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Wikimedia Commons // Public Domain
Wikimedia Commons // Public Domain

Cats Helped Drive Some Early Dogs in North America to Extinction

Wikimedia Commons // Public Domain
Wikimedia Commons // Public Domain

A recent study offers cat lovers some brand new ammunition in the endless “cat vs. dog” debate. According to this research, the arrival of felines had a bigger, and more devastating, impact on North America’s dog population than did climate change.

The dog family first appeared around 40 million years ago, possibly in modern-day Texas. Over time, three main subgroups arose: the extinct Borophaginae (meaning "bone-crushing dogs"), Hesperocyoninae ("evening" or "Western dog"), and the still-living Caninae (which includes wolves, foxes, and domesticated dog breeds). Around 28 million years ago, this dog diversity peaked, with almost 30 species roaming North America. 

But then the Hesperocyoninae started dying out, and they completely disappeared about 15 million years ago, seemingly outcompeted by the faster, bigger, bone-crushing dogs. But the latter group faced stiff competition itself from some relatively new arrivals on the scene: cats. And in the end, the cats bested them.

That's the conclusion scientists from Sweden, Switzerland, and Brazil came to after examining more than 2200 North American carnivore fossils, about 1500 from 120 canine species, and another 744 from 115 other carnivore species, including bears, bear-dogs, and cats. Their findings were published in the Proceedings of the National Academy of Sciences

Around 18.5 million years ago, primitive cats crossed the Bering Strait and arrived in Canada. Just three million years later, as felids started to become numerous across North America, the Borophaginae population took a nosedive. Borophagines went completely extinct more than 2 million years ago.

As study lead author Daniele Silvestro explains to mental_floss, this probably wasn’t a coincidence. Several Borophaginae species had a body structure that somewhat resembles that of a big felid more than that of a dog, Silvestro notes. Like cats, they could rotate their palms upwards, a useful adaptation for grabbing prey. They were also likely ambush predators in the vein of mountain lions or tigers. Because of these similarities, Borophagines and felids competed within many of the same niches.

But these early cats may have been better hunters, an edge that could have helped drive up to 40 dog species into extinction over the course of the approximately 15 million years the groups competed. (Unlike their bone-crushing relatives, members of the Caninae family, which began flourishing around 10 million years ago, weren’t especially affected by feline invaders. With their slender builds, canine dogs were, by and large, designed to run down their meals across great distances.) Based on the analytical models the researchers tested, Silvestro thinks this competition drove the eventual extinction of bone-crushing dogs above all other factors, including environmental and climate shifts.

When one group of organisms supplants another, evolutionary scientists characterize it as "passive replacement” if the new arrivals don’t take over until some external factor kills off the first bunch. A good example is mammals and dinosaurs. When Earth was dominated by dinosaurs, mammals already existed but were not very diverse or abundant because dinosaurs were using most of the resources. It was only when dinosaurs finally perished that mammals diversified and thrived, becoming Earth’s dominant land animals.

In the case of North America’s cat-and-dog saga, it looks like “active displacement” by cats did the dogs in. Advantage: cats.

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Ted Cranford
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science
Scientists Use a CT Scanner to Give Whales a Hearing Test
Ted Cranford
Ted Cranford

It's hard to study how whales hear. You can't just give the largest animals in the world a standard hearing test. But it's important to know, because noise pollution is a huge problem underwater. Loud sounds generated by human activity like shipping and drilling now permeate the ocean, subjecting animals like whales and dolphins to an unnatural din that interferes with their ability to sense and communicate.

New research presented at the 2018 Experimental Biology meeting in San Diego, California suggests that the answer lies in a CT scanner designed to image rockets. Scientists in San Diego recently used a CT scanner to scan an entire minke whale, allowing them to model how it and other whales hear.

Many whales rely on their hearing more than any other sense. Whales use sonar to detect the environment around them. Sound travels fast underwater and can carry across long distances, and it allows whales to sense both predators and potential prey over the vast territories these animals inhabit. It’s key to communicating with other whales, too.

