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What makes a dinosaur a dinosaur?
Truth is, dinosaurs aren’t as distinct as you may think, but to find out why, we first have to consider how we got the term “dinosaur.”
Imagine you traveled back in time some 280 million years ago. Gazing out the portside window of your time-ship/DeLorean/phone-booth, you spy a large, reptilian creature among the reeds at the river’s edge. You estimate it’s 11 feet long, from snout to tail. It has a scrunched crocodilian-like mouth filled with the sharp, jagged teeth of a carnivore. It stands on squat legs and wears an eye-catching sail on its back, perhaps to soak up sunny rays to warm its cold blood.
How would you classify this creature? Given the era, its reptilian appearance, and its size, most people would call it a dinosaur, but they would be wrong. What you’ve stumbled across is a dimetrodon, a therapsid, and it belongs to a group of reptiles that are the ancient ancestors of mammals.1
But it’s understandable why people would make this classification. Pop culture has primed us to view any animal that’s large, reptilian, and went extinct millions of years ago as a dinosaur. Consider Pteranodons. These flying reptiles have terrorized Jurassic World and own lifetime tickets aboard the Dinosaur Train, but they are members of the order Pterosauria, not Dinosauria.
So, what makes a dinosaur a dinosaur? What characteristics connect genus as varied as Triceratops, Diplodocus, and Tyrannosaurus rex (all true dinosaurs) into a single clade? Truth is, dinosaurs aren’t as distinct as you may think, but to find out why, we first have to consider how we got the term “dinosaur.”
A (brief) history of discovery
From the Greeks to Native Americans to prehistoric tribes, people all over the world have recognized dinosaur fossils as unique well before science gave them a name.2 In fact, Western society likely stumbled across evidence for these Mesozoic beasts for centuries before anyone bothered to take notice.
In America, for example, the Lewis and Clark expedition traveled through what is today Hell Creek Formation, Montana, known as the “paleontologist’s dream” for its bountiful fossilized specimens literally sticking out of the rock. In 1818, a farm boy with the glorious name of Plinus Moody found fossil footprints in a Massachusetts rock ledge. These led to the discovery of Anchisaurus bones, but no one recognized them as significant at the time.3
With America wasting several chances to “discover the first dinosaur,” the honor ultimately went to William Buckland, a professor of geology at Oxford University. More specifically, Buckland was the first person to correctly identify a set of bones as belonging to an extinct, large carnivorous lizard. He called the species Megalosaurus in 1824, the first dinosaur to be named.
The British paleontological hunt was on. Thanks to Buckland, scientists now knew what to look for and past discoveries could be reevaluated.
Geologist Gideon Mantell and his wife, May Ann Mantell, discovered Iguanodon in 1822, but Mantell didn’t publish until 1825, making theirs the second named dinosaur. Between 1809 and 1811, a girl named Mary Anning and her family discovered Ichthyosaurus (not technically a dinosaur, but Mary Anning’s story is too cool to not give a shout out). Then in 1833, Gideon Mantell discovered Hylaeosaurus.
Jumping forward about a decade, biologist Sir Richard Own compared the bones of Megalosaurus, Iguanodon, and Hylaeosaurus. He found that these creatures shared features with each other but no other known animal, such as upright legs tucked beneath their bodies and five vertebrae connected to the pelvis.5 In 1842, he named the taxon Dinosauria, or “fearfully great reptiles.”
Of course, paleontologists have discovered hundreds of dinosaurs since Sir Owen’s founding trio, and with these discoveries, our definition of what is or is not a dinosaur has been refined. For example, as ScienceNews points out, dinosaurs used to exhibit several unique features, including:
a deep depression at the top of the skull to attach jaw muscles,
an enlarged crest on the upper arm bone (also to attach muscles),
bony projections at the back of the neck vertebrae (epipophyses),
a fourth muscle attachment site where the femur meets the hip, and
a complete hole in the hip socket.
However, most dinosaur-specific features were eventually found in non-dinosaur creatures. All save one: that complete hole in the hip socket. This feature, and this feature alone, is ultimately what defines a dinosaur. The reason Dimetrodon, Pteranodon, and Ichthyosaurus aren’t card-carrying dinosaurs is because they lack this feature.
“What is a dinosaur?” Paleontologist Sterling Nesbitt told ScienceNews. “It’s essentially arbitrary.”
This complete hole allowed dinosaurs to position their legs under their bodies (as Sir Owen noted), which separates dinosaurs from lizards, whose hips force their legs to jut out from the side. Dinosaur pelvises further divide them into two groups: Saurischia (lizard-hipped) and Ornithischia (bird-hipped).6
This updated definition leads to an interesting—if counterintuitive—conclusion: Dinosaurs are not extinct. Not technically. Phylogenetically speaking, birds are the descendants of dinosaurs, and since they continue to thrive, the clade as not been rendered extinct. Today, a scientist may refer to traditional dinosaurs as “non-avian dinosaurs” and birds as “avian dinosaurs.”7
This means your family’s Thanksgiving turkey is actually a distant relative of the Tyrannosaurus rex. How the mighty have fallen.
