Isegoria

My childhood knowledge of dinosaurs is drifting away — not from senescence but from obsolescence. First they went from slow and cold-blooded to quick and warm-blooded. Then the brontosaur reverted to the apatosaur. Now the triceratops may be a torosaur:

Triceratops had three facial horns and a short, thick neck-frill with a saw-toothed edge. Torosaurus also had three horns, though at different angles, and a much longer, thinner, smooth-edged frill with two large holes in it. So it’s not surprising that Othniel Marsh, who discovered both in the late 1800s, considered them to be separate species.

Now [ John Scannella and Jack Horner at the Museum of the Rockies in Bozeman, Montana] say that triceratops is merely the juvenile form of torosaurus. As the animal aged, its horns changed shape and orientation and its frill became longer, thinner and less jagged. Finally it became fenestrated, producing the classic torosaurus form (see diagram, [left]).

This extreme shape-shifting was possible because the bone tissue in the frill and horns stayed immature, spongy and riddled with blood vessels, never fully hardening into solid bone as happens in most animals during early adulthood. The only modern animal known to do anything similar is the cassowary, descended from the dinosaurs, which develops a large spongy crest when its skull is about 80 per cent fully grown.

Robins can literally see magnetic fields — but only if their right eye can see clearly:

Years of careful research have told us that the ability depends on light and particularly on the right eye and the left half of the brain. The details still aren’t quite clear but, for now, the most likely explanation involves a molecule called cryptochrome. Cryptochrome is found in the light-sensitive cells of a bird’s retina and scientists think that it affects just how sensitive those cells are.

When cryptochrome is struck by blue light, it shifts into an active state where it has an unpaired electron — these particles normally waltz in pairs but here, they dance solo. The same thing happens in a companion molecule called FAD. Together, cryptochrome and FAD, both with unpaired electrons, are known as a “radical pair”. Magnetic fields act upon the unpaired electrons and govern how long it takes for the radical pair to revert back to their normal, inactive state. And because cryptochrome affects the sensitivity of a bird’s retina, so do magnetic fields.

The upshot is that magnetic fields put up a filter of light or dark patches over what a bird normally sees. These patches change as the bird turns and tilts its head, providing it with a visual compass made out of contrasting shades.

To test the bounds of this ability, Stapput wanted to see what would happen if she blurred a robin’s vision. She outfitted her robins with somewhat unflattering goggles, with clear foil on one side and frosted foil on the other. Both allowed 70% of light to get through, but the frosted foil disrupted the clarity of the image.

The robins were kept in cages until they were ready to migrate and let loose in funnel-shaped cages lined with correction fluid. As they orientated themselves and changed course, they created scratches on the cage walls which told Stapput which direction they were heading in. These scratches revealed that with both eyes open, the robins flew straight north as they would normally do in the wild. If their left field of vision was frosted, they went the same way. But if their right eye was covered, they became disorientated, heading in completely random directions.

Everyone knows that the sabertooth “tiger” (Smilodon fatalis) had massive fangs — I can’t bring myself to call the big cat’s teeth canines — but its secret weapon was exceptional forelimb strength:

The sabertooth cat, Smilodon fatalis, was an enigmatic predator without a true living analog. Their elongate canine teeth were more vulnerable to fracture than those of modern felids, making it imperative for them to immobilize prey with their forelimbs when making a kill. As a result, their need for heavily muscled forelimbs likely exceeded that of modern felids and thus should be reflected in their skeletons.
[...]
Using radiographs of the sabertooth cat, Smilodon fatalis, 28 extant felid [cat] species, and the larger, extinct American lion Panthera atrox, we measured cross-sectional properties of the humerus [upper arm bone] and femur [thigh bone] to provide the first estimates of limb bone strength in bending and torsion.

We found that the humeri of Smilodon were reinforced by cortical thickening to a greater degree than those observed in any living felid, or the much larger P. atrox. The femur of Smilodon also was thickened but not beyond the normal variation found in any other felid measured.

(Hat tip to io9.)

Estuarine crocodiles (Crocodylus porosus) range from India to China to Australia — where the saltwater crocs are known as salties.

I like to think of them as sharks that will follow you onto the beach. While they predominantly live in rivers, mangrove swamps, and brackish estuaries, salties have also been found far off shore:

The researchers acoustically tagged 27 crocodiles from the Kennedy River in Australia. The team inserted small transmitters in the crocs and placed receptors along the river’s coastline.

Whenever a crocodile came within a quarter mile of the receptor, the movement was recorded. After a year of monitoring the reptiles along the river, the scientists discovered that they habitually travel from their home area to the river mouth, a distance upwards of 31 miles away.

Whenever the gigantic beasts traveled more than 6 miles a day, they surfed. The crocs always started their journey immediately after the tides turned, securing them a solid 6 to 8 hours of speedy travel.

Every time the tides changed to an unfavorable direction, the crocodiles took a rest stop. They retreated to the nearby shore for a period of hours to days.

As a short term solution to unfavorable tides, the animals would dive to the bottom of the river, where they can spend up to an hour lounging on the river floor, rather than moving back to land.

In a previous study, the researchers outfitted three crocodiles with satellite transmitters. This allowed the team to follow the “salties” — the Australian nickname for the predators — beyond the river mouth and into the ocean.

One of the crocodiles journeyed down the west Coast of Cape York Peninsula. The trip coincided with changes in seasonal currents. Over the course of 25 days, the salty moved a whooping 367 miles!

Similarly, two of its brethren also covered hundreds of miles in a few weeks.

Achieving these arduous journeys is made possible by the crocodiles’ acute sense of direction.

Estuarine crocodiles depend on an internal magnetic compass to reach their desired location, similar to birds and turtles.

Additionally, these reptiles can easily endure long trips and remain physically strong despite a lack of eating and drinking due to amazing internal engineering.

Saltwater crocodiles only drink fresh water and rely on ambushing prey, a strategy difficult to maintain during sustained ocean travel.

But the creatures developed the ability to maintain nutrients from ingested food long after feeding. As a result, they can last up to 4 months in the ocean without regular eating or drinking.

Researchers in the Northwest Territories say they may have found the first recorded offspring of a hybrid female polar-grizzly bear in the wild:

Government officials say an Inuvialuit hunter, David Kuptana, shot an unusual-looking bear during a hunting trip April 8 near Banks Island, in the Inuvik region.

He provided federal scientists with samples to see what type of bear it was.

Officials with the territorial government say those test showed that the dead bear was the offspring of another hybrid bear — a female polar-grizzly mix who had mated with a male grizzly.

Scientists confirmed this by comparing the dead bear’s DNA with that of local polar bear and grizzly populations, and that of a male polar-grizzly hybrid, which was shot on Banks Island in 2006.