суббота, 15 февраля 2020 г.

One-third of plant and animal species could be gone in 50 years

Accurately predicting biodiversity loss from climate change requires a detailed understanding of what aspects of climate change cause extinctions, and what mechanisms may allow species to survive.

One-third of plant and animal species could be gone in 50 years
The common giant tree frog from Madagascar is one of many species impacted
by recent climate change [Credit: John J. Wiens]
A new study by University of Arizona researchers presents detailed estimates of global extinction from climate change by 2070. By combining information on recent extinctions from climate change, rates of species movement and different projections of future climate, they estimate that one in three species of plants and animals may face extinction. Their results are based on data from hundreds of plant and animal species surveyed around the globe.

Published in the Proceedings of the National Academy of Sciences, the study likely is the first to estimate broad-scale extinction patterns from climate change by incorporating data from recent climate-related extinctions and from rates of species movements.

To estimate the rates of future extinctions from climate change, Cristian Roman-Palacios and John J. Wiens, both in the Department of Ecology and Evolutionary Biology at the University of Arizona, looked to the recent past. Specifically, they examined local extinctions that have already happened, based on studies of repeated surveys of plants and animals over time.

Roman-Palacios and Wiens analyzed data from 538 species and 581 sites around the world. They focused on plant and animal species that were surveyed at the same sites over time, at least 10 years apart. They generated climate data from the time of the earliest survey of each site and the more recent survey. They found that 44% of the 538 species had already gone extinct at one or more sites.

"By analyzing the change in 19 climatic variables at each site, we could determine which variables drive local extinctions and how much change a population can tolerate without going extinct," Roman-Palacios said. "We also estimated how quickly populations can move to try and escape rising temperatures. When we put all of these pieces of information together for each species, we can come up with detailed estimates of global extinction rates for hundreds of plant and animal species."

One-third of plant and animal species could be gone in 50 years
A dead Alligator Juniper from Arizona. Unable to cope with rising temperature extremes,
repeated surveys have shown that this species is literally being pushed up the mountain
slopes under the impact of climate change [Credit: Ramona Walls]
The study identified maximum annual temperatures -- the hottest daily highs in summer -- as the key variable that best explains whether a population will go extinct. Surprisingly, the researchers found that average yearly temperatures showed smaller changes at sites with local extinction, even though average temperatures are widely used as a proxy for overall climate change.

"This means that using changes in mean annual temperatures to predict extinction from climate change might be positively misleading," Wiens said.

Previous studies have focused on dispersal -- or migration to cooler habitats -- as a means for species to "escape" from warming climates. However, the authors of the current study found that most species will not be able to disperse quickly enough to avoid extinction, based on their past rates of movement.

Instead, they found that many species were able to tolerate some increases in maximum temperatures, but only up to a point. They found that about 50% of the species had local extinctions if maximum temperatures increased by more than 0.5 degrees Celsius, and 95% if temperatures increase by more than 2.9 degrees Celsius.

Projections of species loss depend on how much climate will warm in the future. "In a way, it's a 'choose your own adventure,'" Wiens said. "If we stick to the Paris Agreement to combat climate change, we may lose fewer than two out of every 10 plant and animal species on Earth by 2070. But if humans cause larger temperature increases, we could lose more than a third or even half of all animal and plant species, based on our results."

The paper's projections of species loss are similar for plants and animals, but extinctions are projected to be two to four times more common in the tropics than in temperate regions. "This is a big problem, because the majority of plant and animal species occur in the tropics," Roman-Palacios said.

Source: University of Arizona [February 12, 2020]

* This article was originally published here

‘Ghost’ of mysterious hominin found in West African genomes

Ancestors of modern West Africans interbred with a yet-undiscovered species of archaic human, similar to how ancient Europeans mated with Neanderthals, researchers report.

