Affichage des articles dont le libellé est Synapsides. Afficher tous les articles
Affichage des articles dont le libellé est Synapsides. Afficher tous les articles
Oeuf de Lystrosaurus et évolution de l'allaitement
Scientists have their first proof that the ancestors of some mammals laid eggs, thanks to a 250-million-year-old fossil embryo discovered in South Africa in 2008. The specimen, described this week in PLOS One, belongs to a piglike animal with tusks and a beak called Lystrosaurus that famously and mysteriously survived the Great Dying, one of Earth’s worst extinction events. The embryo’s curved position and the incomplete development of its jaw, pelvis, and ribs hint that it was in an egg when it died (artist’s rendition above). The fossil could shed light on how Lystrosaurus survived the high temperatures of the extinction event, as the large size of the eggs would have prevented the water loss that comparable species faced, CNN reports. The find may also help researchers learn why and when lactation developed in mammals, providing evidence it initially evolved to allow mothers to keep their eggs moist.
Oeuf de synapside
En 150 ans de recherches paléontologiques en Afrique du Sud, on avait encore jamais découvert d'oeuf de synapside ! A tel point qu'on se demandait s'ils n'étaient pas déjà vivipares. Et pourtant....
Ce petit embryon appartient à Lystrosaurus, et la taille de l'oeuf qui le contient nous indique qu'il ne produisait pas de lait, que le petit était précoce et que ses parents devaient prendre soin de lui, ce qui a certainement contribué à la survie de cette espèce durant la crise Permien-Trias.
Fossilized vomit reveals 290-million-year-old predator’s diet
Two hundred and ninety million years ago, in a mountain valley within the central region of the supercontinent Pangaea, an apex predator snapped up at least three other animals and sometime later puked up the bones.
That material hardened over the ages, and is now the oldest fossilized vomit ever discovered from a land-based ecosystem. The cluster of bones and digestive material provides rare information, published January 30 in Scientific Reports, about the behavior of some of the world’s earliest land predators.
“It’s kind of like a photograph of a moment in the past that is telling us about the animal that was living,” says Arnaud Rebillard, a paleontologist at Museum für Naturkunde in Berlin. “Any data that we can find about their behavior is very precious.”
Paleontologists discovered the lime-sized specimen in 2021 at a site called the Bromacker locality in central Germany. Researchers then scanned the bones to create 3-D models showing a cluster of parts from different animals, suggesting they had come from a predator’s gut. They also chemically analyzed the material surrounding the bones and found that it was low in phosphorus, suggesting it was not a fossilized dropping.
While the specific predator that regurgitated the bones is unknown, the researchers strongly suspect that it was one of two animals that resemble today’s monitor lizards like Komodo dragons: Dimetrodon teutonis, with a prominent sail on its back, and Tambacarnifex unguifalcatus. Though reptilian in appearance, both are from a group of animals called synapsids that includes mammals and their extinct relatives.
Among the 41 disgorged bones, the researchers were able to distinguish two small lizardlike reptiles and a limb bone from a larger reptilelike herbivore. This collection of remains, along with several unidentified bones, indicates that the predator ate whatever it could find rather than specializing in a specific type of prey.
Because the fossilized vomit, or regurgitalite, contains three different animals eaten by one predator, “we can literally say, for sure, that these three animals were living at exactly the same place and exactly the same time, maybe to the week or even to the day,” Rebillard says.
Several living predators habitually regurgitate bones and other body parts that are tough to digest after eating. Scientists don’t know if this is why the ancient animal spit up the bones, but it is one of the most plausible explanations, along with simply overeating, Rebillard says.
Fossils of partially digested material, including regurgitalites, as well as fossilized feces, are valuable clues for studying Earth’s past. “We need fossils like this to really tie together how the ecosystem functioned and how the food webs were structured,” says Martin Qvarnström, a paleontologist at Uppsala University in Sweden who was not involved in the new study.
The German regurgitalite is particularly exciting because the Bromacker site preserves a snapshot of an early terrestrial ecosystem. Older predators that could travel on land often lived in semiaquatic environments where they hunted crustaceans and fish. The Permian period represents a time when large herbivores became prominent in inland environments, followed by new predators. Fossil dung and vomit are much rarer in inland environs than in aquatic ones.
“We’re talking about almost 300-million-year-old ecosystems,” Rebillard says. “So to have such a temporal vision about this to the day they were living, in the same area and the same moment, is extremely fascinating.”
Dimetrodon (D DesignHub)
Meet the dinosaur that wasn't. This is Dimetrodon, the Pioneer of Predation. Long before T. rex, this creature wrote the first rulebook for being a top land predator.
In the Permian Period, over 280 million years ago, Dimetrodon was a revolutionary. It was a synapsid—a member of the lineage that leads to mammals. Its innovations were groundbreaking:
The First Complex Teeth: Its name means "two measures of teeth." It had differentiated canines, incisors, and shearing teeth, a first for large land animals and the blueprint for every mammalian smile since.
