Le tsunami
The 14-kilometer-wide Chicxulub asteroid responsible for the mass extinction of the dinosaurs caused a gigantic global tsunami, much larger than what we know from modern history.
The meteor that killed all dinosaurs 65 million years ago caused a one-and-a-half-mile tsunami when it hit the Gulf of Mexico.
The First Moments After Impact
To make accurate estimates of the size of the tsunami, the researchers used a computer model that could calculate the large-scale deformation of the Earth’s crust and the chaotic waves caused directly by the impact and the recoil of the water in the formed crater.
That model detailed the events in the first ten minutes after the asteroid's impact: the impact crater — initially 1.5 kilometers deep — did not contain any water at the time. That was blown away by the force of the impact. The water then ran into the crater, creating a collapsing wave and flowing out again.
The Biggest Tsunami In History
Based on data about the sea level and the speed of the water, the researchers then calculated how that tsunami moved over all the world’s oceans. The US researchers’ findings are also supported by geological evidence: the tsunami caused erosion and displacement of sediments that are still measurable today.
In the Gulf of Mexico, the wave was a mile high, moving at 143 km/h. Then the water spread to the Atlantic Ocean, and — via the Central American Seaway, which no longer exists today — also to the Pacific Ocean. At that point, the size of the wave had diminished to 14 meters.
By comparison, the largest wave in modern history was barely 23.8 meters high.
According to the researchers, a comparison with the tsunami in the Indian Ocean that claimed 225,000 lives in 2004 is also impossible. They were as different as night and day.
In the first 7 hours of both tsunamis, the Chicxulub’s impact was 2,500 to 29,000 times greater than the 2004 tsunami.
As severe as the effects of the tsunami were, it was not the only cause of the extinction of the dinosaurs. The asteroid’s impact also released a massive amount of particulate matter into the atmosphere, burning animals alive and setting wildfires.
That dust also blocked the sunlight on earth for years, so that plant growth and the entire food chain were disrupted.
The Chicxulubcrater
Chicxulub Crater is the 180-kilometer-wide remnant of an asteroid impact that occurred about 65 million years ago. The crater was discovered in 1991. Its impact probably led to the end of the age of the dinosaurs.
The crater had gone undetected for decades as it was hidden by 1000 meters of younger rocks. As a result, there is not much to see on the surface today except for the ring of underground pools that line the old crater rim.
The crater was eventually found because geological research revealed anomalies in the gravitational field, among other things.
In the Cretaceous-Tertiary transition, almost all larger animal species became extinct, including the dinosaurs.
Diadectes (Emiliano Troco)
First image is a beautiful illustration by Emiliano Troco of the Bromacker bogs with a Diadectes (crosswise-biter) walking between some Walchia - a conifer, cypress-like genus that lived in the Carboniferous (Upper Pennsylvanian) to lower Permian (310-290 MYA) rocks of Europe and North America. Diadectes was named by Edward Drinker Cope in 1878, with five species identified; D. sideropelicus (type, Cope, 1878), D. lentus (Marsh, 1878), D. tenuitectus (Cope, 1896), D. carinatus (Case and Williston, 1912) and D. absitus (Berman, 1998). Remains are found in Texas, USA, concentration in the Texas Red Beds and Clear Fork. It lived during the Early Permian Period (Artinskian - Kungurian Ages 290 - 272 MYA), with many specimens known allowing for accurate reconstruction. A heavily built animal ranging from 1.5 - 3 meters (5 - 10 feet) long. Classified as Amphibia, Reptiliomorpha, Diadectomorpha and Diadectidae.
Othniel Charles Marsh and Edward Drinker Cope, the two central players of the ‘bone wars’, both discovered and named Diadectes. Marsh named his Nothodon while five days later Cope released the name Diadectes. Now technically, Nothodon would have precedence but in a twist, when they were synonymized in 1912 Diadectes was given precedence. This is against the standard practice of ICZN (International Commission on Zoological Nomenclature) rules that state that the first name should be used. One interesting thing about Diadectes that must be realised is that it represents the earliest known amphibian to be herbivorous. It had a particularly large skeleton to accommodate an extended intestinal system so that it could digest plant material. It contains peg like teeth at the front that would have been especially efficient for stripping the leaves off ferns, it also had flat molar teeth for grinding the plant material. The skull also has a partial second palate study of which suggests that this would have allowed Diadectes to breathe while it chewed its food. An ability that even some more advanced reptiles were unable to do. Second image is a mounted skeleton of D. sideropelicus at the American Museum of Natural History in New York.
