Science news in brief: From giant rodents with tiny brains to Canada's new tyrannosaur

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Ancient rat ancestors may have weighed up to 81kg
Ancient rat ancestors may have weighed up to 81kg

This rodent was giant. Its brain was tiny

When you look at a reconstruction of the skull and brain of Neoepiblema acreensis, an extinct rodent, it’s hard to shake the feeling that something’s not quite right.

Huddled at the back of the cavernous skull, the brain of the South American giant rodent looks really, really small. By some estimates, it was around three to five times smaller than scientists would expect from the animal’s estimated body weight of about 81kg, and from comparisons to modern rodents. In fact, 10 million years ago the animal may have been running around with a brain weighing half as much as a mandarin orange, according to a paper published in Biology Letters.

The glory days of rodents, in terms of the animals’ size, were quite a long time ago, says Leonardo Kerber, a paleontologist at Universidade Federal de Santa Maria in Brazil and an author of the new study. Today rodents are generally dainty, with the exception of larger creatures like the capybara that can weigh as much as 68kg. But when it comes to relative brain size, N acreensis, represented in this study by a fossil skull unearthed in the 1990s in the Brazilian Amazon, seems to be an extreme.

The researchers used an equation that relates the body and brain weight of modern South American rodents to get a ballpark estimate for N acreensis, then compared that with the brain weight implied by the volume of the cavity in the skull. The first method predicted a brain weighing about 1.8kg, but the volume suggested a dinky 0.77kg. Other calculations, used to compare the expected ratio of the rodent’s brain and body size with the actual fossil, suggested that N acreensis’ brain was three to five times smaller than one would expect.

There is some uncertainty about whether the process of fossilisation might have compressed the brain cavity, Kerber cautions. But making reasonable estimates about that effect did not significantly affect the overall picture.

Big brains are useful but can take a lot of calories to maintain, so it makes sense to have one no larger than needed. Perhaps one reason N acreensis had such a small brain is that it lived relatively isolated in South America, Kerber says. Its primary predators may have been giant, crocodilelike animals that preferred to lie in wait. That particular environment may have resulted in the ancient rodents evolving a smaller brain.

The creatures live upside down and release mucus to trap prey (National Aquarium)

You didn’t touch these jellyfish, but they can sting you with tiny grenades

Jellyfish are very sneaky about stinging. Some have venom that kicks in on a time delay. Many species even manage to get in a few zingers after they’re dead.

But according to research published in Communications Biology, the stealthiest stinging strategy belongs to Cassiopea xamachana, a species of upside down jellyfish found in the Caribbean Sea, the Gulf of Mexico, and warm parts of the western Atlantic. When disturbed, this creature acts like a space movie mother ship – it emits tiny balls of stinging cells that then swim around on their own, zapping anything in their path.

These “self-propelling microscopic grenades”, which the researchers have named cassiosomes, also appear to stun and kill prey for the jellyfish, says Cheryl Ames, an associate professor at Tohoku University in Japan and lead author of the study.

The finding is “paradigm-shifting” and will change how researchers think about how jellyfish eat and sting, says Angel Yanagihara, a jellyfish envenomation expert at the University of Hawaii who was not involved with the study.

Upside down jellyfish spend most of their time on the ocean floor, nestled in sea grass or the roots of mangrove forests. And as their name suggests, they orient themselves differently than other jellies, resting on their gelatinous heads while their frilly arms stretch upward.

Ames noticed that when she and her colleagues admired the upside down jellies, they often came out of the water covered in “itchy and irritating” stings, she says.

The US Navy has long been curious about difficult-to-source jellyfish stings, says Gary Vora, the deputy laboratory head within the Centre for Bio/Molecular Science and Engineering at the Naval Research Laboratory in Washington, DC, and another author of the paper. Navy divers will sometimes get in what looks like clear water, and end up “lit up like a Christmas tree”, he says.

Because upside down jellyfish can’t move, they release clouds of mucus that trap prey. When the researchers put this mucus under a microscope, they found it was studded with “self-propelling, jelly-filled packages of stinging cells,” Ames says. In most jellyfish, stinging cells are part of the tentacles.

But these packages were swimming on their own, propelled by waving hairs called cilia.

The researchers named the strange clusters cassiosomes. Hundreds of thousands of them, at least, are released at a time. They can sting a brine shrimp to death on contact. And in the lab, the sting packs survived on their own for up to 10 days.

The oldest nests date back 48,000 years ago (Rob Harbert)

Reading the past in old, urine-caked rat’s nests

For paleoecologists studying the prehistoric natural world, ancient, urine-soaked rat nests can be a treasure trove, not unlike owl pellets dissections that you might have done during a school trip to a natural history museum. Since the 1960s, scientists have examined thousands of fossil rat nests, or middens, to learn about regional changes in climate and ecosystems over time.

Today, with advanced molecular technology, scientists can even tease apart the owners of millenniums-old DNA preserved in those middens. Until now, they’ve targeted small genetic fragments from specific organisms such as plants or viruses. But in a study recently published in Ecology and Evolution, paleoecologists show that an expansive approach can be used to sequence all kinds of DNA found in a single midden – the scientific equivalent of moving from spear fishing to casting a broad net.

“There’s a very rich picture that takes a lot of work to paint – but is now paintable,” says Michael Tessler, an evolutionary biologist at the American Museum of Natural History and one of the study’s authors

For a variety of reasons, rat middens make excellent stockpiles of ancient DNA. Nest building materials, such as bones, twigs, insects and plant fragments, are biologically diverse but come from within a 100m radius of the pack rat that built them. Those rodents also constructed their middens in dry caves or rock shelters, where both the animals and, later, DNA are protected from moisture and wind. And because rodents urinate in their nests, their urine eventually crystallises into a shellac, cementing the midden into an impenetrable, well-preserved mass.

