Once a week.
Subscribe to our weekly newsletter.
Ancient deer-like creatures returned to the ocean to become whales. But why?
Researchers are starting to get a handle on why ancient creatures returned to the ocean after their ancient ancestors climbed out of it.
The ocean may be the origin of all life on Earth, but that isn’t to say that all the animals who evolved on land left the water behind forever. In fact, we’re starting to get a pretty good picture of why certain species that returned back to the water decided to do so and how they developed into the marine animals we know today. Paleontologists say creatures began exploring the land during the Silurian period (440-410 million years ago). No one is sure why this occurred. Some scientists say it may have been tight competition for resources in marine environments that pushed species to look for food elsewhere.
The first land explorers were arthropods, who started spending just a little bit of time on the surface and then began doing so more and more. They were pre-adapted to land exploration because of their hard shells, which helped retain water. Around 370 million years ago, certain species became permanent land residents. Spiders, mites, and centipedes were the first inhabitants. Then, over the next few million years, amphibians, reptiles, and finally mammals made it onto the scene. But that doesn’t mean they all stayed on land.
During the Early Triassic period (approx. 252-247 million years ago) onward, dozens of terrestrial and freshwater animals returned to the sea. Birds, reptiles, amphibians, and mammals were among them. They evolved and eventually became dominant players in their ecosystems during the Mesozoic and Cenozoic eras. Today, lots of the marine mammals we know and love started out as land-based species.
For instance, a walrus’s ancestor resembles the modern otter, while whales come from a species of ancient deer-like creatures known as Indohyus. They roamed southern Asia about 48 million years ago. An Indohyus was only about the size of a raccoon, and researchers believe that they fed on aquatic plants.
Model of an Indohyus. Note its deer-like feet. (Credit: Ghedoghedo, Wikimedia Commons.)
So what coaxed these creatures back into the ocean 100 million years after their ancestors climbed out of it? A duo of researchers contend that this question has received far too little attention, until now. The results of their study has been published in a report in the journal Paleobiology. To date, there have been two prevailing hypotheses.
In one, ecosystem collapse caused mass extinction, pushing animals back toward the sea for food. In another, competition added pressure on species while abundant food sources in the ocean, particularly in areas near the shoreline, pulled species back toward the sea. Geerat Vermeij at the University of California-Davis and his colleague Ryosuke Motani decided to test these theories to see which one was more likely.
The scientists isolated 69 incidents in which a terrestrial species decided to live in or extract sustenance from the ocean after a mass extinction had taken place. In two of the largest such events, one that occurred 201 million years ago at the end of the Triassic and another at the end of the Cretaceous period, there was no grand exodus of land animals back into the sea. A 2014 South African study discovered an increase in species returning to the ocean 66 million years ago, at the tail end of the Cretaceous extinction. What differed in this study was that the previous one only included animals which are still around today.
Vermeij and Motani’s study supports the idea that terrestrial animals took advantage of food sources in the ocean periodically, not just after mass extinctions, and the trend has only increased over the past 60 million years or so. One reason that may be a pull factor: kelp and seagrass beds developed over this period, allowing for more marine life to sprout and proliferate closer to shore.
To learn more about whale evolution, click here.
What is human dignity? Here's a primer, told through 200 years of great essays, lectures, and novels.
- Human dignity means that each of our lives have an unimpeachable value simply because we are human, and therefore we are deserving of a baseline level of respect.
- That baseline requires more than the absence of violence, discrimination, and authoritarianism. It means giving individuals the freedom to pursue their own happiness and purpose.
- We look at incredible writings from the last 200 years that illustrate the push for human dignity in regards to slavery, equality, communism, free speech and education.
