Utah fossil reveals global exodus of mammals' near relatives to major continents

A nearly 130-million-year-old fossilized skull found in Utah is an Earth-shattering discovery in one respect.

The new species Cifelliodon wahkarmoosuch is estimated to have weighed 2.5 pounds and probably grew
to be about the size of a small hare [Credit: Keck School of Medicine of USC/Jorge A. Gonzalez]

The small fossil is evidence that the super-continental split likely occurred more recently than scientists previously thought and that a group of reptile-like mammals that bridge the reptile and mammal transition experienced an unsuspected burst of evolution across several continents.

"Based on the unlikely discovery of this near-complete fossil cranium, we now recognize a new, cosmopolitan group of early mammal relatives," said Adam Huttenlocker, lead author of the study and assistant professor of clinical integrative anatomical sciences at the Keck School of Medicine of USC.

The study, published in the journal Nature, updates the understanding of how mammals evolved and dispersed across major continents during the age of dinosaurs. It suggests that the divide of the ancient landmass Pangea continued for about 15 million years later than previously thought and that mammal migration and that of their close relatives continued during the Early Cretaceous (145 to 101 million years ago).

"For a long time, we thought early mammals from the Cretaceous (145 to 66 million years ago) were anatomically similar and not ecologically diverse," Huttenlocker said. "This finding by our team and others reinforce that, even before the rise of modern mammals, ancient relatives of mammals were exploring specialty niches: insectivores, herbivores, carnivores, swimmers, gliders. Basically, they were occupying a variety of niches that we see them occupy today."

The study reveals that the early mammal precursors migrated from Asia to Europe, into North America and further onto major Southern continents, said Zhe-Xi Luo, senior author of the study and a paleontologist at the University of Chicago.

Fossil find: a new species

Huttenlocker and his collaborators at the Utah Geological Survey and The University of Chicago named the new species Cifelliodon wahkarmoosuch.

The new species Cifelliodon wahkarmoosuch is estimated to have weighed 2.5 pounds and probably grew
to be about the size of a small hare [Credit: Keck School of Medicine of USC/Jorge A. Gonzalez]

Found in the Cretaceous beds in eastern Utah, the fossil is named in honor of famed paleontologist Richard Cifelli. The species name, "wahkarmoosuch" means "yellow cat" in the Ute tribe's language in respect of the area where it was found.

Scientists used high-resolution computed tomography (CT) scanners to analyze the skull.

"The skull of Cifelliodon is an extremely rare find in a vast fossil-bearing region of the Western Interior, where the more than 150 species of mammals and reptile-like mammal precursors are represented mostly by isolated teeth and jaws," said James Kirkland, study co-author in charge of the excavation and a Utah State paleontologist.

With an estimated body weight of up to 2.5 pounds, Cifelliodon would seem small compared to many living mammals, but it was a giant among its Cretaceous contemporaries. A full-grown Cifelliodon was probably about the size of a small hare or pika (small mammal with rounded ears, short limbs and a very small tail).

It had teeth similar to fruit-eating bats and could nip, shear and crush. It might have incorporated plants into its diet.

The newly named species had a relatively small brain and giant "olfactory bulbs" to process sense of smell. The skull had tiny eye sockets, so the animal probably did not have good eyesight or color vision. It possibly was nocturnal and depended on sense of smell to root out food, Huttenlocker said.

Supercontinent existed longer than previously thought

Huttenlocker and his colleagues placed Cifelliodon within a group called Haramiyida, an extinct branch of mammal ancestors related to true mammals. The fossil was the first of its particular subgroup - Hahnodontidae - found in North America.

The fossil discovery emphasizes that haramiyidans and some other vertebrate groups existed globally during the Jurassic-Cretaceous transition, meaning the corridors for migration via Pangean landmasses remained intact into the Early Cretaceous.

Most of the Jurassic and Cretaceous fossils of haramiyidans are from the Triassic and Jurassic of Europe, Greenland and Asia. Hahnodontidae was previously known only from the Cretaceous of Northern Africa. It is to this group that Huttenlocker argues Cifelliodon belongs, providing evidence of migration routes between the continents that are now separated in northern and southern hemispheres.

"But it's not just this group of haramiyidans," Huttenlocker said. "The connection we discovered mirrors others recognized as recently as this year based on similar Cretaceous dinosaur fossils found in Africa and Europe."

