Affichage des articles dont le libellé est Dinosaures. Afficher tous les articles
Affichage des articles dont le libellé est Dinosaures. Afficher tous les articles
We've Been Wrong About The Dinosaur Extinction (New Scientist)
Note: Entre Montréal et le cratère de Chicxulub dans le Yucatán, la distance en ligne droite (également connue sous le nom de distance du grand cercle) est d'environ 3 105 kilomètres (ou environ 1 929 miles).
Les cératopsiens d'Appalachie
Des cératopsiens, plus précisément des leptocératopsiens indéterminés, vivaient dans les Appalaches au Crétacé supérieur. Des indices suggèrent qu'ils étaient distincts des espèces de Laramidie. Un fossile clé, un maxillaire partiel (YPM-PU 24964) découvert dans la formation de Tar Heel (Campanien) en Caroline du Nord, a confirmé leur présence.
D'autres restes potentiels de cératopsiens, notamment des dents et d'éventuels fossiles de chasmosaurinés, ont été mis au jour dans la région, révélant une faune plus complexe et diversifiée qu'on ne le pensait.
Plateosaurus (Fernando Usabiaga Bustos)
Plateosaurus was one of the earliest large-bodied dinosaurs to walk the Earth.
Living during the Late Triassic, around 216–204 million years ago, Plateosaurus thrived across what is now Europe. It belonged to the early sauropodomorphs, a group that would later give rise to the giant long-necked sauropods.
Reaching lengths of up to 10 meters, Plateosaurus was primarily herbivorous, feeding on prehistoric vegetation in forested and swampy environments. Its anatomy shows a transitional stage in dinosaur evolution, combining traits of both early bipedal dinosaurs and later massive quadrupeds.
Plateosaurus offers a rare glimpse into the early rise of dinosaurs, long before they dominated the Jurassic world.
Study: Dinosaurs’ Free-Range Parenting Strategy Fundamentally Reshaped Mesozoic World
University of Maryland paleontologist Thomas R. Holtz Jr. has spent decades puzzling over how dinosaurs fit into their ancient worlds — and how those worlds differ from our own. His latest research reveals that scientists may have missed something important when comparing ancient dinosaurs with modern mammals.
“A lot of people think of dinosaurs as sort of the mammal equivalents in the Mesozoic era, since they’re both the dominant terrestrial animals of their respective time periods,” Dr. Holtz said.
“But there’s a critical difference that scientists didn’t really consider when looking at how different their worlds are: reproductive and parenting strategies.”
“How animals raise their young impacts the ecosystem around them, and this difference can help scientists reevaluate how we perceive ecological diversity.”
“Young mammals remain under intensive maternal care until they’re nearly full-grown.”
“Mammal offspring occupy essentially the same ecological role as their parents — eating the same food and interacting with the same environment — because the adults do most of the heavy lifting.”
“You could say mammals have helicopter parents, and really, helicopter moms,” he explained.
“A mother tiger still does all the hunting for cubs as large as she is.”
“Young elephants, already among the biggest animals on the Serengeti at birth, continue to follow and rely on their moms for years.”
“Humans are the same in that way; we take care of our babies until they’re adults.”
“On the other hand, dinosaurs operated very differently. While they did provide some parental care, young dinosaurs were relatively independent.”
“After just a few short months or a year, juvenile dinosaurs left their parents and roamed alone, watching out for each other.”
Dr. Holtz pointed out a similar case in adult crocodilians, some of the closest living analogs for dinosaurs.
Crocodiles guard nests and protect hatchlings for a limited period, but within a few months, juveniles disperse and live independently, taking years to reach adult size.
“Dinosaurs were more like latchkey kids,” Dr. Holtz said.
“In terms of fossil evidence, we found pods of skeletons of youngsters all preserved together with no traces of adults nearby.”
“These juveniles tended to travel together in groups of similarly aged individuals, getting their own food and fending for themselves.”
Dinosaurs’ free-range parenting style complemented the fact that they hatched eggs, forming relatively large broods in a single attempt.
Because multiple offspring were born at once and reproduction occurred more frequently than in mammals, dinosaurs increased the chances of survival for their lineage without expending much effort or resources.
“The key point here is that this early separation between parent and offspring, and the size differences between these creatures, likely led to profound ecological consequences,” Dr. Holtz said.
“Over different life stages, what a dinosaur eats changes, what species can threaten it changes and where it can move effectively also changes.”
“While adults and offspring are technically the same biological species, they occupy fundamentally different ecological niches.”
“So, they can be considered different ‘functional species’.”
For example, a juvenile Brachiosaurus the size of a sheep can’t reach vegetation 10 m above the ground like a grown-up Brachiosaurus.
It must feed in different areas and on different plants and face threats from carnivores that would avoid fully grown adults.
As a young Brachiosaurus grows — rom dog-sized to horse-sized to giraffe-sized to its final enormous proportions — its ecological role shifts continuously.
“What’s interesting here is that this completely changes how scientists view ecological diversity in that world,” Dr. Holtz said.
“Scientists generally think that mammals today live in more diverse communities because we have more species living together.”
“But if we count young dinosaurs as separate functional species from their parents and recalculate the numbers, the total number of functional species in these dinosaur fossil communities is actually greater on average than what we see in mammalian ones.”
So, how could ancient ecosystems support all these functional roles? Dr. Holtz believes that two explanations could be plausible.
First, the Mesozoic world had different environmental conditions, such as warmer temperatures and higher carbon dioxide levels.