History in the making
As new fossils and information amass, paleontologists will continue to revise our understanding of dinosaurs. Spinosaurus was originally thought to be a terrestrial carnivore, but thanks to the latest computer models, scientists now believe it was an aquatic hunter. A recent study flirted with the idea that Tyrannosaurus rex sported decadent plumage, while another study challenged the notion.
Even the dinosaur family tree is up for debate. A new hypothesis restructured the phylogenetic relationships of Dinosauria, suggesting that ornithischians and therapods are closer related than sauropods. If evidence bears this view out, it would mean rewriting a lot of textbooks.
While one study or hypothesis does not a scientific consensus make, these examples show us how new ideas and information will continuously require us to revise and redefine what makes a dinosaur. Years from now, the answer to our question may be entirely different.
But for now, if you can remember that the hip bone connects from the thigh bone, then you know what makes a dinosaur a dinosaur.
1. “Therapsid: fossil tetrapod order.” Encyclopedia Britannica. Retrieved on July 20, from https://www.britannica.com/animal/therapsid
2. “A brief history of hidden dinosaurs.” Brian Switek. Smithsonian.com. Retrieved on July 21, from https://www.smithsonianmag.com/science-nature/a-brief-history-of-hidden-dinosaurs-9663115/
3. A short history of nearly everything. Bill Bryson. Broadway Books; New York. 2003. Pg. 106–107.
4. “Mary Anning.” University of California Museum of Paleontology website. Retrieved on July 20, from http://www.ucmp.berkeley.edu/history/anning.html.
5. “New fossils are redefining what makes a dinosaur.” Carolyn Gramling. ScienceNews. Retrieved on July 19, from https://www.sciencenews.org/article/new-fossils-are-redefining-what-makes-dinosaur.
6. “What makes a dinosaur a dinosaur?” Luis Villazon. Science Focus. Retrieved on July 19, from http://www.sciencefocus.com/article/nature/what-makes-a-dinosaur-a-dinosaur.
7. “The Dinosauria.” University of California Museum of Paleontology website. Retrieved on July 19, from http://www.ucmp.berkeley.edu/diapsids/dinosaur.html.
Ever since we've had the technology, we've looked to the stars in search of alien life. It's assumed that we're looking because we want to find other life in the universe, but what if we're looking to make sure there isn't any?
Here's an equation, and a rather distressing one at that: N = R* × fP × ne × f1 × fi × fc × L. It's the Drake equation, and it describes the number of alien civilizations in our galaxy with whom we might be able to communicate. Its terms correspond to values such as the fraction of stars with planets, the fraction of planets on which life could emerge, the fraction of planets that can support intelligent life, and so on. Using conservative estimates, the minimum result of this equation is 20. There ought to be 20 intelligent alien civilizations in the Milky Way that we can contact and who can contact us. But there aren't any.
The Drake equation is an example of a broader issue in the scientific community—considering the sheer size of the universe and our knowledge that intelligence life has evolved at least once, there should be evidence for alien life. This is generally referred to as the Fermi paradox, after the physicist Enrico Fermi who first examined the contradiction between high probability of alien civilizations and their apparent absence. Fermi summed this up rather succinctly when he asked, “Where is everybody"?
But maybe this was the wrong question. A better question, albeit a more troubling one, might be “What happened to everybody?" Unlike asking where life exists in the universe, there's a clearer potential answer to this question: the Great Filter.
Why the universe is empty
Alien life is likely, but there is none that we can see. Therefore, it could be the case that somewhere along the trajectory of life's development, there is a massive and common challenge that ends alien life before it becomes intelligent enough and widespread enough for us to see—a great filter.
This filter could take many forms. It could be that having a planet in the Goldilocks' zone—the narrow band around a star where it is neither too hot nor too cold for life to exist—and having that planet contain organic molecules capable of accumulating into life is extremely unlikely. We've observed plenty of planets in the Goldilock's zone of different stars (there's estimated to be 40 billion in the Milky Way), but maybe the conditions still aren't right there for life to exist.
The Great Filter could occur at the very earliest stages of life. When you were in high school bio, you might have the refrain drilled into your head “mitochondria are the powerhouse of the cell." I certainly did. However, mitochondria were at one point a separate bacteria living its own existence. At some point on Earth, a single-celled organism tried to eat one of these bacteria, except instead of being digested, the bacterium teamed up with the cell, producing extra energy that enabled the cell to develop in ways leading to higher forms of life. An event like this might be so unlikely that it's only happened once in the Milky Way.