Source: University of Southern California [May 23, 2018]

Coprolites reveal Early Cretaceous aquatic vertebrate diversity

Ancient fossils faeces found in central Spain belonged to fish-eating carnivores from the Early Cretaceous, according to a study published in the open-access journal PLOS ONE by Sandra Barrios de Pedro from the Universidad Autónoma de Madrid, Spain, and colleagues.

Coprolites [Credit: Barrios de Pedro, et al. (2018)]

Fossilized faeces, or coprolites, provide unique clues about the diet and feeding behaviors of extinct animals. These fossils are relatively abundant in marine and terrestrial sediments, but coprolites from river, lake, or wetland environments are harder to find. In this study, the research team analyzed a large collection of coprolites found in freshwater sediments dating from about 129 to 125 million years ago, at the Las Hoyas site in central Spain.

The researchers selected 433 coprolites from a collection of almost 2,000 and then analyzed their shape, contents, and chemical composition. The specimens varied widely in shape and size, suggesting they belonged to a diverse range of aquatic vertebrates. These animals were likely carnivores that fed mainly on fish, such as ray-finned fishes and crocodiles, because their faeces were filled with bits of fish scales and small fish bones. This hypothesis was supported by chemical analyses, which revealed large amounts of bone residues in the coprolites.

These findings uncover some of the feeding behaviors of Early Cretaceous aquatic vertebrates and support previous fossil evidence suggesting that Las Hoyas was a rich and diverse wetland ecosystem.

"Hundreds of coprolites from the early Cretaceous of Las Hoyas show that most of the coprolites were produced by carnivorous animals with ichtyophagous diets," says Barrios de Pedro. "The coprolites' content reveal differences on the efficacy of the digestive processes of the producers."

Source: Public Library of Science [May 23, 2018]

Why birds don't have teeth

Why did birds lose their teeth? Was it so they would be lighter in the air? Or are pointy beaks better for worm-eating than the jagged jaws of dinosaur ancestors?

New research suggests that birds gave up teeth to speed up egg hatching
[Credit: Yuri Kadobinov/AFP]

Actually, birds gave up teeth to speed up egg hatching, a research paper published in Biology Letters suggests, challenging long-held scientific views on the evolution of the toothless beak.

Compared to an incubation period of several months for dinosaur eggs, modern birds hatch after just a few days or weeks.

This is because there is no need to wait for the embryo to develop teeth -- a process that can consume 60 percent of egg incubation time, said researchers Tzu-Ruei Yang and Martin Sander from the University of Bonn.

While in the egg, the embryo is vulnerable to predators and natural disasters, and faster hatching boosts survival odds.

This would be a concern for dinos and birds -- all egg layers. In mammals, embryos are protected inside the mother.

"We suggest that (evolutionary) selection for tooth loss (in birds) was a side effect of selection for fast embryo growth and thus shorter incubation," Yang and Sander wrote in the journal Biology Letters.

Previous studies had concluded that birds -- living descendants of avian dinosaurs -- lost their teeth to improve flight.

Oviraptosaurs were omnivores but had a toothless beak [Credit: University of Nagoya,
Japan/Masato Hattori/AFP] 

But this did not explain why some non-avian dinosaurs in the Mesozoic era had independently evolved similar toothless beaks, said the duo.

Other studies had concluded that beaks were better for eating bird food.

But some dinosaurs with a very different, meat-eating diet had also discarded teeth in favour of pointed beaks.

Yang and Sander said their breakthrough came from a study published last year, which found that the eggs of non-flying dinosaurs took longer to hatch than previously thought -- about three to six months.

This was because of slow dental formation, which researchers analysed by examining growth lines -- almost like tree rings -- in the fossilised teeth of two dinosaur embryos.

Faster incubation would have been aided by early birds and some dinos taking to brooding their eggs in open nests rather than burying them as of old, said the research team.

They conceded their hypothesis was not consistent with toothlessness in turtles, which still have a long incubation period.

Source: AFP [May 23, 2018]

Study casts doubt on traditional view of pterosaur flight

Most renderings and reconstructions of pterodactyls and other extinct flying reptiles show a flight pose much like that of bats, which fly with their hind limbs splayed wide apart. But a new method for inferring how ancient animals might have moved their joints suggests that pterosaurs probably couldn't strike that pose.

