[reprint] Mass extinction and the rise of the dinosaurs

 Growing quickly helped the earliest dinosaurs and other ancient reptiles flourish in the aftermath of mass extinction

Eoraptor lunensis lived roughly 230 million years ago, at a time when dinosaurs were small and rare. Jordan Harris courtesy of Kristi Curry Rogers, CC BY-SA

Kristi Curry Rogers, Macalester College

It may be hard to imagine, but once upon a time, dinosaurs didn’t dominate their world. When they first originated, they were just small, two-legged carnivores overshadowed by a diverse array of other reptiles.

How did they come to rule?

My colleagues and I recently studied the fossilized bones of the earliest known dinosaurs and their nondinosaur rivals to compare their growth rates. We wanted to find out whether early dinosaurs were somehow special in the way they grew – and if this may have given them a leg up in their rapidly changing world.

Before dinosaurs – the Great Dying

Life on Earth was flourishing 250 million years ago. Dinosaurs had yet to evolve. Instead, giant amphibians and sail-backed reptiles called therapsids thrived.

But within a blink of geologic time, in a span of about 60,000 years, scientists estimate 95% of all living things went extinct. Known as the Permian extinction or the Great Dying, it is the largest of the five known mass extinction events on Earth.

Most scientists agree this near total die-off was caused by extensive volcanic activity in modern-day Siberia, which covered millions of square miles with lava. The resulting noxious gases and heat combined to push global temperatures dramatically upward, eventually leading to ocean acidification, a loss of oxygen in ocean waters and a profound ecosystem collapse, both on land and in the ocean.

Only a few lucky survivors made it through.

The survivors and their descendants

In the ecological vacuum after the mass extinction event, on the stage of a healing Earth, the ancestors of dinosaurs first evolved – along with the ancestors of today’s frogs, salamanders, lizards, turtles and mammals. It was the dawn of the Triassic Period, which lasted from 252 million years ago to 201 million years ago.

Collectively, the creatures that survived the Great Dying were not particularly remarkable. One animal group, known as Archosauria, started off with relatively small and simple body plans. They were flexible eaters and could live in a wide variety of environmental conditions.

Archosaurs eventually split into two tribes – one group including modern crocodiles and their ancient relatives and a second including modern birds, along with their dinosaur ancestors.

This second group walked on their tiptoes and had big leg muscles. They also had extra connections between their back bones and hip bones that allowed them to move efficiently in their new world.

Instead of directly competing with other archosaurs, it seems this group of dinosaur ancestors exploited different ecological niches – maybe by eating different foods or living in slightly different geographical areas. But early on, the dinosaurlike archosaurs were far less diverse than the crocodile ancestors they lived alongside.

Slowly, the dinosaur lineage continued to evolve. It took tens of millions of years before dinosaurs became abundant enough for their skeletons to show up in the fossil record.

The Ischigualasto Provincial Park in San Juan Province, Argentina, where the earliest dinosaur fossils have been discovered. Kristi Curry Rogers, CC BY-SA

The oldest known dinosaur fossils come from an area in Argentina now called Ischigualasto Provincial Park. Rocks there date back to roughly 230 million years ago.

The Ischigualasto dinosaurs include all three dinosaur groups: the meat-eating theropods, the ancestors of giant sauropods and the plant-eating ornithischians. They include Herrerasaurus, Sanjuansaurus, Eodromaeus, Eoraptor, Chromogisaurus, Panphagia and Pisanosaurus.

These early dinosaurs represent only a small fraction of animals found from that time period. In this ancient world, the crocodilelike archosaurs were on top. They had a wider array of body shapes, sizes and lifestyles, easily outpacing early dinosaurs in the diversity race.

It wouldn’t be until closer to the end of the Triassic Period, when another volcanism-induced mass extinction event occurred, that dinosaurs got their lucky break.

The late Triassic extinction event killed 75% of life on Earth. It decimated the crocodilelike archosaurs but left early dinosaurs relatively untouched, paving the way for their rise to dominance.

Before long, dinosaurs went from representing less than 5% of animals on Earth to constituting more than 90%.

Bones tell the story of growth

My collaborators from the Universidad Nacional de San Juan, Argentina, and I wondered whether the rise of dinosaurs may have been underpinned, in part, by how fast they grew. We know, through microscopic study of fossilized bones, that later dinosaurs had fast growth rates – much faster than that of modern-day reptiles. But we didn’t know whether that was true for the earliest dinosaurs.

We decided to examine the microscopic patterns preserved in thigh bones from five of the earliest known dinosaur species and compare them with those of six nondinosaur reptiles and one early relative of mammals. All the fossils we studied came from the 2-million-year interval within the Ischigualasto Formation of Argentina.