The Advanced Posture: Its legs were positioned more underneath its body than the sprawling reptiles of its time, granting it more efficient, powerful movement.
The Thermal Edge: That iconic sail likely acted as a solar panel, allowing it to warm up fast and remain active when other animals were sluggish.
Dimetrodon didn't just live in its world; it invented the rules that would govern land ecosystems for millions of years. It's not a dinosaur—it's the architect of the world dinosaurs would inherit.
Les pélycosaures
Cette mâchoire de pélycosaure a été découverte dans un puits sur l’Île-du-Prince-Édouard au 19e siècle.
Bien avant l’ère des dinosaures, les pélycosaures dominaient la Terre. Ces vertébrés font partie des premiers synapsides, le groupe ancestral qui donnera naissance aux mammifères.
Le célèbre Dimetrodon, reconnaissable à sa grande voile dorsale, est l’un des exemples les plus fascinants de ce groupe !
Comment créer un mammifère en neuf étapes évolutives (Smithsonian)
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.
Un fossile de Nouvelle-Écosse est le premier exemple de soins parentaux
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.
Dimetrodon
The prehistoric predator Dimetrodon had a multipurpose mouth. Big fangs in the front pierced deep into prey, while smaller, tightly-spaced teeth in the back formed a sheering edge. This skull is at the Whiteside Museum of Natural History, where CofC paleontologist Dr. Scott Persons is presenting at Permian Fest.
Un reptile mammalien géant vieux de 200 millions d’années découvert en Pologne
Lisowicia bojani tire son nom du village de Lisowice, où il a été mis au jour. Long de 4,5 mètres et haut de 4,6 mètres, il est le représentant adulte le plus massif de son espèce découvert à ce jour : les dicynodontes, un groupe de non-dinosauriens qui peuplaient la Terre à l’ère du Trias. Cette découverte remet en question l’idée d’une domination sans partage des dinosaures vers la fin de cette époque, il y a plus de 200 millions d’années.
UNE ADAPTATION HORS NORME
Décrit par les chercheurs Tomasz Sulej et Grzegorz Niedzwiedzki de l’Académie polonaise des sciences, dans Science, Lisowicia bojani étonne. Tout d’abord parce que les dicynodontes étaient très rares en Europe, mais surtout parce que le fossile retrouvé, complet à 70 % selon les scientifiques, montre un animal bien plus gros que les autres membres de son espèce. Les dicynodontes observés jusqu’à présent pesaient au maximum 2 tonnes, quand Lisowicia bojani atteignait vraisemblablement les 9 tonnes. Il est donc le plus gros animal à quatre pattes hors dinosaures vivant à la fin du Trias. Une question se pose alors pour les scientifiques : pourquoi ce gigantisme a-t-il surgi dans un groupe qui, jusqu’alors, ne présentait que des espèces de taille « moyenne » ? Des réponses seront peut-être apportées à l’étude de ce spécimen.
Lisowicia bojani est à mi-chemin entre le reptile et le mammifère. Contrairement à d’autres spécimens de son espèce ou de la plupart des reptiles, la forme de ses pattes avant n’est pas arquée vers l’intérieur, ce qui pourrait signifier une adaptation qui a accompagné sa grande taille ou son poids important. Il se rapproche en cela des grands dinosaures. Ses autres caractéristiques morphologiques cependant ne laissent aucun doute quant à son appartenance aux dicynodontes. Doté d’un bec et de défenses, il était herbivore et se nourrissait principalement de plantes qu’il avalait sans mâcher.
LA FIN DES DICYNODONTES
Les dicynodontes se sont éteints il y a plus de 200 millions d’années. Ils ont pourtant fait preuve d’une grande résistance à leur environnement hostile : lors de la crise menant l’ère du Permien à l’ère du Trias, 70 % des vertébrés terrestres, dont la quasi-totalité des reptiles, avaient disparus. Pas les dicynodontes. « Sans doute parce qu’ils étaient à l’époque de petite taille, semi-aquatiques ou fouisseurs » avance Chloé Olivier, experte en dicynodontes. Après la crise, « le groupe s’est ensuite complètement diversifié, avec quarante genres regroupant une centaine d’espèces de plus en plus grosses. » Le dicynodonte aurait-il fait preuve d’un grand sens de l’adaptation et de la survie ?
La crise suivante leur sera cependant fatale. è la fin du Trias, une nouvelle extinction signe la fin définitive des dicynodontes, laissant la place aux dinosaures du Jurassique. Il faudra ensuite attendre environ 150 million d’années pour voir l’avènement des grands mammifères et des herbivores aussi massifs que le dicynodonte.
How Did This Animal Survive the Worst Mass Extinction Event Ever? (Ben G Thomas)
Comment Lystrosaurus a-t-il survécu à l'extinction du Permien?
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