This is an image of a reliable reconstruction. Soft tissues like ligaments play a big role in determining a joint's range
of motion. But soft tissues rarely fossilize, causing problems for paleontologists trying to reconstruct who extinct
creatures may have lived. Now researchers have shown a new method for inferring the extent to which ligaments
inhibit joint movement, which could be helpful in reconstructing ancient species
[Credit: Armita Manafzadeh]

"Most of the work that's being done right now to understand pterosaur flight relies on the assumption that their hips could get into a bat-like pose," said Armita Manafzadeh, a Ph.D. student at Brown University who led the research with Kevin Padian of the University of California, Berkeley. "We think future studies should take into account that this pose was likely impossible, which might change our perspective when we consider the evolution of flight in pterosaurs and dinosaurs."

The research, published in Proceedings of the Royal Society B, is an effort to help paleontologists infer the range of motion of joints in a way that takes into account the soft tissues -- particularly ligaments -- that play key roles in how joints work. Generally, soft tissues don't fossilize, leaving paleontologists to infer joint motion from bones alone. And there aren't many constraints on how that's done, Manafzadeh says. So she wanted to find a way to use present-day animals to test the extent to which ligaments limit joint motion.

It's an idea that started with grocery store chickens, Manafzadeh says.

"If you pick up a raw chicken at the grocery store and move its joints, you'll reach a point where you'll hear a pop," she said. "That's the ligaments snapping. But if I handed you a chicken skeleton without the ligaments, you might think that its joints could do all kinds of crazy things. So the question is, if you were to dig up a fossil chicken, how would you think its joints could move, and how wrong would you be?"

For this latest study, she used not a grocery store chicken, but dead quail. Birds are the closest living relative of extinct pterosaurs and four-winged dinosaurs. After carefully cutting away the muscles surrounding the birds' hip joints, she manipulated the joints while taking x-ray videos. That way, she could determine the exact 3-D positions of the bones in poses where the ligaments prevented further movement.

This technique enabled Manafzadeh to map out the range of motion of the quail hip with ligaments attached, which she could then compare to the range of motion that might have been inferred from bones alone. For the bones-only poses, Manafzadeh used traditional criteria that paleontologists often use -- stopping where the two bones hit each other and when the movement pulled the thigh bone out of its socket.

She found that over 95 percent of the joint positions that seemed plausible with bones alone were actually impossible when ligaments were attached.

The next step was to work out how the range of motion of present-day quail hips might compare to the range of motion for extinct pterosaurs and four-winged dinosaurs.

The assumption has long been that these creatures flew a lot like bats do. That's partly because the wings of pterosaurs were made of skin and supported by an elongated fourth finger, which is somewhat similar to the wings of bats. Bat wings are also connected to their hind limbs, which they splay out widely during flight. Many paleontologists, Manafzadeh says, assume pterosaurs and four-winged dinosaurs did the same. But her study suggests that wasn't possible.

In quail, a bat-like hip pose seemed possible based on bones alone, but outward motion of the thigh bone was inhibited by one particular ligament -- a ligament that's present in a wide variety of birds and other reptiles related to pterosaurs. No evidence, Manafzadeh says, suggests that extinct dinosaurs and pterosaurs wouldn't have had this ligament, too.

And with that ligament attached, this new study suggests that the bat-like pose would be impossible. According to Manafzadeh's work, this pose would require the ligament to stretch 63 percent more than the quail ligament can. That's quite a stretch, she says.

"That's a huge difference that would need to be accounted for before it can be argued that a pterosaur or 'four-winged' dinosaur's hip would be able to get into this bat-like pose," Manafzadeh said. And that, she says, may require a rethinking of the evolution of flight in these animals.

In addition to calling into question traditional ideas about flight in pterosaurs and early birds, the research also provides new ways of assessing joint mobility for any joint of any extinct species by looking at its living relatives.

"What we've done is to provide a reliable way to quantify in 3-D everything a joint can do," Manafzadeh said.

She hopes other researchers will use the method to study other joint systems and to better understand how other species may have moved their joints, walked and flown.

Source: Brown University [May 22, 2018]

How coyotes conquered North America

Coyotes now live across North America, from Alaska to Panama, California to Maine. But where they came from, and when, has been debated for decades. Using museum specimens and fossil records, researchers from the North Carolina Museum of Natural Sciences and North Carolina State University have produced a comprehensive (and unprecedented) range history of the expanding species that can help reveal the ecology of predation as well as evolution through hybridization. Their findings appeared in ZooKeys.