Or, the filter could be the development of large brains, as we have. After all, we live on a planet full of many creatures, and the kind of intelligence humans have has only occurred once. It may be overwhelmingly likely that living creatures on other planets simply don't need to evolve the energy-demanding neural structures necessary for intelligence.
What if the filter is ahead of us?
These possibilities assume that the Great Filter is behind us—that humanity is a lucky species that overcame a hurdle almost all other life fails to pass. This might not be the case, however; life might evolve to our level all the time but get wiped out by some unknowable catastrophe. Discovering nuclear power is a likely event for any advanced society, but it also has the potential to destroy such a society. Utilizing a planet's resources to build an advanced civilization also destroys the planet: the current process of climate change serves as an example. Or, it could be something entirely unknown, a major threat that we can't see and won't see until it's too late.
The bleak, counterintuitive suggestion of the Great Filter is that it would be a bad sign for humanity to find alien life, especially alien life with a degree of technological advancement similar to our own. If our galaxy is truly empty and dead, it becomes more likely that we've already passed through the Great Filter. The galaxy could be empty because all other life failed some challenge that humanity passed.
If we find another alien civilization, but not a cosmos teeming with a variety of alien civilizations, the implication is that the Great Filter lies ahead of us. The galaxy should be full of life, but it is not; one other instance of life would suggest that the many other civilizations that should be there were wiped out by some catastrophe that we and our alien counterparts have yet to face.
Fortunately, we haven't found any life. Although it might be lonely, it means humanity's chances at long-term survival are a bit higher than otherwise.
Cross-disciplinary cooperation is needed to save civilization.
- There is a great disconnect between the sciences and the humanities.
- Solutions to most of our real-world problems need both ways of knowing.
- Moving beyond the two-culture divide is an essential step to ensure our project of civilization.
For the past five years, I ran the Institute for Cross-Disciplinary Engagement at Dartmouth, an initiative sponsored by the John Templeton Foundation. Our mission has been to find ways to bring scientists and humanists together, often in public venues or — after Covid-19 — online, to discuss questions that transcend the narrow confines of a single discipline.
It turns out that these questions are at the very center of the much needed and urgent conversation about our collective future. While the complexity of the problems we face asks for a multi-cultural integration of different ways of knowing, the tools at hand are scarce and mostly ineffective. We need to rethink and learn how to collaborate productively across disciplinary cultures.
The danger of hyper-specialization
The explosive expansion of knowledge that started in the mid 1800s led to hyper-specialization inside and outside academia. Even within a single discipline, say philosophy or physics, professionals often don't understand one another. As I wrote here before, "This fragmentation of knowledge inside and outside of academia is the hallmark of our times, an amplification of the clash of the Two Cultures that physicist and novelist C.P. Snow admonished his Cambridge colleagues in 1959." The loss is palpable, intellectually and socially. Knowledge is not adept to reductionism. Sure, a specialist will make progress in her chosen field, but the tunnel vision of hyper-specialization creates a loss of context: you do the work not knowing how it fits into the bigger picture or, more alarmingly, how it may impact society.
Many of the existential risks we face today — AI and its impact on the workforce, the dangerous loss of privacy due to data mining and sharing, the threat of cyberwarfare, the threat of biowarfare, the threat of global warming, the threat of nuclear terrorism, the threat to our humanity by the development of genetic engineering — are consequences of the growing ease of access to cutting-edge technologies and the irreversible dependence we all have on our gadgets. Technological innovation is seductive: we want to have the latest "smart" phone, 5k TV, and VR goggles because they are objects of desire and social placement.
Are we ready for the genetic revolution?
When the time comes, and experts believe it is coming sooner than we expect or are prepared for, genetic meddling with the human genome may drive social inequality to an unprecedented level with not just differences in wealth distribution but in what kind of being you become and who retains power. This is the kind of nightmare that Nobel Prize-winning geneticist Jennifer Doudna talked about in a recent Big Think video.
CRISPR 101: Curing Sickle Cell, Growing Organs, Mosquito Makeovers | Jennifer Doudna | Big Think www.youtube.com
At the heart of these advances is the dual-use nature of science, its light and shadow selves. Most technological developments are perceived and sold as spectacular advances that will either alleviate human suffering or bring increasing levels of comfort and accessibility to a growing number of people. Curing diseases is what motivated Doudna and other scientists involved with CRISPR research. But with that also came the potential for altering the genetic makeup of humanity in ways that, again, can be used for good or evil purposes.
