Extinction changes rules of body size evolution

A trilobite fossil from the Ordovician period, which lasted from about 485 to 443 million years ago. A new analysis of marine fossils from most of the past half-billion years shows the usual rules of body size evolution change during mass extinctions and their recoveries.
(Image credit: Smithsonian)

Scientists at Stanford University have discovered a surprising pattern in how life reemerges from cataclysm. Research published in Proceedings of the Royal Society B shows the usual rules of body size evolution change not only during mass extinction, but also during subsequent recovery.

Since the 1980s, evolutionary biologists have debated whether mass extinctions and the recoveries that follow them intensify the selection criteria of normal times – or fundamentally shift the set of traits that mark groups of species for destruction. The new study finds evidence for the latter in a sweeping analysis of marine fossils from most of the past half-billion years.

Whether and how evolutionary dynamics shift in the wake of global annihilation has “profound implications not only for understanding the origins of the modern biosphere but also for predicting the consequences of the current biodiversity crisis,” the authors write.

“Ultimately, we want to be able to look at the fossil record and use it to predict what will go extinct, and more importantly, what comes back,” said lead author Pedro Monarrez, a postdoctoral scholar in Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “When we look closely at 485 million years of extinctions and recoveries in the world’s oceans, there does appear to be a pattern in what comes back based on body size in some groups.”

The Climate-Driven Mass Extinction No One Had Seen

 

Fossils of the key groups used to unveil the Eocene-Oligocene extinction in Africa with primates on the left, the carnivorous hyaenodont, upper right, rodent, lower right. These fossils are from the Fayum Depression in Egypt. (Credit: Matt Borths)

Sixty-three percent. That’s the proportion of mammal species that vanished from Africa and the Arabian Peninsula around 30 million years ago, after Earth’s climate shifted from swampy to icy. But we are only finding out about it now.

Compiling decades of work, a new study published this week in the journal Communications Biology reports on a previously undocumented extinction event that followed the transition between the geological periods called the Eocene and Oligocene.

That time period was marked by dramatic climate change. In a reverse image of what is happening today, the Earth grew cooler, ice sheets expanded, sea levels dropped, forests started changing to grasslands, and carbon dioxide became scarce. Nearly two-thirds of the species known in Europe and Asia at that time went extinct.

Oldest theropod dinosaur in the UK discovered

Scientists from the Natural History Museum and the University of Birmingham have described a new species of dinosaur from specimens found in a quarry in Pant-y-ffynnon in southern Wales.

Following on from a new species of ankylosaur, Pendraig milnerae marks the second new species of dinosaur described by Museum scientists in the last few weeks.

The new dinosaur is a theropod, a group which also includes T. rex and modern birds. Pendraig milnerae is the earliest example of a theropod found in the UK so far, living between 200 and 215 million years ago during the Late Triassic period. It likely had a body size around that of a modern-day chicken and would have been a meter long including its tail.

The fragmentary fossils of the species consist of an articulated pelvic girdle, sacrum and posterior dorsal vertebrae, and an associated left femur, and by two referred specimens, comprising an isolated dorsal vertebra and a partial left ischium.

Richard Butler, co-author on the paper and Professor of Paleobiology at the University of Birmingham, said: ‘Dinosaur discoveries are really rare in Wales, and this is only the third dinosaur species known from the country. It’s very exciting to learn more about the dinosaurs that lived here in the UK during the Triassic, right at the dawn of dinosaur evolution.’

Geologists solve half-century mystery with a rock from almost two billion years ago

 

Quartzite with traces of burrowing animals. The scale is marked in centimeters.
Credit: Stefan Bengtson/Swedish Museum of Natural History

Geologists have been baffled by perforations in an Australian quartzite (rock), identical in shape to burrows made in sands by crustaceans; the original sandy sediment is a billion years older than the oldest known animals. An international team of scientists has now resolved the mystery.

When animals move, they leave traces, such as dinosaur footprints or the burrows of worms. These reveal how ancient animals moved, how they foraged and how they interacted with one another. Trace fossils are as old as the animal world.

Geologists were therefore stunned by the discovery in Western Australia of traces of burrowing animals in ancient quartzite, a rock type that was formed when sandy sediments were subjected to high pressures and temperatures.

“Quartzite is as hard as concrete and impossible for burrowing animals to penetrate,” said Bruce Runnegar, UCLA professor emeritus in the Department of Earth, Planetary, and Space Sciences and co-author of the new research, published today in the journal Proceedings of the National Academy of Sciences. “The traces would therefore have had to be made while the sand was still loose. But the sand was deposited 1.7 billion years ago — a billion years prior to the appearance of the first animals in the fossil record, and its transformation to quartzite occurred more than 1.2 billion years ago, much earlier than the oldest animal fossils, which are less than 0.6 billion years old.”

A Swedish-Australian-Chinese-American team has now offered a solution to this riddle. The scientists present an explanation that does not require unreasonably ancient animals or concrete-chewing worms with diamond teeth.

The team measured the age of sand in the burrows using unusual radioactive minerals.

“The age turned out to be more than a billion years younger than the enclosing quartzite,” said co-author Birger Rasmussen, adjunct professor at the University of Western Australia. “The burrows could therefore have been made by animals.”

But how can animals burrow through hard quartzite? The answer was given by microscopic investigations, which showed that the grains had first separated at contact surfaces, resulting in a friable matrix, and then been fused again through later deposition of quartz, returning the rock to the state of hard quartzite.

“A similar process produced the stuff of the standing stones of Stonehenge,” Runnegar said.

A window in time had thus been opened to enable burrowing, the researchers report. Through comparisons with surrounding sedimentary strata, the scientists could date this window to about 40 million years ago, during the Eocene epoch of Earth’s history.