The inherent worth of all human beings<p>Human dignity is the inherent worth of each individual human being. Recognizing human dignity means respecting human beings' special value—value that sets us apart from other animals; value that is intrinsic and cannot be lost.</p> <p>Liberalism—the broad political philosophy that organizes society around liberty, justice, and equality—is rooted in the idea of human dignity. Liberalism assumes each of our lives, plans, and preferences have some unimpeachable value, not because of any objective evaluation or contribution to a greater good, but simply because they belong to a human being. We are human, and therefore deserving of a baseline level of respect. </p> <p>Because so many of us take human dignity for granted—just a fact of our humanness—it's usually only when someone's dignity is ignored or violated that we feel compelled to talk about it. </p> <p>But human dignity means more than the absence of violence, discrimination, and authoritarianism. It means giving individuals the freedom to pursue their own happiness and purpose—a freedom that can be hampered by restrictive social institutions or the tyranny of the majority. The liberal ideal of the good society is not just peaceful but also pluralistic: It is a society in which we respect others' right to think and live differently than we do.</p>
From the 19th century to today<p>With <a href="https://books.google.com/ngrams/graph?year_start=1800&year_end=2019&content=human+dignity&corpus=26&smoothing=3&direct_url=t1%3B%2Chuman%20dignity%3B%2Cc0" target="_blank" rel="noopener noreferrer">Google Books Ngram Viewer</a>, we can chart mentions of human dignity from 1800-2019.</p><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDg0ODU0My9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY1MTUwMzE4MX0.bu0D_0uQuyNLyJjfRESNhu7twkJ5nxu8pQtfa1w3hZs/img.png?width=980" id="7ef38" class="rm-shortcode" data-rm-shortcode-id="9974c7bef3812fcb36858f325889e3c6" data-rm-shortcode-name="rebelmouse-image" />
American novelist, writer, playwright, poet, essayist and civil rights activist James Baldwin at his home in Saint-Paul-de-Vence, southern France, on November 6, 1979.
Credit: Ralph Gatti/AFP via Getty Images
The future of dignity<p>Around the world, people are still working toward the full and equal recognition of human dignity. Every year, new speeches and writings help us understand what dignity is—not only what it looks like when dignity is violated but also what it looks like when dignity is honored. In his posthumous essay, Congressman Lewis wrote, "When historians pick up their pens to write the story of the 21st century, let them say that it was your generation who laid down the heavy burdens of hate at last and that peace finally triumphed over violence, aggression and war."</p> <p>The more we talk about human dignity, the better we understand it. And the sooner we can make progress toward a shared vision of peace, freedom, and mutual respect for all. </p>
Scientists find that bursts of gamma rays may exceed the speed of light and cause time-reversibility.
- Astrophysicists propose that gamma-ray bursts may exceed the speed of light.
- The superluminal jets may also be responsible for time-reversibility.
- The finding doesn't go against Einstein's theory because this effect happens in the jet medium not a vacuum.
Jet bursting out of a blazar. Black-hole-powered galaxies called blazars are the most common sources detected by NASA's Fermi Gamma-ray Space Telescope.
Cosmic death beams: Understanding gamma ray bursts<div class="rm-shortcode" data-media_id="cu2knVEk" data-player_id="FvQKszTI" data-rm-shortcode-id="c6cfd20fdf31c82cb206ade8ce21ba3f"> <div id="botr_cu2knVEk_FvQKszTI_div" class="jwplayer-media" data-jwplayer-video-src="https://content.jwplatform.com/players/cu2knVEk-FvQKszTI.js"> <img src="https://cdn.jwplayer.com/thumbs/cu2knVEk-1920.jpg" class="jwplayer-media-preview" /> </div> <script src="https://content.jwplatform.com/players/cu2knVEk-FvQKszTI.js"></script> </div>
Researchers dramatically improve the accuracy of a number that connects fundamental forces.
- A team of physicists carried out experiments to determine the precise value of the fine-structure constant.
- This pure number describes the strength of the electromagnetic forces between elementary particles.
- The scientists improved the accuracy of this measurement by 2.5 times.
The process for measuring the fine-structure constant involved a beam of light from a laser that caused an atom to recoil. The red and blue colors indicate the light wave's peaks and troughs, respectively.
Scientists at Washington University are patenting a new electrolyzer designed for frigid Martian water.
- Mars explorers will need more oxygen and hydrogen than they can carry to the Red Planet.
- Martian water may be able to provide these elements, but it is extremely salty water.
- The new method can pull oxygen and hydrogen for breathing and fuel from Martian brine.