This is not a sci-fi movie plot. The main difference between biohacking and nuclear hacking is one of scale. Nuclear technologies require industrial-level infrastructure, which is very costly and demanding. This is why nuclear research and its technological implementation have been mostly relegated to governments. Biohacking can be done in someone's backyard garage with equipment that is not very costly. The Netflix documentary series Unnatural Selection brings this point home in terrifying ways. The essential problem is this: once the genie is out of the bottle, it is virtually impossible to enforce any kind of control. The genie will not be pushed back in.
Cross-disciplinary cooperation is needed to save civilization
What, then, can be done? Such technological challenges go beyond the reach of a single discipline. CRISPR, for example, may be an invention within genetics, but its impact is vast, asking for oversight and ethical safeguards that are far from our current reality. The same with global warming, rampant environmental destruction, and growing levels of air pollution/greenhouse gas emissions that are fast emerging as we crawl into a post-pandemic era. Instead of learning the lessons from our 18 months of seclusion — that we are fragile to nature's powers, that we are co-dependent and globally linked in irreversible ways, that our individual choices affect many more than ourselves — we seem to be bent on decompressing our accumulated urges with impunity.
The experience from our experiment with the Institute for Cross-Disciplinary Engagement has taught us a few lessons that we hope can be extrapolated to the rest of society: (1) that there is huge public interest in this kind of cross-disciplinary conversation between the sciences and the humanities; (2) that there is growing consensus in academia that this conversation is needed and urgent, as similar institutes emerge in other schools; (3) that in order for an open cross-disciplinary exchange to be successful, a common language needs to be established with people talking to each other and not past each other; (4) that university and high school curricula should strive to create more courses where this sort of cross-disciplinary exchange is the norm and not the exception; (5) that this conversation needs to be taken to all sectors of society and not kept within isolated silos of intellectualism.
Moving beyond the two-culture divide is not simply an interesting intellectual exercise; it is, as humanity wrestles with its own indecisions and uncertainties, an essential step to ensure our project of civilization.
New study analyzes gravitational waves to confirm the late Stephen Hawking's black hole area theorem.
- A new paper confirms Stephen Hawking's black hole area theorem.
- The researchers used gravitational wave data to prove the theorem.
- The data came from Caltech and MIT's Advanced Laser Interferometer Gravitational-Wave Observatory.
The late Stephen Hawking's black hole area theorem is correct, a new study shows. Scientists used gravitational waves to prove the famous British physicist's idea, which may lead to uncovering more underlying laws of the universe.
The theorem, elaborated by Hawking in 1971, uses Einstein's theory of general relativity as a springboard to conclude that it is not possible for the surface area of a black hole to become smaller over time. The theorem parallels the second law of thermodynamics that says the entropy (disorder) of a closed system can't decrease over time. Since the entropy of a black hole is proportional to its surface area, both must continue to increase.
As a black hole gobbles up more matter, its mass and surface area grow. But as it grows, it also spins faster, which decreases its surface area. Hawking's theorem maintains that the increase in surface area that comes from the added mass would always be larger than the decrease in surface area because of the added spin.
Will Farr, one of the co-authors of the study that was published in Physical Review Letters, said their finding demonstrates that "black hole areas are something fundamental and important." His colleague Maximiliano Isi agreed in an interview with Live Science: "Black holes have an entropy, and it's proportional to their area. It's not just a funny coincidence, it's a deep fact about the world that they reveal."
What are gravitational waves?
Gravitational waves are "ripples" in spacetime, predicted by Albert Einstein in 1916, that are created by very violent processes happening in space. Einstein showed that very massive, accelerating space objects like neutron stars or black holes that orbit each other could cause disturbances in spacetime. Like the ripples produced by tossing a rock into a lake, they would bring about "waves" of spacetime that would spread in all directions.
As LIGO shared, "These cosmic ripples would travel at the speed of light, carrying with them information about their origins, as well as clues to the nature of gravity itself."
The gravitational waves discovered by LIGO's 3,000-kilometer-long laser beam, which can detect the smallest distortions in spacetime, were generated 1.3 billion years ago by two giant black holes that were quickly spiraling toward each other.
What Stephen Hawking would have discovered if he lived longer | NASA's Michelle Thaller | Big Think www.youtube.com
Confirming Hawking's black hole area theorem
The researchers separated the signal into two parts, depending on whether it was from before or after the black holes merged. This allowed them to figure out the mass and spin of the original black holes as well as the mass and spin of the merged black hole. With this information, they calculated the surface areas of the black holes before and after the merger.
"As they spin around each other faster and faster, the gravitational waves increase in amplitude more and more until they eventually plunge into each other — making this big burst of waves," Isi elaborated. "What you're left with is a new black hole that's in this excited state, which you can then study by analyzing how it's vibrating. It's like if you ping a bell, the specific pitches and durations it rings with will tell you the structure of that bell, and also what it's made out of."
The surface area of the resulting black holes was larger than the combined area of the original black holes. This conformed to Hawking's area law.