“Most likely, the traces were made by crustaceans, which invaded southwestern Australia during a short-lived marine transgression associated with the opening of the Southern Ocean,” said senior author Stefan Bengtson, professor emeritus and paleontologist at the Swedish Museum of Natural History.

“These trace fossils in the ‘wrong’ rocks have been a mystery for half-a-century,” Bengtson said. “We are glad to have been able to demonstrate geological processes that resolve this conundrum.”

Source/Credit: UCLA / Stuart Wolpert

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Dinosaurs' ascent driven by volcanoes powering climate change

 The rise of dinosaurs coincided with environmental changes driven by major volcanic eruptions over 230 million years ago, a new study reveals.

The Late Triassic Carnian Pluvial Episode (CPE) saw an increase in global temperature and humidity - creating a major impact on the development of animal and plant life, coinciding with the establishment of modern conifers.

Researchers analyzed sediment and fossil plant records from a lake in northern China’s Jiyuan Basin, matching pulses of volcanic activity with significant environmental changes, including the CPE’s ‘mega monsoon’ climate, some 234 million to 232 million years ago.

The international research team, including experts at the University of Birmingham, today published their findings in Proceedings of the National Academy of Sciences (PNAS) – revealing four distinct episodes of volcanic activity during this time period, with the most likely source being major volcanic eruptions from the Wrangellia Large Igneous Province, the remnants of which are preserved in western North America.

Peabody fossils illuminate dinosaur evolution in eastern North America

Tyrannosaurus rex, the fearsome predator that once roamed what is now western North America, appears to have had an East Coast cousin.

A new study by Yale undergraduate Chase Doran Brownstein describes two dinosaurs that once roamed the eastern United States from fossils housed at the Yale Peabody Museum of Natural History: an herbivorous hadrosaur (depicted in the silhouette) and a tyrannosaur.

A new study by Yale undergraduate Chase Doran Brownstein describes two dinosaurs that inhabited Appalachia — a once isolated land mass that today composes much of the eastern United States — about 85 million years ago: a herbivorous duck-billed hadrosaur and a carnivorous tyrannosaur. The findings were published Aug. 25 in the journal Royal Society Open Science.

Chase Doran Brownstein

The two dinosaurs, which Brownstein described from specimens housed at Yale’s Peabody Museum of Natural History, help fill a major gap in the North American fossil record from the Late Cretaceous and provide evidence that dinosaurs in the eastern portion of the continent evolved distinctly from their counterparts in western North America and Asia, Brownstein said.

“These specimens illuminate certain mysteries in the fossil record of eastern North America and help us better understand how geographic isolation— large water bodies separated Appalachia from other landmasses — affected the evolution of dinosaurs,” said Brownstein, who is entering his junior year at Yale College. “They’re also a good reminder that while the western United States has long been the source of exciting fossil discoveries, the eastern part of the country contains its share of treasures.”

For most of the second half of the Cretaceous, which ended 66 million years ago, North America was divided into two land masses, Laramidia in the West and Appalachia in the East, with the Western Interior Seaway separating them. While famous dinosaur species like T. rex and Triceratops lived throughout Laramidia, much less is known about the animals that inhabited Appalachia. One reason is that Laramidia’s geographic conditions were more conducive to the formation of sediment-rich fossil beds than Appalachia’s, Brownstein explained.

The specimens described in the new study were discovered largely during the 1970s at the Merchantville Formation in present day New Jersey and Delaware. They constitute one of the only known dinosaur assemblages from the late Santonian to early Campanian stages of the Late Cretaceous in North America. This fossil record period, dating from about 85 to 72 million years ago, is limited, Brownstein noted.

Brownstein examined a partial skeleton of a large predatory therapod, concluding that it is probably a tyrannosaur. He noted that the fossil shares several features in its hind limbs with Dryptosaurus, a tyrannosaur that lived about 67 million years ago in what is now New Jersey. The dinosaur has different hands and feet than T. rex, including massive claws on its forelimbs, suggesting that it represents a distinct family of the predators that evolved solely in Appalachia.

“Many people believe that all tyrannosaurs must have evolved a specific set of features to become apex predators,” Brownstein said. “Our fossil suggests they evolved into giant predators in a variety of ways as it lacks key foot or hand features that one would associate with western North American or Asian tyrannosaurs.”

The partial skeleton of the hadrosaur provided important new information on the evolution of the shoulder girdle in that group of dinosaurs, Brownstein found. The hadrosaur fossils also provide one of the best records of this group from east of the Mississippi and include some of the only infant/perinate (very young) dinosaur fossils found in this region.

Brownstein, who works as a research associate at the Stamford Museum and Nature Center in Stamford, Connecticut, has previously published his paleontological research in several peer-journals, including Scientific Reports, the Journal of Paleontology, and the Zoological Journal of the Linnaean Society. In addition to eastern North American fossils, he currently focuses his research on the evolution of fishes, lizards, and birds. He is particularly interested in how geographic change and other factors contribute to how fast different types of living things evolve.

He currently works in the lab of Thomas J. Near, curator of the Peabody Museum’s ichthyology collections and professor and chair of the Department of Ecology and Evolutionary Biology at Yale. Brownstein also collaborates with Yale paleontologists Jacques Gauthier and Bhart-Anjan Bhullar in the Department of Earth and Planetary Sciences.

While Brownstein is considering pursuing an academic career in evolutionary biology, he says his research is driven by enjoyment.

“Doing research and thinking about these things makes me happy,” he said. “Like biking, it’s something I love to do”

Source / Credit: Yale University

By Mike Cummings