A coyote in Yosemite National Park, California, USA [Credit: Christopher Bruno]

The geographic distribution of coyotes has dramatically expanded since 1900, spreading across much of North America in a period when most other mammal species have been declining. Although this unprecedented expansion has been well documented at the state/provincial scale, the continent-wide picture of coyote spread was coarse and largely anecdotal. A more thorough compilation of available records was needed.

"We began by mapping the original range of coyotes using archeological and fossil records," says co-author Dr. Roland Kays, Head of the Museum's Biodiversity Lab and Research Associate Professor in NC State's Department of Forestry and Environmental Resources. "We then plotted their range expansion across North America from 1900 to 2016 using museum specimens, peer-reviewed reports, and game department records." In all, Kays and lead author James Hody reviewed more than 12,500 records covering the past 10,000 years for this study.

Ranges are based on occurrence of museum specimens, peer-reviewed literature with associated specimens or
photographs, and reports from state game departments. The distribution of coyotes between the Yucatán
Peninsula and Nicaragua is coarsely depicted due to the paucity of available data, representing the
earliest confirmed occurrence [Credit: James Hody]

Their findings indicate that coyotes historically occupied a larger area of North America than generally suggested in the literature. Previous maps, as it turns out, had ancient coyotes only located across the central deserts and grasslands. However, fossils from across the arid west link the distribution of coyotes from 10,000 years ago to specimens collected in the late 1800s, proving that their geographic range was not only broader but had been established for hundreds, perhaps thousands of years, which also contradicts some widely-cited descriptions of their historical distribution.

It wasn't until approximately 1920 that coyotes began their expansion across North America. This was likely aided by an expansion of human agriculture, forest fragmentation, and hybridization with other species. Eastern expansion in particular was aided by hybridization with wolves and dogs, resulting in size and color variation among eastern coyotes.

Before too long, coyotes may no longer be just a North American species. Kays notes that coyotes are continually expanding their range in Central America, crossing the Panama Canal in 2010. Active camera traps are now spotting coyotes approaching the Darien Gap, a heavily forested region separating North and South America, suggesting that they are at the doorstep of South America.

"The expansion of coyotes across the American continent offers an incredible experiment for assessing ecological questions about their roles as predators, and evolutionary questions related to their hybridization with dogs and wolves," adds Hody. "By collecting and mapping these museum data we were able to correct old misconceptions of their original range, and more precisely map and date their recent expansions.

"We hope these maps will provide useful context for future research into the ecology and evolution of this incredibly adaptive carnivore."

Source: North Carolina Museum of Natural Sciences [May 22, 2018]

Research suggests sweet potatoes didn't originate in the Americas as previously thought

New research by an Indiana University paleobotanist suggests sweet potatoes originated in Asia, and much earlier than previously known.

A) Modern distribution of the sweet potato family (yellow line) and genus (white line). B) Fossil leaf of Ipomoea
meghalayensis. C) Modern leaf of Ipomoea eriocarpa, showing similar size, shape and vein pattern
[Credit: Indiana University]

IU Bloomington emeritus professor David Dilcher and colleagues in India identified 57-milion-year-old leaf fossils from eastern India as being from the morning glory family, which includes sweet potatoes and many other plants. The research suggests the family originated in the late Paleocene epoch in the East Gondwana land mass that became part of Asia.

"I think this will change people's ideas," Dilcher said. "It will be a data point that is picked up and used in other work where researchers are trying to find the time of the evolution of major groups of flowering plants."

Previous fossil evidence had suggested the morning glory family may have originated in North America about 35 million years ago. But molecular analyses had supported the idea that it originated earlier and in the Old World. The new research provides evidence for that conclusion.

The discovery also suggests the morning glory family and the nightshade family, which includes potatoes and tomatoes, diverged earlier than previously thought. Together with the recent, separate discovery of 52-million-year-old nightshade fossils in Argentina, it suggests that morning glories developed in the East and nightshades in the West.

The 17 fossils analyzed in the study are the earliest recorded fossils for both the morning glory family, known as Convolvulaceae, and the order Solanales, which includes morning glories and nightshades. Morning glory fossils are rare because the plants' soft structure was not easily preserved in rocks.

Dilcher's collaborators, Gaurav Srivastava and Rakesh C. Mehrotra of India's Birbal Sahni Institute of Palaeosciences, discovered the fossils in Meghalaya, a state in northeastern India.

The researchers used microscopic analysis of the shape and structure of the leaves, comparing details of the leaf veins and cells with plants in the genus Ipomoea. Using such analysis to examine evolutionary relationships has been a hallmark of Dilcher's paleobotany research career.

