An international team of researchers has discovered that the asteroid that wiped out almost all the dinosaurs came down in spring. This is indicated by the growth and feeding patterns of fish that died immediately after the impact.
Most palaeontologists agree that a massive asteroid impact around 66 million years ago on the Yucatán peninsula in nowadays Mexico marked the end of the non-flying dinosaurs, along with three quarters of all fauna at that time: the fifth mass extinction. Since it was presented in 2019, the Tanis site in North Dakota, USA, is one of the most promising sites about that milestone in Earth’s history. It houses fossil fauna and flora: remains of dinosaurs, pterosaurs, a mosasaur, mammals, fishes, an ants’ nest, plants … They were covered in sediment less than an hour after the Chicxulub asteroid impact and therefore fossilized extremely well.
‘The impact rocked the continental plate and caused massive standing waves in water bodies. These mobilised enormous volumes of sediment that engulfed fishes and buried them alive,’ says Melanie During from VU Amsterdam and Uppsala University, who led the study published in Nature. Meanwhile, impact spherules – small melted rocks ejected from the crater – rained down from the sky less than an hour after the impact.’
Three times evidence of spring
The researchers found these spherules in the gills of the fossil sturgeons from the Tanis site, proof of their death shortly after the asteroid impact. They were clearly visible on the X-ray scans of the Synchrotron in Grenoble,’ says Koen Stein, from Vrije Universiteit Brussel (VUB) and the Royal Belgian Institute of Natural Sciences. ‘We also studied the internal bone structure of six fossil sturgeons. From that you can read the seasonal growth, just like in trees. The rings not only tell us how old the sturgeons are, but also the season in which they died: when it was spring in the Northern Hemisphere.’
A second clue: the bone cells of the fish. Their density and size also change with the seasons. ‘In all studied fishes, bone cell density and volumes can be traced over multiple years. These were on the rise but had not yet peaked during the year of death,’ says Dennis Voeten of Uppsala University.
Another confirmation came from one of the fossil paddlefishes. The stable carbon isotope of that specimen was analyzed to reconstruct the animal’s diet. The availability of zooplankton, its favorite food, fluctuated with the seasons and peaked between spring and summer. ‘When the paddlefish eats more zooplankton, it leaves traces in its skeleton: more of the heavier carbon 13 isotope relative to the lighter carbon 12 isotope,’ explains Melanie During. ‘We saw in this sturgeon that the feeding season had not yet climaxed – death came in spring.’
Sensitive moment
The mass extinction that followed in the thousands of years after the asteroid impact is a turning point in the history of life on our planet: the demise of all non-flying dinosaurs, pterosaurs, most marine reptiles, ammonites, … while mammals, birds, crocodiles and turtles survived.
Melanie During: ‘We now know that the asteroid hit at a sensitive time, when it was spring in the Northern Hemisphere, the season when many animals start their reproductive cycle. The incubation period for reptiles such as dinosaurs and pterosaurs is longer than for other animal groups, such as birds, so they may have been more sensitive to this sudden disturbance of their environment.’
And in the Southern Hemisphere it was autumn then. ‘Animals that had already begun their winter rest underground, including some early mammals, may thus have survived the first months after the asteroid impact, with large-scale forest fires.’
Studies like this will help answer why some animal groups escaped the extinction wave and others did not.
Advance announcement for a scientific paper: Pneumaticity in sauropods provides evidence for non-avian flight in dinosaurs
Abstract- While it is widely known that sauropods (and most groups of dinosaurs) had heavily pneumaticized bone structures which are generally accepted as evidence for air sacs and bird-style respiration, it is not widely known that this system of internal air sacs when paired with certain gases would have allowed the earth’s largest land animals to have also been the largest animals to achieve flight. A forthcoming paper will document how sauropods achieved lift to become Mesozoic airships. This theory also sheds light on the creatures’ long necks and tails, which would be necessary for feeding on treetops beneath the floating giants and anchoring themselves via the long tail to tree trunks during rest periods. The theory though seemingly radical, is no more ludicrous than others that have cropped up (repeatedly) in the literature and can be at least equally well supported. And given time, will certainly be welcomed by paleontology as the only rational explanation for the evolution of these great Zeppelins of history.
…I will be accepting questions, offers for book deals and speaking tours. . . #allyesterdays #darrennaish #johnconway #dinosaur #brontosaurus #mesozoic #sauropods #evolution #theory #doodle #sketchbook #artistsoninstagram #paleoart https://www.instagram.com/p/B24sxgrlywK/?igshid=3y9h0ui75adl
It’s mid-morning in Late Cretaceous Canada (77 million years ago), a small group of Struthiomimus altus take shelter from the summer heat near the outskirts of a small forest bordering a flood plain. While some rest on the ground, others forage for food in the scrub and bushes that grow throughout the area. A lone female takes a drink at the edge of a narrow body of water, not far from the rest of her group, she does not notice the young Daspletosaurus edging it’s way around the edge of the trees nearest to the water.
By the time members of her flock call out they are already running. Startled, she looks back to see just under 2 tons of teeth and claws lunging towards her, almost closing the gap before she turns and runs the other way.
S. altus was an omnivorous theropod, measuring around 14 feet in length and weighing in at about 330 lbs. Much like their namesake, the modern day Ostrich, their primary means of defense is thought to be running with their maximum speed being thought to have reached close to 50 miles per hour, if that didn’t work they could likely have kicked very hard with powerful legs.
hey i think im ready to give this blog some love again! vectiraptor is a dromaeosaurid described in december 2021 that was found on the isle of wight :)
