Equus scotti et Panthera atrox (Beth Zaiken)




 

Quel est l’âge du cratère de Charlevoix?



Extraits de cet article:

Charlevoix ne s’est pas toujours trouvé sous le 47e parallèle nord. À une époque géologique lointaine, il y a autour de 450 millions d’années, la région se situait à moins de 1000 km au sud de l'Équateur.

Le climat y est chaud, mais on est encore bien loin des paysages tropicaux actuels. En fait, la nature comme nous la connaissons ne s’est pas encore imposée sur la terre ferme. Des champignons et de petites plantes commencent alors à apparaître ici et là dans le panorama, mais les premières espèces animales n’ont colonisé que les eaux peu profondes de la planète.

Charlevoix se trouve d’ailleurs à une centaine de mètres sous l’eau, dans l’océan Iapétus (aussi appelé proto-Atlantique), campé entre le Bouclier canadien et les Appalaches.

Le niveau d'eau est alors beaucoup plus élevé tout le long du fleuve Saint-Laurent actuel. Montréal, Trois-Rivières, Québec, Charlevoix, et la Côte-Nord se trouvent sous l'eau, explique Jean-Michel Gastonguay, professeur de physique et d'astronomie au Centre d'études collégiales en Charlevoix et directeur des Observatoires astronomique et de l'Astroblème de Charlevoix.

Le Québec frappé en plein cœur

Un peu avant la fin de l’Ordovicien, il y a entre 430 et 453 millions d’années, Charlevoix est frappée par une météorite d’environ 6 km de diamètre qui pénètre dans l’atmosphère et percute la croûte terrestre à toute vitesse pour s’y enfoncer jusqu’à 12 km de profondeur.

Sous l’impact, la région se transforme en un immense cratère de roche en fusion. La météorite fond et se vaporise; les roches situées en périphérie du cratère se fracturent.

Des fragments et de la poussière de roche sont éjectés dans les airs pour ensuite retomber à l’intérieur et autour du cratère. Des fragments seraient tombés aussi loin qu’à Trois-Rivières, situé à 250 km, indique Jean-Michel Gastonguay.

C'est une force qui dépasse l'entendement. Même la couleur de l'atmosphère aurait changé pendant un certain temps, ajoute le professeur.

La géologie et la morphologie de la région subissent en quelques instants des transformations qui sont encore visibles de nos jours.

La chute de ce corps céleste venu de la ceinture d’astéroïdes – ou de l’orbite terrestre, selon une récente théorie – marque aussi l’ensemble de la planète.

Pour M.Gastonguay, l’événement cataclysmique présente des similitudes avec celui survenu sur le territoire mexicain plus récemment, il y a 66 millions d'années, et qui a mené à l'extinction des dinosaures. Si les deux météorites sont tombées en eau peu profonde près de l’Équateur, celle tombée au Yucatan a cependant libéré une quantité d’énergie beaucoup plus importante.

Cela ne veut pas dire que l’impact de Charlevoix a été sans conséquence. L'énergie dégagée est hallucinante! C'est plusieurs centaines de millions de fois plus puissants que la bombe qui a été larguée sur Hiroshima, illustre M.Gastonguay.

On soupçonne d’ailleurs que cet impact a accéléré le refroidissement climatique global qui a été enclenché il y a 485 millions et a qui a mené à la glaciation hirnanti enne, l’événement qui a mis fin à l’Ordovicien et entraîné la mort de 70 % des espèces vivantes sur terre.

Plus vieux qu’on pensait

Les premières études sur l’âge du cratère ont été réalisées dans les années 1970 à partir de la datation d’impactites trouvées dans un affleurement du secteur de Sainte-Marie-de-Charlevoix.

Les impactites sont des roches créées par la chaleur, la pression et les mouvements de la croûte terrestre lors d'un impact météoritique important, précise M. Gastonguay.

Des études effectuées au début des années 2000 tendent cependant à montrer que l’impact s’est produit il y a plus longtemps qu’on pensait, jusqu'à il y a 410 millions d'années.

Ce n'est toutefois qu'en 2019 que des travaux ont montré que la chute de la météorite s’est produite il y a 450 millions d’années (plus ou moins 20 millions d’années), ce qui correspond à près de 100 millions d'années plus tôt que les estimations précédentes.

Vers une datation plus précise

Pour le chercheur Nicolas Pinet, de la Commission géologique du Canada (CGC), une estimation de plus ou moins 20 millions d’années reste très imprécise.

En géologie, on est maintenant capable de circonscrire l'âge [d'une roche] de manière beaucoup plus précise; autour de deux à trois millions d’années, explique le géologue.

Ce dernier participe à l’étude géochronologique dont l'objectif est de mieux circonscrire l’âge de l’astroblème de Charlevoix.

La tâche n’est pas facile, puisque la région géologique née il y a plus d'un milliard d'années a connu de multiples événements géologiques, observe Nicolas Pinet.

Trouver les roches témoignant de la chute de la météorite est donc un exercice compliqué qui demande du flair. Et du flair, Jean-Michel Gastonguay en a, lui qui parcourt la région depuis des dizaines d’années. À ses yeux, le projet de datation de l’astroblème est un bel exemple de collaboration entre une organisation de haut niveau, la Commission géologique du Canada, et des chercheurs du collégial. Pour nous, c’est une grande fierté, dit le professeur, qui espère que la collaboration se poursuivra dans le futur.