Eoraptor bone tissue under a polarizing light microscope shows evidence of rapid, continuous growth – common to both the earliest dinosaurs and many of their nondinosaur contemporaries. Kristi Curry Rogers, CC BY-ND

Bones are an archive of growth history because, even in fossils, we can see the spaces where blood vessels and cells perforated the mineralized tissue. When we look at these features under a microscope, we can see how they are organized. The more slowly growth occurs, the more organized microscopic features will be. With quicker growth, the more disorganized the microscopic features of the bone look.

We discovered early dinosaurs grew continuously, not stopping until they reached full size. And they did indeed have elevated growth rates, on par with and, at times, even faster than those of their descendants. But so did many of their nondinosaur contemporaries. It appears most animals living in the Ischigualasto ecosystem grew quickly, at rates that are more like those of living mammals and birds than those of living reptiles.

Our data allowed us to see the subtle differences between closely related animals and those occupying similar ecological niches. But most of all, our data shows that fast growth is a great survival strategy in the aftermath of mass destruction.

Scientist still don’t know exactly what made it possible for dinosaurs and their ancient ancestors to survive two of the most extensive extinctions Earth has ever undergone. We are still studying this important interval, looking at details such as legs and bodies built for efficient, upright locomotion, potential changes in the way the earliest dinosaurs may have breathed and the way they grew. We think it’s probably all these factors, combined with luck, that finally allowed dinosaurs to rise and rule.

Kristi Curry Rogers, Professor of Biology and Geology, Macalester College

This article is republished from The Conversation under a Creative Commons license. Read the original article.

New Evidence on How the Dinosaurs Died

 Such a cool article from Universe Today, I think it merits a post all to itself!

Devastating Clouds of Dust Helped End the Reign of the Dinosaurs

When a giant meteor crashed into Earth 66 million years ago, the impact pulverized cubic kilometers of rock and blasted the dust and debris into the Earth’s atmosphere. It was previously believed that sulfur from the impact and soot from the global fires that followed drove a global “impact winter” that killed off 75% of species on Earth, including the dinosaurs.

A new geology paper says that the die-off was additionally fueled by ultrafine dust created by the impact which filled the atmosphere and blocked sunlight for as long as 15 years. Plants were unable to photosynthesize and global temperatures were lowered by 15 degrees C (59 F).

Most scientists agree the disaster started with an asteroid impact, where an asteroid at least 10 kilometers wide struck the Chicxulub region in the present-day Yucatán Peninsula in Mexico. The impact released 2 million times more energy than the most powerful nuclear bomb ever detonated.

The devastation created layer of ash sandwiched between layers of rock, known as the Cretaceous-Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K-T) boundary, which is found across the world in the geologic record. It includes a layer of iridium, an element common in asteroids but rare on Earth. It was this ‘iridium anomaly’ that first revealed the extinction event as an asteroid strike to geologists more than three decades ago.

What has been debated is what created conditions for the post-impact winter. The leading candidates were sulphur from the asteroid’s impact, or soot from global wildfires that ensued after the impact. Both would have blocked out sunlight and plunged the world into a long, dark winter, collapsing the food chain and creating a chain reaction of extinctions.  

Tyrannosaurus Lips and Other Wonders of Science

 Once my science classes progressed beyond "the parts of the cell," I loved them. So much so that my college degree is in Biology, which entailed many classes in Physics and General and Organic Chemistry. Fast forward many decades, I had the joy to attend Launch Pad Astronomy Workshop, about which I have previously blogged. But I've never given up my love of Things Prehistoric. Here are some wonderful new stories:

T. rex had thin lips and a gummy smile, controversial study suggests

Theropod dinosaurs — a group of bipedal, mostly meat-eating dinosaurs that included T. rex, Velociraptor and Spinosaurus — may instead have concealed their deadly chompers behind thin lips that kept their teeth hydrated and tough enough to crush bones. 

Paleontologists had already suggested that T. rex may have had lips, and there has been debate whether carnivorous dinosaurs looked more like present-day crocodiles, which don’t have lips and have protruding teeth, or if they more likely resembled monitor lizards, whose large teeth are covered by scaly lips.

Rhino-like 'thunder beasts' grew massive in the evolutionary blink of an eye after dinos died off

In the aftermath of the dinosaur-killing asteroid impact, a second explosion rocked the animal kingdom. 

This time, it was the mammals that blew up. Rhino-like horse relatives that had lived in the shadow of the dinosaurs became gigantic "thunder beasts" as suddenly as an evolutionary lightning strike,  new research, published Thursday (May 11) in the journal Science(opens in new tab), shows.

"Even though other mammalian groups attained large sizes before [they did], brontotheres were the first animals to consistently reach large sizes," study first author Oscar Sanisidro(opens in new tab), a researcher with the Global Change Ecology and Evolution Research Group at the University of Alcalá in Spain. "Not only that, they reached maximum weights of 4-5 tons [3.6 to 4.5 metric tons] in just 16 million years, a short period of time from a geological perspective."