“It ends up very rocklike,” says Robert Harbert, a co-author of the journal article and a biologist at Stonehill College in Massachusetts. “Whatever’s inside of them is embedded in this crystalline matrix of 20,000-year-old rat urine.”

For the latest study, researchers extracted DNA from 25 middens, the oldest of which dates back 48,000 years. Then they tried to identify as many genetic scraps as possible.

DNA from grass and sunflower families dominated the oldest middens, suggesting a treeless shrub land landscape tens of thousands of years ago. But in samples from 1,000 to 5,000 years ago, the scenery changed to woodlands, with DNA profiles shifting to include pines, junipers and mountain mahoganies.

“We see massive migrations of plants across thousands of kilometers”, as glaciers retreat, Harbert says. “This is probably the best system that we have for observing how populations of organisms responded to massive global climate change.”

The piglike creatures are extremely vulnerable to human activity (Apolinar Basora)

White-lipped Peccary species may be in steep decline

White-lipped peccaries travel in large packs throughout the forest. The hairy, piglike creatures play a crucial role in their ecosystems, dispersing seeds and creating habitats for insects and amphibians.

Now the species is facing a crisis. A recent study published in the journal Biological Conservation finds that the territory roamed by white-lipped peccaries in Mexico and Central America has shrunk by as much as 87-90 per cent from their traditional range, and 63 per cent from previous estimates.

“It’s shocking for me how fast this population is declining compared to the last assessment,” says Harald Beck, chair of the peccary specialist group of the nonprofit International Union for Conservation of Nature. Beck was not involved in the new study but conducted a similar one in 2012 that found a habitat loss at the time of 21 per cent. “We did not know it was that bad.”

It’s not clear exactly how many animals remain, because of the difficulty of counting them, says Daniel Thornton, an assistant professor at Washington State University, who led the research. The new study relied on camera traps and local experts to identify territory where the social creatures still roam.

A new study suggests that the territory roamed by the species in Mexico and Central America has shrunk by as much as 87 to 90 percent (Roan McNab)

White-lipped peccaries are extremely vulnerable to human activity. They need a wide territorial range, they move in big groups and aggressively face threats instead of fleeing to safety, and their meat is highly prized, Thornton says. “They have the trifecta of bad characteristics for a species that wants to survive in human-dominated landscapes, unfortunately for them,” he says.

Development of land that used to be forested has substantially limited the white-lipped peccaries’ foraging grounds, according to Rony Garcia-Anleu, a researcher based in Guatemala with the Wildlife Conservation Society who worked on the study.

Unless hunting and habitat destruction are quickly controlled, it could mean the end of a species that once roamed much of the New World tropics, and will lead to substantial degradation of the handful of large forests that remain between Mexico and Panama, where most of the region’s white-lipped peccaries now live.

Their frequent mud baths create depressions in the soil that fill with water and become important breeding habitats for insects and amphibians, Beck says. The white-lipped peccaries are also important for dispersing seeds across the forest, Garcia-Anleu says. And they are important in the forest food chain. In addition to people, the peccaries are hunted by wild jaguars and puma, who will also die off if they lack for protein, Garcia-Anleu says.

Teeth from the potential new species (Jared Voris)

Canada’s newest tyrannosaur is named for a ‘Reaper of Death’

Paleontologists in the province of Alberta have announced the discovery of Canada’s oldest known tyrannosaur: Thanatotheristes degrootorum, or “the Reaper of Death”.

With its razor-sharp teeth and formidable two-tonne frame, the newly discovered species terrorised the region some 79.5 million years ago. Though smaller than Tyrannosaurus rex, it still measured about 30ft long and about 8ft tall. The new species was at least 2.5 million years older than its closest relatives, which may provide insight into when tyrannosaurs grew from small carnivores into the apex predators that perished 66 million years ago.

“Prior to the discovery, we knew all the most famous tyrannosaurs like T rex, Albertosaurus, Gorgosaurus, were all coming from the last 10 or so million years of the Cretaceous,” says Francois Therrien, a paleontologist at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta, and an author on the paper. “Now, with the new species we’ve actually pushed back the record of tyrannosaurs.”

The finding was published in January in the journal Cretaceous Research, based on bones discovered by a pair of paleo-enthusiasts, Sandra and John De Groot. The De Groots were walking in southern Alberta along the shore where Oldman River meets the Bow River when they made an exciting discovery: A dinosaur bone. They recovered three large brown chunks of a dinosaur jaw.

The De Groots donated the specimen to the museum and uncovered more skull pieces. The scientists knew it was a tyrannosaur, but not what kind.

For nearly a decade, the bones sat in a drawer until Jared Voris, a graduate student at the University of Calgary, began examining them. The long and deep snout was similar to Daspletosaurus, another tyrannosaur group. He also noticed interesting vertical ridges that lined the dinosaur’s upper jaw.

Voris also observed other features that set the tyrannosaur apart from its relatives, such as its oval-shaped cheekbone and aspects of its skull. Those differences, along with the tyrannosaur’s old age, led the team to classify it as a new species.

But some paleontologists took issue with calling it a distinct genus.

Thomas Carr, a paleontologist at Carthage College in Wisconsin, agrees the specimen had enough unique features to call it a new species, but he would have preferred “Daspletosaurus degrootorum”.

One of the paper’s co-authors, Darla Zelenitsky, a paleontologist at the University of Calgary, defended the classification, saying the ridges on the tyrannosaur’s upper jaws and its distinct cheekbones warranted the new name.

© The New York Times

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