AbstractThe late Quaternary megafauna extinction was a severe global-scale event. Two factors, climate change and modern humans, have received broad support as the primary drivers, but their absolute and relative importance remains controversial. …
We present, to our knowledge, the first global analysis of this extinction based on comprehensive country-level data on the geographical distribution of all large mammal species (more than or equal to 10 kg) that have gone globally or continentally extinct between the beginning of the Last Interglacial at 132 000 years BP and the late Holocene 1000 years BP, testing the relative roles played by glacial–interglacial climate change and humans.
We show that the severity of extinction is strongly tied to hominin palaeobiogeography, with at most a weak, Eurasia-specific link to climate change. …
IMAGE Global maps of late Quaternary [a, b] large mammal extinction severity, [c] hominin palaeobiogeography, [d] temperature anomaly and [e] precipitation velocity. [More detail here…]
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.
“Though most scientists believe that a series of volcanic eruptions, occurring in large pulses over a period of a million years in what is now Siberia, were the primary cause of the end-Permian extinction, the lag between the land extinction in the Southern Hemisphere and the marine extinction in the Northern Hemisphere suggests different immediate causes.”
![mucholderthen: Global late Quaternary [132,000 to 1,000 years ago] Megafauna Extinctions linked to](https://64.media.tumblr.com/104acfb5a9a09f60a9a4e69dfbe911da/tumblr_n8s612mmnq1rhb9f5o2_r1_1280.jpg "mucholderthen: Global late Quaternary [132,000 to 1,000 years ago] Megafauna Extinctions linked to")