462 million-year-old fossilized eyes and brains uncovered in 'secret' Welsh fossil site

Last year, weird "bramble snout" fossils were documented at the site called "Castle Bank," but new research published May 1 in the journal Nature Ecology and Evolution(opens in new tab) describes the whole fossil deposit.

Sea Serpents and other Cool Science Stories

 

Mysterious 'hypercarnivore' with blade-like teeth roamed California 42 million years ago

The hypercarnivore may have hunted tapirs and tiny rhinos.

An unidentified fossil collected more than three decades ago was actually a mysterious species of saber-toothed carnivore that once stalked prey through the ancient rainforests of Southern California.

Hugh Wagner, a paleontologist at the San Diego Natural History Museum, later suggested that the jawbone might belong to a more mysterious group of hypercarnivores with scant representation in the fossil record: the machaeroidines. Remains of these strange beasts have been uncovered only at select sites in Asia and North America, and prior to the new study, only 14 specimens had ever been found, according to the PeerJ report. The now-extinct group includes the earliest known saber-toothed mammalian carnivores, which are not closely related to any living carnivores.

Our universe may have a twin that runs backward in time

An anti-universe running backwards in time could explain dark matter and cosmic inflation.

A wild new theory suggests there may be another "anti-universe," running backward in time prior to the Big Bang.

The idea assumes that the early universe was small, hot and dense — and so uniform that time looks symmetric going backward and forward.

To preserve the CPT [charge, parity, time] symmetry throughout the cosmos, there must be a mirror-image cosmos that balances out our own. This cosmos would have all opposite charges than we have, be flipped in the mirror, and run backward in time. Our universe is just one of a twin. Taken together, the two universes obey CPT symmetry.[Click through to read the whole article; it's quite accessible to the non-physicist.]

Ferocious 'Ocucaje Predator' was a sea serpent-like mammal with knives for teeth

The creature is probably a new species of basilosaurus, a ferocious ancestor of modern whales.

Researchers digging in Peru's Ocucaje desert have uncovered the skull of an enormous marine predator thought to be the ancestor of modern whales and dolphins.

Four feet long (1.2 meters) and lined with knife-like teeth, the skull appears to be a new species of Basilosaurus — a genus of ferocious marine mammals that lived some 36 million years ago during the Eocene epoch, researchers from the National University of San Marcos (UNMSM) in Lima told Reuters. From snout to tail, the creature probably measured about 39 feet (12 meters) long, or about the size of a city bus.

For now, researchers are calling this ancient beast the "Ocucaje Predator." It won't be formally named until the team publishes a scientific description of the species in a peer-reviewed journal.

How did cockroaches survive the asteroid that led to the extinction of dinosaurs?

When the meteor struck, temperatures on Earth’s surface skyrocketed. Many animals had nowhere to flee, but roaches could take shelter in tiny soil crevices, which provide excellent protection from heat.

The meteor’s impact triggered a cascade of effects. It kicked up so much dust that the sky darkened. As the sun dimmed, temperatures plunged and conditions became wintry around the globe. With little sunlight, surviving plants struggled to grow, and many other organisms that relied on those plants went hungry.

Not cockroaches, though. Unlike some insects that prefer to eat one specific plant, cockroaches are omnivorous scavengers. This means they will eat most foods that come from animals or plants as well as cardboard, some kinds of clothing and even poop. Having appetites that aren’t picky has allowed cockroaches to survive lean times since the Chicxulub extinction and other natural disasters.

Another helpful trait is that cockroaches lay their eggs in little protective cases. These egg cartons look like dried beans and are called oothecae, which means “egg cases.” Like phone cases, oothecae are hard and protect their contents from physical damage and other threats, such as flooding and drought. Some cockroaches may have waited out part of the Chicxulub catastrophe from the comfort of their oothecae.

Cockroach egg cases are about 0.5 inches long (10 millimeters) and contain up to 50 eggs, depending on the species. VitalisG/iStock via Getty Images

Cockroach egg cases are about 0.5 inches long (10 millimeters) and contain up to 50 eggs, depending on the species. VitalisG/iStock via Getty Images

New part of the body found hiding in the lungs

The newfound cells help to maintain a healthy respiratory system.

Scientists have discovered a brand-new type of cell hiding inside the delicate, branching passageways of human lungs. The newfound cells play a vital role in keeping the respiratory system functioning properly and could even inspire new treatments to reverse the effects of certain smoking-related diseases, according to a new study. 

The cells, known as respiratory airway secretory (RAS) cells, are found in tiny, branching passages known as bronchioles, which are tipped with alveoli, the teensy air sacs that exchange oxygen and carbon dioxide with the bloodstream. The new RAS cells are similar to stem cells — "blank canvas" cells that can differentiate into any other type of cell in the body — and are capable of repairing damaged alveoli cells and transforming into new ones. 