These factors would have made plants more productive, generating more food energy to support more animals.
Second, dinosaurs might have had somewhat lower metabolic rates than similarly sized mammals, meaning they needed less food to survive.
“Our world might actually be kind of starved in plant productivity compared to the dinosaurian one,” Dr. Holtz said.
“A richer base of the food chain might have been able to support more functional diversity.”
“And if dinosaurs had a less demanding physiology, their world would’ve been able to support a lot more dinosaur functional species than mammalian ones.”
Dr. Holtz believes his theories don’t necessarily indicate that dinosaur ecosystems were significantly more diverse than our own mammalian world — just that diversity might take forms scientists currently don’t recognize.
He plans to continue exploring similar patterns within this framework of functional diversity across different dinosaur life stages to better understand the world they lived in and how it evolved into the one humans live in today.
“We shouldn’t just think dinosaurs are mammals cloaked in scales and feathers,” Dr. Holtz said.
“They’re distinctive creatures that we’re still looking to capture the full picture of.”
His paper appears in the Italian Journal of Geosciences.
Saurornitholestes
Fossil vomit contains new species of pterosaur from Brazil
One hundred and ten million years ago in what is now Brazil, a dinosaur’s dinner got the best of it. The reptile regurgitated its meal, leaving behind a pile of vomit that happened to fossilize—a stroke of geologic luck that preserved the remains of a newly discovered species.
When paleontologists recently examined the petrified puke (pictured), known scientifically as a regurgitalite, they found the bones within it came from two pterosaurs representing a previously unknown species. The discovery, published this week in Scientific Reports, is the first instance of an animal being described based on remains found in fossilized vomit.
The team named the new pterosaur Bakiribu waridza, which means “comb mouth” in the Indigenous Kariri language spoken in northeastern Brazil’s Araripe region, where the fossil was unearthed. The name references the animal’s bristlelike teeth, which it likely used to catch crustaceans and other small aquatic animals. The first filter-feeding pterosaur ever found in Brazil, B. waridza exhibits a mix of features seen in both older pterosaurs from Germany and slightly younger species from Argentina.
It's hard to tell which species of dinosaur devoured the two pterosaurs and then threw them back up. The researchers think the most likely culprit is a spinosaur (illustration), a group of dinosaurs with crocodilelike jaws that dominated the region during the early Cretaceous period. These predators apparently had a taste for pterosaurs: Another pterosaur skeleton from this area of Brazil was found with a spinosaur tooth lodged in its neck.
Griffes de droméosauridés
Scénarios proposés pour la fonction faucille-griffe, avec C, D et F comme comportements les plus plausibles.
Mont Saint-Hilaire
Le mont Saint-Hilaire a environ 125 millions d'années. Il s'est formé au Crétacé, lorsqu'une colonne de magma s'est infiltrée dans la croûte terrestre, refroidissant et durcissant progressivement. Ce processus s'est achevé il y a entre 133 et 120 millions d'années. Pendant des millions d'années, l'érosion a usé les roches environnantes plus tendres, laissant subsister la roche ignée plus dure et plus résistante de la montagne.
Il y a environ 125 millions d'années, l'est de l'Amérique du Nord était habité par divers dinosaures, bien que sa faune spécifique fût moins diversifiée que celle de la partie occidentale du continent à cette époque. Parmi les groupes clés, on trouve les premiers hadrosaures comme Protohadros, Claosaurus et Lophorhothon, le théropode Eubrontes et le sauropode à long cou Astrodon johnstoni.
Astrodon johnstoni : Sauropode herbivore à long cou qui vivait dans un environnement tropical de l'actuel Maryland. Eubrontes : Considéré comme le premier grand théropode (un type de dinosaure carnivore) découvert sur la côte Est.
Protohadros, Claosaurus et Lophorhothon : Premiers parents des hadrosaures, ou dinosaures à bec de canard.
Hypsibema : Autre dinosaure hadrosauroïde des Appalaches, comme Hypsibema crassicauda et Hypsibema missouriensis.
Hadrosaurus : et Eotrachodon : Exemples de la famille des Hadrosauridae découverts en Appalachie.
Pekinosaurus olseni : Dinosaure ornithischien primitif, ou herbivore, de Nouvelle-Angleterre.
Neovenator : Grand théropode. Bien que ses fossiles aient été découverts en Europe, ses dents sont similaires à celles de l'Allosaurus, plus grand, qui vivait plus tôt au Jurassique supérieur.
Il y a 125 millions d'années, l'écosystème de l'est de l'Amérique du Nord était chaud, humide et dominé par les cycadales, les fougères et les conifères. Les dinosaures parcouraient les terres et une vie marine diversifiée occupait les eaux peu profondes des mers intérieures. C'était le Crétacé inférieur, caractérisé par un niveau marin élevé, un climat plus chaud sans glace polaire et l'apparition précoce de plantes à fleurs qui allaient se diversifier au fil du temps.
Le climat était plus chaud et plus équitable qu'aujourd'hui, sans calottes glaciaires polaires. Les forêts étaient composées de plantes non fleuries comme les cycadales, les ginkgos, les conifères et les fougères.
Les premières plantes à fleurs (angiospermes) sont apparues et ont commencé à se diversifier à cette époque, bien qu'elles ne constituaient pas encore le groupe végétal dominant. Le plus ancien fossile d'angiosperme connu, Montsechia vidalii, date d'environ 125 millions d'années.
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