‘Ghost’ of mysterious hominin found in West African genomes
Credit: Zacarias Pereira da Mata/Shutterstock
Their work helps inform how archaic hominins added to the genetic variation of present-day Africans, which has been poorly understood, in part because of the sparse fossil record in Africa and the difficulty of obtaining ancient DNA.

The authors’ computer modelling technique overcomes these challenges, enabling the discovery of genetic contributions from archaic hominins when fossils or DNA are lacking. Well-established research shows that sequences of Neanderthal DNA are found in modern European populations, and Denisovan DNA appears in Oceanian populations.

‘Ghost’ of mysterious hominin found in West African genomes
Demography relating known and proposed archaic lineages to modern human populations. (A) Basic demographic model
with CSFS fit. W Afr, West Africans; Eur, European; N, Neanderthal; D, Denisovan; UA, unknown archaic [see (18)].
Below, we show the CSFS in the West African YRI when restricting to SNPs where a randomly sampled allele from the
high-coverage Vindija Neanderthal was observed to be derived [Neanderthal (data)], as well as where a randomly
sampled allele from the high-coverage Denisovan genome was observed to be derived [Denisovan (data)]. We also
show the CSFS under the proposed model [Neanderthal (model) and Denisova (model)]. Migration between Europe
 and West Africa introduces an excess of low-frequency variants but does not capture the decrease in intermediate
frequency variants and increase in high-frequency variants. (B) Newly proposed model involving introgression
into the modern human ancestor from an unknown hominin that separated from the human ancestor before
 the split of modern humans and the ancestors of Neanderthals and Denisovans. Below, we show
the CSFS fit from the proposed model, which captures the U-shape observed in the data
[Credit: Durvasula et al. 2020]
These segments arrived in modern humans through introgression, the process by which members of two populations mate, and the resulting hybrid individuals then breed with members of the parent populations. Recent studies have shown that, though modern West Africans do not have Neanderthal or Denisovan ancestry, there may have been introgression by other ancient hominins in their past.

Now, by comparing 405 genomes of West Africans with Neanderthal and Denisovan genomes, Arun Durvasula and Sriram Sankararaman found differences that could be best explained by introgression by an unknown hominin whose ancestors split off from the human family tree before Neanderthals.

The authors’ data suggests this introgression may have happened relatively recently, or it may have involved multiple populations of archaic human, hinting at complex and long-lived interactions between anatomically modern humans and various populations of archaic hominins. The authors call for more analysis of modern and ancient African genomes to reveal the nature of this complex history.

The findings were published in Science Advances.

Source: American Association for the Advancement of Science [February 12, 2020]

* This article was originally published here

Distant giant planets form differently than 'failed stars'

A team of astronomers led by Brendan Bowler of The University of Texas at Austin has probed the formation process of giant exoplanets and brown dwarfs, a class of objects that are more massive than giant planets, but not massive enough to ignite nuclear fusion in their cores to shine like true stars.

Distant giant planets form differently than 'failed stars'
This image of the low-mass brown dwarf GJ 504 B was taken by Bowler and his team using adaptive optics
with the NIRC2 camera at Keck Observatory in Hawaii. The image has been processed to remove light
from the host star (whose position is marked with an "x"). The companion is located at a separation
of about 40 times the Earth-Sun distance and has an orbital period of about 240 years. By returning
to this and other systems year after year, the team is able to slowly trace out part of the companion's
orbit to constrain its shape, which provides clues about its formation and history
[Credit: Brendan Bowler (UT-Austin)/W. M. Keck Observatory]
Using direct imaging with ground-based telescopes in Hawaii - W. M. Keck Observatory and Subaru Telescope on Maunakea - the team studied the orbits of these faint companions orbiting stars in 27 systems. These data, combined with modeling of the orbits, allowed them to determine that the brown dwarfs in these systems formed like stars, but the gas giants formed like planets.

In the last two decades, technological leaps have allowed telescopes to separate the light from a parent star and a much-dimmer orbiting object. In 1995, this new capability produced the first direct images of a brown dwarf orbiting a star. The first direct image of planets orbiting another star followed in 2008.

