Some 65 million years ago, a 10-km-wide asteroid crashed into Earth near what is today Mexico. It triggered a mass extinction. Nearly 75 percent of life — including non-avian dinosaurs and large marine reptiles — was wiped out. But what happened to sharks? The marine predators survived. But, researchers say that their survival and evolution through multiple mass extinctions received little analytical attention. A new study has now attempted to shed some light on their evolution during the catastrophic event. The researchers studied the morphology of 1,239 fossil shark teeth to see how their diversity was affected during the mass extinction.
Mohamad Bazzi of Sweden’s Uppsala University and colleagues found shark-tooth diversity remained relatively constant across the end-Cretaceous mass extinction event. The researchers looked at the teeth morphology of the species in eight existing orders and one now-extinct order. The fossil teeth the researchers studied spread out over a 27-million-year period — from 83.6 million years ago to 56 million years ago. This geological period traversed the so-called Cretaceous–Paleogene (K-Pg) boundary that ended the age of the dinosaurs.
Their study was published this week in the open-access journal PLOS Biology.
The researchers said their study found that sharks’ dental diversity was already declining before the K-Pg boundary, but remained relatively constant during the mass-extinction. “Our results show that selachimorphs (sharks) maintained virtually static levels of dental disparity in most of their constituent clades across the Cretaceous–Paleogene interval,” they said in the study.
However, they added, some groups of apex predators — those with triangular blade-like teeth — suffered selective extinctions, possibly as a result of the extinction of preys.
Other shark lineages increased in dental diversity after the K-Pg boundary: Sharks in the Odontaspididae family, that have narrow teeth adapted for feeding on fish, showed increase in diversity. The selective extinctions may reflect an ecological shift from specialist tetrapod (four-limbed animal) predators to more general bony fish diets.
Based on the study, the researchers concluded that the overall static disparity indicates that sharks experienced no demonstrable pre-extinction decline as suffered by other vertebrate groups.
NASA's Mars InSight Lander Data Reveals Surprising Results About Possibility of Life on the Red Planet
A new study has curbed the chances of humans finding life on Mars. According to the study, conducted by the researchers at the University of California San Diego, Mars’ subsurface has little to no evidence of water. The surprising results were derived after studying the seismic data from NASA’s Mars InSight mission. The Mars InSight lander is located on Elysium Planitia, a flat smooth surface near the Martian equator. The InSight lander studies the subsurface of the red planet digging roughly 300 meters beneath the landing site.
The seismic data revealed that there is negligible evidence of water. “We find that Mars‘ crust is weak and porous. The sediments are not well-cemented. And there is no ice or not much ice filling the pore spaces,” said Vashan Wright, co-author of the study, in a statement.
Wright, however, stated that these findings do not eliminate the idea of ice existing or contributing to other minerals.
Researchers believe that water does not exist in the form of liquid but is part of the mineral structure. The study’s co-author, Michael Manga, from the University of California Berkeley, has explained that if water makes contact with rocks, it produces a brand-new set of minerals like clay.
Addressing the observation, Michael added, “There is some cement, but the rocks are not full of cement. The lack of cemented sediments points to an acute water scarcity 300 metres below the landing site of InSight’s probe spacecraft.”
The Mars InSight mission was initiated in 2018 with the aim to study Mars’ quakes. The instruments, on the lander, measure the vibrations on the surface of the red planet.
Wright and the team have studied these vibrations using rock physics computer modelling to deduce which type of minerals these vibrations travel through.
Different minerals would affect the seismic velocities in a certain way. Simulations that the rock model ran showed that the subsurface consisting mostly of uncemented minerals. Scientists believe that if life existed on Mars, it would be on the subsurface since it will have a protective layer to keep out radiation. Now, the researchers are looking forward to a sample-return mission that would make it easy for them to study the surface better.
Research Suggests Stomata Doesn’t Control Loss of Water From Plant Leaves
Conducting a series of experiments over years, scientists have gained a deeper understanding of plant physiology and their water requirements. When plants take in carbon dioxide during photosynthesis, they tend to lose a large amount of water. This water is crucial for them as it makes up their dry plant matter besides providing hydration to it. In the new study, scientists have discovered a long-hidden secret that might now help in making plants survive even using less water.
Plants need around 300 grams of water just to produce one gram of dry mass. This is because plants source water from the soil through the roots, which then end up evaporating in the atmosphere from the leaves.
The leaves have microscopic valves called stomata that open for taking in carbon dioxide which is required for plant growth and photosynthesis. When these pores open up, the moist internal tissue of the leaves gets exposed to the dry air outside. This suggests that water vapour can diffuse out whenever the stomata are open.
Researchers have long believed that the stomata controlled the amount of water escaping the leaves. This stemmed from the belief that the air inside a leaf is saturated while the air outside it is relatively drier. But now, after conducting experiments over the past 15 years, researchers have found evidence against the assumption.
They have noted that when the humidity level dropped outside the leaf, the relative humidity in the air space inside also witnessed a decline, which was sometimes as low as 80 percent. However, it was also observed that despite the drop in humidity level inside the leaves, the photosynthesis did not stop or slowed down.
This indicated that the rate of water loss from the plants was not affected by the increase in the evaporative demand of the outside air. Hence, if the plants were controlling the water loss through stomata, one would have witnessed the photosynthesis getting stopped or slowing down. The study suggests that plants can control water loss from their leaves while absorbing carbon dioxide and keeping the stomata open. The findings, published in Nature Plants, pointed towards a possibility that the plants may be using special water-gating proteins called aquaporins to control the movement of water in them.
New Gel-Based Artificial Cartilage Might Eliminate the Need for Total Knee Replacement
Knee pain is one of the most rampant health issues for many. This pain stems from the wear and tear of the cartilage in a medical condition called osteoarthritis. Seeking relief, people commonly turn to steroid injections, pain relievers, physical therapies, or getting their knee joint replaced. But, a new development might prove to be a game changer. Researchers from Duke University have created the first gel-based substitute for natural cartilage, which, according to them, is more durable than the original. The hydrogel material is made of water and absorbing materials, and can effectively resist wear and tear up to three times more than the natural cartilage.
To develop the material, the team infused thin sheets of cellulose fibres with a polymer named polyvinyl alcohol and create a gel. The polymer has a viscous gum-like consistency and has stringy chains of repeating molecules.
The cellulose mimics the function of the collagen fibres in natural cartilage and provides strength to the gel when it is stretched. The polyvinyl alcohol, meanwhile, helps the gel regain its original shape. With these properties, a Jello-like material was created that has 60 percent water but still offers great strength.
Testing revealed that the material was even stronger than the natural cartilage. Our cartilage can resist 5,800 pounds of tugging and 8,500 pounds of squishing. However, the artificial cartilage proved to be 26 percent stronger in tension and 66 percent stronger in terms of compression than the natural cartilage.
“It’s really off the charts in terms of hydrogel strength,” said Duke University’s professor Benjamin Wiley. He is the lead author of the study published in Advanced Functional Materials.
The team had developed the hydrogel in 2020 but has now put it to practical use as artificial cartilage. With the massive strength of the cartilage, researchers faced challenges trying to secure it to the joint. For this, they cemented and clamped the hydrogel on a titanium base which was then pressed and anchored into a hole in the place of the damaged cartilage. This helped them maintain the cartilage in place.
According to Wiley, artificial cartilage is better than going for a total knee replacement. He said artificial joints require major surgery to be implanted and need to be replaced later. Talking of the new material, he added, “I think this will be a dramatic change in treatment for people at this stage.” Researchers are now looking forward to the clinical trials of artificial cartilage.
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