En septembre dernier, il a accompagné Nicolas Pinet et son collègue Antoine Godet, de la CGC, dans leur recherche des échantillons parfaits. Ensemble, ils ont parcouru la zone du pic central du cratère à la recherche de roches qui pourraient les aider dans leur effort de datation.

Ils ont prélevé une vingtaine d'échantillons dans un rayon allant jusqu’à 7 km du point d'impact (dont le centre est le pic du mont des Éboulements).

Les géologues ont porté une attention particulière aux matériaux vitrifiés et aux cônes associés aux impacts.

Nicolas Pinet rappelle qu’il est difficile de départager les minéraux qui ont été formés lors de l'impact de ceux qui étaient là avant, et de déterminer lesquels ont gardé une partie de leur composition originale. De plus, comme l'histoire de la région est longue et complexe, il y a aussi des pierres ressemblant beaucoup à des roches fondues qui ne sont pas associées à l'impact.

Il y a donc un facteur de chance associé à l’échantillonnage. Le trio de chercheurs espère quand même avoir mis la main, parmi les échantillons, sur celui qui pourrait préciser le moment de l’impact. Dans la vingtaine d'échantillons sélectionnés, on espère avoir deux ou trois bons candidats, indique Nicolas Pinet.

À l'heure actuelle, les échantillons de roche sont transformés en lames minces, c'est-à-dire des tranches extrêmement fines de roche qui sont posées sur une lame de verre, et qui permettent à la lumière de passer à travers afin d'être observée au microscope.

Des photos à très haute résolution seront réalisées de leur contenu, ce qui servira à bien caractériser les minéraux.

Des analyses de pétrographie et de chimie minérale seront également réalisées dans les prochains mois.

Les échantillons les plus prometteurs seront ensuite analysés avec des techniques très précises de datation au laboratoire d’Ottawa de la CGC.

Si on arrive à faire la corrélation entre la chute de la météorite de Charlevoix et la baisse de la température moyenne globale sur terre à la même époque, on pourra penser que cette chute est liée à la première grande extinction de la fin de l’Ordovicien-Silurien, dit avec enthousiasme Jean-Michel Gastonguay, qui rêve de voir la région s’inscrire dans l’histoire de l’évolution de la vie sur la planète.

Le géologue Nicolas Pinet rappelle que le lien entre les deux événements est impossible à établir tant que l’âge de l’astroblème n’est pas précisé, une précision qui pourrait arriver à la fin 2025.

En outre, l'équipe s'intéresse à certaines roches sédimentaires de la région, dont l'analyse pourrait permettre de dater l'impact par une méthode différente et complémentaire.

La théorie des anneaux

En octobre dernier, des scientifiques de l'Université de Monash, en Australie, ont publié une étude dans laquelle ils ont analysé la position et les caractéristiques géologiques de 21 cratères d'impact de météorites – dont celui de Charlevoix – apparus sur terre au cours d'une période connue sous le nom de pic d'impact de l'Ordovicien.

Selon leur théorie, la désintégration d'un astéroïde passant dans le voisinage de la Terre il y a 466 millions d’années aurait mené à la formation d’un système d’anneaux autour de la planète dont la matière serait retombée sur terre pendant une période.

Leurs travaux incluent trois cratères situés de nos jours sur le territoire canadien, dont celui de Charlevoix, et ce dernier est de loin celui qui présente le diamètre le plus important.

De cratère à astroblème

Ce n’est qu’en 1965, grâce aux travaux du géologue Jehan Rondot, du ministère des Ressources naturelles et de la Faune du Québec, que la structure semi-circulaire de Charlevoix a été officiellement associée à un cratère d’impact.

Le géologue y décrit une cicatrice géologique typique observée grâce aux impactites. Dans l'astroblème de Charlevoix, on en observe plusieurs types. Les plus faciles à identifier sont les cônes de percussion qui se forment lorsque l'onde de choc se propage dans la croûte.

Ce sont des roches dont les surfaces présentent des fracturations caractéristiques en forme de queue de cheval, ou de cônes, explique le professeur Castonguay.

De nos jours, la moitié sud du cratère est enfoui sous le fleuve Saint-Laurent, et la moitié nord du cratère est délimitée par la région de Baie-Saint-Paul, à l’ouest, et la région de La Malbaie. à l’est. Le mont des Éboulements correspond au pic central du cratère.

On décrit maintenant les traces de l’impact comme un astroblème puisque le terme désigne les restes d'un ancien cratère d'impact météoritique très érodé.

À l’origine, le choc a créé un cratère de 70 km de diamètre semblable à celui de Tycho, sur la Lune. Ce type de cratère possède une montagne dans le centre, indique Jean-Michel Gastonguay.

De nos jours, le diamètre de l’astroblème est plutôt de 52 km en raison de l’usure du temps.

Le saviez-vous?

L’astroblème de Charlevoix est le troisième plus grand site d'impact connu au Canada, derrière ceux de Sudbury, en Ontario, et de Manicouagan, au Québec, et le onzième plus grand de la planète.

Le Québec possède sur son territoire sept autres astroblèmes, dont ceux de Manicouagan, de Pingualuit, du lac à l'Eau Claire, et du lac Couture.


 

Des ailes pour courir plus vite



Extraits de cet article:

Une piste fossile vieille de 106 millions d’années découverte en Corée du Sud montre la démarche d’un des ancêtres des oiseaux modernes. Les premières empreintes sont rapprochées, signifiant qu’il marchait lentement, à environ deux kilomètres par heure.