"Over the past 20 years, we've been leaping down and down in mass," Bowler said of the direct imaging capability, noting that the current limit is about 1 Jupiter mass. As the technology has improved, "One of the big questions that has emerged is 'What's the nature of the companions we're finding?'"

Brown dwarfs, as defined by astronomers, have masses between 13 and 75 Jupiter masses. They have characteristics in common with both planets and with stars, and Bowler and his team wanted to settle the question: Are gas giant planets on the outer fringes of planetary systems the tip of the planetary iceberg, or the low-mass end of brown dwarfs? Past research has shown that brown dwarfs orbiting stars likely formed like low-mass stars, but it's been less clear what is the lowest mass companion this formation mechanism can produce.

"One way to get at this is to study the dynamics of the system -- to look at the orbits," Bowler said. Their orbits today hold the key to unlocking their evolution.

Using Keck Observatory's adaptive optics (AO) system with the Near-Infrared Camera, second generation (NIRC2) instrument on the Keck II telescope, as well as the Subaru Telescope, Bowler's team took images of giant planets and brown dwarfs as they orbit their parent stars.

Distant giant planets form differently than 'failed stars'
By patiently watching giant planets and brown dwarfs orbit their host stars, Bowler and his team were able
to constrain the orbit shapes even though only a small portion of the orbit has been monitored. The longer
 the time baseline, the smaller the range of possible orbits. These plots show nine of the 27 systems
 from their study [Credit: Brendan Bowler (UT-Austin)]
It's a long process. The gas giants and brown dwarfs they studied are so distant from their parent stars that one orbit may take hundreds of years. To determine even a small percentage of the orbit, "You take an image, you wait a year," for the faint companion to travel a bit, Bowler said. Then "you take another image, you wait another year."

This research relied on AO technology, which allows astronomers to correct for distortions caused by the Earth's atmosphere. As AO instruments have continually improved over the past three decades, more brown dwarfs and giant planets have been directly imaged. But since most of these discoveries have been made over the past decade or two, the team only has images corresponding to a few percent of each object's total orbit. They combined their new observations of 27 systems with all of the previous observations published by other astronomers or available in telescope archives.

At this point, computer modeling comes in. Coauthors on this paper have helped create an orbit-fitting code called "Orbitize!" which uses Kepler's laws of planetary motion to identify which types of orbits are consistent with the measured positions, and which are not.

The code generates a set of possible orbits for each companion. The slight motion of each giant planet or brown dwarf forms a "cloud" of possible orbits. The smaller the cloud, the more astronomers are closing in on the companion's true orbit. And more data points -- that is, more direct images of each object as it orbits -- will refine the shape of the orbit.

"Rather than wait decades or centuries for a planet to complete one orbit, we can make up for the shorter time baseline of our data with very accurate position measurements," said team member Eric Nielsen of Stanford University. "A part of Orbitize! that we developed specifically to fit partial orbits, OFTI [Orbits For The Impatient], allowed us to find orbits even for the longest period companions."

Finding the shape of the orbit is key: Objects that have more circular orbits probably formed like planets. That is, when a cloud of gas and dust collapsed to form a star, the distant companion (and any other planets) formed out of a flattened disk of gas and dust rotating around that star.

Distant giant planets form differently than 'failed stars'
These two curves show the final distribution of orbit shapes for giant planets and brown dwarfs. The orbital
eccentricity determines how elongated the ellipse is, with a value of 0.0 corresponding to a circular orbit
and a high value near 1.0 being a flattened ellipse. Gas giant planets located at wide separations from their
host stars have low eccentricities, but the brown dwarfs have a wide range of eccentricities similar
 to binary star systems. For reference, the giant planets in our solar system have eccentricities
less than 0.1 [Credit: Brendan Bowler (UT-Austin)]
On the other hand, the ones that have more elongated orbits probably formed like stars. In this scenario, a clump of gas and dust was collapsing to form a star, but it fractured into two clumps. Each clump then collapsed, one forming a star, and the other a brown dwarf orbiting around that star. This is essentially a binary star system, albeit containing one real star and one "failed star."

