This ancient predator had two spiny appendages sticking out of its face. This creature Anomalocaris canadensis may have been the freakiest thing to ever haunt the sea. For decades, scientists thought it used those strange limbs to snatch trilobites off the seafloor. The beast could then crush and eat these crunchy snacks. But a new study hints that A. canadensis instead used its spiny limbs to swiftly hunt soft prey. 



Researchers shared their new findings on July 12. The work appeared in Proceedings of the Royal Society B.





A. canadensis means the abnormal shrimp from Canada. It prowled the seas roughly 500 million years ago. Only about as long as a housecat, it still was one of the biggest animals of the Cambrian Period. (The Cambrian ran from about 540 million to 485 million years ago.) That makes A. canadensis one of the earliest top predators.





These sea monsters were like the orcas or great white sharks of their time, says Jakob Vinther. He did not take part in the new study. But he is a paleontologist at the University of Bristol in England. 



Some researchers thought A. canadensis hunted another iconic Cambrian critter the trilobite. Thats because people have unearthed lots of fossils of injured trilobites. This hinted that something had attacked them. A. canadensis became a prime suspect.



But Russell Bicknell wasnt so sure. After all, trilobites have hard, thick exoskeletons. And no one had shown that A. canadensis could crack that armor.



Bicknell is a paleobiologist. He works at the American Museum of Natural History in New York City. He was part of a team that set out to learn if A. canadensis really could have crushed and chowed down on trilobites.



This is a closeup of an A. canadensis fossil. It was found in the Burgess Shale of Canada. The fossil shows the creatures head and curled front appendages.Allison Daley


Pinning softies with its spikes



The researchers compared the ancient creatures bendy appendages to those of modern arthropods. These animals include todays insects, spiders and crustaceans. Bicknells team also built computer models of the limbs on A. canadensis. Using those models, the team tested the limbs toughness, range of motion and best swimming position.



The ancient spiky limbs would have been good at grabbing prey. In that way, A. canadensis may have hunted much like todays whip spiders. But the limbs of A. canadensis probably were too fragile to attack armored prey. Those would have included trilobites.





Plus, A. canadensis would have moved most efficiently when its appendages were stretched out front. (Think of how Superman holds his arms while in flight.)



Together, these results suggest that A. canadensis was best suited for chasing soft creatures swimming through the water. It would have snagged prey in its spiky clutches, Bicknell says. It was going to absolutely pincushion something soft and squishy.

Butterflies and bees do it. Frogs and even salmon do it. What is it? Its metamorphosis.



The term describes a series of dramatic physical changes that an organism undergoes as it matures. The term comes from the Greek word for change of form.



Lets learn about amphibians



Lots of young animals look different from their parents. But metamorphosis is distinct from just growing up. Some animals emerge from metamorphosis with brand-new organs, such as wings or lungs. Others switch what types of food they eat or may wind up not eating at all! These differences may benefit animals by minimizing competition for resources between adults and babies of the same species.Insects, amphibians and certain fish are among the more well-known animals that metamorphose. But theyre not the only ones. Jellyfish, mollusks and sea stars have all been observed undergoing this real-life shapeshifting. Crabs, lobsters and other crustaceans have, too.





Body remodel



Many animals that metamorphose have babies that look entirely different from their adult forms. Think of a frog. Frogs have powerful back legs and lungs. But many frog species start life underwater as tadpoles. Unlike frogs, tadpoles rely on gills and long tails to maneuver underwater.



Jellyfish, meanwhile, start out as free-swimming young called larvae. These larvae attach to hard surfaces and transform into anemone-like polyps. These polyps spend much of their early lives using their tentacles to catch passing prey. Eventually, the tentacles begin to bud into free-floating jellies. They then detach from their home surface and hit the high seas.



Like jellyfish, sea urchins also start their lives as larvae swimming in the ocean. These larvae use long arms to snag phytoplankton to eat. During metamorphosis, a sea urchin grows adult limbs and organs from a cluster of cells inside its body called a rudiment. The urchins absorb their larval arms and mouths into their bodies. Then they drop to the seafloor as newly formed adults.



These spiky purple sea urchins started out life as free-swimming larvae before they underwent metamorphosis into their current forms.Brent Durand/Getty Images


Insect transformations



Metamorphosis is especially common in insects. But some insect transformations are more dramatic than others.