Le vol des oiseaux a évolué au moins trois fois
(...) Given that all living vertebrates capable of powered flight leap into the air—whether bats or birds—Pittman and colleagues hypothesize that dinosaurs did the same. Even though paleontologists previously debated whether dinosaurs evolved flight from the “ground up” by running and jumping, or from the “trees down” by gliding, the fact that living animals take off by leaping indicates that deinonychosaurs did, too, regardless of what substrate they pushed off from. “This isn’t exclusive to take off from the ground or from height,” Pittman notes, “so birds in a tree also leap to take off.”
(...) In addition to the deinonychosaurs most closely-related to birds, the paleontologists found that two other deinonychosaur lineages had wings capable of powered flight. Within a group of Southern Hemisphere raptors called unenlagines, a small, bird-like dinosaur called Rahonavis would have been able to fly. On a different branch, the four-winged, raven-shaded dinosaur Microraptor shared similar abilities. More than that, the researchers found a few other species on varied parts of the deinonychosaur family tree—such as Bambiraptor and Buitreraptor—that were getting anatomically close to fulfilling the requirements for flight. Flight wasn’t just for the birds, in other words. Many non-bird dinosaurs were evolving aerodynamic abilities, but only a few were able to actually flap their wings and fly.
“The new paper is really exciting and opens new views on bird origins and the early evolution of flight,” says Bernardino Rivadavia Natural Sciences Argentine Museum paleontologist Federico Agnolin. So far, other studies haven’t found the same pattern of dinosaurs evolving flight more than once. Given that dinosaur family trees are bound to change with the discovery of new fossils, Agnolin adds, this might mean that the big picture of how many times flight evolved might change. All the same, he adds, “I think that the new study is really stimulating.”
D'anciens amphibiens redevenus aquatiques
One of the greatest transitions in evolutionary history was the emergence of tetrapods, or four-legged vertebrates, onto land. By about 340 million years ago, fins had become fingers and limbs, shoulder and hip joints had changed to bear weight on land, and an entire array of amphibious creatures had begun to live along the water’s edge. But an analysis of some early tetrapods now suggests that not long after they made a home on land, some species became adapted to life in the water all over again.
Aja Mia Carter at the University of Pennsylvania and colleagues focused on a group of early amphibians called temnospondyls, roughly salamander-like tetrapods that spun off a great diversity of species between 330 and 295 million years ago.
Rather than looking at the limbs of these animals, though, Carter’s team analysed the backbone anatomy of over a dozen temnospondyl species. They also used a previously published evolutionary tree to understand how these species were inter-related, and searched the scientific literature for information on the likely lifestyles of each species – in particular whether that was either more aquatic or terrestrial.
Temnospondyls, Carter and colleagues found, most likely evolved from a land-dwelling ancestor. Surprisingly, from there, some species changed course and became adapted to life in the water all over again in an evolutionary reversal.
Read more: These fish are evolving right now to become land-dwellers
The analysis also revealed that relatively stiff backbones were not an adaptation to life on land. Researchers have typically assumed that early land animals evolved a stiffer spine to help support their bodies, but it was actually the water-dwelling temnospondyls that had a more rigid spine.
“I was stunned to see that between individual vertebrae, aquatic species were stiffer than terrestrial species,” Carter says. In other words, a stiffened spine was not essential for these early amphibians to walk on land.
“This research is resetting how we think about locomotion in [early] amphibians,” says Julia McHugh at the Museums of Western Colorado.
The study suggests temnospondyl backbone anatomy is a good predictor of the complicated evolutionary history of these early four-legged animals. It can help establish whether a species lived on land but had an aquatic ancestor, or lived in water but had a land-based ancestor.
“This study is the best of modern science,” McHugh says, putting longstanding ideas to the test.
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