"Even though these companions are millions of years old, the memory of how they formed is still encoded in their present-day eccentricity," Nielsen added. Eccentricity is a measure of how circular or elongated an object's orbit is.

The results of the team's study of 27 distant companions was unambiguous.

"The punchline is, we found that when you divide these objects at this canonical boundary of more than about 15 Jupiter masses, the things that we've been calling planets do indeed have more circular orbits, as a population, compared to the rest," Bowler said. "And the rest look like binary stars."

The future of this work involves both continuing to monitor these 27 objects, as well as identifying new ones to widen the study. "The sample size is still modest, at the moment," Bowler said. His team is using the Gaia satellite to look for additional candidates to follow up using direct imaging with even greater sensitivity at the forthcoming Giant Magellan Telescope (GMT) and other facilities. UT-Austin is a founding member of the GMT collaboration.

Bowler's team's results reinforce similar conclusions recently reached by the GPIES direct imaging survey with the Gemini Planet Imager, which found evidence for a different formation channel for brown dwarfs and giant planets based on their statistical properties.

The research is published in the current issue of The Astronomical Journal.

Source: W. M. Keck Observatory [February 10, 2020]

* This article was originally published here

Roman Carved Stones, Chesters Roman Fort, Hadrian’s Wall, Northumberland, 8.2.20.

Roman Carved Stones, Chesters Roman Fort, Hadrian’s Wall, Northumberland, 8.2.20.

* This article was originally published here

SwRI models hint at longer timescale for Mars formation

The early solar system was a chaotic place, with evidence indicating that Mars was likely struck by planetesimals, small protoplanets up to 1,200 miles in diameter, early in its history. Southwest Research Institute scientists modeled the mixing of materials associated with these impacts, revealing that the Red Planet may have formed over a longer timescale than previously thought.

SwRI models hint at longer timescale for Mars formation
A Southwest Research Institute team performed high-resolution, smoothed-particle simulations of a large, differentiated
projectile hitting early Mars after its core and mantle had formed. The projectile's core and mantle particles are
 indicated by brown and green spheres respectively, showing local concentrations of the projectile materials
assimilated into the Martian mantle [Credit: Southwest Research Institute]
An important open issue in planetary science is to determine how Mars formed and to what extent its early evolution was affected by collisions. This question is difficult to answer given that billions of years of history have steadily erased evidence of early impact events. Luckily, some of this evolution is recorded in Martian meteorites. Of approximately 61,000 meteorites found on Earth, just 200 or so are thought to be of Martian origin, ejected from the Red Planet by more recent collisions.

These meteorites exhibit large variations in iron-loving elements such as tungsten and platinum, which have a moderate to high affinity for iron. These elements tend to migrate from a planet's mantle and into its central iron core during formation. Evidence of these elements in the Martian mantle as sampled by meteorites are important because they indicate that Mars was bombarded by planetesimals sometime after its primary core formation ended. Studying isotopes of particular elements produced locally in the mantle via radioactive decay processes helps scientists understand when planet formation was complete.

SwRI models hint at longer timescale for Mars formation
Scientists developed this illustration of how early Mars may have looked, showing signs of liquid water, large-scale
volcanic activity and heavy bombardment from planetary projectiles. SwRI is modeling how these impacts
may have affected early Mars to help answer questions about the planet's evolutionary history
[Credit: SwRI/Marchi]
"We knew Mars received elements such as platinum and gold from early, large collisions. To investigate this process, we performed smoothed-particle hydrodynamics impact simulations," said SwRI's Dr. Simone Marchi, lead author of a Science Advances paper outlining these results. "Based on our model, early collisions produce a heterogeneous, marble-cake-like Martian mantle. These results suggest that the prevailing view of Mars formation may be biased by the limited number of meteorites available for study."