Romancing De-Extinction

I was – note the past tense – going to write a post about re-entry after Covid-19 vaccination and how awesome it was to give my younger daughter a hug after over a year, but then I saw this story from Science magazine and could not resist.

Did you ever wish you could see a living dinosaur? I sure did! (I still do…but from a safe

distance.) As a child I loved movies with stop-action animation of dinosaurs, like the original King Kong or the Ray Harryhausen movie, The Valley of Gwangi. In high school I wrote a short novel about two teenagers and their horses who discover a hidden valley where dinosaurs still roam. Jurassic Park and its sequels blew me away, the movies even more so than the novels. The novels were longer on explanation, the movies far more powerful in vividness. The moment when Alan Grant, upon learning that Professor Hammond has created a T. rex and almost faints, that’s how I would have felt. Great acting and directing aside, these books and films spoke to a universal or near-universal human longing to see amazing charismatic animals from the distant past.

The earlier stories, at least the ones I read and watched, made no effort at a scientific basis for the present-day existence of prehistoric animals. It was all “Land That Time Forgot” hand-waving. Crichton took a different tack: dinosaurs did not persist in some undiscovered corner of or beneath the Earth: humans re-created them using DNA preserved in amber. We’ve been able to recover DNA from Pleistocene mammals, but never anything as old as 65 million years. Many scientists doubt that DNA could survive that long, no matter how preserved. When an animal dies, its DNA begins to decay. A 2012 study on moa bones showed that genetic material deteriorates at such a rate that it halves itself every 521 years. This speed would mean paleontologists can only hope to recover recognizable DNA sequences the past 6.8 million years. In 2020, Chinese Academy of Sciences paleontologist Alida Bailleul and her colleagues proposed they had found a chemical signature suggestive of DNA in a 70 million year old baby hadrosaur fossil. If confirmed, this material would be so degraded into components, not sequences. It’s also possible the chemical signature was that of bacteria, not the dinosaur itself.

The Siberian permafrost that has yielded mammoth DNA is about 2.6 million years old, but freezing turns out to be a pretty good preservative of DNA. Scientists have now been able to sequence DNA from extinct mammoths 1.2 million years ago. That’s a world record. The previous record, in 2013, was from a 750,000-year-old horse. The new study includes DNA from three species of mammoth from three time periods (1.2 million, 1 million, and 700,000 years ago) and there are all kinds of reasons to be excited about it, not just the age but the evolutionary relationships and a previously unknown type.

Which brings us to the question we’re all asking: Once we’ve sequenced this DNA, whether from mammoths, saber-toothed cats, ground sloths, or whatever – what do we do with it? What we can do now is better understand the evolution and relationships of these amazing animals. What popular media want, however, is to use the material to create living extinct species. The process of de-extinction can proceed either by cloning – taking material from a recently extinct species and replicating it – or by using ancient, fragmentary DNA. We’ve got a long way to go with either technique. Many extinct species lack contemporary surrogates to carry the artificially created embryos to term. For others, suitable habitat no longer exists (really? Where would you turn a giant ground sloth loose? A saber-toothed cat? Or would these animals exist only in the unnatural environment of zoos?) Back in 2009, Spanish scientists cloned a newly extinct Pyrenean ibex, although the clone died within a few hours of birth.

There are, however, a few good candidates for which possibly viable DNA sources exist. Species like the passenger pigeon and Carolina parakeet might fare well, given the human responsibility for their disappearance, although they might turn out to be temporally invasive species.

Scientific Wonders, July 2018 edition

A potpourri of nifty discoveries to remind us, in the midst of so much political anguish, what an amazing universe we live in.

Baby Snake That Lived Among Dinosaurs Found Preserved in Amber

Using uranium-lead dating, a research team led by Lida Xing from the China University of Geosciences and Michael Caldwell from the University of Alberta dated the fossils to about 99 million years old. A technique called synchrotron x-ray micro–computed tomography allowed the researchers to get a close look at the tiny specimens inside the amber without having to break them apart.

Wandering Star May Have Disrupted Outer Solar System's Order

Astronomers have been wrestling with a few puzzles about the neighborhood for a while now. First, there's just not nearly as much stuff out there, all told, as they would expect. Also, it's odd that Neptune is more massive than the closer-in Uranus. And many of the small objects in the outer swath — like Sedna, a strange dwarf planet — follow extreme, stretched orbits at stark angles to the rest of the solar system's more orderly inhabitants.

Those quirks suggest that something must have stirred up the pot after the planets and large moons clumped together and formed out of the cloud of dust surrounding our sun early in its life. One possible culprit is a star that might have slipped next to our solar system and tugged objects off their original paths, throwing some out of the solar system entirely and skewing the orbits of others.