dinosaurs, like the giant long-necked sauropods also had dense bones, but the researchers don’t think that meant they were swimming. “Very heavy animals like elephants and rhinos, and like the sauropod dinosaurs, have very dense limb bones, because there’s so much stress on the limbs,” said Fabbri. “The other bones are pretty lightweight. That’s why it was important for us to look at a variety of bones from each of the animals in the study.” And while there are limitations to this kind of analysis, there is potential for this study to tell us about how dinosaurs lived.

“One of the big surprises from this study was how rare underwater foraging was for dinosaurs, and that even among spinosaurids, their behaviour was much more diverse that we’d thought,” said Navalón.

The study shows how much information can be gleaned from incomplete specimens. “The good news with this study is that now we can move on from the paradigm where you need to know as much as you can about the anatomy of a dinosaur to know about its ecology, because we show that there are other reliable proxies that you can use,” said Fabbri.

Reference:
Matteo Fabbri, Guillermo Navalón, Roger B J Benson et al. ‘Subaqueous foraging among carnivorous dinosaurs.’ Nature (2022). DOI: 10.1038/s41586-022-04528-0

Adapted from a Field Museum press release.

Its close cousin Baryonyx probably swam too, but Suchomimus might have waded like a heron.

There’s nothing like Spinosaurus in our modern world, but they had a number of traits that we see today in semi-aquatic animals who specialise in aquatic prey

Guillermo Navalón

Davide Bonadonna

Spinosaurus

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Tree-dwelling mammals survived after asteroid strike destroyed forests

cmm201 — Thu, 14 Oct 2021 12:10:32 +0000

Overall, the study supports the hypothesis that the widespread destruction of forests following the asteroid’s impact favoured ground-dwelling mammals over their arboreal counterparts. However, it also provides strong evidence that some tree-dwelling animals also survived the cataclysm, possibly nesting in branches through the Cretaceous-Paleogene (K-Pg) extinction event.

“The recovery of terrestrial vertebrate life following the end-Cretaceous asteroid impact was one of the most important events in the history of life on Earth,” said senior author Dr Daniel Field, from ��Ī’s Department of Earth Sciences. “In this study, we drew on our previous work at ��Ī to investigate whether there were similarities in the ecological attributes of avian and mammalian survivors of the end-Cretaceous mass extinction.”

The K-Pg mass extinction event occurred when a meteor slammed into Earth at the end of the Cretaceous period. The impact and its aftereffects killed roughly 75% of the animal and plant species on the planet, including whole groups like the non-avian dinosaurs.

For the study, the researchers analysed patterns of substrate preferences among all modern mammals and their ancestors, working backwards from the present day to before the K-Pg extinction event by tracing these traits along numerous phylogenetic trees — diagrams that illustrate the evolutionary relationships among species.

“Our study takes advantage of an ongoing revolution in our understanding of the tree of life, only made possible by researchers working in association with natural history collections,” said co-lead author Jacob Berv, from the University of Michigan, USA. “By integrating data from such collections with modern statistical techniques, we can address new questions about major transitions in evolutionary history.”

The researchers classified each mammalian species as arboreal, non-arboreal, or semi-arboreal. To be considered arboreal, the species had to nearly always nest in trees. Categorising some species could be tricky. For example, many bat species spend a lot of time among trees but nest in caves, so bats were mostly categorised as non-arboreal or semi-arboreal.

“We were able to see that leading up to the K-Pg event, there was a spike in transitions from arboreal and semi-arboreal to non-arboreal habitat use across our models,” said co-lead author Jonathan Hughes, from Cornell University, USA.

The work builds on a previous study led by Field, which used the same analytical method — known as ancestral state reconstruction — to show that all modern birds evolved from ground-dwelling ancestors after the asteroid strike.

“The fossil record of many vertebrate groups is sparse in the immediate aftermath of the extinction,” said Field, who is also curator of ornithology at the ��Ī Museum of Zoology. “Analytical approaches like ancestral state reconstruction allow us to establish hypotheses for how groups like birds and mammals made it through this cataclysm, which palaeontologists can then test when additional fossils are found.”

The analysis helps illuminate ecological selectivity of mammals across the K-Pg boundary despite the relatively sparse fossil record of mammalian skeletal elements from the periods immediately preceding and following the asteroid’s impact.

How the tree-dwelling ancestors of primates survived the asteroid’s destruction is unclear. According to the authors, it’s possible that some forest fragments survived the calamity or that early primates and their relatives were ecologically flexible enough to modify their substrate preferences in a world mostly denuded of trees.

Reference:
Jonathan J Hughes et al. ‘Ecological selectivity and the evolution of mammalian substrate preference across the K–Pg boundary.’ Ecology and Evolution (2021). DOI: 10.1002/ece3.8114

Adapted from a Yale news release.

An asteroid strike 66 million years ago wiped out the non-avian dinosaurs and devastated the Earth’s forests, but tree-dwelling ancestors of primates may have survived it, according to a new study published in the journal Ecology and Evolution.