Based on the ratio of tungsten isotopes in Martian meteorites, it has been argued that Mars grew rapidly within about 2-4 million years after the Solar System started to form. However, large, early collisions could have altered the tungsten isotopic balance, which could support a Mars formation timescale of up to 20 million years, as shown by the new model.

Для бесконечной шлифовальной ленты в кольце. Отличная балансировка колес. Отсутствует биение и вибрация.
Контактное колесо. Шлифовальное колесо.
Для бесконечной шлифовальной ленты в кольце. Отличная балансировка колес. Отсутствует биение и вибрация.  Контактное колесо. Шлифовальное колесо.
Grinding drums
For endless sanding belt in the ring.
Contact wheel. Grinding wheel.
Wheels are used by knife makers to bring down slopes on knives, to grind radii on a belt grinder. Using various sanding belts, any materials can be processed by grinding.

ESO Telescope Sees Surface of Dim Betelgeuse

SPHERE’s view of Betelgeuse in December 2019

SPHERE’s view of Betelgeuse in January 2019

Betelgeuse before and after dimming

Betelgeuse’s dust plumes seen by VISIR image

A plume on Betelgeuse (artist’s impression with annotations)

The star Betelgeuse in the constellation of Orion


ESOcast 217 Light: ESO Telescope Sees Surface of Dim Betelgeuse
ESOcast 217 Light: ESO Telescope Sees Surface of Dim Betelgeuse

Zooming in on Betelgeuse
Zooming in on Betelgeuse

Betelgeuse before and after dimming (animated)
Betelgeuse before and after dimming (animated)

From Betelgeuse’s surroundings to its surface
PR Video eso2003d
From Betelgeuse’s surroundings to its surface

Using ESO’s Very Large Telescope (VLT), astronomers have captured the unprecedented dimming of Betelgeuse, a red supergiant star in the constellation of Orion. The stunning new images of the star’s surface show not only the fading red supergiant but also how its apparent shape is changing.

Betelgeuse has been a beacon in the night sky for stellar observers but it began to dim late last year. At the time of writing Betelgeuse is at about 36% of its normal brightness, a change noticeable even to the naked eye. Astronomy enthusiasts and scientists alike were excitedly hoping to find out more about this unprecedented dimming.

A team led by Miguel Montargès, an astronomer at KU Leuven in Belgium, has been observing the star with ESO's Very Large Telescope since December, aiming to understand why it’s becoming fainter. Among the first observations to come out of their campaign is a stunning new image of Betelgeuse’s surface, taken late last year with the SPHERE instrument.

The team also happened to observe the star with SPHERE in January 2019, before it began to dim, giving us a before-and-after picture of Betelgeuse. Taken in visible light, the images highlight the changes occurring to the star both in brightness and in apparent shape.

Many astronomy enthusiasts wondered if Betelgeuse’s dimming meant it was about to explode. Like all red supergiants, Betelgeuse will one day go supernova, but astronomers don’t think this is happening now. They have other hypotheses to explain what exactly is causing the shift in shape and brightness seen in the SPHERE images. “The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us,” says Montargès [1]. “Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen.”

Montargès and his team needed the VLT at Cerro Paranal in Chile to study the star, which is over 700 light-years away, and gather clues on its dimming. “ESO's Paranal Observatory is one of few facilities capable of imaging the surface of Betelgeuse,” he says. Instruments on ESO’s VLT allow observations from the visible to the mid-infrared, meaning astronomers can see both the surface of Betelgeuse and the material around it. “This is the only way we can understand what is happening to the star.”

Another new image, obtained with the VISIR instrument on the VLT, shows the infrared light being emitted by the dust surrounding Betelgeuse in December 2019. These observations were made by a team led by Pierre Kervella from the Observatory of Paris in France who explained that the wavelength of the image is similar to that detected by heat cameras. The clouds of dust, which resemble flames in the VISIR image, are formed when the star sheds its material back into space.