The leaves the researchers studied are in the genus Ipomoea, which includes sweet potato but also hundreds of other plants, most of which don't produce food for humans.

"We don't know that these were sweet potatoes," said Dilcher, emeritus professor in the Department of Earth and Atmospheric Sciences and the Department of Biology in the IU Bloomington College of Arts and Sciences. "We can't say there were delicious sweet potatoes there. There may have been, or there may not."

The morning glory family is widely distributed in tropical and subtropical regions and includes about 57 plant genera and 1,880 species. The sweet potato is the world's second most important root crop, and other members of the family are medicinally and culturally significant.

The study has been published in the Proceedings of the National Academies of Science.

Source: Indiana University [May 21, 2018]

Major fossil study sheds new light on emergence of early animal life 540 million years ago

All the major groups of animals appear in the fossil record for the first time around 540-500 million years ago - an event known as the Cambrian Explosion - but new research from the University of Oxford in collaboration with the University of Lausanne suggests that for most animals this 'explosion' was in fact a more gradual process.

Model of the Cambrian stem lineage euarthropod Peytoia, based on fossils from the Burgess Shale. Top left: Closeup
of the mouth parts and frontal appendages. Bottom right: Overall view of the body [Credit: E. Horn]

The Cambrian Explosion produced the largest and most diverse grouping of animals the Earth has ever seen: the euarthropods. Euarthropoda contains the insects, crustaceans, spiders, trilobites, and a huge diversity of other animal forms alive and extinct. They comprise over 80 percent of all animal species on the planet and are key components of all of Earth's ecosystems, making them the most important group since the dawn of animals over 500 million years ago.

A team based at Oxford University Museum of Natural History and the University of Lausanne carried out the most comprehensive analysis ever made of early fossil euarthropods from every different possible type of fossil preservation. In an article published in the Proceedings of the National Academy of Sciences they show that, taken together, the total fossil record shows a gradual radiation of euarthropods during the early Cambrian, 540-500 million years ago.

The new analysis presents a challenge to the two major competing hypotheses about early animal evolution. The first of these suggests a slow, gradual evolution of euarthropods starting 650-600 million years ago, which had been consistent with earlier molecular dating estimates of their origin. The other hypothesis claims the nearly instantaneous appearance of euarthropods 540 million years ago because of highly elevated rates of evolution.

Reconstruction of the Cambrian predator and stem-lineage euarthropod Anomalocaris canadensis,
based on fossils from the Burgess Shale, Canada [Credit: Natalia Patkiewicz]

The new research suggests a middle-ground between these two hypotheses, with the origin of euarthropods no earlier than 550 million years ago, corresponding with more recent molecular dating estimates, and with the subsequent diversification taking place over the next 40 million years.

"Each of the major types of fossil evidence has its limitation and they are incomplete in different ways, but when taken together they are mutually illuminating and allow a coherent picture to emerge of the origin and radiation of the euarthropods during the lower to middle Cambrian," explains Professor Allison Daley, who carried out the work at Oxford University Museum of Natural History and at the University of Lausanne. "This indicates that the Cambrian Explosion, rather than being a sudden event, unfolded gradually over the ~40 million years of the lower to middle Cambrian."

The timing of the origin of Euarthropoda is very important as it affects how we view and interpret the evolution of the group. By working out which groups developed first we can trace the evolution of physical characteristics, such as limbs.

Exceptionally preserved soft-bodied fossils of the Cambrian predator and stem-lineage euarthropod Anomalocaris
canadensis from the Burgess Shale, Canada.Top left: Frontal appendage showing segmentation similar to modern-day
euarthropods. Bottom right: Full body specimen showing one pair of frontal appendages (white arrows)
and mouthparts consisting of plates with teeth (black arrow) on the head [Credit: A. Daley]

It has been argued that the absence of euarthropods from the Precambrian Period, earlier than around 540 million years ago, is the result of a lack of fossil preservation. But the new comprehensive fossil study suggests that this isn't the case.

"The idea that arthropods are missing from the Precambrian fossil record because of biases in how fossils are preserved can now be rejected," says Dr Greg Edgecombe FRS from the Natural History Museum, London, who was not involved in the study. "The authors make a very compelling case that the late Precambrian and Cambrian are in fact very similar in terms of how fossils preserve. There is really just one plausible explanation - arthropods hadn't yet evolved."

