To err is human; to mistakenly bite is baby white shark
Baby white sharks learn to hunt on the fly. Though monthsold pups feast on fish and other small fry, older juveniles are finally big enough to tackle seals and other meatier meals.
It might seem easy to spot a blubbery seal in the waves. But young white sharks have less than stellar eyesight and are also likely colorblind, rendering the ocean in shades of gray. So you can hardly blame a young white shark for seeing an appetizingly shadowy oval above and chomping.
For decades, scientists have floated this theory of “mistaken identity” as an explanation behind unprovoked shark bites on humans, which are rare. A paper published in the Journal of the Royal Society Interface puts this theory to the test. Based on their simulations of how a juvenile white shark sees the world, they found no meaningful difference between a plump sea lion, a person paddling on a surfboard or even a person paddling on their own — supporting the theory that sometimes sharks make mistakes.
Charles Bangley, a marine ecologist at Dalhousie University in Nova Scotia who was not involved with the research, said the paper supports common sense advice for anyone hoping to avoid being bitten by a shark: Swim in calm, clear water away from seals and other prey.
Catherine Macdonald, a lecturer at the University of Miami and the co-founder of the marine science program Field School, said the study was “well-executed” and opened up new questions about sharks and people.
“Does it make a difference if it’s an honest mistake?” Macdonald said. “We can’t tolerate those risks to people regardless.”
Baby white sharks are blissfully unaware of the bad rap they are born into. “White sharks have been described as these mindless killers,” said Laura Ryan, a neurobiologist at Macquarie University in Australia and an author on the paper. But she hopes they may begin to be seen “in another light by understanding their world.”
White sharks, along with bull sharks and tiger sharks, are responsible for most injuries and fatal bites to humans — who are most often surfers. And the most frequent biters appear to be juveniles, between 8 to 10 feet long. But white sharks usually release a person after the first bite, which may suggest they do not actively hunt humans as prey.
“As a general rule for shark bites, the vast majority of them are one and done,” Macdonald said.
— Sabrina Imbler
Why strawberries turn a ghostly shade of white
Strawberries are not always red. Fragaria nubicola, native to the Himalayas, can produce a vivid red fruit or a ghostly white one; another species, F. vesca, can produce a white fruit with brilliant scarlet seeds, as well as a conventional red type. What gives some strawberries such a ghostly pallor?
One answer has been uncovered by scientists curious about the humble strawberry’s genetic material. There are numerous species of the fruit, and some sport five times as many chromosomes as others. Strawberry scientists think this means that as the plants evolved, they acquired extra genes that could provide a playground for unusual new traits.
While the core genes kept the day-to-day affairs of the plant running, the extras could be tweaked to yield a new shade of pink, a new hardiness to drought or particularly prickly leaves — whatever the strawberry’s unique environment demanded.
In a paper published in the Proceedings of the National Academy of Sciences, biologists reported that they have sequenced the genomes of a handful of strawberry species and identified a set of genes that are common across all of them, representing the core genome of the strawberry. Along the way, the researchers identified a set of mutations that turned strawberries white, while keeping the taste and aroma the same. The findings open the door to understanding how strawberries manage their bulky genetic inheritance, as well as suggesting the possibility of more targeted breeding.
Strawberries grow wild in places as varied as Alaska and Southern California beaches, said Patrick Edger, a professor of horticulture at Michigan State University and an author of the new paper. But they likely originated in Asia. For this study, the scientists collected samples from 128 wild strawberry plants in China and sequenced their genes, looking for commonalities across species.
The scientists found that as many as 45% of a strawberry’s genes were shared among the 10 species examined in the paper. That implies that the remainder — more than half of a strawberry’s genetic material — is used to adapt a species to its particular location and situation. Breeders could bring these genes to existing commercial species in the future, helping strawberry farmers address problems like drought.
The research also pieced together the genetic puzzle of what makes some strawberry species turn white. The team found that lighter fruits were linked to mutations in a gene called MYB10, which controls the production of pigments called anthocyanins. Lower levels of anthocyanins would be expected to result in a paler color.
— Veronique Greenwood
Dinosaurs may have been socializing nearly 200 million years ago
Paleontologists have found the earliest known evidence that dinosaurs lived in herds — unlike reptiles, and more like penguins and other birds do today — and socialized with each other by age groups.
The scientists, working a rich deposit of fossils at a site in Argentina’s province of Santa Cruz, at the southern tip of South America, found more than 100 eggs and the skeletons of 80 individuals ranging in age from embryos to adults.