Mais plus loin, l’espace entre les traces de pattes s’allonge à 30 centimètres. Comme ce petit dinosaure mesurait seulement 5 cm à la taille, cela signifie qu’il courait à 40 km/h.

Selon l’auteur principal de l’étude, Hans Larsson, de l’Université McGill, ce dinosaure n’aurait jamais pu atteindre cette vitesse en utilisant uniquement ses muscles.

« Les muscles n’étaient pas non plus assez forts. Il fallait qu’il ait un autre mode de propulsion que ses deux pattes. »

C’est la première preuve que des dinosaures à plumes se servaient de leurs ailes pour courir plus vite.

L’étude a été publiée dans la revue universitaire PNAS.

Cousin du vélociraptor

Comment M. Larsson sait-il qu’il s’agit d’un dinosaure et non d’un oiseau – les premiers étant apparus il y a 150 millions d’années ? « Ce sont des empreintes à deux doigts, et pendant tout le Crétacé [il y a 145 à 66 millions d’années], les oiseaux avaient trois ou quatre doigts », répond M. Larsson.

Il sait aussi qu’il s’agit d’un Dromaeosauriformipes rarus, un « microraptor » cousin du vélociraptor des films Jurassic Park, parce qu’aucun autre groupe de dinosaures n’avait deux doigts. Il s’agit d’un des plus petits dinosaures connus.

Boue séchée en Corée du Sud

Les empreintes ont été découvertes sur une plaque préservée de boue séchée, trouvée près de Jijun, en Corée du Sud. « On voit tout, même les traces de gouttes d’eau et d’insectes », souligne M. Larsson.

L’absence d’autres empreintes exclut que l’animal ait utilisé ses pattes d’en avant pour aller plus vite.

M. Larsson est spécialiste de l’évolution des squelettes, des jointures et des musculatures. « Alex [Dececchi, coauteur de l’étude venant de l’Université d’État du Dakota] m’a parlé de ces empreintes quand elles ont été décrites dans Scientific Reports en 2018. Il me disait qu’il devait y avoir une erreur. »

Un biplan sur quatre pattes

Dromaeosauriformipes rarus avait des ailes sur ses quatre pattes. « Comme il ne pouvait pas bouger les ailes autant que les oiseaux d’aujourd’hui, ça lui donnait l’air d’un biplan. »

Ce microraptor aurait pu faire des bonds de 100 à 200 mètres. « Un chercheur dans les années 1990 avait suggéré cette possibilité. Nous avons confirmé que c’était possible avec des modèles de squelettes, mais c’est la première preuve fossile. »

La prochaine étape consistera à reconstruire un modèle numérique du squelette du microraptor pour simuler la marche, la course et les bonds.

Évolutions

Cette découverte montre qu’il y a eu plusieurs évolutions du vol animal. « À l’origine, on avait l’idée que des dinosaures sont montés dans les arbres et ont commencé par planer, dit M. Larsson. Il y a plus de diversité que ce que nous pensions. »

Les dinosaures arboricoles planeurs ont existé, mais ils étaient très rares. « Et ils ne sont pas les ancêtres des oiseaux, comme les microraptors. »

Comme ce microraptor est apparu avant les oiseaux, il y a 164 millions d’années, il pourrait être celui qui a « inventé » le vol.

Les reptiles volants, comme le ptérodactyle, sont apparus plus tard, il y a 150 millions d’années.




 

Comment créer un mammifère en neuf étapes évolutives (Smithsonian)




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Mammals are familiar beasts. From a squirrel on a power line to a blue whale swimming through the sea, we share the world with more than 6,000 mammal species of all shapes and sizes. While we can easily distinguish a creature like a jaguar from a reptile or a bird in the modern world, however, mammals as we know them are the result of hundreds of millions of years of evolutionary changes. In fact, many of the key features that make us mammals evolved even before the dinosaurs.

Paleontologists have known for decades that mammals emerged from a broader, diverse group of creatures called synapsids. The very first synapsids of about 306 million years ago were small and lizard-like, but distinguishable by a single opening in their skull behind their eye socket. (We have a modified version of this hole, the space between your cheekbone and your cranium where a jaw-closing muscle runs through.) Nevertheless, a big evolutionary gap exists between a very early, lizard-like synapsid and modern mammals like ourselves. The following list will take you through nine of the essential evolutionary shifts that allowed mammals to thrive from the Age of Dinosaurs to this moment.

A toolkit of teeth

Most mammals have a dental tool kit of differently shaped teeth. In our own mouths, for example, we have incisors to nip with, canine teeth to puncture, and premolars and molars to crush and mash grub. The diversity lets mammals handle a great variety of food and make the most of our meals, whether it’s a wolf nipping the last muscle of an elk leg or an elephant chewing grass.

Paleontologists can see the beginnings of this differentiation in synapsids more than 295 million years old. Despite its lizard-like appearance, the sail-backed Dimetrodon was a synapsid and more closely related to us than any dinosaur or other ancient reptile. Such pre-mammal synapsids are often called “proto-mammals” as their anatomy set the stage for what mammals would eventually become. Dimetrodon, in particular, illustrates an early dental shift that mammals would later take to extremes. The ancient carnivore’s name means “two measures of teeth,” referring to the stark difference between the large, piercing teeth in the canine tooth position and smaller teeth behind it along the jaw. The difference is the beginning of what anatomists call heterodonty, or having differently shaped teeth in different jaw positions. The condition differs from most reptiles, which are homodont and have teeth about the same size and shape along their jaws. As early synapsids went about feeding on the plants and animals of their world, what started as basic, conical teeth were modified into different feeding specialties. Mammal teeth eventually became so diverse in shape and so distinctive that paleontologists often tell the difference between one species and another based on their dental details.