The recovery of terrestrial vertebrate life following the end-Cretaceous asteroid impact was one of the most important events in the history of life on Earth

Daniel Field

Rod Waddington

Chimpanzee, Uganda

Yes

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Scientists zero in on the role of volcanoes in the demise of dinosaurs

cmm201 — Mon, 29 Mar 2021 19:00:00 +0000

Earth has experienced five major extinction events over the last 500 million years, the fifth and most recent responsible for wiping out the dinosaurs 66 million years ago. Massive volcanic eruptions have been identified as a major driver in the environmental change which triggered at least three of these extinctions.

But what dealt the final blow to the dinosaurs – whether an enormous outpouring of lava from the Deccan Traps volcanic province in India or a large asteroid impact or perhaps a combination of the two – has remained open to debate.

Now, a multi-institutional research team, led by scientists from the City University of New York (CUNY), and involving the ��Ī, has, for the first time, accurately pinpointed the timing and amount of carbon released from Deccan Traps volcanic province. The new data means scientists can now assess the role of volcanism in climate shifts around the End-Cretaceous mass extinction.

The team’s data show that CO₂ outgassing from Deccan Traps magmas can explain a warming of Earth’s global temperatures by roughly 3 degrees Celsius during the early phases of Deccan volcanism, but shows that the warming had lessened by the time of the mass extinction event.

Their findings support the theory that later Deccan magmas were not releasing that much CO₂, suggesting that volcanic carbon emissions didn’t play a major role in the dinosaur’s extinction.

“The results are important because they show that major volcanic events can release substantial amounts of CO₂ not just from surface vents, but also from the large and complex plumbing systems that feed them. Even though volcanic carbon emissions alone couldn’t have triggered the mass extinction, our data highlights their influence on our planet's climate and habitability,” said co-author Professor Sally Gibson, from ��Ī's Department of Earth Sciences.

The team had to search through hundreds of Deccan lava samples to identify suitable candidates to profile for their trapped CO₂ content. “In modern volcanic eruptions, such as the current one in Iceland, the CO₂ is trapped in crystals that are embedded in glassy fragments of rapidly cooled magma, but these are fragile and not preserved in the 65 million-year-old Deccan Traps,” said Gibson.

Recent research has identified a global warming event that occurred several hundred thousand years before the End-Cretaceous extinction. Some scientists have linked the eruption of the Deccan Traps to this warming event, but there is debate over whether the lavas that erupted could have released enough CO₂ into the atmosphere to cause it. Adding to this mystery, the lava volumes that erupted during this time are relatively small compared to the volumes erupted during subsequent stages of Deccan Traps activity. A major challenge in this debate has been the lack of CO₂ data on Deccan magmas from this time.

“The new data highlights that carbon outgassing from lava volumes alone couldn’t have caused that level of global warming. But, when we factored in outgassing from magmas that froze beneath the surface rather than erupting, we found that the Deccan Traps could have released enough CO₂ to explain this warming event,” said lead-author Andres Hernandez Nava, a PhD student in The Graduate Center, CUNY Earth.

For their study, the team used lasers and beams of ions to measure the amount of CO₂ inside tiny droplets of frozen magma trapped inside Deccan Traps crystals from the End Cretaceous time period. They also measured the amounts of other elements, such as barium and niobium, which are indicators for how much CO₂ the magmas started out with. Finally, they performed modeling of latest Cretaceous climate to test the impacts of Deccan Traps carbon release on surface temperatures.

“Our lack of insight into the carbon released by magmas during some of Earth’s largest volcanic eruptions has been a critical gap for pinning down the role of volcanic activity in shaping Earth’s past climate and extinction events,” said Black, the study’s principal investigator and a professor in the Earth and Environmental Science program at The Graduate Center CUNY and City College of New York. “This work brings us closer to understanding the role of magmas in fundamentally shaping our planet’s climate, and specifically helps us test the contributions of volcanism and the asteroid impact in the end-Cretaceous mass extinction.”

Reference:
Hernandez Nava et al. Reconciling early Deccan Traps CO2 outgassing and pre-KPB global climate. PNAS (2021). DOI : 10.1073/pnas.2007797118

Adapted from a press release by The Graduate Center, CUNY.

Researchers have uncovered evidence suggesting that volcanic carbon emissions were not a major driver in Earth’s most recent extinction event.

Even though volcanic carbon emissions alone couldn’t have triggered the mass extinction, our data highlights their influence on our planet's climate and habitability

Sally Gibson

Loÿc Vanderkluysen, Drexel University

Deccan Traps, India

Yes

Scelidosaurus: ready for its closeup at last

sc604 — Wed, 26 Aug 2020 15:05:09 +0000

The first complete dinosaur skeleton ever identified has finally been studied in detail and found its place in the dinosaur family tree, completing a project that began more than a century and a half ago.

‘Wonderchicken’ fossil from the age of dinosaurs reveals origin of modern birds

sc604 — Wed, 18 Mar 2020 15:19:43 +0000

The oldest fossil of a modern bird yet found, dating from the age of dinosaurs, has been identified by an international team of palaeontologists.

‘Treasure trove’ of dinosaur footprints found in southern England

sc604 — Mon, 17 Dec 2018 09:00:46 +0000

More than 85 well-preserved dinosaur footprints – made by at least seven different species – have been uncovered in East Sussex, representing the most diverse and detailed collection of these trace fossils from the Cretaceous Period found in the UK to date. Click here to find out more.

Neil Davies

Two large iguanodontian footprints with skin and claw impressions

Yes

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