All of the fossils, including the embryos inside the eggs, are of the species Mussaurus patagonicus. These dinosaurs were about 10 feet high and 26 feet in length when fully grown, with a long tail balanced by an equally long neck that ends in a head that seems too small for the enormous animal it is attached to. This is the only place Mussaurus remains have ever been found.
Little is known about the behavior of dinosaurs, but this large number of fossils, and their distribution at the site, has given scientists new information about their social lives. The study appeared in Scientific Reports.
The bones and eggs are spread over about 250 acres — a small area for finding so many fossils of the same species. Most of the eggs were found in clutches of eight to 30 in nests close together, which suggests that the animals used a common breeding ground. Within the nests, the eggs are arranged in trenches that the animals apparently excavated for the purpose.
The scientists found eggs, neonates, juveniles and adults clustered close to each other, which indicates that the animals lived in socially cohesive groups, rather than gathering only temporarily to breed and lay eggs. Age groupings like this, the authors write, suggest that the animals maintained social connections with each other across their life spans.
Among the specimens are 11 1-year-olds, and an analysis of the bones suggests that they were probably members of a single brood, buried together. The researchers also found many adults close to each other, in natural resting poses, suggesting that the animals lived and died together.
Often fossils are found in large numbers at one location not because the animals died together, but because a stream or river transported bones of different ages and species. But these Mussaurus bones were found in deposits made from windblown dust, and the authors conclude that they probably died simultaneously in periodic droughts.
“The sediments also have evidence that the animals still had soft tissue when they were buried,” said the lead author, Diego Pol, a researcher at the Museo Paleontologico Egidio Feruglio in Trelew, Argentina. “This indicates a simultaneous death.”
— Nicholas Bakalar
How did elephants and walruses get their tusks? It’s a long story.
Elephants have them. Pigs have them. Narwhals and water deer have them. Tusks are among the most dramatic examples of mammal dentition: ever-growing, projecting teeth used for fighting, foraging, even flirting.
So why, across the broad sweep of geologic history, do such useful teeth only appear among mammals and no other surviving groups of animals? According to a study published in the journal Proceedings of the Royal Society B, it takes two key adaptations to teeth to make a tusk — and the evolutionary pathway first appeared millions of years before the first true mammals.
Around 255 million years ago, a family of mammal relatives called dicynodonts — tusked, turtle-beaked herbivores ranging in stature from gopher-size burrowers to 6-ton behemoths — wandered the forests of the supercontinent Pangea. A few lineages survived the devastating Permian extinction period, during which more than 90% of Earth’s species died out, before being replaced by herbivorous dinosaurs.
“They were really successful animals,” said Megan Whitney, a paleontologist at Harvard University and the lead author of the study. “They’re so abundant in South Africa that in some of these sites, you just get really sick of seeing them. You’ll look out over a field and there’ll just be skulls of these animals everywhere.”
To work out how these animals evolved their tusks, Whitney and her colleagues collected bone samples from 10 dicynodont species, among them the tiny, big-eyed Diictodon and the tank-like Lystrosaurus. They looked at how their canines attached to the jaw, whether they regularly regenerated lost teeth, like many reptiles do, and for indicators that their teeth grew continuously.
Many mammal families have evolved long, saber-toothed fangs or ever-growing incisors for gnawing. Several early dicynodonts also had a pair of long canine teeth poking from their beaks. But these teeth, like most animal teeth, are composed of a substance called dentine, capped by a hard, thin covering of enamel. Tusks have no enamel, Whitney said, and grow continuously even as the comparatively softer dentine gets worn away.
Examining the dicynodont skulls, the team found that a shift occurred midway through the group’s evolution: the appearance of soft tissue attachments supporting the teeth, akin to the ligaments present in modern mammals. And like modern mammals, dicynodonts didn’t continuously replace their teeth.
Both of these shifts laid the groundwork for the development of an ever-growing, well-supported tooth — a tusk. Afterward, Whitney said, late dicynodonts developed tusks in at least two different lineages, and possibly more.
This evolutionary pathway is reminiscent of another group of tusked animals: elephants. Early elephant relatives had enlarged canines that were covered with enamel, Whitney said. Later members of the family reduced the enamel to a thin band on one side of the tooth, like a rodent incisor, allowing the tooth to grow continuously.
Finally, they ditched the enamel entirely.