Harriet Drage, a PhD student at Oxford University Department of Zoology and one of the paper's co-authors, says: "When it comes to understanding the early history of life the best source of evidence that we have is the fossil record, which is compelling and very complete around the early to middle Cambrian. It speaks volumes about the origin of euarthropods during an interval of time when fossil preservation was the best it has ever been."

Source: University of Oxford [May 21, 2018]

Establishing a timescale for more than 10 million years ago

The timescale is the base to reconstruct the history of the Earth and the biological evolution. A research on a chronostratigraphic sequence of the Chinese Neogene with accurate geological datings was published online in Science China: Earth Sciences.

This is an image of the exposure of the Neogene strata in the Linxia Basin of Gansu Province
[Credit: Science China Press]

The Chinese Neogene terrestrial deposits are widely exposed. In the Linxia Basin of Gansu Province, for example, there are continuous deposits from Oligocene to Pleistocene, covering complete Neogene period and bearing rich mammalian fossils. The rapidly evolved mammalian fossils contribute efficiently to the division and correlation of Neogene strata.

A uniform Neogene biostratigraphic framework for China has already been established, with seven mammalian ages named. With a developed stratigraphic basis for the geochronologic ages, seven chronostratigraphic stage have been established for the Chinese Neogene terrestrial strata, namely the Miocene Xiejian, Shanwangian, Tunggurian, Bahean, and Baodean stages, and the Pliocene Gaozhuangian and Mazegouan stages.

This is an image of an upper jaw fossil and a reconstruction of Hipparion forstenae
[Credit: Chen Yu/Science China Press]

Based on a series of research achievements, refined biostratigraphic, paleomagnetic and isotopic methods were combined and applied to continuous sections, and a Chinese Neogene chronostratigraphic sequence with accurate geological ages was established and improved by the research team of Prof. Deng Tao at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences in recent years.

In Eurasia, Chinese Neogene deposits are more suitable for the establishment of an accurate Neogene biostratigraphic sequence than those of Europe, since the terrestrial deposits in Europe often limited, and many important faunas are unearthed from fissure-fillings. Chinese Neogene deposits are widespread and well suited for magnetostratigraphic analysis, despite the few radiometric dates available.

This is an image of the comprehensive column section at Xiejia of the Xining Basin, Qinghai Province
[Credit: Science China Press]

The lower boundaries of most of the stages could be correlated with those of the marine stages in the International Chronostratigraphic Chart, except the Tunggurian Stage, which is correlated with the European land mammal age. The biostratigraphic markers of the Chinese Neogene stages are usually first appearance of a single taxon, some representing regional species replacement, others indicating intercontinental migration of certain taxa.

For instance, the lower boundaries of the two Upper Miocene stages, Bahean and Baodean have the first appearances of Hipparion dongxiangense and H. forstenae as biostratigraphic markers, respectively, and the geological ages of their lower boundaries are corresponding to those of the marine Tortonian (11.63 Ma) and Messinian (7.25 Ma).

The Chinese Neogene mammalian biostratigraphic divisions have become the core to establish the Asian framework. Candidate stratotype sections have been proposed for all the Chinese Neogene stages according to the principle and rule of modern stratigraphy, and other Chinese Neogene strata in different regions are comprehensively correlated.

Source: Science China Press [May 21, 2018]

Scientists find widespread ocean anoxia as cause for past mass extinction

For decades, scientists have conducted research centered around the five major mass extinctions that have shaped the world we live in. The extinctions date back more than 450 million years with the Late Ordovician Mass Extinction to the deadliest extinction, the Late Permian extinction 250 million years ago that wiped out over 90 percent of species.

UNM Researcher Maya Elrick gathers samples on Anticosti Island [Credit: University of New Mexico]

Over the years, scientists have figured out the main causes of the mass extinctions, which include massive volcanic eruptions, global warming, asteroid collisions, and acidic oceans as likely culprits. Other factors sure to play part include methane eruptions and marine anoxic events - when oceans lose life-supporting oxygen.

The events that triggered the Late Ordovician Mass Extinction or LOME of marine animals and plants has largely remained a mystery until now. The Ordovician was a dynamic time interval in Earth history that recorded a major increase in marine biologic diversity and a greenhouse-to-icehouse climatic transition. Researchers believe this cooling period, which culminated in the first Phanerozoic glaciation led to the Late Ordovician Mass Extinction.