“The phrase ‘we are all made of stardust’ is one we hear a lot in popular astronomy, but where exactly does this dust come from?” says Emily Cannon, a PhD student at KU Leuven working with SPHERE images of red supergiants. “Over their lifetimes, red supergiants like Betelgeuse create and eject vast amounts of material even before they explode as supernovae. Modern technology has enabled us to study these objects, hundreds of light-years away, in unprecedented detail giving us the opportunity to unravel the mystery of what triggers their mass loss.”

Souce: ESO/News


[1] Betelgeuse's irregular surface is made up of giant convective cells that move, shrink and swell. The star also pulsates, like a beating heart, periodically changing in brightness. These convection and pulsation changes in Betelgeuse are referred to as stellar activity. 

More Information

The team is composed of Miguel Montargès (Institute of Astronomy, KU Leuven, Belgium), Emily Cannon (Institute of Astronomy, KU Leuven, Belgium), Pierre Kervella (LESIA, Observatoire de Paris - PSL, France), Eric Lagadec (Laboratoire Lagrange, Observatoire de la Côte d'Azur, France), Faustine Cantalloube (Max-Planck-Institut für Astronomie, Heidelberg, Germany), Joel Sánchez Bermúdez (Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico City, Mexico and Max-Planck-Institut für Astronomie, Heidelberg, Germany), Andrea Dupree (Center for Astrophysics | Harvard & Smithsonian, USA), Elsa Huby (LESIA, Observatoire de Paris - PSL, France), Ryan Norris (Georgia State University, USA), Benjamin Tessore (IPAG, France), Andrea Chiavassa (Laboratoire Lagrange, Observatoire de la Côte d'Azur, France), Claudia Paladini (ESO, Chile), Agnès Lèbre (Université de Montpellier, France), Leen Decin (Institute of Astronomy, KU Leuven, Belgium), Markus Wittkowski (ESO, Germany), Gioia Rau (NASA/GSFC, USA), Arturo López Ariste (IRAP, France), Stephen Ridgway (NSF’s National Optical-Infrared Astronomy Research Laboratory, USA), Guy Perrin (LESIA, Observatoire de Paris - PSL, France), Alex de Koter (Astronomical Institute Anton Pannekoek, Amsterdam University, The Netherlands & Institute of Astronomy, KU Leuven, Belgium), Xavier Haubois (ESO, Chile), Eric Pantin (CEA, France), Ralf Siebenmorgen (ESO, Germany).

The VISIR image was obtained as part of the NEAR science demonstration observations. NEAR (Near Earths in the AlphaCen Region) is an upgrade of VISIR, which was implemented as a time-limited experiment.

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.</ div>



Miguel Montargès
FWO [PEGASUS]² Marie Skłodowska-Curie Fellow / Institute of Astronomy, KU Leuven
Leuven, Belgium
Tel: +32 16 32 74 67
Email: miguel.montarges@kuleuven.be

Emily Cannon
Institute of Astronomy, KU Leuven
Leuven, Belgium
Tel: +32 16 32 88 92
Email: emily.cannon@kuleuven.be

Pierre Kervella
LESIA, Observatoire de Paris - PSL
Paris, France
Tel: +33 0145077966
Email: pierre.kervella@observatoiredeparis.psl.eu

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: pio@eso.org

* This article was originally published here

Roman Iron Wrecking Bars, Chesters Roman Fort, Hadrian’s Wall, Northumberland, 8.2.20.These...

Roman Iron Wrecking Bars, Chesters Roman Fort, Hadrian’s Wall, Northumberland, 8.2.20.

These bars are for levering stone and virtually identical versions are in use today. These could be used even today.