Long lost ribs

The mammalian backstory isn’t just one of gaining new features. Some ancient traits were lost and had a major influence on mammal evolution. One of the significant losses among mammal ancestors was gastralia, or belly ribs.

Early synapsids like Ophiacodon had thin ribs running along their bellies between their shoulders and hips. Synapsids of the time sprawled with their legs out to the side, like lizards, and so the belly ribs offered some extra protection from the rough ground. As synapsids continued to evolve during the Permian Period, however, they lost their belly ribs. Creatures like our cynodont ancestors, as well as the saber-toothed gorgonopsians, didn’t have belly ribs. Instead, organs like the heart and lungs would be enclosed in the rib cage, and lower organs, such as the stomach and intestines, would be held in by the body cavity and surrounding muscle. Even though the change left proto-mammals more vulnerable to injury across their abdomens, the shift afforded more flexibility in more upright postures with better up-and-down flexibility.

A new roof in the mouth

Ever since fishy creatures crawled out of swamps to drag themselves across the land, breathing while eating has been a problem. Among those early creatures, no divider was present between the nose and throat within the mouth. One big cavity led toward the very closely arranged larynx and pharynx, used for breathing and swallowing. If early tetrapods had their mouths full, breathing at the same time would be a challenge.

Synapsids evolved an anatomical solution to this problem, and they did so more than once. Several synapsid groups evolved a secondary palate during the Permian, or a shelf of bone that separates the nose from the mouth and throat. If you stick your tongue to the roof of your mouth, that’s the secondary palate. The separation allowed predatory synapsids, in particular, the ability to catch prey and feed while still breathing through their noses, letting them hunt and eat more efficiently than their predecessors. Among the groups with a secondary palate were the weasel-like cynodonts, such as the Triassic species Thrinaxodon, who passed the secondary palate on to their mammal descendants.

An earful of jaw

One of the key traits that makes mammals what they are isn’t something you can easily see on the outside, but tucked away inside the ear. The earliest synapsids, much like reptiles, had lower jaws that were made up of several different bones. Behind the tooth-bearing dentary were several other bones notched together like puzzle pieces leading to the jaw joint. Over time, however, synapsid jaws shifted. The dentary expanded to become the entirety of the lower jaw, a single bone that afforded synapsids stronger bites. Paleontologists see the shift in some early mammals such as the tiny, shrew-like Morganucodon. At the same time, the jaw bones closest to the back of the jaw became smaller and specialized to transmit vibrations to the ear, improving synapsid hearing. The incus, malleus and stapes of our inner ear are the remnants of these ancient jaw bones. By the early part of the Jurassic, about 191 million years ago, mammals had very sensitive ears that helped them navigate a dinosaur-filled world.

Fur and whiskers

Fossils preserving the body coverings of proto-mammals are rare. The few examples that paleontologists have found so far indicate that early synapids had scaly, lizard-like skin, which eventually shifted to smoother, softer skin through the Permian. The question is when synapsids evolved fur.

No matter the age, most synapsid and mammal fossils are not found with any indication of how furry they might have been. But there are a few clues about when fur and whiskers began to be important to synapsids. Whiskers are a modified form of hair, and the sensitive hairs send a great deal of information to the brain. By looking at the proportions of proto-mammal and early mammal brains, paleontologists found that mammal predecessors had fur and whiskers by about 240 million years ago. The timing coincides with when reptiles were proliferating, perhaps indicating that an insulating fur coat and whiskers to help navigate the dark allowed mammals to become more nocturnal and thrive at small size as the Mesozoic got underway.

Eye bones disappeared

Mammals don’t have bones in their eyes, but some of our ancestors and relatives did. Much like many reptiles and birds today, early synapsids had a circle of thin bones inside the eye called the scleral ring. Exactly what these bones do is still mysterious. Anatomists hypothesize that the bones are attachment sites for muscles that help animals change different viewing distances, or perhaps help support the eye during changes in pressure like diving deep or flying high. When cynodonts, a diverse group of weasel-like synapsids gave rise to the earliest mammals during the Triassic, however, the scleral rings were lost. Paleontologists hypothesize that the evolutionary miniaturization of early mammals might have something to do with the shift, as the supportive roles of the scleral ring were not needed at smaller sizes. Whatever happens, mammals don’t have to worry about potentially breaking an eye bone.

Walking postures shifted

Dimetrodon and other early proto-mammals had their bellies close to the ground. Such synapsids moved almost like monitor lizards or crocodiles, their bodies flexing from side to side as they walked. While such early synapsids would have been capable of bursts of speed, they weren’t especially quick and lacked the endurance seen in many mammals today. During the Permian, however, some synapsid groups began evolving more upright body postures. Their limbs took on more column-like arrangements, lifting the body higher off the ground and shifting motion to up-and-down movements of the spine rather than side-to-side. Standing taller, and losing their gastralia, allowed proto-mammals and mammal ancestors to move faster and more efficiently, and better forage for food and escape potential predators. Cynodonts, especially, evolved more and more upright body postures during the Triassic, setting up the way mammals move today.