Now a team of researchers, including Maya Elrick at The University of New Mexico, Elrick's former master's student Rick Bartlett, now earning his doctorate at Louisiana State University, James Wheeley from the University of Birmingham (England) and the University of Ottawa's Andre Desrochers, have deciphered geochemical evidence left behind in marine limestone sediment that suggests this extinction was caused by a period of global cooling that created a global marine anoxic event.

The research, "Abrupt global-ocean anoxia during Late Ordovician-early Silurian detected using uranium isotopes of marine carbonates," was published in Proceedings of the National Academy of Sciences. It was supported, in part, through a three-year, $680,000 National Science Foundation grant.

"This extinction is the first of the 'big five' extinctions that hit the Earth and our research indicates that it was coincident with the abrupt development of widespread ocean anoxia that lasted for at least 1 million years," said Elrick.

Working with an international crew, Elrick and her team travelled to Anticosti Island in the St. Lawrence seaway of Quebec, Canada where they collected limestone rock samples. The returned samples were analyzed for uranium isotopes using a mass spectrometer housed in the UNM Department of Earth and Planetary Sciences. Results from the study indicate that abrupt and widespread marine anoxia occurred at the same time 85 percent of marine life went extinct.

Researchers gather samples on Anticosti Island [Credit: University of New Mexico]

"These results provided the first evidence for abrupt global ocean anoxia initiating and continuing through peak and waning glacial conditions," Elrick said. "We suggest that the anoxia was driven by global cooling which reorganized large-scale ocean circulation and led to decreased deep-ocean oxygenation and, enhanced nutrient fluxes, which caused phytoplankton blooms and expanded the areas of low oxygen concentrations. These results also provide the first evidence for widespread ocean anoxia initiating and continuing during glacial conditions."

Elrick and Bartlett's research is the first study of this type that uses a geochemical proxy (uranium isotopes) which integrates the entire ocean oxygen concentration. The results agree with what other scientists had been saying before, although the earlier studies were assessing only local oxygen concentrations rather than globally integrated concentrations. Further, Elrick and her team are modeling global ocean oxygen concentrations to evaluate how much of the seafloor went anoxic during the Late Ordovician extinction.

The team compared conditions 450 million years ago to those of today and determined that about there was about a 15 percent increase in anoxic seafloor during the Late Ordovician mass extinction. The modern ocean has less than a half a percent of seafloor that is anoxic (mainly the Black Sea), so a 15 percent increase in seafloor anoxia is quite significant.

"Anticosti Island is the best natural laboratory in the World for studying fossils and sedimentary strata dating from the first mass extinction nearly 445 million years ago. The island is now awaiting recognition at the UNESCO World Heritage program because of its exceptional geology and paleontology," said the University of Ottawa's Andre Desrochers.

Elrick is also studying three of the other 'big five' mass extinctions using uranium isotopes as oxygenation proxy.

"So far each of them have widespread anoxia associated with them, so we are finding that low seawater oxygen concentrations is a major killer," Elrick said

These results for the past 'big five' mass extinctions have implications for the modern extinction our planet is presently experiencing.

"We are warming and acidifying the oceans today and warmer oceans hold less and less oxygen. Some marine organisms can handle the heat and the acidity, but not the lack of oxygen" Elrick said. "All these things are happening today and the results from the Late Ordovician study indicate the potential severity of marine anoxia as an extinction driver for many of the past and ongoing biologic extinction events."

Source: University of New Mexico [May 21, 2018]

Could recent supernovae be responsible for mass extinctions?

Two nearby supernovae that exploded about 2.5 and eight million years ago could have resulted in a staggered depletion of Earth’s ozone layer, leading to a variety of repercussions for life on Earth.

The ultraviolet radiation from a nearby supernova may have resulted in changes in life on Earth
[Credit: David Aguilar (CfA)]

In particular, two-and-a-half million years ago the Earth was changing dramatically. The Pliocene, which was a hot and balmy epoch, was ending and the Pleistocene, an era of repeated glaciation known as the Ice Age, was beginning. Natural variations in Earth’s orbit and wobble likely accounted for the change in climate, but the simultaneous event of a supernova could provide insight on the diversification of life during this epoch.

This supernova is thought to have occurred between 163 and 326 light years away (50–100 parsecs) from Earth. For perspective, our closest stellar neighbor, Proxima Centauri, is 4.2 light years away.