* This article was originally published here

Boom and bust for ancient sea dragons

A new study by scientists from the University of Bristol's School of Earth Sciences, shows a well-known group of extinct marine reptiles had an early burst in their diversity and evolution—but that a failure to adapt in the long-run may have led to their extinction.

Boom and bust for ancient sea dragons
This very complete specimen of the ichthyosaur Suevoleviathan is from the Early Jurassic of Germany. Many excellently
 preserved ichthyosaur fossils are known from this time and have been collected from the UK and Germany. Mary
Anning from Lyme Regis is intimately associated with fossil collection and found the first recognized
ichthyosaur fossils in 1810 [Credit: Dr Ben Moon & Dr Tom Stubbs]
Ichthyosaurs were fish-like reptiles that first appeared about 250 million years ago and quickly diversified into highly capable swimmers, filling a broad range of sizes and ecologies in the early Mesozoic oceans. However, this rapid pace didn't last long and an evolutionary bottleneck 200 million years ago, through which only one lineage of ichthyosaurs survived, led to much slower evolution in much of their long history.

Dr. Ben Moon, who led the research, published in the journal Communications Biology, said: "Ichthyosaurs are a fascinating group of animals to work on because they evolved so many adaptations for living in water very quickly: a fish-like body and tail fin, giving birth to live young rather than laying eggs, and lots of different feeding styles.

"Because of this we expected to see a rapid evolution early after ichthyosaurs first appeared, but we were staggered by just how big this early burst was and how relatively short it was."

There are over 100 known species of ichthyosaur from between 250–90 million years ago in the Mesozoic Era, when the infamous dinosaurs ruled the land and the seas were full of marine reptiles, the top predators that filled comparable roles to dolphins, orcas, and sharks in modern seas.

Boom and bust for ancient sea dragons
The huge ichthyosaur Temnodontosaurus from the Early Jurassic of Germany. This specimen is about 7 m long,
but other ichthyosaurs grew up to 21 m [Credit: Dr Ben Moon & Dr Tom Stubbs]
The study used state-of-the-art computational methods and looked at two types of data, one covering skull size and the other including many features of ichthyosaurs' skeleton. All methods show an 'early burst' of evolution in ichthyosaurs, with high rates and rapid variation soon after the appearance of the group, that quickly diminishes later on.

Co-author Dr. Tom Stubbs said: "Ichthyosaurs really dominated early in the Triassic (252–201 million years ago), rapidly evolving in an ocean with few predators soon after the largest known mass extinction in Earth's history. However, the seas quickly became more crowded and competitive, and ichthyosaurs lost their top position in the Jurassic (201–145 million years ago) to other marine reptiles like plesiosaurs and pliosaurs.

"It may well have been the ichthyosaurs' decreasing evolutionary rates which made them less able to adapt quickly, and therefore less diverse and competitive, allowing other marine reptiles to take over as the top predators."

Despite slower evolution and going through a bottleneck at the end of the Triassic period, ichthyosaurs remained a common group but had less variation between them. These are perhaps best known ichthyosaurs, found in several UK locations, including Lyme Regis in Dorset, and first collected by Mary and Joseph Anning.

Boom and bust for ancient sea dragons
Ichthyosaurs rapidly evolved a large range of forms and sizes early in their evolution, but after
a bottle neck at the end of the Triassic, show much slower rates and more restricted variety
[Credit: Dr Ben Moon & Dr Tom Stubbs]
Dr. Ben Moon added: "Even though ichthyosaurs were evolving more slowly in their last 100 million years, they are still known from many species, but with less variety between them.

"It's possible that we might find more ichthyosaurs out there that buck this trend, but it seems that this lack of variety was eventually the cause of their extinction when global conditions became less favourable around 90 million years ago. Ichthyosaurs were simply unable to adapt."

Source: University of Bristol [February 13, 2020]

* This article was originally published here


https://t.co/hvL60wwELQ — XissUFOtoday Space (@xufospace) August 3, 2021 Жаждущий ежик наслаждается пресной водой после нескольких дней в о...