Take butterflies. A crawling, leaf-munching caterpillar can transition into a flying, nectar-sipping butterfly within a few weeks. This is an example of complete metamorphosis. During this type of metamorphosis, insects go through four life stages: egg, larva, pupa and adult. At each stage, the insect will look completely different.



Explainer: Insects, arachnids and other arthropods



The process begins with an egg laid by an adult. A small, soft-bodied larva, such as a caterpillar, hatches from this egg. Larvae do not have many of the organs found in adults. And they have one goal: eat as much as they can.A caterpillar doesn’t have wings, doesn’t have any reproductive organs, says Jens Rolff. It’s just like a big bag of tissues moving on a plant and feeding. Constantly feeding. Rolff is an evolutionary biologist who studies insects. He works at Freie Universitt in Berlin, Germany.Healthy appetites help a larva pack on fat. And that will fuel the development of its organs once the larva becomes a pupa. At the pupa stage, the larva stops eating and develops a protective covering. Caterpillars develop a hard, outer layer called a chrysalis.







When the larva pupates, the job is to generate a new animal, says Rolff. Inside the pupa, proteins called enzymes begin to break down the larvas tissues. These dissolved tissues are used to rebuild muscles and organs such as the brain and gut. Special groups of cells called imaginal discs become activated and help create wings, new mouthparts and reproductive organs. Once these changes are complete, an adult insect emerges.



That adult often moves and eats in totally different ways than it did as a pupa.



About eight in every 10 insect species undergo complete metamorphosis. Beetles, flies, bees, ants and fleas are just a few examples. Together, this group makes up about 60 percent of all animals on Earth. Complete metamorphosis has been around for a while, too. Fossils suggest that insects were doing it at least 250 million years ago, Rolff says.





Check out one of the worlds largest beetles going through metamorphosis in this video from Nat Geo WILD.



Not all insects go through this full process, though. Grasshoppers, cockroaches, cicadas and dragonflies go through a three-stage version known as incomplete metamorphosis.



Here, insects emerge from eggs as nymphs, which look much like miniature adults. They are just missing developed wings and sex organs. Nymph forms of these species gradually get larger by shedding their hard outer shell, or exoskeleton, through a process called molting. Wings and reproductive organs continue to develop with each molt. All insects grow by molting. But insects that undergo complete metamorphosis only do so while plumping themselves up as larvae. Nymphs will go through multiple molts until they reach adulthood.

Pulsar (noun, PUHL-sahr)



Pulsars are dense, quickly spinning cores of dead stars that blast radio waves into space.



When a star thats a few times as big as the sun dies, it shoots most of its mass off into space in a huge explosion. That explosion is called a supernova. But the core of the star collapses in on itself and forms an ultra-dense neutron star. All that mass clumps together under the force of gravity. That causes the dead star to spin faster, just like an ice skater pulling in their arms during a turn. Neutron stars can spin faster than the tires on a race car at top speed anywhere from once every few seconds to hundreds of times per second. Thats millions of times faster than the Sun spins.





A pulsar is a special kind of neutron star that blasts out two beams of radio waves in opposite directions. As the dead star spins, those beams sweep through space like the lights on a lighthouse. If Earth is in the path of one of those beams, we see a flash of radio waves every time it sweeps past us. That makes the pulsar appear to pulse at very regular intervals.



This animation shows a pulsars radio beams (purple) sweeping through space. When one of the beams passes over Earth, the pulsar appears to flash.



Astronomer Jocelyn Bell Burnell first discovered pulsars in 1967. At first, some scientists thought the radio beams she saw might be coming from aliens. That was because the pulses were so regular. But then Bell Burnell found radio pulses coming from a different part of space, far from the first signal. It was unlikely that two groups of aliens were signaling us at the same time from so far apart, so scientists looked for a different explanation. They eventually learned the radio waves were coming from pulsars scattered throughout space.



Scientists today use pulsars to make maps of space and keep time in the cosmos. Pulsars can also be used study the fundamental laws of physics that rule the universe.



In a sentence



Scientists time the radio flashes from pulsars to look for gravitational waves.



Check out the full list of Scientists Say.