Milk fueled mammal growth

Mammals aren’t the only creatures to make milk, but it’s as much a defining feature for us as our peculiar inner ear bones. Even the egg-laying duck-billed platypus makes milk, exuding the protein-rich substance from glands on its belly. The questions facing paleontologists are how and when milk evolved among mammals. Some experts place the origin around the rise of synapsids. Perhaps, as the lizard-like proto-mammals became accustomed to life on land, they oozed a protein-rich substance from their bellies that kept their eggs moist on dry land. Over time, the fluid changed and gained new uses, nourishing young that hatched out of eggs or were born live to help them grow faster. More fossil evidence will be needed to investigate and test these ideas, but clues from Jurassic mammals indicate that they were both making milk and weaning their fast-growing young.



Agriculture

La propagation de l'agriculture du Moyen-Orient vers l'Europe entre 9600 et 3800 avant notre ère.




Trouvé ici.


La Province de Grenville





Extraits de ce site:

La Province de Grenville représente l’empreinte du dernier évènement tectonique (orogenèse) à avoir façonné le Bouclier canadien. Le Grenville s’est construit étape par étape le long de la marge est du continent Laurentia (noyau continental de l’Amérique du Nord). Il constitue la racine profonde d’une ancienne chaîne de montagnes comparable à l’Himalaya actuel (Windley, 1986). Cette chaîne de montagnes résulterait d’une collision continent-continent entre les continents Laurentia et Amazonia (1090-980 Ma; par ex. Rivers et al., 1989, 2012)

Au Canada, la Province de Grenville s’étend sur plus de 2000 km selon une direction NE entre les Grands Lacs, au SW, et le Labrador, au NE, avec une largeur moyenne de 350 km. Elle correspond au plus long segment continu d’une ceinture orogénique d’âge mésoprotérozoïque tardif dans le monde (Wynne-Edwards, 1972; Davidson, 1995).

Au Québec, la Province de Grenville occupe un territoire très étendu de près de 495 000 km2. Elle est limitée au nord par les provinces du Supérieur et de Churchill et au sud par les roches sédimentaires de la Plate-forme du Saint-Laurent et la Province des Appalaches. Le Front de Grenville, bien visible sur les cartes aéromagnétiques, sépare la Province de Grenville de la Province du Supérieur. D’un point de vue géographique, la Province de Grenville est subdivisée en trois secteurs : ouest, central et est. De façon arbitraire, la partie ouest du Grenville s’étend de Trois-Rivières jusqu’à la frontière avec l’Ontario. La partie est occupe la région de Sept-Îles jusqu’au Labrador (Terre-Neuve) et la partie centrale se situe entre les deux, soit à partir de Sept-Îles à l’est jusqu’à Trois-Rivières à l’ouest (Moukhsil et Solgadi, 2018).

À l’extérieur du Bouclier canadien, la Province de Grenville s’étire vers le sud-ouest jusqu’au Texas et au Mexique. Au sud des Grands Lacs, elle se prolonge sous la couverture des roches paléozoïques du centre des États-Unis jusqu’au nord des monts Ouachita, à l’est des provinces de Yavapai et de Mazatzal d’âge précambrien moyen (Hoffman, 1988, 1989). Des roches précambriennes d’âge grenvillien se retrouvent aussi imbriquées dans les Appalaches. Elles forment la grande écaille du Long Range dans la Zone de Humber, à Terre-Neuve, et des copeaux dans des zones de failles taconiques au Québec. Dans l’est et le sud du Mexique, des roches ignées d’âge mésoprotérozoïque et métamorphisées au cours de l’Orogenèse grenvillienne sont exposées au sud de la suture de Ouachita (Cameron et al., 2004).

Au-delà de l’Amérique du Nord, la Province de Grenville a été reconnue à l’intérieur de boutonnières dans les Calédonides de l’Irlande du Nord, en Écosse, puis en Norvège et dans la Province svéconorvégienne en Scandinavie (Davidson, 1998; Lorenz et al., 2012). Selon plusieurs auteurs, elle se poursuivrait de l’Amérique centrale à l’Antarctique, et de l’Inde à l’Australie (par ex. Karlstrom et al., 1999).



La Terre il y a 1 milliard d'années







Trouvé ici.


Hesperornis (kepyle2055)




Trouvé ici.




Patriofelis (Rom-u)



Patriofelis  (Patriofelis Leidy, 1870)

Order: †Oxyaenodonta

Family: Oxyaenidae

Temporal range: during the Miocene (North America)

Dimensions: length - 1,8 m, height - 70 сm, weight - 30 - 100 kg

A typical representative: Patriofelis ferox

In North America during the Miocene, some 45 million years ago, the cat-like creodont Patriofelis hunted in the conifer forests.  About the size of a modern-day jaguar, Patriofelis had short legs, a long tail, and broad paws.  The paws suggest that the creodont may not have run fast, but could have been a good swimmer.  Modern jaguars often hunt in the rivers.  At the very least, Patriofelis was probably an ambush hunter.

Game in Nevada and Oregon was plentiful.  Small horses started to travel in herds, taking advantage of the receding forests.   Could Patriofelis lay in wait near watering holes, picking off unwary prehistoric horses and other herbivores.

One theory about Patriofelis' habits suggest that it led a semi-aquatic life.  A specimen found in the Bridger Lake sediment had very well-worn teeth.  Bridger Lake once swarmed with turtles.  If so, the turtles may have been a staple part of Patriofelis' diet!  To support this theory, coprolites containing fragments of turtle shells have been found in the Bridger Lake sediment.  Patriofelis definitely had jaws robust enough to dine on turtles.