Consequences for Earth

Supernovae can sterilize any nearby inhabited planets that happen to be in the path of their harmful ionizing radiation. Could nearby supernovae wreak havoc on the existing biology of our planet? One researcher wanted to find out. Dr Brian Thomas, an astrophysicist at Washburn University in Kansas, USA, modeled the biological impacts at the Earth’s surface, based on geologic evidence of nearby supernovae 2.5 million and 8 million years ago. In his latest paper, Thomas investigated cosmic rays from the supernovae as they propagated through our atmosphere to the surface, to understand their effect on living organisms.

The globally averaged change in ozone density, as a percent difference at 100 years, 300 years,
and 1000 years after a nearby supernova explosion [Credit: Brian Thomas]

Looking at the fossil record during the Pliocene–Pleistocene boundary (2.5 million years ago), we see a dramatic change in the fossil record and in land cover globally. Thomas tells Astrobiology Magazine that “there were changes, especially in Africa, which went from being more forested to more grassland.” During this time the geologic record shows an elevated global concentration of iron-60 (60Fe), which is a radioactive isotope produced during a supernova.

“We are interested in how exploding stars affect life on Earth, and it turns out a few million years ago there were changesin the things that were living at the time,” says Thomas. “It might have been connected to this supernova.”

For example, there was a change in the abundance of species during the Pliocene–Pleistocene boundary. Although no major mass extinctions happened, there was a higher rate of extinction in general, more speciation and a change in vegetation.

Not quite so deadly

How would a nearby supernova affect life on Earth? Thomas laments that supernovae often are exemplified as “supernova goes off and everything dies”, but that is not quite the case. The answer lies in the atmosphere. Beyond sunscreen, the ozone layer protects all biology from harmful, genetically altering ultraviolet (UV) radiation. Thomas used global climate models, recent atmospheric chemistry models and radiative transfer (the propagation of radiation through the layers of the atmosphere) to better understand how the flux of cosmic rays from supernovae would alter Earth’s atmosphere, specifically the ozone layer.

One of the the last supernovae known to have exploded in our Milky Way Galaxy was the star that left behind the
Cassiopeia A supernova remnant over 300 years ago, which is 11,000 light years away – much too far
 to have affected Earth [Credit: NASA/JPL-Caltech/O. Krause (Steward Observatory)]

One thing to note is that cosmic rays from supernovae would not blast everything in their paths all at once. The intergalactic medium acts as a kind of sieve, slowing down the arrival of cosmic rays and “radioactive iron rain” (60Fe) over hundreds of thousands of years, Thomastells Astrobiology Magazine. Higher energetic particles will reach Earth first and interact with our atmosphere differently than lower energy particles arriving later. Thomas’s study modeled the depletion in ozone 100, 300, and 1,000 years after the initial particles from a supernovabegan penetrating our atmosphere. Interestingly, depletion peaked (at roughly 26 percent) for the 300-year case, beating out the 100-year case.

The high-energy cosmic rays in the 100-year case would zip right through the stratosphere and deposit their energy below the ozone layer, depleting it less, while the less energetic cosmic rays arriving during the 300-year interval would deposit more energy in the stratosphere, depleting ozone significantly.

A decrease in ozone could be a concern for life on the surface. “This work is an important step towards understanding the impact of nearby supernovae on our biosphere,” says Dr Dimitra Atri, a computational physicist at the Blue Marble Space Institute of Science in Seattle, USA.

Mixed effects

Thomas examined several possible biologically-damaging effects (erythema, skin cancer, cataracts, marine phytoplankton photosynthesis inhibition and plant damage) at different latitudes as a result of increased UV radiation resulting from a depleted ozone layer. They showed heightened damage across the board, generally increasing with latitude, which makes sense given the changes we see in the fossil record. However, the effects aren’t equally detrimental to all organisms. Plankton, the primary producers of oxygen, seemed to be minimally affected. The results also suggested a small increase in the risk of sunburn and skin cancer among humans.

So, do nearby supernovae result in mass extinctions? It depends, says Thomas. “There is a subtler shift; instead of a ‘wipe-out everything’, some [organisms] are better off and some are worse off.” For example some plants showed increase yield, like soybean and wheat, while other plants showed reduced productivity.  “It fits,” Thomas states, referring to the change in species in the fossil record.

In the future, Thomas hopes to expand on this work and examine possible linkages between human evolution and supernovae.

Author: Julia Demarines | Source: Astrobiology Magazine [May 18, 2018]