A CT scan of two halves of a dead whale
Ted Cranford, San Diego State University

Human technology, meanwhile, has made the ocean a noisy place. The propellers and engines of commercial ships create chronic, low-frequency noise that’s within the hearing range of many marine species, including baleen whales like the minke. The oil and gas industry is a major contributor, not only because of offshore drilling, but due to seismic testing for potential drilling sites, which involves blasting air at the ocean floor and measuring the (loud) sound that comes back. Military sonar operations can also have a profound impact; so much so that several years ago, environmental groups filed lawsuits against the U.S. Navy over its sonar testing off the coasts of California and Hawaii. (The environmentalists won, but the new rules may not be much better.)

Using the CT scans and computer modeling, San Diego State University biologist Ted Cranford predicted the ranges of audible sounds for the fin whale and the minke. To do so, he and his team scanned the body of an 11-foot-long minke whale calf (euthanized after being stranded on a Maryland beach in 2012 and preserved) with a CT scanner built to detect flaws in solid-fuel rocket engines. Cranford and his colleague Peter Krysl had previously used the same technique to scan the heads of a Cuvier’s beaked whale and a sperm whale to generate computer simulations of their auditory systems [PDF].

To save time scanning the minke calf, Cranford and the team ended up cutting the whale in half and scanning both parts. Then they digitally reconstructed it for the purposes of the model.

The scans, which assessed tissue density and elasticity, helped them visualize how sound waves vibrate through the skull and soft tissue of a whale’s head. According to models created with that data, minke whales’ hearing is sensitive to a larger range of sound frequencies than previously thought. The whales are sensitive to higher frequencies beyond those of each other’s vocalizations, leading the researchers to believe that they may be trying to hear the higher-frequency sounds of orcas, one of their main predators. (Toothed whales and dolphins communicate at higher frequencies than baleen whales do.)

Knowing the exact frequencies whales can hear is an important part of figuring out just how much human-created noise pollution affects them. By some estimates, according to Cranford, the low-frequency noise underwater created by human activity has doubled every 10 years for the past half-century. "Understanding how various marine vertebrates receive and process low-frequency sound is crucial for assessing the potential impacts" of that noise, he said in a press statement.

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Scientific Reports, Fernando Ramirez Rozzi
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Stones, Bones, and Wrecks
Humans Might Have Practiced Brain Surgery on Cows 5000 Years Ago
Scientific Reports, Fernando Ramirez Rozzi
Scientific Reports, Fernando Ramirez Rozzi

In the 1970s, archaeologists discovered a site in France containing hundreds of cow skeletons dating back 5000 to 5400 years. The sheer number wasn't surprising—human agriculture in that part of the world was booming by 3000 BCE. What perplexed scientists was something uncovered there a few decades later: a cow skull bearing a thoughtfully drilled hole. Now, a team of researchers has released evidence that suggests the hole is an early example of animal brain surgery.

Fernando Ramírez Rozzi, a paleontologist with the French National Center for Scientific Research, and Alain Froment, an anthropologist at the Museum of Mankind in Paris, published their findings in the journal Nature Scientific Reports. After comparing the opening to the holes chiseled into the skulls of humans from the same era, they found the bones bore some striking similarities. They didn't show any signs of fracturing from blunt force trauma; rather, the hole in the cow skull, like those in the human skulls, seemed to have been carved out carefully using a tool made for exactly that purpose. That suggests that the hole is evidence of the earliest known veterinary surgery performed by humans.

Trepanation, or the practice of boring holes into human skulls, is one of the oldest forms of surgery. Experts are still unsure why ancient humans did this, but the level of care that went into the procedures suggests that the surgery was likely used to treat sick patients while they were still alive. Why a person would perform this same surgery on a cow, however, is harder to explain.

The authors present a few theories, the first being that these ancient brain surgeons were treating a sick cow the same way they might treat a sick human. If a cow was suffering from a neural disease like epilepsy, perhaps they though that cutting a hole in its head would relieve whatever was agitating the brain. The cow would have needed to be pretty special to warrant such an effort when there were hundreds of healthy cows living on the same plot of land, as evidenced by the skeletons it was found with.

Another possible explanation was that whoever operated on the cow did so as practice to prepare them for drilling into the heads of live humans one day. "Cranial surgery requires great manual dexterity and a complete knowledge of the anatomy of the brain and vessel distribution," the authors write in the study. "It is possible that the mastery of techniques in cranial surgery shown in the Mesolithic and Neolithic periods was acquired through experimentation on animals."

Either way, the bovine patient didn't live to see the results of the procedure: The bone around the hole hadn't healed at all, which suggests the cow either died during surgery or wasn't alive to begin with.

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