Patriofelis' predecessor Oxyaena, was a good climber but it looks like Patriofelis preferred the water to the trees.  If Patriofelis continued in the water, it may have evolved into modern pinnipeds.  So, the "father of cats" may actually have been more like the "father of seals!" The largest Patriofelis - Patriofelis ferox - was about the size of a small black bear, with a disproportionately large skull.  The skull is also broad and short and have some aspects similar to that of a sea lion's skull.  However, unlike a sea lion, Patriofelis had a small brain case inside its huge, thick skull.  Patriofelis ulta was about a third smaller.  Both species had broad, plantigrade feet and long bodies and tails.  Some of the sketches of Patriofelis resemble an otter on steroids more than a feline.

Trouvé ici.

Le Permien: seule fois où le milieu aquatique était plus sûre que le milieu terrestre (ExtinctZoo )




 

Stégosauridés (artbyjrc)




Trouvé ici.



Un fossile de Nouvelle-Écosse est le premier exemple de soins parentaux



Extraits de l'article:

A partnership between a Nova Scotia fossil hunter and Carleton University researchers has yielded the earliest fossil evidence of a parent caring for its offspring — a skeleton of a 300-million-year-old animal that appeared to be concealing and protecting a juvenile in a den.

The two creature were “synapsids” — commonly known as mammal-like reptiles. While prehistoric synapsids were lizard-like in appearance, they belong to the evolutionary line that eventually led to mammals. The larger of the pair — the parent — was about 30 centimetres long from the tip of the nose to the end of its tail. The juvenile was about a third of that size.

These particular synapsids were likely hiding inside the trunk of tree when they were apparently trapped by a sudden flood. The two skeletons were discovered in 2017 by Brian Hebert, who has been searching for fossils in Nova Scotia for 30 years.

Hebert was combing a section of the east coast of Cape Breton Island near Sydney when he found the fossils in a lithified tree stump from the Carboniferous Period, a time in which the area was covered by a swampy forest, millions of years before the rise of dinosaurs.

Hebert has often found such tree stumps in his searches, but many are empty. Even those with skeletons inside had only one skeleton.

“The tree was not a well-preserved tree, but everything inside was amazingly well-preserved,” he said of the find he made in 2017. “I knew it was something special as soon as I opened it.”

Paleontologist Hillary Maddin, who analyzed the finding with the Carleton University team, said Hebert’s finding predates the previous oldest record of this behaviour by 40 million years. The adult’s tail is wrapped around the juvenile’s hind limbs in a manner common among denning animals.

It is likely the parent was carnivorous, while the juvenile ate insects. “The bugs were quite big back then,” said Maddin.

It is not common to see fossils this well-preserved, she said. “This fossil is just so beautifully articulated,” she said.

Parental care is common in mammals — all mammal offspring require nourishment from their mothers. Some other animals, including birds, some amphibians, reptiles and even fish also care for their young.

Parental care requires animal parents to make an investment, or divert resources away from themselves, to give their young a better chance of survival, said Maddin. Prolonged care of offspring after birth can have the highest cost to parents.

How parental care has evolved as a behavioural strategy is a question not yet answered. Understanding of how parental care evolved can only be done by studying fossils. So far, most evidence of prehistoric parenting has been limited to finding groups of individuals of different ages of the same species.

There are evolutionary advantages and disadvantages to parental care, said Maddin. Some animals demonstrate extended care for their young and some don’t. Some just ditch their offspring, while others protect them until they are better able to care for themselves.

“This confers some sort of advantage to this animal,” said Maddin.

The findings of the Carleton team have been published in the journal Nature Ecology & Evolution. It has created a stir worldwide.

Reaction to the published article has bad been “pretty crazy,” said Maddin. The story has appeared in more than 70 general interest publications and on more than 50 national news broadcasts. “It really kind of exploded.”

Are these two lizard-like animals apparently cuddling together the first example of mother love? Not in the way that humans think of it, said Maddin. Some modern animals not considered intelligent, such as some shrimp and crabs, also demonstrate parental care, she said.

“It’s quite a common strategy. This is just the first example we have seen of it.”

Hebert said fossil hunters have been searching Nova Scotia for almost 200 years. Storm surges can erode cliffs, exposing more finds.

“There’s an untapped resource of amazing fossils to be found,” he said.





Roncellia perceensis



Marc R. Haensel: 
The largest trilobite you've never heard of: Roncellia perceensis from the Lower Devonian of Percé, Quebec. MHC-00639.
With a pygidium nearly 15cms wide, I'd imagine the complete trilobite to be over 40cms long!


Trouvé ici.


Dinosauroïde




 Quand j'étais p'tit gars dans les années 80 et que j'épluchais tous les livres et magasines de préhistoire qui me passaient entre les mains, j'étais tombé sur une expérience étonnante d'évolution conjecturale. Des scientifiques s'étaient demandé comment auraient pu évoluer les dinosaures s'ils n'avaient pas été anéantis par la fameuse comète. Dans leur scénario, un Stenonychosaurus avait évolué pour devenir un être bipède et intelligent, un "dinosauroïde". Ils avaient même fabriqué un modèle vibrant de vie dont les photos étaient publiées un peu partout. Inutile de dire que l'idée m'avait complètement fasciné.

Imaginez ma surprise de tomber nez à nez avec ce cher dinosauroïde 40 ans plus tard dans l'entrepôt du musée de la nature, situé à Gatineau! J'ai été complètement émerveillé de rencontrer cette créature qui avait captivé mon imagination lorsque j'étais enfant. En espérant que ce magnifique modèle sera à nouveau exposé au public afin d'éveiller la fascination de nouvelles générations!




Gregory Aldrete parle de l'histoire de Rome (Lex Fridman Podcast)




 

La théorie du "stoned ape" de Terence McKenna



There seems to have been a profound difference in cognitive abilities between early Homo sapiens and our immediate predecessor, Homo erectus. Sure, erectus stood upright — a big, um, step forward — but with the emergence of Homo sapiens, we see traces of art, pictography, and tool usage, and we believe humankind made its first forays into language.

In the early 1990s, psychedelic advocate and ethnobotanist Terence McKenna published his book Food of the Gods in which he surmised that Homo sapiens‘ cognitive leap forward was due to their discovery of magic mushrooms. The scientific community never took McKenna’s theory very seriously, considering it mostly trippy speculation — these days, his ideas have largely been relegated to the spacier corners of Reddit. Now, however, the idea has acquired a new advocate, psilocybin mycologist Paul Stamets, who’s suggesting McKenna was right all along.

The stoned ape

In McKenna’s Stoned Ape hypothesis,” he posited that as humans began to migrate to new areas, at some point they came upon psychedelic mushrooms growing in cow droppings, as is their wont, and then ate them. After ingesting them, and more specifically the psilocybin they contained, their brains kicked into overdrive, acquiring new information-processing capabilities, and a mind-blowing expansion of our imaginations in the bargain. Many modern users of psychedelics claim the world never looks the same again after such an experience. As McKenna put it, “Homo sapiens ate our way to a higher consciousness,” and, “It was at this time that religious ritual, calendar making, and natural magic came into their own.”

The return of the stoned ape

Regarding this theory, Stamets presented “Psilocybin Mushrooms and the Mycology of Consciousness” at Psychedelic Science 2017. In his talk he sought to rehabilitate McKenna’s hypothesis as a totally plausible answer to a longstanding evolutionary riddle. “What is really important for you to understand,” he said, “is that there was a sudden doubling of the human brain 200,000 years ago. From an evolutionary point of view, that’s an extraordinary expansion. And there is no explanation for this sudden increase in the human brain.”

Why not mushrooms? Stamets portrayed a group of early humans making their way through the savannah and happening across “the largest psilocybin mushroom in the world growing bodaciously out of dung of the animals.” It needn’t have been unusually large to have its effect, of course. In any event, he invited the crowd to suspend their disbelief and admit that McKenna’s idea constitutes a “very, very plausible hypothesis for the sudden evolution of Homo sapiens from our primate relatives,” even if it’s an unprovable one.

The audience’s response was reportedly enthusiastic, though it’s fair to note that these were people attending a conference on psychedelic science, and thus pre-disposed toward such chemicals’ importance.

Just tripping?

Certainly, there’s general agreement on the mystery Stamets cited, if not so much on timing details. And consciousness, the “hard problem” even in its modern form, is an area rife with unanswered questions. What is consciousness, anyway? Is it a simple enough thing that it could have a single root cause as McKenna and Stamets say? Many experts suspect our brains gained new capabilities as the result of early community ties and the requirements of social interaction, but when?

Anthropologist Ian Tattersall tells Inverse that the where seems obvious enough: Africa, “For it is in this continent that we find the first glimmerings of ‘modern behaviors’. . . But the moment of transformation still eludes us and may well do so almost indefinitely.”

There are other researchers who’ve studied early humanity’s use of drug plants but who are skeptical of the stoned ape notiion. Elisa Guerra-Doce, an expert in the field, considers the idea too simplistic, potentially a reduction of a complex evolutionary process into a single “aha” — or maybe “oh, wow” — moment. She’s also troubled by there being little evidence of such a pivotal moment, or of drug use at all, so early in the archeological record.

Amanda Feilding of the psychedelic think tank Beckley Foundation says, however, that the stoned ape theory is at the very least a valid reminder that humans have always been drawn to and fascinated by mind-altering substances: “The imagery that comes with the psychedelic experience is a theme that runs through ancient art, so I’m sure that psychedelic experience and other techniques, like dancing and music, were used by our early ancestors to enhance consciousness, which then facilitated spirituality, art, and medicine.”

Just how early our love affair with hallucinogenic states began may have something to say about the plausibility of McKenna’s hypothesis, but, alas, we don’t know when that would have been. And, as the saying about the 1960s goes, even if any of these people were still around to ask, anyone who was really there wouldn’t be able to remember.


Trouvé ici. 



Eusmilus (Mario Lanzas)




A wonderful reconstruction of the prehistoric nimravid - ‬mammalian predators better known as "false saber-toothed cats‭" - ‬Eusmilus, by the talented artist Mario Lanzas. Anyone who is already familiar with nimravids knows that Eusmilus looks like one of the famously called saber-toothed cats,‭ but for those who don't know; nimravids like Eusmilus evolved down a separate genetic line,‭ they found themselves living in a world where there was a predatory niche open for cat-like predators. Growing large, they developed enlarged upper canine teeth that were almost as long as their skulls, fossil evidence suggests that nimravids went along derived evolutionary pathways; resulting in conical teeth, dirk teeth, and scimitar teeth, with that their evolutionary paths then split in two, leading to saber-toothed and conical-toothed forms that convergently evolved with those of true felids tens of millions of years later. Meaning, despite Eusmilus having long saber teeth and looking like a saber-toothed cat, nimravids were actually a so-called "false saber-tooth" that only bore this resemblance due to convergent evolution. There are only three valid species of Eusmilus known; the type species E. bidentatus (Filhol, 1873), along with E. villebramarensis (Peigne and Brunet, 2003), and lastly, E. adelos (Barrett, 2021) the largest species in the genus. Ironically, Eusmilus' name means "true saber" - despite having the nickname 'false saber-tooth' - or "‭early knife," depending on the translation. Eusmilus is classified as Eukaryota, Animalia, Chordata, Mammalia, Carnivora, Feliformia, Nimravidae, and Hoplophoninae. 

Fossils of Eusmilus have been unearthed throughout Europe and North America. It lived during the Paleogene Period, Late Eocene to Early Oligocene Epochs, Priabonian to Rupelian Ages 37.2 - 28.4 million years ago. Most Eusmilus species had a long body, and compared to modern leopards their legs were short, but despite that were about as tall as leopards, reaching a shoulder height of 60 - 70 centimeters (24 - 28 inches). Some specimens reached 2.5 meters (8 feet) long, E. adelos was comparable to African lion proportions, reaching a weight of 111 kilograms (244.7 lbs), and thus was the largest of the holplophonine nimravids. Eusmilus would have been a hunter of medium to large sized animals; much like rhinoceratids, tapirids, anthracotheriids, or upon the diversity of ‘oreodont', equid, and camelid taxa. Their enlarged canines were the primary killing tools employed by Eusmilus, and analysis of the skeleton supports this.‭ ‬The muscle attachment points on the skull show that Eusmilus actually had weak jaw closing muscles,‭ ‬but this was to allow for a wide jaw opening angle. To properly use their saber teeth, Eusmilus could open their jaw to an impressive ninety degrees wide,‭ ‬thirty degrees more than a modern African lion‭ (‬Panthera leo‭)‬. 

 Curiously, Eusmilus possessed fewer teeth than other mammalian carnivores, only 26 instead of the usual 44 teeth. To help compensate for the weak bite force,‭ ‬the neck and shoulders evolved to allow for powerful downward thrusts that drove the saber-teeth through its victim without the need for using the jaw muscles. Once punctured into a critical area such as the neck,‭ ‬death would come in a matter of‭ ‬minutes at most for the prey. Unfortunately, nimravids most likely went extinct due to general faunal turnover that saw a major reduction in diversity of numerous prey taxa, such as equids, camelids, antilocaprids and dromomerycids, from about 7.5 to 6.8 million years ago. The second image shows the partial skeleton of Eusmilus adelos specimen USNM 12820, with shaded known elements. Cranial abbreviations: fr frontal, na nasal, mp mastoid process, (A) cn carnassial notch, mc main cusp of P3, pa paracone, pcc posterior cingular cusp of P3, ps parastyle; (B - D) bis brachialis insertion site, lg lateral groove of ulna, rn radial notch, sln semilunar notch, (E - G) ce capitular eminence of radius, rt radial tuberosity, (H - J) dpc delto-pectoral crest, of olecranon fossa, sc supinator crest (brachial flange), remnants of bridge enclosing epicondylar foramen. Eusmilus adelos skeletal reconstruction by Dhruv Franklin. Photo credit: Paul Zachary Barrett, 2021.


Trouvé ici.



La côte Est des États-Unis s'enfonce




Extraits de l'article:

In many parts of the U.S. East Coast, rising seas driven by melting ice and the thermal expansion of warming water is only part of what threatens coastal areas. The land is also sinking. This geologic two-step is happening rapidly enough to threaten infrastructure, farmland, and wetlands that tens of millions of people along the coast rely upon, according to a NASA-funded team of scientists at Virginia Tech’s Earth Observation and Innovation (EOI) Lab.

The researchers analyzed satellite data and ground-based GPS sensors to map the vertical and horizontal motion of coastal land from New England to Florida. In a study published in PNAS Nexus, the team reported that more than half of infrastructure in major cities such as New York, Baltimore, and Norfolk is built on land that sank, or subsided, by 1 to 2 millimeters per year between 2007 and 2020. Land in several counties in Delaware, Maryland, South Carolina, and Georgia sank at double or triple that rate. At least 867,000 properties and critical infrastructure including several highways, railways, airports, dams, and levees were all subsiding, the researchers found.

The findings follow a previous study from the EOI Lab, published in Nature Communications, that used the same data to show that most East Coast marshes and wetlands—critical for protecting many cities from storm surge during hurricanes—were sinking by rates exceeding 3 millimeters per year. They found that at least 8 percent of coastal forests had been displaced due to subsidence and saltwater intrusion, leading to a proliferation of “ghost forests.”

(...) Part of the reason that the Mid-Atlantic is sinking more rapidly than the northeastern U.S. is because the edge of the massive Laurentide ice sheet, which covered much of northern North America during the height of the most recent Ice Age, ran through northern Pennsylvania and New Jersey. Ice-free lands to the south of that line, especially in the Mid-Atlantic, bulged upward while ice-covered lands to north were pushed downward by the weight of the ice, Shirzaei explained. When the ice sheet started retreating 12,000 years ago, the Mid-Atlantic region began sinking gradually downward—and continues to do so today—while the northeastern U.S. and Canada began rising as part of a rebalancing process called glacial isostatic adjustment.

While the edge of the Laurentide ice sheet never got close to northern Florida, that region has relatively high rates of uplift due to another geologic process—the gradual dissolution and lightening of karst landscapes due to the infiltration of groundwater.